Exam 4 bio

Geographical trends in species diversity: Species richness in the tropics

-*there is greater species richness in the tropics, for all phylogenetic lineages* Trinidad: Ants - 134 Birds - 600 Mammals - 140 Iowa: Ants - 73 Birds - 121 Mammals - 65 Alaska: Ants - 7 Birds - 80 Mammals - 40

Alpha diversity indices: Simpson's Index

(in image, D represents N2) -the second type of diversity index that uses both evenness and richness in its calculation is called the *Simpson's Index (N2)* (the Simpson's reciprocal index, specifically) -it's based on the probability of randomly selected individuals being different -if you were to go into a community, such as a forest, and pick two trees at random, what is the probability of both of them being of the same species? ^N2 is the probability of doing so -N2 also can be interpreted as the # of equally common species needed to produce the same diversity value as the observed community -the probability of getting two individuals is (pi)(pi) or pi^2 -we get N2 by summing all of the probabilities for all individual species (I) and dividing it into 1 -like N1, N2 then ranges from anywhere from 1 to S, depending on the evenness of the species abundances -the evenness index for N2 is E(D), calculated as: E(D) = N2/S -S is species richness -the evenness E(D) ranges from 0 (low evenness) to 1 (each species is represented by the same # of individuals) *Simpson's index gives more weight to common species*

Beta Diversity: Application

*Beta diversity is a measure of the rate of species change b/w two or more communities* 1) Beta diversity -the ecologist *R. H. Whittaker* came up with the term *beta diversity* in 1960 -Whittaker devised the simplest way of measuring the degree of difference or similarity among two or more communities is the gamma diversity of the region divided by the *average* alpha diversity of the various communities: gamma / alpha = beta (alpha, in this case, is the average species richness of all communities) -Whittaker's beta thus can vary from 1 to Nc, where Nc = the # of communities sampled -beta diversity can be viewed as the # of unique communities there would be if alpha stays the same from community to community, but the communities share all, none, or some species in common Figure in notes: -there are 3 sample sites w/ communities (labeled 1, 2, and 3) that consist of various species (labeled A through L) present -in one situation (X), all of the species present are the same in each sampled community, so gamma = alpha and beta = 1 -in the second situation (Y), all of the species are different, so gamma = 3alpha and beta = 3 -the alpha value is the same, but gamma and beta differ in the two situations -in the first situation, all three communities are identical and beta = 1 -in the second situation, all three communities are completely unique, and beta = 3 (which is equal to the # of communities examined, Nc) 2. *How does beta diversity change?* -there are two ways that beta can change -in situation V, if alpha diversity does not change from community to community, there can be the replacement of species with an equal # of other species -in situation W, as you go from richest to poorest communities, where the poorer communities are a nested subset of richer communities, you can obtain the identical diversity values as in situation V, but the distribution of species is very different -both situations: a) total replacement, or b) a nested loss/gain of species w/out replacement, affect each diversity metric differently, but the numeric outcomes (the diversity values) are the same -the mechanisms that cause changes in alpha, gamma and beta diversity depend upon both local adaptation to the environment and predation, competition and other species interactions, as well as long-term evolutionary processes, such as speciation 3. Interpreting beta diversity -one important interpretation of beta diversity mentioned above (a measure of the similarity or differences in the species richness of sites) is to relate beta diversity to the species/area curves we discussed earlier -as one increases the sample area, new species will be discovered -one way to describe beta diversity is that it's the rate of accumulation of species richness (increasing the # of species encountered, [S]) as you incrementally increase the # of sites sampled (increasing the area [A] sampled) -beta diversity would be high initially, but as you add more areas, eventually, you do not add additional new species, and beta would decline

Causes of autogenic succession: What impact, if any, do animals have on plant succession, and are animals affected by succession?

*What impact, if any, do animals have on plant succession, and are animals affected by succession?* 1) Animals are often viewed as passive followers of the successional sequence -the plants determine the base for the food web in the area, and this affects what types of animals are present 2) However, sometimes animals help determine the fate of the successional sequence -marine crabs affect the succession of various seaweeds, as can sea otters -the presence of predatory seastars or snails affect the composition of the intertidal zone -in terrestrial environments, white-tailed deer feed on sugar maple and eastern hemlock seedlings, and hemlocks are severely damaged -in places that the deer were excluded, sugar maples didn't replace hemlocks in the exclusion plots

Geographical trends in species diversity: 5 factors that affect the diversity gradients of North American animals

-*George Gaylord Simpson* (American evolutionary biologist) noted *5 different factors* that affected the diversity gradients of North American mammals: 1) The north-south gradient was not smooth -- some mammalian groups are more diverse in the temperate zone 2) Topographic relief affected diversity -- the Rocky Mountains and Appalachians supported more species what would be at a given latitude 3) East-west trends existed in diversity -- more species in the western part of the continent than the eastern end 4) There were areas of abrupt changes, associated w/ mountain ranges 5) Peninsular 'lows' exist -- fewer species were present on peninsulas than on adjacent continental areas

Other examples of Successions: Cowles' work on sand dunes of Lake Michigan

-*H.C. Cowles' work on the sand dunes of Lake Michigan* (Henry Chandler, American, 1899) -Cowles work was followed up by Jerry Olson (American, 1958) -at the sand dunes, the soils increase in dead organic matter (DOM), decrease in Ca2+, pH, and at the black oak stage, it may not reach the typical climax sere (beech maple) due to low nutrients or moisture (see notes)

Succession: 2 main types of succession: primary succession

-*primary succession* is the process where succession begins from bare rock/substrate -there is no soil present, and no plants are present as well (at least initially) -this bare substrate can be from a variety of sources 1) As a volcano erupts and emits lava, it either creates a new island, expands the area of a previously existing island, or completely covers an old island or site 2) Glaciation scrapes the entire area clean of soil and vegetation -as the glacier recedes, it exposes new bare rock for colonization 3) At the edge of the sea, newly exposed or deposited substrates (debris, vulcanism, wind-produced sand banks and dunes) provide new habitat 4) Bare rock outcrops that become exposed over time 5) Abandoned man-made buildings or structures (roads, buildings) that have completely covered the soils and the local community

Succession: 2 main types of succession: secondary succession

-*secondary succession* occurs after a disturbance event has partially cleared or opened up an environment -plants and animals already are present, and soil is present and ready for use by plants 1) Once an agricultural field has been abandoned, certain species invariably invade during the first few years after abandonment -however, bc the ground is bare doesn't mean that nothing is there - there may be as many as 100,000 seeds per meter of soil in an abandoned field 2) The early species are well-adapted for good dispersal, short life spans, quick growth on poor soil, and high reproductive rates -these *r-selected* species are commonly called *colonizers* or *pioneer species* -you may know these species as '*weeds*' -a weed, in human terms, is an undesired wild plant growing in an area where humans don't want it to grow -however, 'weeds' generally are r-selected plants growing where other plants cannot easily grow -an open area, perhaps exposed down to the bare soil, is filled by ragweeds, horseweeds and crabgrass and a few broad-leaved weeds -the pioneer seres are usually observed for a few years post-abandonment 3) After several years of species colonization, competition, and eventual extinction, important changes occur in the physical environment and in community composition of the previously abandoned field -the soil increases and is improved -the ground is no longer barren -the community composition then shifts to larger grasses and larger weeds, such as sunflowers and goldenrods -light begins to become a limiting factor for germinating seedlings, due to shading by taller plants -the early colonizers are usually *shade-intolerant* and are outcompeted eventually by more *shade-tolerant species* -after the broad-leaved sunflowers and composite flowers have established, large grasses begin to dominate 4) After the grasses and larger broad-leaved weeds are present, shrubby species (ex: sumac and multiflora rose) and small trees (ex: the eastern red-cedar) invade and eventually come to dominate the community, roughly 10-50 years after the field was abandoned -some larger trees (ex: the thorny locust trees) may invade at this time -intermediate seral stage trees, such as sweet gums, elms and maples, may be found as well w/ the shrubs 5) After perhaps 50-100 years post-abandonment, relatively shade-tolerant, long-lived woody trees begin to occupy the area where weeds once grew -red oaks, white oaks, and hickories now dominate -the trees may form a dense forest of small-boled (small diameter) trees 6) Finally, after 100 years or more, a mature forest dominated by widely-spaced, large trees is established on the abandoned farm -these trees are under more competition for light and water -they are members of *K- selected* species that are adapted for conditions where competition may be keen (longer-lived, w/ larger, fewer seeds, repeated reproductive seasons) 7) If left undisturbed, the *climax community* of long-lived species perpetuate itself -the climax community is the final seral stage, it will not be replaced by another community (ex: trees that produce shade-tolerant seedlings may persist in an area for long periods of time) -at this point, succession is considered to have reached a climax community or stage

Causes of autogenic succession: Three contrasting theories/models

-*Joseph Connell* (American) and *R.O. Slatyer* (Ralph Owen, Australian, 1977) proposed 3 contrasting theories or models as the mechanisms to cause *autogenic succession* -these models are called: *facilitation, inhibition, and tolerance* -these models describe the effects of one species upon another 1) *Facilitation model* -years ago, *Frederic Clements* first presented the facilitation model -Clements viewed succession as a developmental sequence: each sere paves the way for the next, just like development proceeds in an animal (various structures form, disappear, or are modified during ontogeny) -earlier stages enable climax species to invade (analogous to how wooden forms are essential to pore concrete; when the concrete hardens, you can remove the forms) -earlier species build and enhance soils by increasing nutrient levels and water levels, increasing the amount of humus, and accelerating the breakdown of rock (ex: alder trees have nitrogen-fixing bacteria in root nodules; these bacteria help to fix nitrogen into riverine soils next to rivers) -black locusts do same thing in North American forests -in the facilitation model, the first species presumably makes the environment less suitable for themselves 2) *Inhibition model* -*F. E. Egler* (Frank Edwin, American, 1954) first described the inhibition model -an important part of this hypothesis is that established species tend to suppress new colonists -the initial species (which theoretically could be any species, but often the pioneering species mentioned above) modifies the environment and makes it *less likely* for the invasion of subsequent species -the pioneers are eventually replaced by the sequential colonization of other species, although the first species does not necessarily make the habitat more suitable for further colonists -no one species is necessarily competitively superior, and whichever species gets to a site first can often hold it against subsequent settlers -however, disturbance occurs, opening up space for further colonists -in this model, succession is not totally predictable and there is no distinct climax community 3) *Tolerance model* -*Connell* and *Slatyer* introduced the tolerance model -succession leads to species that are most efficient at using resources -in this model, it is assumed that each species can invade new habitat equally -early colonizing species are not necessary, and subsequent seral stages are determined by competition and by longer-lived, slower-growing species that 'wait out' the shorter-lived ones -*some evidence exists for all three models to some degree*

Succession: Allelopathy

-*allelopathy* often plays a major role during succession (wiki: a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms) -once certain plants are established, they produce chemicals that inhibit the growth or germination of other plants, or even their own seedlings -this 'chemical warfare' may even affect the plants producing the chemicals -- the chemicals may build up in the soil to the point that the seedlings of the allelopathic species can't survive -this is one way the species composition of the area could change w/ time -another way that the composition may change is that the seedlings of trees may not be able to grow in the shade of their parents, but the seedlings of shade-tolerant species may grow there instead -when the older tree dies, one of the adjacent shade-tolerant seedlings takes its place

Complex interactions in communities: Bottom-up control hypotheses

-*bottom-up controls* have also been hypothesized -changes or alteration in lower trophic level organisms (ex: plants) can alter the abundance and species composition of the higher trophic level consumers -bottom-up control in a community often occurs bc changes in nutrient availability and the autotrophic productivity of terrestrial and aquatic plants/phytoplankton influence the entire food web -a bottom-up effect is often through resource availability or nutrient limitation, while top-down controls involved predation -top-down or trophic cascade effects may be at work as well as bottom-up effects, altering the bottom-up effect -a trophic cascade effect doesn't often occur w/ bottom-up controls -*'the world is prickly and tastes bad' hypothesis*: *William Murdoch* (1966) argued that the world may be green, but it also is a 'world that is prickly and tastes bad' -many plants have chemical and morphological traits that make them unpalatable to herbivores -the herbivores thus are food-limited, restricted to the limited # of palatable plants, and thus herbivore competition is actually fierce -in addition, the herbivores' predators are limited as well, so a strong bottom-up control is in effect -it's possible that any community may not show a trophic cascade (and consequently show top-down control), bc of some intermediate trophic level consumer is relatively invulnerable to its predators, leading to a more bottom-up level of control -*'the environmental stress hypothesis'*: *Bruce Menge* and *John Sutherland* in the late 1980s suggested that 3 factors are involved: physical disturbance, predation, and competition -the strength of predation and competition is governed by environmental stress -food web complexity is low in habitats w/ high disturbance (high stress) -in habitats where stress is severe, the upper trophic levels are much smaller in size or are absent altogether, and the persistence of organisms is due to greater physiological tolerances -if the environment is more benign, the strength of top-down forces increase; carnivores are affected by competition, herbivores are affected by predation and a smaller degree to competition, and plants are affected by predation (including omnivory from some carnivores)

Causes of autogenic succession: Diversity often is highest in the intermediate seres

-*diversity often is highest in the intermediate seres* -one reason is that species of different seres could coexist for awhile -the *intermediate disturbance hypothesis* predicts that patches of disturbed areas in the climax stage allow a few individuals of pioneer species to live -at climax stage, diversity in the entire community may slightly decrease due to competition and extinction of some of the pioneer and mid-successional species

Communities and Ecosystems: Food chains

-*food chains* represent links of population relationships (ex: Algae -> Daphnia -> Fish -> Eagle) -the typical # of links along food chains varies from about 3 to a maximum observed of about 9 links -the max # of trophic levels to a food web can be determined by determining what is the longest food chain in the web -the *top carnivore* sits on top ^by definition, no higher-order predators consume them (although decomposers and detritivores can break down their dead bodies)

Why are there more species in the tropics? All hypotheses are operating to some degree

-*in reality, all of the mechanisms posited by these hypotheses are probably operating (in varying degrees) to increase diversity in the tropics* -the lack of glaciation, the greater productivity, the more favorable climates to a greater # of living things, and the generally more stable climates of the tropics may help to explain regional diversity patterns, whereas predation, competition, spatial heterogeneity and disturbance may play important roles at the local level

Keystone species: keystone predators and ecosystem engineers Keystone predator

-*keystone species* (first described by Robert Paine) has a disproportionately large effect to the structure, composition or function of a community or ecosystem -the impacts are disproportionately large relative to the keystone species' abundance or biomass -well-studied examples of keystone species include sea stars, bears, wolves, and other organisms -*there are several types of keystone species recognized* -one type of keystone species is called a keystone predator ^a top carnivore (such as a sea star) selectively feeds on a number of potential competitors on lower trophic levels (snails, barnacles, mussels), lowering their population sizes ^the top carnivore thus reduces competitive exclusion from occurring and the potential extinction from predation effects among the lower trophic level consumers -the elimination of many top predators can destabilize communities, causing a trophic cascade down the food web, reducing species diversity, and it can also literally affect the abiotic environment in complex ways -one important line of evidence pointing to the potential of a species to be a keystone predator is if a trophic cascade event occurs following the removal or reintroduction of the species in question -after a removal, the altered community is less species rich and simpler in structure -Paine removed a species of starfish from study plots in the rocky intertidal along the coast of Washington, and observed a rapid and persistent series of changes in the community composition -a subdominant snail increased in abundance, which in turn decimated various algal and animal -the plots also were overrun by mussels that were kept in check by the starfish -re-establishment of the keystone predator often reverses this effect of reduced community richness -keystone species are probably the least likely species to be considered 'redundant' in their communities

Complex interactions in communities: EEH (aka 'the world is white yellow or green') Hypothesis

-*top-down controls* (indirect effects), also called *trophic cascade effects* are related to the HSS hypothesis -we have seen evidence for this trophic cascade effect in pelagic food webs -addition of a piscivore could have an effect on lake water quality by decreasing phytoplankton -*'The world is white yellow or green' hypothesis* -- *Lauri Oksanen* and colleagues expanded the HSS model -different communities would have different structures based on the # of trophic levels -this model is referred to as the *ecosystem exploitation hypothesis*, or *EEH* -some books also refer to this concept as the 'world is white, yellow or green' hypothesis (Figure 5) -in low productivity habitats (white, Figure 8A), herbivores ('H') and carnivores ('C') are relatively scarce, and herbivores would have little effect on plants ('P') -competition b/w plant species would be important -as productivity increases (yellow, Figure 8B), herbivores compete w/ each other and exert strong top-down impacts on plants -finally, in more productive environments (green, Figure 8C), the carnivores would increase (and compete w/ each other), and the carnivores would control the herbivores, and the plant trophic level would increase -however, this model is similar to HSS in that it's a trophic cascade model -- if one adds a fourth level (the top carnivores, 'TC', Figure 8D), then the carnivores would be suppressed from top carnivore predation, which then frees the herbivores, which in turn exert more predatory control over the plants

Ecosystems and energy transfer: Tansley's definition of ecosystem

-Arthur Tansley (British, 1930s) coined the term ecosystem as "the sum total of all interactions of all populations in a community, including those interactions that occur among themselves and those that occur with the physical, nonliving environment"

Stability and diversity: equilibrium versus nonequilibrium communities Elton's arguments

-Charles Elton (British, 1958, 'The ecology of invasions by animals and plants') argued that community 'stability' is greater in more 'diverse' communities -some of Elton's arguments are as follows: 1) Outbreaks of pest species are more common in simple systems, especially in cropland monocultures, particularly after pesticide use killed the pests' predators, parasitoids and parasites 2) Species that have gone extinct were often on species-poor islands 3) Species invasions occur in simple systems, or species-poor systems (like small islands) 4) Species-rich tropical forests do not have insect outbreaks like that observed in temperate forests (which are comparatively species-poor) 5) Mathematical models suggested it is difficult to maintain constant numbers of individuals in all populations (numerical stability), and Gause's lab work showing the difficulty of achieving numerical stability in simple communities consisting of simple physical structure and few species

Ecosystem energetics: Energy budget

-Eugene Odum and Howard Odum (Americans) described communities as energy transforming machines, and this idea was important in the 1960s -Odums' 1953 book (Fundamentals of Ecology) was the standard ecology textbook for years -the Odums championed the use of energy as a common currency for describing communities and ecosystems -the following section discusses the energy budget - we could be talking about an organism, an entire population, or an entire trophic level of a community -the energy budget for a given animal is equal to: T = NU + C -T = total amount of energy at one trophic level of the food web that is available to the next -NU (not used, energy that is not grazed or eaten - not harvested at the next level) -C = gross energy intake, or the amount of energy ingested or consumed by the animal (this energy is measured in calories or in Joules)

Efficiencies in the flow of energy in an ecosystem: Biomagnification and food chain length

-Gilbert Cabana and Joseph Rasmussen demonstrated that food chain length affected biomagnification -they studied a food web in which the Hg levels in lake trout (Salvelinus namaycush) varied considerably -the food chains on which Salvelinus resided on top varied from three to five levels -when the food chain was longer, the mercury load carried by the fish increased considerably, because of the concentrating effect of biomagnification by two additional intermediate trophic level consumers

Ecosystems and energy transfer: Lindeman efficiency

-Raymond Lindeman (American, 1942) brought the idea of ecosystems as an energy-transforming system to ecology -Lindeman used Tansley's ecosystem concept and Elton's ideas of ecological pyramids (numbers and biomass) -Elton described ecosystems as layered into trophic (feeding) levels, Lindeman took this concept further, stating that the laws of thermodynamics holds for plants and animals arranged in trophic levels (some of the net energy of one level can be passed to the next) -Lindeman provided a formal notation for both the flux of energy through the trophic levels and the efficiency of energy transfer -Lindeman efficiency: amount of energy taken in at level N, relative to (divided by) the amount of energy taken in by the trophic level below it (N-1) Production(predator)/Production(prey) x 100 or the ratio of production for the two levels

Succession: Disturbances

-once a *climax community* has been reached, this doesn't mean that the community will not change in the future -fire or some other *disturbance* event could reset the sequence back to some earlier seral stage by killing off the dominant competitive species, thus allowing species usually found in earlier stages of succession to grow again -the Midwestern prairies are thought to be maintained by periodic fire disturbances -many herbaceous prairie plant populations are unaffected or even enhanced by fire -fire burns off much of the litter -litter may contain allelopathic chemicals that could inhibit growth of many plants -fire also kills the woody (potentially competitively dominant) trees -after a fire, the soil is enriched by nutrients from the burned litter -in addition, the soil is warm from being exposed to full sunlight -the combination of nutrient enrichment and soil warmth facilitates many weedy plants to grow

Stability and diversity: equilibrium versus nonequilibrium communities MacArthur's logic

-Robert MacArthur (American, 1955) suggested that stability is linked to the number of linkages in the food web -MacArthur thought that more trophic links present in the community (as shown greater species diversity and /or more interactions among species) causes a greater stability of the community -the presence of more species and a greater number of links means the community is more resistant to rapid changes in the numbers of individuals of any given species -in other words, MacArthur argued from an energetics standpoint - the more pathways there were for energy to flow through the food web, the less likely it was that the densities of all of the species in the food web would change in response to abnormal increases or decreases in one species -for example, suppose a massive increase in the number of plants that a particular herbivore eats occurs in a forest (like a mast year in oak trees, where tons of oak acorns fall to the forest floor) -this increase in seeds will not necessarily lead to a large increase in a given carnivore population -the potential increase in herbivores feeding on the seeds will be distributed among all of the herbivores, which in turn may not lead to a large increase in the higher trophic level carnivores

Why are there more species in the tropics? 8 Hypotheses

-a # of hypotheses have been put forth to explain why more species are in the tropics 1) *The Time Hypothesis* -see higher #s of tree genera, families, and species in tropical places, such as Costa Rica, than one would observe in the USA -this suggests that these tropical areas are ancient roots of diversity -tropics have a longer geological history -- more speciation has occurred in the tropics than in the temperate zone (glaciation has repeatedly occurred and covered the polar and temperate zones and stopped speciation, driven species southward, and increased extinction) -the ice ages fragmented the tropical forests but allowed speciation to continue, whereas speciation didn't occur in the polar regions during glaciation -*Alfred Russell Wallace* (British) mentioned something similar to this as a cause over a century ago (1878) 2) *The Spatial Heterogeneity Hypothesis* -the tropics have more species bc tropical communities are in areas that are physically more complex -the physical topography of the land, as well as the effect of the large trees, creates more niches (more 'niches' on the tops and sides of the tree trunks) 3) *The Competition Hypothesis* -competition is greater in the tropics, which results in niche partitioning and character displacement/release -competition may be keen in the tropical zones, and the niche breadth is smaller or the amount of niche overlap is larger in the tropics than in the temperate zones -recall *David Lack's* (British, 1940s) example of character displacement (each of the two Geospiza species shifted their beak sizes when they were found together on the same islands, presumably avoiding competition by feeding on different-sized seeds) ^character release is observed when each species is found alone (allopatric) on an island ^in the absence of the other species, they both may shift to an intermediate beak size 4) *The Predation Hypothesis* -this hypothesis suggests that predation is more severe in the tropics, and thus predators keep competitive exclusion from occurring, which would drive weak competitors to extinction -perhaps greater #s of specialists, especially insects, exist in the tropics, but this is not conclusive -there is also a second predation effect hypothesis, put forth by *Dan Janzen* (American, 1970s) -this hypothesis is called the pest pressure hypothesis -specialized insect/vertebrate pests concentrate on a parent tree (easier to spot in the forest than the smaller seedlings) -all offspring near the parent tree are eaten, and only the few seedlings that establish far from the parent plant survive -the level of competition from the many seedlings near the parent tree, as well as from the parent tree itself, may be quite intense, thus reducing seedling survival 5) *The Climate Hypothesis* -the tropics are more favorable for species from year to year and are more stable seasonally year-round -the tropical climate is very favorable for many organisms -stable environments also may support more specialized species -bc the tropics are more stable seasonally, this stability allows organisms to specialize and 'fine tune' to resources, thus allowing more species to pack into area (narrow niche breadth) -in polar and temperate zones, species have to show a broader range of tolerance to climatic factors 6) *The Productivity Hypothesis* -production (measured by net primary productivity or NPP) is higher in tropics, which allows more species to coexist -higher production reduces the effect of food limitations and consequent competition -more energy strikes the tropics on a yearly basis, compared to the poles -we see high productivity in some locations in the temperate zones as well, but this higher productivity occurs over a narrow time window during the spring/summer -greater productivity would increase species, especially if you have temporal partitioning of resources (ex: different trees flower and produce fruits at different times) -basically, if more food exists, more heterotrophs (fungi, decomposers, animals) could be present as well 7) *The Disturbance Hypothesis* -suggests that moderate disturbance impedes competitive exclusion, allowing greater diversity -an intermediate amount of disturbance may allow the highest species richness -it's not clear if the tropics have an intermediate amount of disturbance compared to other zones 8) *Geographic Area Hypothesis* -one explanation may be that the greater species richness of the tropics is due simply to the fact that there is a significantly larger land area (and oceanic areas) in the tropic zone compared to the temperate and polar zones -*John Terborgh* noted that the annual air temps are more uniform, high and constant over a broad range of latitudes (a 50° belt of latitude - 25°N to 25°S), which means that organisms can spread over a huge area and not encounter a dramatic change in temps -*Michael Rosenzweig* suggested that w/in this much larger area, populations could be much larger (and thus less likely to go extinct) -furthermore, allopatric speciation may be more likely for species w/ large geographic ranges -geographic barriers separate populations, which then evolve separately to the point of divergence

Nonequilibrium communities and disturbance: Disturbances

-a disturbance is any event that disrupts the community, population, or ecosystem, often by eliminating individuals or altering resource availability -disturbance changes the resources of the habitats, changes substratum availability, or changes the physical environment -organisms are usually removed or killed -fire, floods, tree falls, overturned rocks, nutrient inputs - all of these phenomena are disturbances at different scales -often 'disturbance' is not a single factor: disturbance often is a combination of factors that currently or recently disrupted a system

Pollution: Persistence

-a pollutant's persistence refers to how long the pollutant stays around, affecting the environment, until the pollutant is broken down by physical and biological degradation, or diluted to the point that it no longer has an effect 1) Some pollutants are degradable (broken down by physical or biological activity), either slowly or fairly rapidly -a biodegradable chemical is one that can be degraded by the enzymatic activity of living things, especially by bacteria 2) Some pollutants are not broken down by physical or biological processes -we call these persistent or nondegradable pollutants

Resources: What is a resource?

-a resource is anything we get from the physical environment to meet our needs and wants -some resources are directly available for use: fresh air, fresh water, naturally growing edible plants -but many potential resources, such as oil, iron, groundwater, crops, fish and game animals, are not directly available -they become usable resources only because of our ingenuity, economic incentives, cultural beliefs or to fulfill a need (for example, certain cultures eat insects. Could you eat a grasshopper, or beetle grub, or a slug? Before you go "Ewwww", think about lobsters, shrimp and oysters)

Keystone species: keystone predators and ecosystem engineers Ecosystem engineer

-a second type of keystone species is called an ecosystem engineer -an ecosystem engineer is an organism that significantly creates, modifies, maintains or destroys a physical habitat, which in turn affects the species diversity and habitat heterogeneity of the environment -most ecologists view engineers as a subset of keystone species -there are two distinct 'types' of engineers: allogenic and autogenic 1) Classic *allogenic ecosystem engineers* change the physical environment by transforming living and nonliving materials into another state -beavers and elephants are classic examples -by cutting down trees and using the logs to build dams, beavers create relatively permanent pond habitat out of streams, which allows other aquatic and riparian species to persist, increasing the biodiversity of an area -by migrating over long distances and moving through forests, browsing on the trees and digging up trees, elephants convert woodlands in grasslands and shrublands, and they maintain the grassland / shrubland habitats over time -when you remove beavers and elephants, the habitats revert back to their original states -humans, through our activities, can greatly modify the environment and alter community richness 2) Classic *autogenic ecosystem engineers* change the environment using parts of their own physical bodies (both living and dead) -the classic examples are corals -as these organisms grow, they create habitat for other species -again, once these species are lost in an area, species diversity declines -as corals die, the reef no longer grows and many species are lost over time -large trees and kelps also act as autogenic engineers, creating habitat through the 3D increase in habitat complexity from their physical bodies

Causes of autogenic succession: All 3 models predict earlier species usually will be pioneer species

-all 3 models predict earlier species *usually* will be pioneer species, due to the need of rapid colonization -they differ by the method succession proceeds: facilitation by earlier species (facilitation), species replacement inhibited by previous colonists until the latter are killed/weakened (inhibition), or more efficient, slower growing, competitive species wait out short-lived species (tolerance) -facilitation predominates in many instances in early primary succession, whereas inhibition could be more common in secondary succession (allelopathy, for example, is considered to be a major factor for inhibition)

Biogeochemical cycles (and environmental impacts of pollution): Characteristics of systems: Systems may be open or closed

-an open system exchanges factors or materials (inputs and outputs) with other systems -the Earth is actually an open system, because it receives inputs in the form of sunlight -a system that is closed in regards to one factor does not exchange the factor with another system -systems may be closed with respect to one factor and open for others -for example, the amount of phosphate (a nutrient needed for growth) is small and tends to remain in a lake system, thus little or no phosphate enters or leaves the system -phosphates are recycled (i.e., the lake is essentially 'closed' with respect to phosphates) -water (rain and rivers, underground aquifers) flows freely from one system (streams) to the next (lake or ocean) -the lake ecosystem thus would be considered 'open' with respect to water -in reality, no system on Earth is a totally closed system that is completely separate from other systems with respect to all factors -we refer to systems as closed, with respect to one factor, if the system retains and recycles that factor

History of Community Ecology: Ecotones, continuums, and gradients

-as discussed earlier, *ecotones* are regions of rapid replacement of species along an environmental gradient - the transition zone b/w two different types of habitat -closed communities would have distinct ecotones or sharp distinctions b/w adjacent communities ex: the boundary b/w the terrestrial forest and the lake usually is quite distinct, due to a sharp physical boundary - the water's edge -changes in soil chemical composition can be another cause of a sharp, distinct boundaries -small, regional scale differences in microclimate (sunlight, rainfall, humidity) are another cause -north and south slopes of mountains have different plant communities, presumably due to the change in aspect affects amount of solar radiation that strikes the slope, as well as differences in humidity and rainfall patterns -many ecotones should thus be quite clearly defined and they should be commonly observed as you move from one community to another Figure 4: -depicts a clearly defined ecotone, where two distinct communities (represented by the different species) are clearly distinguishable from each other -this leads to the next question on the existence of open or closed communities: do the dominant species' ranges signal the distributional limits for all other species of their communities? -Gleason argued that w/ open communities you would see few ecotones -according to Gleason, species are distributed randomly w/ respect to each other -in this case, ecologists often would have to arbitrarily define the community's boundaries Figure 5: -there is no clearly defined ecotone -as you move along the transect, few (if any) of the relative importance or distributions of the different species correlate w/ each other

Biogeochemical cycles (and environmental impacts of pollution): The Hubbard Brook Experimental Forest

-classic experiments showing the retention or loss of nutrients was conducted by Gene Likens and his collaborators at The Hubbard Brook Experimental Forest site -the amount of nutrients that are in flux is quite small compared to the size of the resource pools in ecosystems -thus, turnover rates tend to be quite small in undisturbed sites and nutrients are retained by the ecosystems -however, with a large disturbance event, the flux of nutrients could become large and unstable, leading to a dramatic change in the ecosystem -in one study, Liken and collaborators deforested an entire watershed -the rate of nutrient loss leaving the system via the stream subsequently increased 10 to 20 fold compared to undisturbed watersheds nearby -two reasons caused this loss -first with the loss of the trees, a greater volume of water (an increase of 40%) was released from the stream, instead of entering the atmosphere via evapotranspiration of the leaves -this in turn increased the amount of leaching as the water percolated through the bare soils -as decomposers broke down the dead plant material, there were no plants roots taking up the nutrients as the decomposers released them from the litter, so the leached nutrients were carried away

Communities and Ecosystems: The emergent properties of communities

-communities have what some ecologists call emergent properties ^these are attributes that are not seen in an individual or a population -the biggest emergent property is that communities have definite *trophic structure* -describing the trophic structure of a community allows us to ask questions on how efficient energy flow is from one level to the next Ex: Sun 1st trophic level: producers, autotrophs 2nd trophic level: consumers, heterotrophs, herbivores 3rd trophic level: carnivores 4th trophic level: carnivores Prairie 1st trophic level: grasses and forbs 2nd trophic level: insects 3rd trophic level: songbirds 4th trophic level: coyote Forest 1st trophic level: trees and forbs 2nd trophic level: mice 3rd trophic level: fox 4th trophic level: mountain lion Lake 1st trophic level: phytoplankton 2nd trophic level: zooplankton 3rd trophic level: planktivorous fish 4th trophic level: eagles, piscivorous fish

Complex interactions in communities: HSS (aka "the world is green") Hypothesis

-competition, predation and disturbance interact in complex ways to structure communities, bc of both direct and indirect species interactions occurring among species -*Nelson Hairston*, *Fred E. Smith* and *Larry Slobodkin* (1960s, Americans) developed the *HSS hypothesis* also called the "*the world is green*" hypothesis (Figure 7) -in this hypothesis, herbivores as a whole aren't considered food-limited, and are thus not likely to compete for resources -little competition occurs among the herbivores, but they are kept in check by their predators, who compete with each other -at the plant level, competition is an important cause limiting their growth, bc the herbivores are not abundant enough to control plants by herbivory -like keystone predation, and trophic cascade mechanisms, this hypothesis is a 'top-down' type of control

Island biogeography: one major equilibrium theory The effect of size and shape for ecological islands

-ecologists have long noted that the bigger the island, the greater the number of species -we discussed earlier the relationship between area and species diversity (look at the species-area curve figure): the bigger the island, the more niches and habitats, thus more species -at a certain point however, you may reach a leveling point in the additional numbers of species you add with increasing area -with respect to shape, islands should be more circular in shape, not long and thin -in addition, they shouldn't be fragmented -is one large island better than many small islands that collectively are the same size? -the accumulated area of many small islands may be equal to that of one large island, but the larger island may have more species, because there is greater habitat diversity among the patches that make up the landscape of a large island -the area of a given small island may act as one uniform type of patch

Efficiencies in the flow of energy in an ecosystem: Energy flows and nutrients cycle in ecosystems

-energy comes from the sun and is captured and transformed into chemical energy by the autotrophic plants -in turn, the plants become various-sized packets of food for animals, which in turn produce animal-sized packets of food for carnivores -along the way, energy is lost primarily as heat, which escapes ultimately back into outer space -nutrients, however, are recycled back into the food web by the process of biogeochemical cycles: the nutrients return to a nutrient pool, and are reused by plants to form more food

Communities and Ecosystems: Food web

-extending these ideas further is the concept of a *food web* -food webs consists of many interacting and interconnected food chains -detritivores are often considered to be separate food webs, w/ links to the trophic food web Figure 1: -in this example, the raccoon and eagle represent the top carnivores -phytoplankton, algae and macrophytes (aquatic vascular plants with roots) serve as the basal producers -the animals in b/w the top carnivores and the producers represent the various herbivores and carnivores sitting at different levels -*there are two food webs in an ecosystem that are linked by decomposition* -*the typical trophic food web (whose various trophic levels are linked by predator-prey interactions) is connected to the detritivore food web* -organisms, as they die, become dead organic matter, which then is consumed by the detritivores and decomposers -particulate organic matter (POM) consists of dead leaves, stems, and dead animal bodies, along w/ associated fungi and bacteria -dissolved organic matter (DOM) consists of dissolved organic molecules from living and dead organisms (lipids, sugars, amino acids, organic acids, and so on) -the dead organic matter serves as an energy source for the detritivore food web -detritivores and decomposers consume dead top carnivores, for example, but we usually do not include them as a 'supreme' carnivore above the top carnivores (which kill and eat living prey)

Beta Diversity: Description

-gamma diversity is also connected to the *turnover*, or *change in species composition*, of the communities as you move from one site to another -this turnover or change in community composition is called beta diversity (alternatively, it can refer to the *similarity* of two communities, not the difference b/w them)

Gamma Diversity: Description

-gamma diversity refers to the total # of species counted in a broad geographical area (or the total # in the study) -if one community had 20 species, and another community had 30 species (where 10 of the 30 species of community 2 were also in community 1), the overall gamma diversity (the total # of species observed in both sites) is equal to 40 species -gamma diversity obviously is related to the alpha diversity values of all of the communities examined -as you might predict, as you increase the # of communities, the total # of species (gamma diversity) increases

Stability and diversity: equilibrium versus nonequilibrium communities Idea that simple communities are more stable

-however, other data seem to suggest that simple communities are more stable, not less stable, compared to complex communities 1) -counter to Elton's and MacArthur's ideas, Robert May (1974, British-American) championed the opposite idea about the relationship between diversity and stability -May used the following analogy to defend his thesis: simple devices do not break down as often as complex ones (simple can opener versus an electronic one) -in addition, May argued that mathematical models show that increasing complexity reduces stability, in general -in hypothetical models that assigned trophic level links at random, May discovered that more 'diverse' communities were less 'stable' -a loss of a single species caused fluctuations in numerical stability, and subsequent loss of further species -May's hypothesis suggested that the stability of the community goes up with fewer links (connections) among the members -his work showed that if diversity causes stability in the real world, it is not a mathematical consequence of species interactions (Lotka-Volterra growth, predator-prey, and competition models) -May's model suggested that a more diverse community has a more complex web of interactions among its component species, and that the effect of a disturbance on one species may affect many other species -for example, suppose a prolonged drought kills one common species of plant in a diverse community -this single extinction event in turn may cause extinction or fluctuating population sizes among the animals that fed on the plant species, which in turn may affect higher level consumers, possibly causing extinction among the higher trophic level consumers 2) -about a year after his first paper, Robert May suggested a slight alteration with his theory of simpler communities are more stable -May argued that an increase in diversity may make individual species more vulnerable, but the total biomass of the entire ecosystem may be stabilized in a more complex (diverse) ecosystem, because other species can compensate for the species that are negatively affected -in the hypothetical drought example described above, certain plants with greater water storage capacity, or deeper root systems, or greater resistance to drought conditions, can increase as the less drought-tolerant plant species decline -at the level of the population, we may see dramatic variations in population size (no numerical stability in a given population) but at the level of the entire ecosystem, the properties measured at this level (biomass, productivity) may be more constant through time, regardless of disturbance (in this view, more constant = more stable)

Ecosystem energetics: Respiratory costs vs production energy

-humans are very successful but highly inefficient, in terms of generating new tissue (increasing P) -perhaps 90+% of the energy we consume is used to maintain body temperatures and basal metabolism, but perhaps only 1 to 3 % goes into production (growth and gametes) -for many animals, respiratory costs take up as much as 80% of the ingested energy, leaving perhaps 20% for growth and reproduction -clearly, migration and hibernation (and other avoidance mechanisms) can be quite important for energy savings in many animals; savings that can be used for fitness gains -animals that have to live in suboptimal portions of their habitats (as a consequence of predation pressures or intraspecific and interspecific competition) may have to use more energy for basal metabolism, osmoregulation and thermoregulation, and have less evolutionary fitness

Stability and diversity: equilibrium versus nonequilibrium communities Switching between prey species

-in addition, MacArthur and others argued that if one prey species went locally extinct, and the consumers at the next level feed on many different species (more links), then those higher trophic level consumers could switch to other food sources -because of this switching, no further loss of species would need to occur -on the other hand, if a given consumer specializes on only one prey species, the specialist would go extinct when that prey went extinct (fewer links among the species) -if a predator is capable of switching to other prey, then its numerical stability could stay constant, even in the face of fluctuating numbers of its prey populations

Efficiencies in the flow of energy in an ecosystem: The relationship between primary and secondary productivity

-in general the amount of secondary productivity to a system is positively influenced by the amount of net primary productivity, as would be expected -however, most of the primary productivity is not consumed by herbivores -secondary productivity is about 10% of that by the primary producers Why is this? -the productivity of the producers ends up in four distinct components of an ecosystem, as heat, as herbivore/carnivore biomass of higher trophic level consumers, as biomass in the form of decomposers and detritivores, and as organic material transported and buried into geologic sediments

Pollution: "Do trees pollute?"

1) It is true that trees give off measurable amounts of ozone (a harmful pollutant at sea level), as well as other compounds that are identical to manmade 'pollutants' -for this course, we will redefine the definition of pollution to mean the changes in resources due to the usually small amounts of "naturally-produced pollution", along with the additional changes produced by human activity 2) Natural ecosystems are capable of dealing with the small amount of "natural pollution" produced naturally -species have been evolving and interacting for millions of years -however, ecosystems may not be able to handle the additional pollutants produced by human society

Stability and diversity: equilibrium versus nonequilibrium communities Summary - relationship between complexity and stability not clear-cut

-in summary, the relationship between the complexity of a community and its stability is not clear-cut -as mentioned earlier, it depends on the level you look at (population versus community/ecosystem), the way the community is perturbed, and the way stability and diversity and structure are assessed 1) Recently a consensus on this problem is emerging -David Tilman (American, recall his work on competition earlier this semester) reported a few years ago that while increased diversity benefits ecosystems as a whole, stabilizing the system and boosting its overall productivity, the populations of individual species fluctuate more wildly (including extinction) in diverse ecosystems than in simpler ones -according to this idea, May, McArthur and Elton may all be partially correct 2) Tilman and his students watched patches of grassland for several years, noting that more diverse plots did better in resisting disturbance (a long two-year drought had a strong impact on productivity; high diversity plots suffered lower declines in biomass during the drought than species-poor plots), the ability of retaining nutrients was greater in diverse plots, and increased productivity occurred in diverse plots 3) However, populations within diverse plots fluctuated widely, as May predicted in his theoretical research 4) Does this have any consequences for agriculture, or for species conservation? -the results of Tilman and his colleagues suggest that there is a great value in establishing greater diversity in agricultural fields, rangeland and conservation lands -on the other hand, diversity does not guarantee that certain species (for example, the various endangered species we try to protect: spotted owls, snail darters, bald eagles, etc.) will survive, if populations are already too sparse to recover (recall the Allee effect)

Island biogeography: one major equilibrium theory Island size and number of species island could support

-in the 1960s, Robert MacArthur and Edward O. Wilson (American) developed the equilibrium theory of island biogeography (abbreviated M-W) -they were initially interested in the connection between island size and the number of species a given island could support (Islands by the way do not have to be islands. They could be mountaintops, or isolated lakes, or any areas of hospitable land surrounded by inhospitable land) -the number of species on an 'island' is due to a balance between regional processes of immigration and local processes of extinction

Ecosystem energetics: Hypothetical example of the energy budget

-let's say we wanted to know the energy budget of a perch feeding on amphipods -we fed our fish a number of amphipod prey ad libitum for 28 days, and then gathered the following data: -C = number of amphipods x energy in an amphipod (calculated by bomb calorimetry) -F = collect feces and calculate the energy content using a bomb calorimeter -P = increase in tissue = J/g of flesh in perch x grams of new tissue (weighed before and after) -U = amount of NH4 excreted x J/g in ammonia (20.5 J/g) -R = measured by O2 uptake over 28 day period = 19.5 J/liter O2 consumed C = F + U+ R + P (58.9 kJ)= 9.6 kJ 6.4 kJ 32 kJ 11.9kJ = 59.9kJ 101.5% = 16.3% 10.7% 54.3% 20.2% -the above example has the numbers adding up to 59.9 kJ, not 58.9, but it is close -small mistakes occurred probably with the respiration term (the oxygen uptake term is largest) -perhaps oxygen uptake was measured during the day and not at night (when the perch may have lower resting metabolic rates), and thus this difference overestimated the costs

Ecosystem energetics: Aquatic and terrestrial animals differ in their form of stored energy

-many aquatic animals use a variety of materials as their stored energy reserves -for example, many molluscs use proteins or carbohydrates as their stored energy source -many terrestrial animals use fats as food reserves, because it represents less 'weight' to carry around, compared to proteins and glycogen and other carbohydrates -a considerable amount of water is needed to store glycogen -nonetheless, glycogen is an important form of stored energy, especially for animals exposed to anoxic environments, because glycogen can be broken down to glucose, which can be oxidized during both aerobic and anaerobic metabolism

Keystone species: keystone predators and ecosystem engineers Yellowstone Park and the re-establishment of gray wolves

-many scientists have been studying the Yellowstone Park community now for some time -gray wolves were extirpated from Yellowstone during the 1920s -their population size was small, consisting of roughly ten packs; perhaps up to a hundred wolves were in the area at any one time -elk populations (the wolves' major prey) increased ten-fold or more (numbering tens of thousands) over the next seven decades, despite efforts to manage the herd via hunting -the elk caused a major change in the vegetation structure, species composition, and diversity of plants -the elk browsed on trees and shrubs near the lowland streams, instead of higher altitudes -the intense browsing caused the loss of aspen, cottonwood, willow and other trees, as well as the riparian vegetation around wetlands created by beavers -the area become 'open' -once wolves were reintroduced in the mid-1990s, major changes occurred since -wolf populations have returned to about 100 individuals in about ten packs -elk populations dropped to several thousand individuals (the wolves kill rough 22 elk per wolf annually) -the over-browsed vegetation was given a chance to recover -aspens and other trees have increased, particularly along streams and the lower elevations of the park -elk started to shy away from the riparian zones (because they were more vulnerable to wolf predation) and thus spent more time higher up in altitude -the elk population decline was not just due to predation; the elk were under more stress, and elk birth rates were lowered -berry-producing shrubs (another favorite of elk) increased in the aspen stands, in turn, the species diversity of invertebrates, birds and mammals that feed and live in riparian habitat have increased -the grizzly bears increased the proportion of their diet on berries, and small predators, such as red foxes, have returned (coyotes tend to kill the foxes) -although foxes also feed on small mammals and birds, the reduced predation by the coyotes has allowed some small mammal and bird species to recover, which in turn has affected the populations of various small plants -wolves often claim the kills of mountain lions, which generally are run off the carcass -mountain lions have also retreated back into the higher elevations -the reintroduction had several other impacts, including causing other trophic cascades -in the absence of wolves, coyotes had increased, causing some small mammal and pronghorn antelope populations to decline -coyote populations declined by 50% after the wolf reintroduction, and pronghorns have increased by 50% -coyotes now tend to stay in steep upland terrain, where they are more safe from wolves -although wolves are larger and more powerful (coyotes caught in the open flat terrain in the lower altitudes are often killed), the two species can kill each other, depending on the situation and numbers -coyotes are more agile in the steeper terrain and can escape from wolves -the carcasses created by successful wolf hunts provide a large amount of food for carrion eaters, including mustelids (wolverines and badgers), coyotes, foxes, martens, ravens, and eagles -in addition to affecting succession and the diversity of plants and animals, the reintroduction of wolves literally have changed the physical environment as well -beavers rely on willow for their dams and for food to survive the harsh winters -more beavers came back to the willow stands along the streams (beaver colonies have increased roughly ten-fold since the wolf reintroduction) and began to build dams, which in turn created more riparian habitat, stabilized water flow, reduced erosion, retained water (which recharges the water table) and nutrients, and increased the species diversity in the streams -animals that inhabit beaver ponds include moose, otters, mink, many fish, waterfowl, amphibians, and many invertebrates

Stability and diversity: equilibrium versus nonequilibrium communities Numerical stability

-numerical stability of individual populations is but one definition of stability, and its effect is at the level of the population -as discussed above, a predator can switch between two prey species, the predator's numbers may be able to stay constant over time by switching back and forth between two fluctuating prey populations

Biogeochemical cycles (and environmental impacts of pollution): Intro

-nutrients tend to stay within their ecosystems -each element follows a unique pathway, due to the transformation that occur along the way -for example, nitrogen is found in many different molecules in different compartments: N2 in the atmosphere, ammonia (NH or NH +) and nitrates (NO -) in the water or soil, and proteins and urea in animals -although the major elemental cycles have unique properties, all nutrient cycles have the same overall structure -first, let's discuss several terms concerning nutrient cycles (Figure 19): -compartments - are components of the cycle, including resource pools and resource sinks, and organisms -flux - is defined as the movement of nutrients between compartments and their magnitudes -turnover time - is calculated as the amount of nutrient in compartment divided by the average flux into or out of the compartment (assuming that the compartment size stays the same and flux in = flux out) -a system is a part of the universe that can be isolated and studied -we could talk about the entire Earth, a watershed, one population, or a single multicellular organism as a 'system'. -to a parasite, the human digestive tract is the system in which it lives -on the tundra, water in a depression formed by a footstep is a system for microscopic organisms -systems have inputs and outputs, and we can study how different systems function and hopefully create generalizations, regardless of their size

Ecosystem energetics: Often the work component of the energy budget are underestimated

-often the work component of the energy budget are underestimated -however, the energy an animal uses to do work can be large! -think of the energy lost as you plow through water; some of your energy goes into the water as it is being pushed away -you cannot ignore work -for example, animals use energy to alter the environment -beaver dams, beehives, human laborers put energy into ordered structures

Nonequilibrium communities and disturbance: Background ideas

-over the last few decades, many ecologists have concluded that equilibrium communities rarely occur -in most habitats, there is sufficient disturbance occurring to prevent communities from reaching any equilibrium state Background ideas concerning nonequilibrium communities: 1) For a nonequilibrium community, disturbance, environmental heterogeneity, and recruitment (colonization and successful establishment of a new species) are thought to be the important factors affecting species diversity and community structure, not the equilibrium processes of predation and competition 2) About 60 years ago, two prominent ecologists (H. G. Andrewartha [Herbert George, Australian] and L. C. Birch [Louis Charles, Australian]) argued that (animal) communities are determined primarily by harsh abiotic factors of the physical environment, such as weather -abiotic forces set the range for colonization, reproduction, growth, and survival -for the nonequilibrium community, the presence or absence of any given animal species is largely determined by random processes of colonization and disturbance

The oxygen cycle: Complex

-oxygen is the byproduct of photosynthesis, and is very chemically active (form oxides with many other elements: water, carbon, sulfur, nitrogen and phosphorus, iron, and many metals) -its cycle is thus very complex, because it is part of all other cycles -the largest compartment of oxygen is the crust of the Earth, and the second compartment is the atmosphere -along with biotic activities of respiration and photosynthesis, weathering of rocks and organic compounds, along with burial of organic material (and thus oxygen) are the two main routes of oxygen cycling (between organisms [and the atmosphere] with the sediments) -water and carbon dioxide are major molecular reservoirs of oxygen, linked by aerobic respiration and photosynthesis

Alpha diversity indices: Shannon-Weaver Index

-pi is the *importance value* or the proportion of individuals of the species (I) in the total sample of individuals from the quadrat -pi is calculated as: pi = ni/N -ni is the # of individuals in the ith species -N is the total # of individuals of all species in the quadrat -evenness (E(H)) for the Shannon-Weaver Index can be calculated as: E(H) = H/H(max) = species evenness N1 = e^H -H is the Shannon-Weaver diversity index -H(max) is lnS (where S = the # of species) -E(H) therefore varies from 0 (no evenness) to 1.0 (maximal evenness, where the importance values of all species are equal) -H ranges from 0 (low diversity) to lnS (maximal diversity) -bc H is proportional to the natural log of the species #s, we will express N1 as e^H, which is proportional to the # of species (S) (N1 ranges from 1 to S) -in general, H is used only for large samples randomly drawn from large communities, where the # of species of known *Shannon Index gives more weight to rare species*

Resources: Renewable and nonrenewable

-resources come in two forms: renewable and nonrenewable resources 1) Nonrenewable resources -are resources that are not renewed at a rate fast enough to meet our demands -fossil fuels and strategic metals are nonrenewable resources that could be exhausted within a few generations -nonrenewable resources are formed primarily by geological processes, so they can be 'replenished' only over the course of millions of years -resources can also be considered 'depleted' if it is too expensive to extract the last remaining bits of its raw sources from the Earth -a nonrenewable resource usually considered economically depleted when about 80% of its estimated supply is extracted and used -the time, energy, and effort to extract any additional supply is considered to be too prohibitive -some nonrenewable resources (like copper and aluminum) can be recycled and reused, just like renewable resources, but most nonrenewable resources (like fossil fuels) cannot be recycled or reused, certainly not on a human life span (and perhaps not on a human civilization timescale either) 2) A renewable resource -is one that is regenerated by the Earth at a time scale shorter than or similar to our own life spans -air, water, soils, plants - these are renewable resources -these resources are considered renewable because on the time scale of a human lifetime, they are inexhaustible, at least at our current population levels -however, both renewable and nonrenewable resources can be depleted by excessive use -renewable resources can be depleted if used up faster than they can be produced -in addition, renewable resources can be degraded by excessive use, so that the usable amounts shrinks -soils, for example, can shrink because they have been paved over by suburban development -soils are lost via soil erosion (which in turn is a result of deforestation or bad soil management) -soils are degraded by air and water pollution -increased use of these resources, which do not renew themselves fast enough, means that less of these renewable resources are available now than in the past

Biogeochemical cycles (and environmental impacts of pollution): Characteristics of systems: Systems are responsive

-responsive, i.e., they change outputs as a result of varying inputs -imagine a lake -if a lot of water flows into a lake, its water levels may rise, and the lake shoreline increases as a result -during a dry season, the lake receives less water from runoff and streams, the lake level drops, and the shoreline recedes, and less water may be lost through outgoing streams -many systems, both physical and living, are responsive to changes in inputs and/or outputs -both pollution and resources can be viewed as inputs and outputs of systems

Island biogeography: one major equilibrium theory Supporting evidence

-supporting evidence for island biogeography comes from Dan Simberloff and E. O. Wilson (1970) -they fumigated small (methyl bromide) mangrove islands, and then watched as species accumulated back on islands (primarily arthropods) -nearest islands colonized more quickly -richness was lower initially on farther islands, and was lower over time, as what would be predicted by the model

Efficiencies in the flow of energy in an ecosystem: How much energy passes up food chains: the 10% rule

-the % of the food energy consumed that is converted to new protoplasm and thus available as food energy for the next organism in the food chain is known as efficiency of energy transfer -the first step in any food chain, the capture of light energy by photosynthesis and the production of energy-containing foods by plants, is relatively inefficient: usually less than 1% of the incident light energy striking the plant is stored as food -the efficiency of energy transfer when one animal eats a plant or another animal is a little higher, ranging from 5% to 30% or more 10% rule: -in general, it is thought that 10% of the energy that is captured at one level is available to the next, as shown by the ecological (Lindeman) efficiencies -ecologists have (very roughly) estimated that about 10% of the high-quality chemical energy available at one trophic level is transferred and stored in usable form in the bodies of the organisms at the next trophic level -the ecological efficiencies tend to stay constant from one level to the next, but they vary by considerable amount (1% to perhaps as high as 90%), so the 10% is only a rough average, but meta-analyses have shown that this general rule appears to be real -the remaining 90% of the chemical energy transferred from one trophic level to another is degraded and lost as low-quality heat to the environment

History of Community Ecology: Species Continuum Concept

-the *species continuum concept* states that w/in broad geographical areas, species replace each other gradually along gradients of physical conditions, such as temp, rainfall, moisture, and soil pH -you move along a transect, pick sample sites along the transect, and then measure the abiotic conditions and presence of species at those sites -*John T. Curtis and Robert H. Whittaker* (Americans, 1940s to 1950s) and other ecologists eventually discarded the Clementsian view using a gradient analysis of communities -each species occupies distinct and unique locations -Curtis saw gradients and a continuum on his analysis of the upland forest vegetation of Wisconsin, and then later Whittaker saw little evidence of a closed community in his study of the changes in species composition as one moved up a mountainside in the Smoky Mountains and elsewhere -each species has its own range of tolerance

Communities and Ecosystems: Community

-the ecological *community* consists of all of the interacting animal and plant species in a habitat -community interactions include feeding relationships and other interactions -a *guild* is a subset of a community - it represents the species that are distinguished by the location or method of obtaining food Ex: herbivores feeding on a tree can be divided into: 1) a leaf eater guild (consumes whole leaves) 2) a leaf miner guild (w/in the epidermis of a leaf, feeding on the parenchyma) 3) a stem borer guild 4) a root chewer guild 5) a nectar sipper guild 6) a bud-nipper guild (consumes the tender terminal ends of stems) -*it's difficult to define communities in time and space* -it's easy to look at a pond community, or the community of an isolated forest -however, a community can be difficult to define when one considers migratory organisms that may be in the community for only part of the year (ex: birds move from temperate to tropical areas) -in addition, many insects, frogs, and salamanders have life cycles that occur in water and on land: many are terrestrial adults, but the larvae are aquatic (and could be viewed as living in another community) -in addition, many mobile animals can move from one community to the next -often, the boundary for a community is impossible to define

Ecosystem energetics: Thermodynamic equation

-the energy budget equation thus is a thermodynamic equation describing the energy flow through an individual, or through the population, or through the community

Island biogeography: one major equilibrium theory Equilibrium number

-the equilibrium number of species (^S) occurs when E = I (Figure 14) -note that the species are not static in their composition; the actual species present on the island can change over time, but S stays constant once a certain time has passed Why do the lines curve? -immigration line curves downward and slope delta(y)/delta(x) decreases (flattens out) with species because of the relative ease of a few species that are good disperses (source pool from mainland is used up) -extinction line curves up with increase in S due to increase in predation and competition (more niches filled)

Stability and diversity: equilibrium versus nonequilibrium communities Max hypothetical # of trophic level links

-the maximum hypothetical number of trophic level (feeding or predator-prey) links is the maximum value for the connectance C = L/{[(S)(S-1)]/2} of the community -L = number of feeding links observed -S = species richness -the [(S)(S-1)]/2 term represents the maximum possible number of links, not counting cannibalism -the statistic C ranges from 0 to 1 -MacArthur would argue that the most stable communities are those with the greatest connectance Figure 9: -if species A was removed, you'd see 1/2 of the species in community 1 eventually go extinct, 1/3 in community 2, but only 1/6 in community 3 (species A itself) -more alternative pathways for energy to flow from one species to the next -productivity would be stable in more diverse communities

Stability and diversity: equilibrium versus nonequilibrium communities Community Structure

-the phrase 'community structure' has been used liberally, yet there are a variety of meanings to what is meant by 'community structure' a) Biological -often, species richness or species diversity is the factor called 'community structure' by the ecologist -other biological components of 'structure' include the number and types of guilds, and the relative abundance and dominance of various organisms b) Physical -the physical structure of the habitat -the type of plants often dictate what type of three-dimensional vertical and horizontal structure seen in the area -the plant types, life forms, leaf types, seasonality of plant flowering and fruiting: these are components of the physical structure of the community -increased plant physical 'structure' increases vertical heterogeneity and thus the potential for more niches

Biogeochemical cycles (and environmental impacts of pollution): Current ecological systems are similar with those of the past

-the principle of uniformitarianism states that biological and physical processes active today were active in the past, and the rates observed today are similar to that of the past -the Scottish geologist James Hutton first stated this principle in 1785 -this means that we can predict future changes in the environment, given what we know of past history -this does not mean that catastrophic changes in the environment do not occur -for example, a commonly accepted hypothesis today is that a meteoric impact 65 million years ago caused mass extinctions of many groups of organisms, including the dinosaurs -the theory of uniformitarianism does suggest that for the most part, gradual changes in the geology of an area occur and that these changes can be predictable, based on observations in the past

Efficiencies in the flow of energy in an ecosystem: Lindeman efficiency is a product of 3 efficiencies

-the rate of production at one trophic level to that of the level below it (the ecological efficiency or Lindeman efficiency) is actually the product of 3 efficiencies -we can look at these efficiencies for a trophic level as a whole, and we can look at them for a single animal 1) Exploitation efficiency (E.E.) =food energy ingested / energy in prey population =(C/T)x100 2) Assimilation efficiency (A.E.) =food energy assimilated / food energy ingested =(A/C)x100 3) Net Production efficiency (P.E.) =energy used in growth and reproduction / food energy assimilated =(P/A)x100 4) Ecological efficiency or Lindeman efficiency (L.E.) =1 x 2 x 3 =energy in growth and reproduction / energy in lower trophic level =(P/T)x100 5) Exploitation efficiency -exploitation efficiency goes up with higher trophic levels (=food energy ingested / energy in prey population = (C/T)x100)

Alpha diversity indices: Why both species richness and species evenness must be counted

-the simplest and oldest measurement of species diversity is a count of the # of species, or *species richness* (S) of a community -a second measurement of species diversity arose from a branch of mathematics called information theory -in this measurement, diversity is influenced by heterogeneity -one common problem using only the # of species as a measure of diversity is that all species are treated equally, regardless of their relative abundances -in addition, species richness is of limited use if the # of uncounted species is large -thus, in some cases, richness alone may be adequate - however, richness by itself may not tell the whole story -the following diversity indexes combine both *species richness* (# of species present in the habitat) and *species evenness* (the relative frequencies of each species) into a single concept that is more robust in describing the diversity of a community Figure 2: -as was mentioned above, species diversity generally consists of two components -the first component is the *species richness* (# of species present) -in the communities depicted in Figure 2 A and B, the left-hand hypothetical community (A) is higher in species richness bc more species are present than in the right-hand community (B) -each symbol represents individuals of different species -the second component of species diversity is *species evenness* -communities are generally characterized by having several common (dominant) species (species w/ large densities), many species of intermediate abundances, and many rare species -look at the two communities depicted in Figure 2 C and D -the hypothetical community on the right (D) has greater evenness than the community on the left (C), but both communities have four species (they have the same richness) -in community C, most of the individuals are of one species

Alpha diversity indices: Alpha diversity depends on two parts

-the species diversity (the alpha diversity) of a given community depends on two parts: a) *species richness* (S) or the total # of species b) the % of individuals of the community in each species, or *species evenness* -*diversity* includes not only the # of species present in a community, but also the relative frequencies of each species -many factors affect diversity (ex: all of the following factors affect the diversity of organisms in the community: disturbance, succession, predation, competition, mutualism, time scales, spatial scales, # of microhabitats and spatial heterogeneity, climatic conditions, and habitat stability)

Pollution: Prevention and cleanup

-there are 2 main approaches for dealing with pollution: prevention and cleanup 1) Prevention -means minimizing the amount of pollutant released into the environment in the first place, and it is done by the companies and businesses using the resources, as mandated by governmental laws 2) Cleanup -unfortunately, cleanup is what typically occurs, removing or detoxifying pollutants after they have been released, done by government agencies and the efforts of individuals and environmental groups -cleanup often entails moving the pollutants from one place to another -once pollutants have been dispersed into the environment (air or water or soil), it costs a lot of money to clean up the dispersed pollutants, far more than the costs that would have been spent to prevent the release of the pollutant in the first place

Ecosystem energetics: Variety of ways to determine components of energy budget

-there are a variety of ways to determine the various components of the energy budget -much of the energy budget is measured indirectly by oxygen consumption (as a measure of metabolic rate), and other methods, such as biomass energy (measured with a calorimeter) -often the heat energy is measured, or the amount of CO2 produced, for the respiration components -radioactive tracers can be used to determine the fate of various foodstuffs

Alpha diversity indices: 3 diversity indices

-these terms are usually applied when considering the species diversity w/in one site or location -this type of diversity is called *alpha diversity* -many methods of measuring alpha diversity have been developed (we will examine three) -the first index of diversity is *species richness* (S) -it's simply the total # of species in the quadrat (or habitat or area or community, depending on how the measurement was taken) -there are two other diversity indexes, however, that take species evenness into account -they are used to answer a simple question: "How difficult would it be to predict the species of the next individual encountered?" -the first is the *Shannon-Weaver Index (H or H')* ^also called the Shannon-Wiener Index, or *Shannon index*

Efficiencies in the flow of energy in an ecosystem: How much of the NPP do humans use?

-we are only one species out of 1.5 million named species, but we use a disproportionate amount of resources -tt depends on the definition of 'use' -Peter Vitousek and his colleagues in the 1980s produced some of the earliest estimates -recently, it is estimated that we use roughly 20% of the world's terrestrial NPP due to food production, shelter, fuel wood, fuels, and clothing -the estimates also include 'missing' production due to deforestation and land use, pollution effects, urban/suburban sprawl, and agriculture -if the Earth's human population were to double in the next 40 years, and many of the developing countries begin to match the lifestyles of the developed countries, we could use up to 35% of the world's terrestrial NPP and a sizable amount of the marine NPP - thus only 65% would be available to the rest of the world's biota! -we humans are large animals, representing roughly 500 million tons of biomass (less than 1% of the estimated animal biomass on Earth, and far less than the estimated organismal biomass of 3 trillion tons present at any one time), but we use up a disproportionate share of the NPP

Efficiencies in the flow of energy in an ecosystem: Production efficiencies decrease with higher trophic levels

-we can look at two different kinds of production efficiencies: gross production efficiency and net production efficiency 1) Gross Production Efficiency (G.P.E.) =P/C x 100 -this is the proportion of consumed energy that goes into the production of gametes and new tissue -in our perch example, the G.P.E. = 20.2% (which is actually fairly high) 2) Net Production Efficiency (N.P.E.) =P/A x 100 -this is the proportion of assimilated energy put into production -of what the animal is able to assimilate, what amount becomes flesh versus what is lost in respiration (in our perch example, N.P.E. = 23.7%) -comparing these two production efficiencies can provide information about food quality ^if G.P.E. = N.P.E., quality of food is high ^if G.P.E. >> N.P.E., quality of food is low -predators have a lower N.P.E. (due to respiration lost actively hunting food of high caloric value) as opposed to cows and other herbivores, who have a low G.P.E. (due to the lower quality of their food) 3) Production efficiencies tend to go down with higher trophic level consumers -plants use 20 to 75% of assimilated energy for respiration, thus their N.P.E. is equal to 25 to 80 % -tropical plants (aquatic and terrestrial) use more energy in respiration than do temperate zone plants -net production efficiencies range around 75 to 85 % for temperate zone plants, and lower (40 to 60%) for tropical plants 4) Most plants' production efficiencies are higher than most animals' production efficiencies because herbivores and carnivores move around, relative to sessile plants -plant production efficiencies tend to be higher than animals, in part because of the higher activity of animals relative to the sessile plants -many herbivores use 60 to 90% of their assimilated energy for respiration (thus their N.P.E. ranges from 10 to 40%); the N. P. E. is low in part because herbivores spend a lot of respiration energy trying to digest inedible plant material (wood) -in addition, some of the quality of the plant material may be low in certain nutrients, such as nitrogen -there are ways to increase the production efficiencies -many herbivores have symbiotic bacteria in their guts to help digest wood by the bacteria's cellulases -some ungulates chew cud or produce special feces that they redigest; this behavior (coprophagy) aids in digestion of plant material by mixing saliva and moisture and bacteria to plant parts, physically breaking the woody material apart to increase the surface area of the wood to be digested 5) Production and Assimilation efficiencies and endotherms/ectotherms -it is important to distinguish between ectothermic and endothermic predators -organisms at higher trophic levels usually have lower production efficiencies (endotherms) but have higher assimilation efficiencies -flesh is easier to digest and is more calorie-rich than the equivalent amount of plant material -fur and bone are of course exceptions, but more protein and fat is present in animal flesh -organisms at lower trophic levels usually have higher production efficiencies, because their respiration costs are lower -the lower trophic level consumers are often ectotherms (for example, insects), and not endotherms -respiration takes up 97 to 99% of the assimilated energy in mammals and birds, and only 1 to 3 % of the assimilated energy goes into production -for insects, the energy loss is less: only 50 to 90% of the assimilated energy goes into respiration 6) Dung can be an important resource -as mentioned earlier, some herbivores are coprophagic (they eat feces) [of herbivores], because the bacteria have worked over the plant material and it thus can be eaten again -some predators may also occasionally eat feces of herbivores for this purpose -however, there are not very many coprophagic animals feeding on carnivore dung -there is relatively less energy available in carnivore dung, because carnivores eat more easily assimilated animal tissue, instead of plant tissue, which is not so easily assimilated 7) Insectivores have an N.P.E. of 20 to 30% -their production efficiencies are lower in large part due to the indigestible chitinous exoskeletons of their insect prey -large amounts of chitin are present in the feces of insectivores 8) Carnivores have to use up 90% or more of their assimilated energy in respiration, particularly because they: a) travel long distances over time, and b) are also endothermic -therefore they must expend a lot of energy in keeping their body temperature constant (their N.P.E. < 10 %) 9) Aquatic animals in general have higher production efficiencies -aquatic animals may channel as much as 75% of their energy into growth and reproduction -why aquatic animals have higher efficiencies is in part due to many of them acting as ectotherms, thus not using large amounts of energy to stay warm in an environment that would rapidly conduct heat energy away from their bodies

Island biogeography: one major equilibrium theory Other factors or complications to take into account that might strongly affect M-W

1) First, there may not have been enough time elapsed for colonization to happen at far islands 2) The rate at which speciation occurs may be as great or greater than colonization and extinction rates, and thus evolution plays a more important role 3) Conditions on the islands exist that preclude many species from establishing populations, even if they colonize -for example, if fresh water sources or food plants for animals are not present, then the animals may not survive after colonizing 4) Not all mainland species have an equal opportunity to colonize a given island, because some can fly or disperse long distances, and others cannot fly or disperse. 5) Extinction and immigration are not independent, because certain species could be 'rescued' from extinction by additional colonists 6) Some islands may simply be too small, thus no species can live on them due to the lack of suitable habitat 7) The dispersal of species among islands also is important, instead of relying solely on the dispersal of mainland species

Succession: Description

-when an area of land is allowed to go undisturbed for a long period of time, a somewhat predictable series of changes in species composition (particularly concerning the dominant plants) occurs -this sequence of change is called *succession* 1) Much of the empirical evidence for succession comes from observing changes in the plant communities on abandoned farm fields (this phenomenon is called *old-field succession*) -old-field succession is one type of *secondary succession*, where a disturbance has reset the community, and succession starts over -there are several types of secondary succession 2) The successional sequence (weeds to grasses to shrubs to trees) is somewhat predictable for a given geographic region and appears to consist of stages -a *seral stage* (*sere*) is the species assemblage (community) observed at one point in time in a given ecosystem undergoing succession -the *pioneer community* and *climax community* are the two end points or communities observed at the beginning and end of succession, respectively 3) *Ecologists recognize two main groups of causal factors that cause succession, where either abiotic and biotic factors are viewed as the main drivers of change* -*autogenic succession* -- succession caused by biotic interactions among the living organisms of the community (caused by the plants and animals themselves) -*allogenic succession* -- caused by changes in the physical or abiotic components of the ecosystem ^these two classes of causal factors generally work together to alter the ecological community over time, although one class may be more influential than the other in different places

Succession: Closed vs. open communities and succession

1) *Frederic Clements* (American, 1916) developed the *monoclimax theory* -Clements thought that a mature community that continually replaces itself indefinitely was a natural unit, and the mature community can be viewed as a *closed community* (where the same species coexisted together and other species would find it hard to invade) -Clements believed that climate alone determined the climax community of an area -he recognized 14 climax communities in North America: 2 grasslands (prairie, tundra), 3 types of shrub areas, and 9 different types of forests (including pine forest and beech-oak forest) -in Clements' view, physical disturbance, soils, animals and topography are not very important -these other factors only cause 'immature' communities to develop - communities that only take longer to mature 2) However, the *polyclimax theory* (*A. Tansley*, British, 1939) recognized that the local climax may be governed by a variety of one or more factors, particularly soil conditions, but climate, topography, and fire are also important -due to the varying impacts of these factors, there is a constellation of similar climax communities that could occur 3) Today, communities are viewed by most ecologists as being *open communities* -their species composition varies over a continuum of environmental gradients: soil type, moisture levels, and so on -*Robert H. Whittaker* (American, 1953) developed the *climax-pattern theory* -in his view, open climax communities are common, where their composition depends on particular environmental conditions -there is a continuity of climax types, which vary gradually along environmental gradients -however, Whittaker's work suggested that different climax communities are not necessarily separable into discrete climax types 4) It is quite difficult to point out a stable climax community in the field -we can point to what looks like a climax community (it's a community that is very long-lived and is replaced quite slowly) (ex: it might take 100-300 years to finish old-field succession, but by that time a major disturbance has reset the clock) -some ecologists believe that the temperate forest communities are still recovering from the last ice age (the Wisconsin Ice Age about 11,000 years ago)

History of Community Ecology: Early History

1) *Stephen A. Forbes* (American, 1887) published "The lake as a microcosm" -this article was the first generally recognized article specifically on the topic of the biological community -Forbes argued that the lake is a complex machine and he viewed the lake as an 'organism' -all species eventually worked out their differences (predator/prey, competition, etc.) via natural selection to the point where the community "looked" as if it was in equilibrium, w/ all species interdependent upon each other -for individuals, life was fierce, but at the community level (species #s), there is more 'constancy' (in the total #s of predators and prey) 2) *Henry A. Cowles* (American, 1899) examined the long-term change in the plant community (succession) of sand dunes next to Lake Michigan, in Indiana -Cowles thought succession worked in predictable manner: herbs are initially seen on the youngest dunes nearest the shoreline, and eventually the climax community (consisting of beach and maples) develops on old dunes some distance from the shore -these back dunes are rarely inundated by the lake -to Cowles, physiography (the importance of geological land forms) and the control exerted by the plants were the two most important factors affecting succession 3) The zoologist *Victor E. Shelford* (American, the first ESA President) and his botanist colleague *Frederic E. Clements* (American) also argued a very *organismal or holistic view of communities* -they (and many others) championed the idea that a community's 'parts' and 'development' are like an organism's 'parts' and 'development' -in their view, communities were sharply-defined units where the same species always occurred together -- two patches of the same association (seral stage) are very similar in species composition -a beech-maple forest would be identical to another beech-maple forest elsewhere 4) Clements (originally at the University of Nebraska) argued that communities are *closed* -the ecological limits are similar for all species of a community, and the species always occur together -change (succession) over time was very predictable, like the changes that occur w/in a cell during the cell life cycle 5) *Clement's ideas concerning the similarity b/w an organism and an organismal community*: a) Both organisms and communities are made up of interacting parts (organism:cells; community:populations) b) Both organisms and communities continue through time, and both develop in a predictable, *orderly* pattern (organism:ontogeny; community:succession) -like organisms, communities are born, develop, mature and eventually die c) Both organisms and communities have a 'physiology' and can 'reproduce' -a community had a way of adapting to change, like an organism does, thus a community maintains a dynamic equilibrium of #s and or species, akin to the mechanism of homeostasis in individual organisms d) Clements and others developed a classification of forests, where a particular stand could be identified as a member of a given association, similar to how one could identify the species of an organism by using a taxonomic key 6) The opposite view of the Clementsian paradigm was championed by *Henry A. Gleason* (American, 1926) -Gleason challenged the holistic view of Clements, who was president of ESA at the time and was among the most influential ecologists in the country -Gleason espoused the *individualistic view of community* -one major disagreement w/ Clements' views concerned the analogy of organism and a community 'superorganism' -Gleason argued that any similarities b/w communities and organisms were superficial -succession wasn't 'autogenic' (caused by biotic interactions among the organisms in the community; succession is due to the organisms altering the environment and affecting each other) -in addition, succession was not deterministic (an outcome in the future is determined only by one specific set of previous conditions) nor is succession orderly in its progression (events occur in a specific sequence) -Gleason argued that an ordered progression towards a climax forest didn't always occur ^a prairie isn't always followed by a forest; sometimes a forest is followed by a prairie -Gleason argued that the sum of all plants in area do not make up one 'superorganism' ^instead, each species is distributed independently of each other, and they just co-occur together in some places (i.e., communities are '*open*'; the observed community is more of an artifact from the overlapping species' distributions) -open communities tend to not have discrete boundaries -in addition, no two patches of forest are ever exactly alike in composition -the local environment, the pool of available species in nearby areas, and random events are the important factors affecting succession and diversity -we now have largely abandoned the classical Clementsian view of communities, but Gleason was not entirely correct either -he didn't frame his work in an evolutionary perspective, and Gleason relied too much on the concept of randomness -we do see natural boundaries in some communities (ex: the boundary b/w the pond and the forest around a pond) ^in other words, we see ecotones in many places -there appears to be a somewhat predictable pattern to the assemblage of species observed at one time in a given community -*how can we distinguish b/w the Clementsian and Gleasonian view of the nature of communities?* -the presence and # of ecotones is one factor that can tell us which 'view' of the community is more correct

Biogeochemical cycles (and environmental impacts of pollution): Characteristics of systems: Systems exhibit feedback

1) A special kind of system response is called feedback -feedback is a system's response to its own output -two types of feedback exist: Positive and Negative 2) A positive feedback loop is one where an increase in the output of a system leads to a further increase in output -positive feedback tends to destabilize a system -in positive feedback, a system's output rapidly increases, perhaps to a point where the system fails -for example, as an off-road vehicle (ORV) trail forms (see Figure 20), the vehicles run over and kill the vegetation that held the soil in place -a gully forms on the path, then rain leads to further widening and erosion -ORV traffic helps to erode the area further, by people staying out of the gully and traveling along its sides -soon the entire habitat is ruined -another example of a positive feedback loop: -many scientists worry about the Greenhouse Effect, where an increase in the heat of the atmosphere due to greenhouse gases may lead to an increase in the emissions of more greenhouse gases into the atmosphere, causing a further increase in the amount of heat retained by the atmosphere 3) Negative feedback occurs when the output of a system tends to shut off its response, not accelerate it -negative feedback systems are stabilizing -one example of negative feedback is the regulation of population growth (see Figure 21) -as a population grows, its demands on the environment increase -if the population is too large, there may not be enough food to support the entire population, and the population declines

Efficiencies in the flow of energy in an ecosystem: Assimilation efficiencies tend to increase with higher trophic levels

1) Assimilation Efficiency (A.E.) =A/Cx100 = (R + P + U)/C x 100 -in our perch example, the assimilated efficiency = 85.4 % -this efficiency tells you how efficient the animal is in assimilating material, as it tells you something about the quality of food it is eating 2) One reason assimilation efficiencies tend to go up with higher trophic levels is that flesh is easier to digest and assimilate than is the same amount of plant material -plants contain indigestible cellulose, lignins and other compounds that many animals cannot chemically digest - most animals lack the digestive enzymes capable of breaking these materials down -compared to herbivores, carnivores have the highest assimilation efficiencies: 60 to 90% 3) Detritivores, usually because they are feeding on very low quality food, have assimilation efficiencies below 15%. -for example, many organisms that feed on decaying wood have A.E. near 15% (because most of the wood is lignin and cellulose) 4) The part of the plant consumed is important for determining assimilation efficiencies -herbivores can assimilate 80% of the energy in seeds (seed predators), this is one reason why there are a lot of seed predators -there are lots of digestible fats and proteins in seeds, relative to indigestible woody plant stems that contain lots of celluloses and lignin -assimilation efficiencies of browsers tend to be a little higher than the efficiencies of animals eating older wood (30 to 60%) because young stems and leaves consumed by browsers are easier to digest than old woody stems -assimilation efficiencies for wood-eating animals is lower (<15%), because of the relatively indigestible celluloses and lignins of wood

Geographical trends in species diversity: Diversity and Niches

1) Niche -recall the definition of the niche -- the functional role of a species in the community -we can think of niches as arranged along an axis that represents a continuum: size of prey, height distribution in the tidal zone, height of forging sites, etc. Figure 3: -each curve represents the niche of a species -niche breadth can be viewed as the 'width' of the curve 2) *How can new species be added to a community?* -there are 4 potential ways to add more species, w/out causing the extinction of a previously existing species Figure 3b: -in the initial situation, let's say there are three species (sp 1-3, each w/ similar niche breadths) that are using a given resource (for discussion, suppose it is fruit size - axis R) A) Situation A: the total size of community resource axis increases (increase the resource axis length), thus additional species can be added into the community B) Situation B: increase the niche resource overlap of each species w/out changing niche breadth of a species -this increases competition and thus productivity of each species decreases -however, you can pack in more species C) Situation C: increase specialization (make the niche breadth very narrow for each species) -in this situation, the average productivity of each species also would decrease, but more niches are now available D) Situation D: exploit the resource R more fully (less of the resource is unused)

Efficiencies in the flow of energy in an ecosystem: Putting the efficiencies together

1) Of the sunlight that strikes the Earth, 20% is absorbed by the atmosphere (roughly) and roughly 30% radiates back out into space -that means that about 50% of the light energy strikes the ground and is subsequently absorbed by the Earth, the oceans and other water bodies, and plants -*only about 1% of the sunlight that hits Earth's atmosphere actually strikes plants* -the 99% that is not used by the plants drives the oceans' currents, the winds, weather and climate, rainfall patterns, allows ectothermic animals (and plants as well as the endothermic animals) to warm up in cold conditions -it also melts ice and powers evapotranspiration in plants., etc. -however, this 99% of the sunlight that hits the Earth is not captured and converted into ATP energy 2) If we look at the 1% of the sunlight that does strike a plant, most of it is not converted into potential energy of ATP -the amount of energy fixed by photosynthesis in a community is called the *gross primary production* or GPP -*net primary production* (NPP) is the GPP minus the energy lost through plant respiration -of the energy that strikes the plants, only 1 to 5 % of this energy is converted into biomass by photosynthesis (in other words, the NPP) -the plants' E.E. ranges from 1 to 5% -some of our crops have some of the highest productivities and exploitation efficiencies that have been calculated for plants, because we have selected productive yields in our food plants -the other 99% of the energy striking a plant bounces off leaves, is lost by radiation and conduction, is lost by respiration, or is used to cause evapotranspiration (the movement of water through the plant) -another part of the reason that plant's exploitation efficiencies are low is that only about 44% of the light energy hitting the plants is in wavelengths that chlorophylls can absorb -however, in reality, light does not limit the rate of production in terrestrial systems, which generally exceeds the saturation points for most plants 3) What limits plant productivity? -as mentioned above, light is generally not a limiting factor for terrestrial plants -plant productivity does increase with temperature (in part because plants generally cannot regulate their metabolism like endothermic animals) -terrestrial plant productivity also increases with the amount of evapotranspiration, which is a measure of the amount of water present in the ecosystem -for terrestrial plants, the length of the growing season also positively correlates with productivity -in addition to light and water, plants need nitrogen, phosphorus, calcium, sulfur, potassium, magnesium, and other ions -most soils have sufficient quantities of most of these nutrients to maintain growth -however, with respect to nutrients, nitrogen and phosphorus levels may limit productivity in many terrestrial ecosystems -many studies have shown that nitrogen scarcity occurs before phosphate limitation; plants increase production when excess nitrogen is added to the environment -in temperate and polar zone terrestrial ecosystems, nitrogen is more limiting than phosphorus -however, after excess nitrogen has been added, phosphate may then limit production (recall the Law of the Minimum we discussed earlier) -one major exception to the relative importance of nitrogen versus phosphorus as the limiting factor is that for tropical forests, phosphorus is more limiting than nitrogen, in part due to the more weathered ancient soils of tropical regions (where little glaciation occurs, exposing undisturbed rock) than in the temperate and polar zones, where the younger soils have more phosphorus present from the relatively recent weathering of rock exposed from glacial activity -nitrogen fixation is relatively lacking in the boreal forests and the tundra ecosystems of polar latitudes, making nitrogen more limiting -nitrogen fixation is much higher in tropical savannas and rain forests -the factors that limit plant productivity can change in temperate zones with distinct seasons -temperature is quite limiting during the winter months, while nitrogen limitation occurs during warmer months -with respect to aquatic systems, nutrient limitation affects productivity -light can be limiting in deep waters, because water strongly absorbs visible light with depth -in shallow zone areas, light may not be much of a problem -in addition to light, nutrient limitation is important in aquatic systems -nitrogen and phosphorus both exert limits on plant growth, even if sufficient light is available 4) For herbivores, the E. E. is higher than that of plants -herbivore E. E. varies from 1 to 10% -for carnivores, E. E. varies from 10 to 90% (herbivores are high quality food as opposed to the high content of inedible plant materials not eaten by herbivorous animals) -many herbivores are captured and killed by carnivores 5) Most of the biomass of the world is consumed by something -the vast amount of energy of dead and living biomass that is not specifically consumed by animal consumers is broken down by various decomposers and detritivores -relatively little material thus is sequestered into geological deposits and stored 6) Physiological ecologists are particularly interested in the assimilation efficiencies and production efficiencies -they may not measure how much of the energy at one trophic level is consumed by the next, so calculating exploitation efficiencies and Lindeman efficiencies are difficult -they can, however, measure assimilation efficiencies (A.E.) and production efficiencies (P.E.)

Nonequilibrium communities and disturbance: Examples of nonequilibrium hypotheses

1) One classic nonequilibrium model is the intermediate disturbance hypothesis -Joe Connell (1978, American) used this hypothesis to explain high diversity in the tropics a) If disturbance is an infrequent event, or is small in scale, then superior competitors (residents) will eliminate inferior competitors, and thus diversity decreases (see Figure 12) b) If disturbance is a strong, frequent event, dominant competitors eliminated, only colonizing species with high dispersal rates are found there (they dominate system in absence of superior competitors), and thus diversity decreases c) If you have an intermediate level of disturbance, then both dominant and colonizing species present (colonizing species exploit disturbed patches, dominant resident species use undisturbed patches), then diversity is highest 2) Michael Huston (American, 1979) demonstrated a similar idea (Figure 13) -in a series of computer simulations, Huston observed that diversity was highest with a moderate amount of disturbance -if there are too few disturbances, competitive exclusion can cause a loss of species -if the disturbances are too frequent, this increased frequency also caused a decrease in diversity, because the early seral stage, weedy species are the only species present 3) Wayne Sousa (American, 1979) showed strong evidence that disturbance forms gaps that cause community diversity to be highest at a mid-successional sequence -overturned boulders represent an intermediate level of a disturbed site -'gaps' of uncolonized space become important factors -in Sousa's experiments, green algae (Ulva sp.) first colonized and subsequently formed ephemeral mats -Ulva is a good colonizing species with high dispersal rates -by end of the first year (fall-winter), several other algal species had also colonized: Gelidium, Gigartina and Rhodoglossum -after a number of years, Gigartina eventually dominates in the absence of disturbance -- Gigartina is a superior competitor that makes a monoculture mat that overgrows and displaces all other species by covering all of the exposed surface of the boulders by vegetative reproduction 4) Another example of the importance of gaps and disturbance: the gaps in the forest canopy -after a tree dies and falls, other trees 'race' to fill the gap -saplings next to the gap begin to grow rapidly upward -if you had a large disturbance in the area, adult canopy trees and saplings are all killed, and the course of succession is determined either by colonizing seeds that survived the fire (or had blown in into the new patch) 5) Interplay of predation/competition and disturbance has been discussed by many authors -one famous article by G. E. Hutchinson (George Evelyn, British-American) titled "The paradox of the plankton" asks why are there so many species of plankton in the open water column -you would think that the open water would be one 'niche' and competitive exclusion would lead to only one species, however, there is constant changes in the physical conditions of the habitat (temperature, pH, DO, nutrients and light levels, etc.) that repeatedly interrupt competitive exclusion from occurring, so that many species can coexist in the open water 6) The Menge and Sutherland model on biodiversity discussed earlier, is important -Menge and Sutherland argued that predation and competition are biological processes where density dependence is important, while disturbance is a physical process (fire, floods, storms, and so on), which acts in a density independent fashion -these two types of forces thus work independently of each other -in times and places of relatively low physical stress, populations grow and predators can exert their effects upon dominant prey, thus allowing coexistence by preventing competitive exclusion -predators are thought to be less important at higher levels of physical stress, and competition becomes more important by limiting species richness -- competitors that are more efficient outcompete other species -at higher levels of stress, the physiological tolerances of species become most important and those species more physiologically stressed go extinct first -the relatively few (and presumably most physiologically tolerant) species are the only species left behind 7) Neutral (lottery) models: Chesson and Warner (1981) described a situation where a number of similar species can coexist in a community, if they have similar competitive effects upon each other (the alphas and betas of Lotka-Volterra) and growth rates, and they have high dispersal rates that allow them or their offspring to reach sites that open up for colonization due to disturbance -chance events thus can allow many different species to coexist, if they are similar in terms of their competitive abilities, reproduction, and dispersal -for this mechanism to work, however, there can be no competitively dominant species that eventually could take over all plots

Pollution: Human-produced pollutants often are novel chemicals to which nature has not evolved ways of detoxifying

1) Our artificial plastics and our pesticides have never before been seen by living organisms, which have not yet evolved ways of dealing with them -thus, living things have never been exposed to these chemicals over the course of evolution 2) The number and volume of plastics, synthetic pesticides, and other artificial pollutants are increasing each year in nature -we have created tens of thousands of different manmade chemicals that are in use, with roughly 1,000 additional chemicals added to the list each year -we do not know the toxic effects of the vast majority of these compounds

Pollution: What is pollution?

1) Pollution is any unwanted change in air, water, soil, or food that can affect the health, survival, or activity of human beings and other organisms -when pollution occurs, that resource that is polluted (air, water, etc.) may become no longer useful 2) These unwanted changes are often chemical in nature -most pollutants are solid, liquid, or gaseous chemicals, or they can be energy emissions (excessive heat, noise, or radiation) -pollution is also defined as excessive inputs of chemicals or energy into the environment, as a result from human activity

Other examples of Successions: Riverine zonation, the interplay of succession and disturbance in allogenic succession

1) Rivers and lakes are dynamic habitats, where erosion of the soils occurs at some locations and deposition of materials occurs at other sites -winter and spring flooding are an annual and predictable occurrence -sandy areas develop along the Ohio and other rivers -these sandy areas (called sand bars or point bars) are made of sediments (especially sand) that doesn't stay in suspension in water -the shorelines along rivers have a characteristic pattern of species composition as you move away from the river (or upward, if you are talking about a river bluff) 2) Next to the river, the river reliably scours the site every year -very few terrestrial plants can live in such a spot and herb cover will be minimal 3) A little ways up from the bank, a few short-lived herbaceous species are found -some grasses, and a few trees (such as black willow, river birch, alder, ash, and swamp dogwood) are the pioneer invaders of sand bars and areas next to the river edge 4) As you travel further up the bank, you will come to a point where the river never exceeds this height (as shown by ancient deposits of fallen trees and logs) -the vegetation changes from those species next to the river bank to trees less tolerant of flooding as you move up the bluff 5) Above the highest possible flood point, up on the river bluffs, you may see a climax community, composed of oaks, hickories and maples

Island biogeography: one major equilibrium theory Assumptions of the M-W theory

1) S is a balance when E= I 2) That the number of species on island reaches some equilibrium - S stays constant with time (see Figure 15) -this does not mean a static equilibrium; there is a turnover in the composition of species comprising the community 3) Effect on island size: M-W theory states that large islands have more niches and less extinctions, smaller islands have higher extinction rates (E) (Figure 16) 4) Effect of island distance from mainland source of colonizing species: immigration rates increase for nearby, close islands (increase I) compared to far away islands of similar size (Figure 17)

Efficiencies in the flow of energy in an ecosystem: Importance of decomposers and detritivores in ecosystems

1) Some of the energy at a given trophic level is not used by the higher trophic level consumers (due to death of the individual), or the energy in feces and urine, or is simply not used by higher trophic level consumers -it instead is used by decomposers -there are thus two major food chains -- the photosynthetic food chain and the detritus-based food chain -unassimilated material can enter the detritus-based food chains -decomposers and detritivores are very important to the web, because they recycle nutrients and reconvert the nutrients back into forms that the plants can use -in general, these detritivores are very specialized in their feeding mode (shredders, collectors, scrapers) and they are selective on the type of dead organic matter they feed upon -as various detritivores work upon detritus, the detritus loses its nutritive value over time, and only a few specialized microbes can metabolize the last indigestible organic compounds (the highly refractive materials of plant matter such as cellulose and lignins) that other detritivores cannot digest -the rate at which decomposition proceeds depends strongly on the nitrogen content of the plant detritus (much of the detritus in communities is plant, not animals, remains) -if the detritus has a high C:N (carbon to nitrogen ratio), the rate at which decomposition proceeds is slow -under conditions of poor soils, acidic conditions, or anoxic conditions, detritivores and decomposers may not be able to decompose all of the detritus, thus, carbon-rich detritus can build up in some environments (peat bogs) -this deposition of organic matter over geological time becomes carbon-rich deposits of coal and oil 2) The detritivorous animals (as well as bacteria, fungi, and protozoans) are quite important in all food webs -herbivores consume 1 to 3% of the NPP of plants in temperate deciduous forests, 12% in old fields, and 60% to 99% in planktonic communities; the detritivores consume the rest -therefore, the relative importance of detritus-based and herbivore-based food webs varies greatly among communities -herbivores predominate in aquatic planktonic communities, and detritivores predominate in most terrestrial communities (forests, grasslands) and certain aquatic communities, including streams and marshes -nonetheless, in almost all communities, the detritivores and decomposer production is greater than that of the herbivores -in streams, herbivores can help detritivores by shredding up and grazing the plant materials into smaller pieces, which makes it easier to detritivores to consume the detritus 3) Many of the detritivores are in reality microbivores or bacteriovores, i.e., they consume the bacteria that feed upon the detritus -many herbivores are actually microbivores -they are not much larger than the decomposers on which they feed, but the microbivores, strictly speaking, do not feed upon detritus -detritivores feed upon detritus, but many of them also consume the bacterial and fungal decomposers

Biogeochemical cycles (and environmental impacts of pollution): Changes and equilibrium in systems

1) Steady state is a term that describes a system in equilibrium, with inputs balancing outputs -any change in either inputs or outputs may disturb the equilibrium of the system -thus inputs must equal outputs for the system to stay in equilibrium -remember our discussion earlier about the responsiveness of systems -a system can respond, yet appear to stay relatively constant, depending on its inputs and outputs -on a global scale, the solar input (ultraviolet, visible, infrared) roughly equals the outgoing radiation (reflected visible light and outgoing infrared heat energy) leaving Earth (in the form of infrared heat energy) -thus the temperature of the atmosphere, the land, and the oceans (temperature is a function of the difference between heat output and solar input) stays constant through time (over the course of thousands of years) -however, if the sun increases its output, or we decrease the ability of heat to leave the planet (by increased CO2, and other pollutants), then the temperature will rise (we call this increase in temperature of the Earth 'global warming') 2) The average residence time is a measure of the time it takes for any or all of the resource in a pool (=reservoir) to be moved through the system -to determine the average residence time, divide the total size of the pool by the average rate of transfer into and out of the pool (the flux rate) -say you have a small lake containing 1000 cubic meters of water (the reservoir), and on average 100 cubic meters of water enters and leaves the lake every day (the average rate of transfer, because inputs = outputs, the lake level stays constant) -thus, 1000/100 = 10 days = average residence time = the average time a molecule of water stays in the lake. Figure 22: -the clear ovals represent water; the filled ovals represent a pollutant -systems A and B are small systems (small reservoirs), with A possessing larger inputs/outputs than B -systems C and D are larger systems (larger reservoirs), with C having larger inputs and outputs than D -A and B become polluted more rapidly than C and D, but A and C, with larger flux rates, could clean up more rapidly -the effects of pollution would be observed more rapidly in B (small system, low flux rates) -the longest residence time would be in D; the shortest residence time would be in A -large systems with long residence times are slowest to change than smaller systems -smaller systems with high rates of inputs and outputs change more rapidly -large systems, once polluted however, are difficult to correct -small systems, though more easily polluted, can be cleared of pollutants faster

Ecosystems and energy transfer: Pyramids - 3 kinds

1) The first pyramid is the pyramid of numbers -it is created by counting all of the individuals of one trophic level -this pyramid can be inverted (for example, many herbivorous insects feed on one large tree) 2) The second pyramid is the pyramid of biomass -the mass at each trophic level is presented -it can also be inverted -for example, the biomass of herbivorous fish and zooplankton may exceed that of the phytoplankton (Figure 18) -however, the phytoplankton survivors can reproduce much more rapidly, so over the course of longer times periods, more biomass can be produced at the producer level 3) The third pyramid is called the pyramid of energy -this pyramid can never be inverted, because it would violate the laws of thermodynamics -the amount of energy produced at one level is greater than the level above it, because some of the energy that is captured at one level is lost by respiration in the organisms of that trophic level, and this energy is not converted into biomass (which the predators or higher trophic level consumers can eat) -Lindeman visualized the trophic levels as trophic levels of energy: less energy reaches the higher trophic levels because it is used up for work (respiration, synthesis, etc.) at lower levels

Other examples of Successions: Succession in marine environments

1) The successional sequences observed on land are similar in marine environments -inhibition and/or tolerance models best fit the typical patterns seen in intertidal communities (ex: in the rocky intertidal zone, a thin film of diatoms and bacteria cover a bare rock ^this conditions the rock so that larvae of a variety of species settles ^seaweeds move in after the bacteria and small algae colonize, and these seaweeds in turn are followed by barnacles and mussels, which are the dominant competitors in many habitats ^predators [especially sea stars, crabs, snails, sea otters, etc.] keep certain species down, and may determine if the final seral stage is a bed of mussels, a kelp bed, or a mixture of species) 2) Disturbance also plays a similar role in marine environments as it does in terrestrial environments -clumps of mussels can be removed by storm wave action, drifting logs, and scouring ice -this removal opens up new space -bryozoans, barnacles and molluscs act as 'weeds'; they can colonize quickly as larvae in the open water quickly settle on the disturbed site 3) In addition to disturbance, dispersal, colonization, predation and competition play important roles -relative to barnacles, some tunicates and sponges aren't as good at dispersing, and thus are poor colonizers -however, many sponges and tunicates are colonial -they can be superior competitors, bc once established, the colonies grow and dislodge/kill/cover over other animals and plants 4) Use of allelopathic chemicals may be quite common in marine environments -many plants and animals are being examined for chemicals that may have some pharmacological use in human health

Pollution: Characteristics of human-produced pollutants

1) They tend to be much more concentrated in a particular place 2) They are artificially produced -many manmade pollutants are chemicals not produced by living things 3) They are produced in great quantities 4) They have many direct and indirect harmful effects (for example, certain chemicals that can mimic hormones and disrupt the normal physiology, development, reproduction, or health of plants and animals) 5) They are less easily decomposed by natural processes (physical/chemical weathering, biological enzymatic degradation), and thus these pollutants persist in the environment for a long time

Biogeochemical cycles (and environmental impacts of pollution): The Earth can be viewed as one large system

1) We call this one system the biosphere - the region of the Earth where life exists -most living things live within a few meters of the Earth's surface, although some organisms either live high in the atmosphere, or deep within the planet's crust -however, this layer of life is thin -if the Earth was shrunk down to the size of an apple, the layer of life would be much thinner than the skin of an apple 2) What is the minimum part of the biosphere necessary to sustain life? -some of you probably made microcosms in grade school -a microcosm consists of a little jar containing water and a few plants, mud, and perhaps an animal or two, all of which is sealed off from the outside -you put the jar close to a window (for sunlight) and you watched the microcosm over time, hoping that you set it up in such a way so that the ecosystem inside the jar survives (keep plants and fish alive) -unfortunately, these microcosms rarely work for long periods of time (You probably added too many fish or snails!) -the minimum number of things needed for life to be maintained is not certain, yet the following points are clear: a) No one organism (or population) is known to produce its own food and recycle all of its wastes back into forms it can use b) All organisms depend on each other for life, for food, or shelter, or to reconvert nutrients back into forms other organisms need c) All organisms depend on the Earth's physical environment for raw materials and on sunlight for energy (Some species live deep inside rocks, or near thermal ocean vents, and rely on energy-rich compounds) d) All species have a minimum population size in order to maintain their genetic diversity and withstand random genetic changes that may affect their evolution e) A fairly large area of land and water is needed to maintain a community f) All life on the planet is dependent upon the local/global movement of matter and energy -we know that the planet has sustained life for 3 billion+ years, but we are not certain if a smaller area can do the same 3) An ecosystem is a community of organisms and their interactions with the nonliving environment -it is characterized by the flow of energy through the system and the cycling of nutrients within the system -an ecosystem can be of almost any size: from a puddle of water, to a large forest, to the entire biosphere -the borders and sizes of these ecosystems are often vague, and they can be artificial (manmade, or defined by human observers) or natural -for example, we can define agriculture as the management of an artificial ecosystem (the farm field) -these artificial fields are very useful to us (they provide us our food and raw materials for clothing and other agricultural products) 4) At the same time, natural ecosystems are also quite useful to us -forests and lakes help to purify the water, because of bacterial activity, as well as the activities of the fungi, unicellular organisms, plants and animals -pollutants can be trapped by trees and other plants, or are converted to molecules harmless to humans and other living things -natural ecosystems are important to us, because they recycle all of our nutrients and help to detoxify our pollutants, to some degree 5) The Earth and its ecosystems are resilient -ecosystems can dilute, break down, and recycle many of the chemicals we add to the air, water, and soil, as long as we do not overload an ecosystem's abilities to process pollutants -the Earth can replenish topsoil, water, air, forests, grasslands, and wildlife, as long as we do not use these resources faster than they are renewed

Efficiencies in the flow of energy in an ecosystem: Ecological efficiencies differ for endotherms and ectotherms

Ecological efficiencies differ for endotherms (1 to 5%) and ectotherms (5 to 30%) 1) Raymond Lindeman had this efficiency in mind -it is identical to P(prey)/P(predator) x 100 or the ratio of the production at the two trophic levels -you can get this ratio by multiplying E. E, A. E and N. P. E. together 2) It can pay to be an ectotherm -as an ectotherm, you can have lower energy costs because you do not need to maintain a high constant metabolic rate like an endotherm -endotherms must always be feeding, which can be a problems in the summer and winter months, when food may be scarce and/or the physical environment is stressful -ectotherms can wait out the winter in some cases 3) It can pay to be an endotherm -ectotherms are much more limited in time and space, they may not be as active, and may not be able to move or defend themselves at certain times of the year

The oxygen cycle: O2 produced by 2 major sources

Oxygen gas is produced by two major sources: 1) The breakdown of water (H2O) into hydrogen gas (which escapes into space) and oxygen gas, which is retained by the atmosphere 2) The process of photosynthesis -if photosynthesis exceeds respiration, oxygen builds up in the atmosphere -the presence of oxygen gas, along with carbon dioxide and methane, points to a disequilibrium in the atmosphere - one caused by the presence of living things

Ecosystem energetics: Total energy budget equation for an individual

Total energy budget equation for an individual: 1) C = F + U + R + P(G) + P(R) -the rates are energy produced or used or obtained per unit time -C = consumed energy (energy of material consumed = gross energy intake) -F = energy in egested material (feces) that was not assimilated ^this energy was not assimilated (never entered the organisms' gut epithelia) -U = energy lost in the energy content of excreted metabolites (particularly urine) -R = respiration, basal metabolism, and work, the energy used in maintaining order (basal metabolism) and the energy used for foraging, for osmoregulation and excretion, for digestion, for proper endocrine system and nervous system function, for immunity and defense, and for thermoregulation ^this also includes all work being done (work in this case refers to dam building, nest building, digging burrows, locomotion, and so on) -P(G) = growth of new tissues -P(R) = reproduction (energy used for gamete production, mating, and parental care) -P(G) and P(R) can be combined in energy used for production (P) 2) If you subtract the energy that remains in the undigested food (the feces) from the total amount of ingested food, the amount remaining has been assimilated C - F = U + R + P = A = assimilated energy ^energy that is absorbed across gut wall into the bloodstream and tissues 3) R + P = M = metabolizable energy -energy that is used for respiration, growth and reproduction -this excludes the energy lost in excreting materials (U: urea, uric acid, various amino acids and organic acids) thus C = F + U + M

Efficiencies in the flow of energy in an ecosystem: Production and the lengths of food chains

What factors affect the lengths of food chains? -ecologists have identified several major drivers - productivity, ecosystem size, and disturbance are often mentioned -Hillary Young and her colleagues determined that for the terrestrial ecosystem they studied (the islets of a remote archipelago of Pacific islands), the ecosystem's productivity has a positive correlation with food chain length, while there was no correlation between ecosystem size (or the productive space) of an ecosystem with food chain lengths -productive space was a measure affected by both ecosystem size and productivity -Stuart Pimm suggested disturbance has an important role -because higher trophic level consumers are fewer to begin with (compared to producers and herbivores) and have slower reproductive rates, they are more negatively affected by disturbance, and systems with high levels of disturbance have shorter food chains -some empirical evidence has supported this hypothesis

Stability and diversity: equilibrium versus nonequilibrium communities Ecologists traditionally thought most stable communities are most diverse ones

What makes some ecosystems more stable than others? What is the effect of disturbance on communities and ecosystems? Are more diverse communities more stable? -ecologists traditionally thought most stable communities are the most diverse (complex) ones -the conventional wisdom for this argument is based on ideas of Elton and MacArthur from the late 1950s and 1960s

Stability and diversity: equilibrium versus nonequilibrium communities Who is correct? (Definitions of stability)

Who is correct? -it depends on your definition of stability, and if you are looking at the population or ecosystem level -first, let's go over a few definitions: 1) Equilibrium -a community is in 'equilibrium' when population sizes and the community's species richness stay constant over time (the community reaches some stable [unchanging] state)(Figure 10) a) Population sizes eventually would stabilize and not vary much b) Equilibrium communities are thought to have many biotic processes (competition and predation) occur, and these processes would act in a density-dependent fashion to regulate any given population's size c) Equilibrium communities would score high on some or all of the following definitions of stability (resilience, resistance, species-deletion stability, and persistence stability, all described below) d) These communities would become 'saturated' with species, so species invasions would be rare e) Few stochastic effects that are due to abiotic processes (weather, disturbance) would presumably occur 2) Nonequilibrium -a nonequilibrium community never reaches some stable state before some disturbance occurs, changing the community a) Population sizes would vary drastically to the point that some species would go extinct b) Density-dependent biotic processes and regulation would be rare c) Nonequilibrium communities would score low on some or all of the definitions of stability that are listed below d) Exotic species would constantly invade (the community is not saturated with species), so that the community composition would change over time e) Stochastic disturbance processes (weather, climatic variability, fire, and other disturbance processes) would be dominant factors limiting or affecting nonequilibrium communities 3) Stability -ecosystems and communities are considered to be stable if they return to their original equilibrium conditions after a disturbance -there are several contrasting definitions of stability -indeed, much of the confusion comes from different measures of stability, community diversity, and community structure -thus ecologists have begun to be more explicit in describing what these terms mean to them 4) Local versus global stability -a community that is locally stable is referring to the tendency of a community to return to its original state after a small perturbation (ex: a storm fells a single tree, does the rest of the community changes as a result?) -global stability refers to the ability of the system to return to its original state after a large disturbance (a hurricane blows down every tree in the forest, for example. Does the entire forest community return intact?) 5) Resistance stability -resistance is the ability of an ecosystem (or community) to withstand or resist variation (Figure 10) -if a community shows little change (in terms of productivity, or in numbers) in response to disturbance when part of the community is altered, this community would be called resistant (see the accompanying figure) -resistance is one form of 'stability' -the function that is measured in this case is productivity (primary and secondary) or biomass -how does biomass or productivity change in the face of increased herbivore or carnivore pressure? Many forests tend to be 'resistant' -the trees can withstand changes in climate and sharp environmental disturbances (weather, fire, drought, insect outbreaks) because the trees can draw on stored food/nutrient reserves -a late spring frost may kill some of the new leaves, but the trees can call on additional stored food reserves to make more leaves -so in the forest, the frost may not have as dramatic effect as it would in some other communities (productivity or biomass is little changed) What factors cause resistance? -the potential for stored food supplies, in order to outlast a disturbance event, is important -the strength or scale of the disturbance is also important: large scale versus small scale clear cutting in a forest (the smaller gaps can be quickly filled in by the forest, and the community would appear to be resistant) -if large areas of the forest are clear cut, then the system collapses, and the community is drastically changed for long periods of time (it is neither resistant nor resilient) 6) Resilience stability -the resilience of a community or ecosystem is measured by the speed with which a disturbed system (community) returns to the original equilibrium (the original, pre-disturbed state) after being changed (see Figure 10) -a rapid return suggests high resilience, but a slow return suggests low resilience -resilience is very different from that of resistance; a resilient system may not be very resistant, and vice versa -productivity and/or biomass may change drastically initially, but quickly returns to its predisturbance level if the system is resilient -as an example of resilience, the spruce budworm occasionally becomes an outbreak pest in the spruce-fir forest -the insect feeds heavily on balsam fir (which, if uninfested, can outcompete other dominant trees, such as spruce and birch) -when the forest is infested, spruce and birch increases in importance and the balsam fir declines, but the balsam fir eventually grows back and predominates once more after the spruce budworm population crashes from the lack of food -this system has high resilience, yet some of the species have low resistance Aquatic ecosystems tend to be resilient -aquatic systems are constantly responding to flooding spates -invertebrates are blown out by the spates, yet most stream invertebrates are rapidly recruited back to the empty patches -the influx of nutrient pollution (nitrogen and phosphorus in wastes, for example), leads to drastic short-term changes in species composition, yet the nutrients are washed out over time, and the system returns to its pre-disturbance state What factors cause resilience? -it depends on the level of biological organization at which you are looking -at the population level, the most resilient species is usually one with high growth rates (high 'r') -the population can rapidly rebound after losing individuals from some disturbance -at the community level, the intrinsic growth rates 'r' of each species, and the species' interactions with each other, are two important factors -a species cannot recover until the other species it is linked to have also recovered -the capacity of the food web to recover depends on the recovery rate of the species with the lowest resilience (often large, long-lived herbivores and carnivores, with low 'r') -at the level of the ecosystem, the rate of how quickly nutrients necessary for the growth of species become available to plants 7) Species deletion stability -Stuart Pimm (American) examined species deletion stability: if one species is removed, does this lead to instability in the remaining species? -Pimm noted that in more diverse (more connected) communities, the removal of a top predator caused instability, but if one basal species (plant) was removed, increased connectance actually stabilized the community, preventing additional extinctions -the impact of species deletion stability depended upon the species removed -Pimm also noted that if you look at the resilience of the stable communities in his model, the increase in connectance (a measure of complexity) caused more webs to demonstrate short return times (i.e., very resilient communities) -the models showed that again as connectance increased, the proportions of the communities from the model that were stable decreased, but for the small subset of communities that were stable, resilience actually increased with complexity [Complexity (connectance) leads to stability (species-deletion stability and resilience stability)] 8) Persistence stability -in another model, Pimm described the relationship between connectance and persistence -persistence is another measure of stability -persistence is how long will a system (ecosystem, community, population) last before it is changed to a new stable state or equilibrium -food webs can change in time due to extinctions of established species and invasions of new species -all food webs change over very long periods of time, but what we want to know is why some webs change more slowly than others -some species are less resilient in the face of change (especially those with low 'r') -habitat loss, or fragmentation may result in localized and regional extinction, or changes in the number of predators, disease organisms and parasites, and competitors makes some species more prone to extinction -a community may be persistent because no invading species are able to reach the habitat in sufficient numbers to overcome the problems associated with small population size (bottlenecks, drift), or the invading species is not able to live under the physical conditions of that habitat -in one respect, a more species-rich community is harder to invade, because the invading species may not be able to find an unexploited niche to fill -this suggests that more complex communities (more species-rich, or more interconnected) may be hard to invade -in another model, Pimm demonstrated that a community with higher connectance was more difficult to invade (Figure 11) -this result suggests that more complex (connected) communities are more persistent [Complexity (in terms of connectance) leads to stability (resistance stability and persistence)]

Alpha diversity indices: Summary of variables

ni = # of individuals of ith species N = total # of individuals of all species pi = importance value for species i S = species richness (# of species) H = Shannon diversity Index ^H(max) = ln S ^H ranges from 0 to lnS N1 = e^H = Shannon diversity Index ^proportional to S ^e^H maximal value = S ^N1 ranges from 1 to S E(H) = evenness index for Shannon Index ^E(H) ranges from 0 to 1.0 N2 = Simpson's diversity Index ^N2 ranges from 1 to S E(D) = evenness index for Simpson's Index ^E(D) ranges from 0 to 1.0