Ecology Exam 3 (16,17,18,19,20,21)

Every community has an associated vertical structure:

A vertical structure is a stratification of often distinct vertical layers.

Describe how the ratio of edge to interior changes with patch size:

As patch size gets bigger, the ratio of the edge area decreases. However, as patch size gets bigger, the ratio of the interior gets bigger. With patches of intermediate size, a general pattern of maximum species diversity results from the negative correlation between edge species and the size of habitat patches, combined with the positive correlation between interior species and increased area.

Mineralization:

As the dead organic matter is consumed, the microbial decomposers (bacteria and fungi) transform nitrogen and other elements contained in organic compounds into inorganic (mineral) forms. This process is called mineralization.

Explain the roles of mineralization and immobilization in the net mineralization rate:

Because both of these processes - mineralization and immobilization - are taking place as decomposer organisms are consuming the litter, the supply rate of mineral nutrients to the soil during the process of decomposition - the net mineralization rate - is the difference between rates of mineralization and immobilization. Net mineralization rate: mineralization(M)-immobilization(I)

Explain how seasonal variation in environmental conditions may influence NPP:

Both photosynthesis and plant growth are directly influenced by seasonal variations in environmental conditions. Regions with cold winters or distinct wet and dry seasons have a period of plant dormancy when NPP ceases. In the wet regions of the tropics, where conditions are favorable for plant growth year-round (high precipitation and warm temps), there is little seasonal variation in primary productivity.

Describe boundaries:

Boundaries are the place where the edge of one patch meets the edge of another adjacent patch (or surrounding matrix).

From top to bottom, these multiple layers of vegetation are:

Canopy Understory Shrub layer Herb or ground layer Forest floor

Examples of heterotrophic succession:

Changes in the composition of animal species inhabiting various stages of plant succession, from old-field to conifer forest, in central New York. Species appear or disappear as vegetation density and height change. This is an example of how changes in species composition and diversity of the heterotrophic communities over time are a product of changes in the associated vegetation during the process of plant succession.

Zonation:

Changes in the physical structure and biological communities across a landscape result in zonation. Zonation is common to all environments, both aquatic and terrestrial. Zonation is most pronounced where sharp changes occur in the physical environment, as in aquatic environments,

Explain how environmental gradients influence community structure by altering the outcome of interactions:

Changing competitive ability along resource gradients results in a pattern of zonation along the gradient that reflects the changing relative competitive abilities. The lower boundary of each species along the gradient is defined by its ability to tolerate resource limitation, whereas the upper boundary is defined by competition. There is a trade-off between the competitive ability and the ability to tolerate the physical stress of resource limitation.

Quality of plant litter as a food source:

Characteristics that influence the quality of plant litter as an energy source relate directly to the types and quantities of carbon compounds present; that is, the types of chemical bonds present and the size and three-dimensional structure of the molecules in which these bonds are formed.

Explain the influence of climate, geology, topography, and disturbance on the formation of landscape patterns:

Climate and geography interact to define the landform, determining patterns of drainage, erosion, and deposition. Climate, geology (rocks/minerals), and topography interact with biotic processes to give rise to patterns of soil formation.

Metapopulation...

Colonization and extinction of local populations of species in an array of patches in the landscape. Subpopulations - local, partially isolated local demographic processes Metapopulation - Interactions between local populations dispersal and colonization

Consumption efficiency:

Consumption efficiency is the ratio of ingestion to production at the lower trophic level: (I n / P n-1) Ingestion of n, divided by the production of n-1. Thus, the consumption efficiency defines the amount of available energy produced by a given trophic level (P of n-1) that is consumed by the next higher level (I of n).

Plant processes enhance the decomposition of soil organic matter in the rhizosphere:

Decomposition in the rhizosphere is more rapid than in the surrounding soil. Roots alter the chemistry of the rhizosphere by secreting carbohydrates into the soil. The growth of bacteria in the rhizosphere is supported by the abundant source of high-quality, energy-rich carbon of the roots. Increased rate of decomposition and immobilization. Predation by protozoa and nematodes. Remobilizes nutrients.

In Robert Paine's experiments, exclusion of the predatory starfish resulted in:

Decrease in the number of prey species (removal of the predator increased competition between the prey)

Detrital food chain:

Detritus --> decomposer herbivores --> carnivores (In the decomposer food chain, the flow of energy is not unidirectional. The waste materials and dead organic matter in each consumer trophic level is recycled, returning as an input to the dead organic matter at the base of the food chain).

Zonation is a result of differences in species' tolerance and interactions along environmental gradients:

Differences in environmental tolerances among species and changes in the nature of species interactions result in shifts in the species present and their relative abundance. These spatial changes in community structure are referred to as zonation. ex. Balanus and Chthamalus (two species of barnacles) in the rocky intertidal environment of coastal marine ecosystems.

The landscape is typically viewed as a shifting mosaic steady state. This phase means:

Different patches are in different stages of succession

Explain diffuse interactions:

Diffuse interactions involve many species... Alone, any one interaction may not be crucial - but the combined affect may have large impacts. Therefore, if the relative abundance of the focal species is impacted by competition with a variety of other species in the community, an experiment that removes only one or a small number of those species may show little effect on the abundance of the focal species. However, the removal or population reduction of many competing species may result in a significant positive impact on the focal species. Diffuse interactions are not limited to just competition.

According to the Theory of Island Biogeography, which factor has the most influence on immigration rates?

Distance from the mainland

The phenomenon caled edge effect refers to the high ____ often found in borders.

Diversity

Dominance can be defined by a number of criteria:

Dominance typically is assumed to mean the greatest in number. But in populations or among species in which individuals vary widely in size, abundance alone is not always a sufficient indicator of dominance. In a forest for example, the small or understory trees can be numerically superior, yet a few large trees that overshadow the smaller ones will account for most of the biomass (living tissue). In such situations, we may wish to define dominance based on some combination of characteristics that includes both the number and size of individuals.

Food webs describe species interactions:

Ecologists studying the structure of communities often focus on the feeding relationships among the component species, or how species interact in the process of acquiring the resources necessary for metabolism, growth, and reproduction.

Characteristics of edge species:

Edge species are restricted exclusively to the edge environment.

Processes of ecosystems:

Exchange of energy Exchange of nutrients

Gross primary productivity (GPP):

Gross primary production is the total rate of photosynthesis, or energy assimilated by the autotrophs. Like all other organisms, autotrophs must expend energy in the process of respiration.

Functional groups:

Groups of species that exploit a common resource in a similar fashion are termed guilds. Functional group or functional type is a more general term used to define a group of species based on their common response to the environment, history characteristics, or role within the community.

Nutrient cycling differs between different ecosystems:

However, in virtually all ecosystems, there is a vertical separation between the zones of production (photosynthesis) and decomposition.

Intermediate disturbance hypothesis:

If the frequency of disturbance (the time interval between disturbances) is high, then later successional species will never have the opportunity to colonize the site and diversity will remain low. In the absence of disturbance, colonization can occur, later successional species displace earlier ones and the species diversity declines. At an intermediate frequency of disturbance, colonization can occur, but competitive displacement is held to a minimum. The pattern of high diversity at intermediate frequencies of disturbance is referred to as the intermediate disturbance hypothesis.

During decomposition, some nutrients are incorporated into living microbial biomass. These nutrients are said to be:

Immbolized.

Aquatic communities:

In aquatic environments, communities are also classified and named in terms of the dominant organisms. (Ex. kelp forests, sea grass meadows, and coral reefs). However, the physical structure of aquatic communities is more often defined by features of the abiotic environment, such as water depth, flow rate, or salinity.

Nutrient cycling in aquatic ecosystems:

In aquatic systems, plants do NOT always function to bridge the zones of production and decomposition - this only occurs in shallow water environments of the shoreline which are emerged in vegetation. As water depths increase, primary production is dominated by free-floating phytoplankton within the upper waters (photic zone). In deeper waters, the zones of decomposition in the bottom sediments and water (the benthic zone) are physically separated from the surface waters, where temp and light availability support primary productivity. Nutrients get from the zone of decomposition to the zone of production through circulation.

Keystone species influence community structure disproportionately to their numbers:

Less abundant species may play a crucial role in the function of the community. A species that has a disproportionate impact on the community relative to its abundance is referred to as a keystone species.

Simpson's Index (D):

Measures the probability that two individuals randomly selected from a sample will belong to the same species. D = sum of p1^2 Species diversity is represented by D, a value between 0-1. As both species richness and species evenness increase, the value of D approaches 0. Therefore, the greater the value of D, the lower the diversity. If a community only had 1 species present, D would = 1. ***As diversity increases, the probability that two randomly selected individuals will belong to the same species decreases.

Metapopulation theory is a central concept in the study of landscape dynamics:

Metapopulation theory examines the colonization and local extinction of local populations of a given species on the array of patches (potential habitats) embedded on the broader landscape.

Describe the effect of patch shape on the ratio:

More fragments creates more edge space and less interior landscapes.

Describe the fate of NPP:

Net primary production is the energy available to the heterotrophic component of the ecosystem. Either herbivores or decomposers eventually consume virtually all primary productivity, but often it is not all used within the same ecosystem - it may be dispersed into another food chain outside of the ecosystem. - Some energy in the form of plant material, once consumed passes from the body as waste products (feces/urine). - Of the energy assimilated part is used as heat for metabolism. - The remainder us available for maintenance - capturing or harvesting good, performing muscular work, and keeping up with wear and tear on the animal's body. The energy used for maintenance is eventually lost to the surrounding environment as heat. - The energy left over from maintenance and respiration goes into production of young - this net energy allocated to production is called secondary productivity.

Apparent competition:

Occurs when two species that do not compete with each other for limited resources affect each other indirectly by being prey for the same predator.

Explain variation in consumer productivity using the model: A = R + P

Of the energy that is assimilated (A), some is used for respiration (R) and the remainder goes toward production (P), which includes production of new tissues as well as reproduction.

Explain variation in consumer productivity using the model: I = A + W

Of the food ingested by a consumer (I), a portion is assimilated across the gut wall (A), and the remainder is expelled from the body as waste products (W).

Describe the physical structure and associated vertical structure of terrestrial communities:

On land, the growth form of the plants largely determines this vertical structure - their size, branching, and leaves - and this vertical structure in turn influences (and is influenced by) the vertical gradient of light. A well-developed forest ecosystem for example has multiple layers of vegetation.

Corridors...

One structural feature of the landscape that can facilitate an organism's movement between patches of suitable habitat is a corridor. Typically, corridors are strips of vegetation similar to the patches they connect but different from the surrounding matrix in which they are set.

The biological structure of a community may be the result of constraints imposed by the fundamental niche. This means:

Only species tolerant of prevailing environmental conditions will be found there. Species interactions do not influence the fundamental niche.

Patch size and shape influence community structure:

Patch size has a crucial influence on community structure, species diversity, and the presence and absence of species. As a general rule, large patches of habitat contain a greater number of individuals (population size) and species (species richness) than do small patches.

Before leaves fall from trees many nutrients are:

Retranslocated

Explain secondary production:

Secondary production or productivity represents the formation of living mass (aka growth and reproduction) of heterotrophic organisms over some period of time (grams per unit area per unit time). Secondary production is greatest when the birthrate of the population and the growth rate of individuals are the highest.

Environmental controls on primary productivity:

Temperature Precipitation Nutrients Light * the availability of essential nutrients directly affect NPP. There is a general pattern of increasing NPP with increasing soil nutrient availability.

Another widely used index of diversity that considers both species richness and evenness is the Shannon-Weiner Diversity Index:

The Shannon index (H) is computed as H = - SIGMA (pi)(ln pi) In the absence of diversity, where only one species is present, the value of H =0. The maximum value of the index, which occurs when all species are present in equal numbers is Hmax = ln(S), where S is the total number of species.

The nature of the herb layer depends on the soil moisture and nutrient conditions, slope position, density of the canopy and understory, and exposure of the slope, all of which vary from place to place throughout the forest.

The final layer, the forest floor, is where the important process of decomposition takes place and where microbial organisms feeding on decaying organic matter release mineral nutrients for reuse by the forest plants.

Explain the concept of the shifting mosaic steady state:

The landscape represents a shifting mosaic of changing communities. Disturbances alter the biological and physical structures of communities making up the landscape, giving way to the process of succession. This view of the landscape suggests shifting mosaic composed of patches, each in a phase of successional development. The tern "steady state" is a statistical description of the collection of patches and thus refers to the average state of the landscape. In other words, the mosaic of patches is not static. Each patch is continuously changing - but although the overall mosaic is continuously changing, the average composition of the landscape my remain fairly constant - or in a steady state.

Assimilation efficiency (A/I):

The ratio of assimilation to ingestion (A/I), the assimilation efficiency. This is a measure of the efficiency with which the consumer extracts energy from food.

Recap of the rhizosphere:

The rhizosphere is an active zone of root growth and death, characterized by intense microbial and fungal activity. Decomposition in the rhizosphere is more rapid than in the bulk soil because plant roots use carbon-rich exudates to supplement the decomposition process of low carbon quality organic matter. Nutrients immobilized in bacteria biomass are then released to the soil as microbivores (protozoa and nematodes) that feed on bacteria.

Describe methods of measuring primary productivity:

The simplest and most common method of measuring net primary production in terrestrial ecosystems is to estimate the change in standing crop biomass (SCB) over a given time interval. Delta SCB = SCB(t2) - SCB (t1) Two possible losses of biomass over this time period must also be recognized: loss of biomass as a result of the death of plants (D) and loss of biomass resulting from consumption by consumer organisms (C). Therefore, the estimate of net primary productivity is: NPP = (change in SCB) + D + C

Define the rhizosphere:

The term rhizosphere is used to describe a region of the soil where plant roots function. It is an active zone of root growth and death, characterized by intense microbial and fungal activity.

One approach being used to understand the influence of species diversity on the structure and dynamics of communities is grouping species into functional categories based on criteria relating to their function within the community.

The trophic levels group species into feeding groups. The concept of guilds is a functional group of species based on sharing similar functions within the community or exploiting the same resource. By aggregating species into a smaller number of functional groups, researchers can explore the processes controlling community structure in more general terms.

Elephants are keystone species on the Africa savanna due to:

Their influence on eradicating woody vegetation.

In general, the greater the contrast between adjoining patches, the greater the diversity of species.

Therefore, a boundary between forest and grassland should support more species than would a boundary between a young and a mature forest.

Ecologists have addressed this shortcoming by developing mathematical indices of species diversity.

These indices consider both the number and relative abundance of species within the community.

The theory of island biogeography can be applied to the theory of landscape patches because:

This theory can apply to landscape patches because any patch of habitat isolated from similar habitat by different, relatively inhospitable terrain traversed only with difficulty by organisms of the habitat patch may be considered an island.

Immobilization:

Whenever mineralization occurs, immobilization - the uptake and assimilation of mineral nitrogen by microbial decomposers - runs counter to it.

Succession...

With time, natural communities change. This gradual sequential change in the relative abundance of species in a community is succession. Opportunistic, early successional species yield to late successional species. Succession occurs in all environments. The similarity of successional patterns in different environments suggests a common set of processes.

Ecosystems have two major food chains:

(1) the grazing food chain (2) the detrital food chain ... The distinction between these two food chains is the source of energy for the first-level consumers, the herbivores. In the grazing food chain, the source of energy is the living pant biomass or net primary production. In the detrital food chain, the source of energy is dead organic matter or detritus. The energy flow between these two major food chains is connected.

Discuss the individualistic concept of a community:

- Stresses the individualistic nature of species distribution - Also known as the continuum concept - States that the relationship among coexisting species (species within a community) is a result of similarities in their requirements and tolerances, not to strong interactions or common evolutionary history. - Changes in species abundance along environmental gradients occur so gradually that it is not practical to divide the vegetation into associations - do not form clusters, but rather represent the independent responses of species **The major difference between these two views is the importance of interactions, evolutionary and current, in the structuring of communities.

The intertidal zone of a sandy beach provides an example in which the zonation is dominated by...

...heterotrophic organisms, rather than autotrophs.

Species richness (S):

A count of the number of species occurring within the community.

The grazing and detrital food chains are connected because:

Dead bodies of producers, herbivores, and carnivores enter the detrital food chain.

What is the relationship between NPP and secondary production?

Herbivore biomass, consumption, and secondary production are all positively related to net primary productivity (NPP).

What component of dead organic matter decomposes the slowest?

Lignin

Converison of nutrients from organic to inorganic form is called:

Mineralization.

Top-Down Control:

Occurs when predator populations control the abundance of prey species.

Grazing food chain:

Primary producers --> herbivores --> carnivores (Energy flow is unidirectional).

Corridors provide structural connectivity in fragmented landscape, true or false?

TRUE.

Community:

The group of species that occupy a given area, interacting either directly or indirectly.

"The world is green" proposition:

"The world is green" proposition suggests the top-down control of primary productivity and standing biomass. This proposes that the world is green (aka plant biomass accumulates) because predators keep herbivore populations in check. A growing body of experimental data suggests that top-down controls are important in many ecosystems and that patterns of NPP are influenced not only by abiotic conditions, but also by controls of herbivore populations (and rates of consumption of primary productivity) by predators. Recall that top-down control in a food web is referred to as a trophic cascade.

For two reasons, the most productive waters of the oceans are shallow waters of the coastal environments.

(1) Shallow waters allow for a greater transport of nutrients from the bottom sediments to the surface waters, aided by wave action and the changing tides. (2) Coastal waters receive a large input of nutrients carried from terrestrial ecosystems by rivers and streams.

Landscape ecology differs in a number of ways from the other areas of ecological study that we have examined thus far:

(1) The focus of landscape ecology is on spatial heterogeneity, which characterizes the spatial pattern of the elements that make up the landscape, determines the process that gives rise to the patterns, and examines how those patterns change through time... Landscape ecology is the study of linking pattern and process. (2) Landscape ecology is distinguished by its focus on broader spatial extends than those traditionally studied in ecology. (3) Landscape ecology often focuses on the role of humans in creating and affecting landscape patterns and processes.

Primary production in aquatic and marine ecosystems:

- Temperature - Nutrients (nitrogen and iron in oceans, phosphorus in some marine habitats, phosphorus in freshwater) - Light

The exact pattern of dynamics during decomposition is a function of:

- The nutrient content of the litter - The demand for the nutrient by the microbial population

Shifting mosaic steady state =

A continuously changing population of patches that remains fairly constant when viewed collectively rather than individually.

Which would NOT be a site for primary succession?

A deforested mountain top (secondary succession - after a disturbance) ... ex. of primary: sand deposited in dunes from strong winds, newly formed volcanic isalnd, cement blocks in a rocky intertidal zone.

Landscape pattern is defined by the spatial arrangement and connectively of patches:

A landscape is a spatially heterogeneous area, a mosaic of elements referred to as patches. Patches are areas that are more or less homogenous compared to their surroundings. The communities that surround a patch constitute its matrix. The proximity of patches to each other influences the ability for interactions to occur; this is called their connectivity. One feature of the landscape that can increase connectivity is the presence of corridors, which are routes that facilitate movement between patches.

Describe negative impacts of edges:

Although edge effect may increase species diversity, it can also create new problems. Narrow, abrupt boundaries appear to be attractive to predators. Predators often use edges as travel lanes, which increases rates of predation in edge habitats.

All of the following statements about energy flow are correct EXCEPT...

All of NPP is consumed by grazer herbivores (not true). ... Statements are true: NPP is less than GPP In an energy pyramid, producers have the most energy At each trophic level, energy dissipated (released) through metabolism enters the environment as heat

Consumers vary in efficiency of production:

Although there is a general relationship between the availability of primary productivity and the productivity of consumer organisms (secondary productivity) across a variety of terrestrial/aquatic ecosystems, within a given ecosystem there is considerable variation among consumer organisms in their efficiency in transforming energy consumed into secondary production.

Climate and nutrient availability are the primary controls on net primary productivity in terrestrial ecosystems:

An array of environmental factors (including climate) influence the productivity of terrestrial ecosystems. NPP increases with increasing mean annual temperature and rainfall. Sites with higher mean annual temperature typically support higher rates of photosynthesis and are associated with a longer time period over which photosynthesis can occur. The higher the rainfall, the more water is available for transpiration.

Describe pyramids of energy and pyramids of biomass:

An important consequence of decreasing energy transfers through the food web is a corresponding decrease in the standing biomass of organisms within each successive trophic level. The pyramid of biomass indicates by weight, or other means of measuring living material, the total bulk of organisms or fixed energy present at any one time - the standing crop. Because some energy or material is lost at each successive trophic level, the total mass supported at each level is limited by the rate at which energy is being stored in the next lower level. In general, the biomass of producers must be greater than that of the herbivores they support, and the biomass of the herbivores must be greater than that of carnivores. That circumstance results in a narrowing pyramid for most ecosystems.

What is the fate of nutrients once they make their way into the food chain?

As these living tissues senesce (age), the nutrients are returned to the soil or sediments in the form of dead organic matter, where they make their way through they decomposer (detrital) food chain. Unlike carbon, most of these nutrients are recycled within the ecosystem. Various microbial decomposers transform the organic nutrients into a mineral form, and the nutrients are once again available to the plants for uptake and incorporation into new tissues. This process, called nutrient cycling, is an essential feature in all ecosystems.

A consumer's ability to convert the energy it ingests into secondary production varies with species and the type of consumer.

Assimilation efficiencies vary widely among ectotherms and endotherms. Endotherms are much more efficient than ectotherms. However, carnivores, even ectothermic ones, have a higher assimilation efficiency than herbivores. Endotherms > ectotherms Carnivores > herbivores

3 components of an ecosystem:

Autotrophs Heterotrophs (consumers and decomposers) Abiotic environment

Explain the edge effect:

Because boundaries often blend elements from the adjacent patches (particularly in the case of ecotones), their structure and composition are often very different from the adjacent patches. Thus, boundaries offer unique habitats with relatively easy access to the adjacent communities.. These diverse conditions enable these boundary zones to support plant and animal species from adjacent patches, as well as those species adapted to the edge environment. As a result, boundaries are often populated by a rich diversity of life. This phenomenon (the edge effect) is influenced by the area of boundary available and by the degree of contrast between adjoining plant communities.

In aquatic ecosystems, the most common method of estimating NPP is the light/dark bottle method:

Because oxygen is one of the most easily measured products of both photosynthesis and respiration, a good way to gauge primary productivity in an aquatic ecosystem is to measure the concentration of dissolved oxygen.

Ex. of disturbances creating and being influenced by patterns on the landscape...

Communities on ridge tops are more susceptible to flooding. In turn, these disturbances result in new patterns of patches on the landscape. However, natural disturbances are not limited to physical processes. Biological processes can also function as disturbances that structure landscapes (ex. grazing by domestic animals).

Rank abundance curves are useful for:

Comparing patterns of species richness and abundance between communities.

In lakes or oceans, the depth at which gross productvity is equal to respiration is the:

Compensation depth

Explain the importance of corridors:

Corridors probably function best as travel lanes for individuals moving within the bounds of their home range, but when corridors interconnect to form networks, they offer dispersal routes for species traveling between habitat patches. They enhance the movement of organisms beyond what is possible through the adjacent matrix. By facilitating the movement among different patches, corridors can encourage gene flow between subpopulations and help reestablish species in habitats that have experienced local extinction. Corridors also acts as filters, providing dispersal routes for some species but not others. Different sized gaps in corridors allow certain organisms to cross while restricting others (the filter effect).

Standing crop biomass:

The amount of accumulated organic matter found in an area at a given time is the standing crop biomass. Biomass is usually expressed as grams of organic matter per square meter (g/m^2) or some other appropriate unit of area. Standing crop biomass differs from productivity. Productivity is the rate at which organic matter is created by photosynthesis. Biomass is the amount of organic matter present at any given time.

Laws of thermodynamics...

Energy flow in ecosystems supports life. As energy moves through an ecosystem, much of it is lost as heat of respiration. Energy degrades from a more organized to a less organized state (entropy). However, a continuous flux of energy from the sun prevents ecosystems from running down.

Maram grass is usually the first plant to colonize sand dunes during succession. This species is a climax species (true or false):

False - it would be a pioneer species.

Basal species:

Feed on no other species but are fed on by others.

Which of the following statements is NOT an explanation of diversity predicted by the intermediate disturbance hypothesis?

Frequent, high intensirt disturbance increases diversity by favoring early successional species (that would actually decrease diversity). Intermediate frequency and intensity of disturbance promotes the highest diversity among organisms.

Nutrient cycling in streams and rivers:

Inputs of dead organic matter from adjacent terrestrial ecosystems (leaves/woody debris), rainwater, and subsurface seepage bring nutrients into streams. Because nutrients are continuously being transported downstream, a spiral (rather than a cycle) better represents the cycling of nutrients. This is referred to as "nutrient spiraling." Flowing water has an added element - a spatial cycle. Nutrients in the form of organic matter are constantly being carried downstream. How quickly these materials are carried downstream depends on how fast the water moves and physical/biological factors that hold nutrients in place.

Relate the metapopulation dynamics to landscape dynamics:

In a metapopulation, both patch size and isolation influence local population dynamics.

Describe interior species and area-insensitive species:

In contrast to edge species, other species, termed interior species, require environmental conditions characteristic of interior habitats and stay away from the abrupt changes associated with boundary environments. Intermediate to these two groups are area-insensitive species, such as the Caroline chickadee and the Eastern wood pewee.

Light bottle/dark bottle method:

In one set of clear glass "light bottles," a water sample from the aquatic ecosystem (and associated autotrophic organisms - phytoplankton) is allowed to incubate in the sealed bottle for a defined time period. If photosynthesis is greater than respiration, oxygen will accumulate in the water, providing an estimate of NPP. Water is also incubated over the same time period in another set of "dark bottles," painted black to prevent light from reaching the water. Because the lack of light will prevent photosynthesis, the oxygen content of the water will decline as a function of respiration. The difference between the values of oxygen in the light (photosynthesis + respiration) and dark (respiration) bottles at the end of the time period therefore provides an estimate of total photosynthesis, or gross primary production.

Explain how plant life-form may influence NPP:

In terrestrial ecosystems, increased standing biomass is related to increased net primary productivity. In aquatic ecosystems, the standing biomass at any time interval is low compared to the accumulated NPP over the course of a year.

Nutrient cycling in terrestrial ecosystems:

In terrestrial ecosystems, plants themselves bridge the physical separation between the decomposition zone at the soil surface and the productivity zone in the plant canopy. The root systems provide access to the nutrients made available in the soil through decomposition, and the vascular system within the plant transports these nutrients to the sites of production (canopy).

Describe the soil microbial loop:

The soil microbial loop is the process of supplementing carbon to microbial decomposers in the rhizosphere, enhancing the decomposition of soil organic matter, and subsequently releasing mineral nutrients for plant uptake by microbial grazers.

Light and nutrient availability are the primary controls on net primary productivity in aquatic ecosystems:

Light is a primary factor limiting productivity in aquatic ecosystems, and the depth to which light penetrates a lake of ocean is crucial in determining the zone of primary productivity. The photosynthetic rate and subsequently the gross primary productivity of phytoplankton are highest at intermediate levels of photosynthetically active radiation. In the oceans, nutrients in deeper waters must be transported to the surface waters, where light is sufficient to support photosynthesis. As a result, nutrients (particularly nitrogen, phosphorus, and iron) are major limitation factors on primary productivity in aquatic ecosystems.

A variety of processes give rise to landscape patterns:

The spatial structure of each landscape is unique and results from the interactions of a variety of factors, including abiotic (physical), biotic, natural disturbances, and human activities.

Ecologists study the process of decomposition by designing experiments that follow the decay of dead plant and animal tissues through time... The most widely used approach is the use of litterbags to examine the decomposition of dead plant tissues.

Litterbags are mesh bags constructed of synthetic material that does not readily decompose. The holes in the bag must be large enough to allow decomposer organisms to enter and feed on the litter, but small enough to prevent decomposing plant material from falling out. A fixed amount of litter is placed in each bag. At multiple intervals over the course of time, bags are collected for each species being measured and the contents are dried and weighed in a lab. From this data, the decomposition rate can be determined for each species studied.

The feedback loop between nutrient availability, litter quality, and NPP...

Low nutrient availability in soil > low nutrient uptake by plants > low concentration of nutrients in plant leafs > low net primary productivity > low nutrient return to soil in litterfall > low net mineralization rate

Explain how ecosystem may influence NPP:

NPP also varies with stand age, particularly in ecosystems that are dominated by woody vegetation. Trees and woody shrubs can survive for a long time, which greatly influences how they allocate energy. Early in life, leaves make up more than one half of their biomass (dry weight), but as trees age, they accumulate more woody growth. Trunks and stems become thicker and heavier, and the ratio of leaves to woody tissue changes. ** As the age if a forest stand increases, more and more of the living biomass occurs as woody tissue whereas the leaf area remains relatively constant or declines. As the stand ages, rates of both photosynthesis and respiration decline. In addition, more of the gross production (photosynthesis) is used for maintenance (respiration of woody tissues) and less remains for growth. The result is a pattern of increasing primary productivity during early stages of development followed by a decline in NPP as the forest ages.

Describe internal cycling of nutrients using the terms: plant uptake, NPP, retranslocation, litterfall, dead organic matter, decomposition, and mineralization. * this description uses nitrogen as an example to represent the internal cycling of any nutrient *

Nitrogen in the soil is taken up through plant roots and used to produce proteins, enzymes, and a variety of other nitrogen-based compounds. This step represents a transformation of nitrogen from inorganic to organic form. The availability of nutrients in the soil will limit the rate of plant uptake and subsequently the rate of NPP. In the case of nitrogen, the rate of plant uptake will directly influence the rate of photosynthesis. As plant tissues senesce, nutrients are returned to the soil surface as dead organic matter. Before senescence occurs, however, plants absorb some nutrients from the senescing tissues into the perennial parts of the plant to be stored and used in producing new tissues... This process of recycling nutrients within the plant is called retranslocation or resorption. As senescence occurs, water and nutrients are drawn into the stems and away from the leaves. The plant can recover up to 70% if nitrogen from its green leaves before they senesce and fall to the forest floor (litterfall), thus reducing the amount of nutrients returned to the soil as dead organic matter. Once on the forest floor, various decomposers break down and consume the dead plant tissues, transforming the organic nutrients into a mineral form through the process of mineralization. The cycle is now complete, and nutrients are once again available for plant uptake.

Distinguish between autochthonous and allochthonous sources of carbon in aquatic ecosystems:

Organic carbon produced within an ecosystem is described as autochthonous, whereas inputs from outside the ecosystem are described as allochthonous. In aquatic ecosystems, the autochthonous input is provided through photosynthesis by aquatic plants, attached algae in shallow waters, and by phytoplankton in the open waters. However, a substantial proportion of organic carbon in these ecosystems is allochthonous, derived from dead organic matter from adjacent terrestrial ecosystems entering the water through both dissolved organic matter (DOM) and particulate organic matter (POM).

This arrangement does NOT hold true for all ecosystems, such as those in lakes and open seas:

Primary production is located in phytoplankton, which have a short life cycle and rapid reproduction. They are heavily grazed by herbivorous zooplankton that are larger/longer lived. Thus, despite the high productivity of algae, their biomass is low compared to that of zooplankton herbivores. The result is an inverted pyramid, with a lower standing biomass of primary producers (phytoplankton) and herbivores (zooplankton).

Relate NPP to secondary production:

Primary productivity limits secondary production. Secondary production depends on primary production for energy, and therefore, primary productivity should function as a constraint on secondary productivity within the ecosystem (bottom-up control of the flow of energy).

Primary succession...

Primary succession begins on new sites devoid of or unchanged by organisms. Examples include newly formed sand dunes, lava flows, or newly exposed glacial sediments.

Primary succession:

Primary succession occurs on a site previously unoccupied by a community - a newly exposed surface (such as the cement blocks in a rocky intertidal environment).

Discuss the feedback system that exists in the internal cycling of nutrients in an ecosystem:

Reduced nutrient availability can have the effect of reducing both the nutrient concentration of plant tissues (primarily leaf tissues) and net primary productivity. This reduction lowers the total amount of nutrients returned to the soil in dead organic matter. The reduced quantity and quality (nutrient concentration) of organic matter entering the decomposer food chain increase immobilization and reduce the availability of nutrients for uptake by plants. In effect, low nutrient availability begets low nutrient availability.

Compare population size and species richness in small versus large patches:

Researchers have found that the species richness of edge species decreased with increasing patch size, while that of an interior species increases.

Secondary succession...

Secondary succession begins after disturbance on sites where organisms are already present. Terrestrial examples include abandoned agricultural lands or the reestablishment of vegetation after logging or fire. In aquatic ecosystems, disturbances caused by storms, wave action, or herbivory can initiate the process of secondary succession.

Distinguish between a border and an ecotone:

Some boundaries between landscape patches are narrow and abrupt with a sharp contrast between adjoining patches, such as between a forest and an adjacent agricultural field - border. Others are much broader, forming a transition zone called an ecotone between adjoining patches.

Ecosystem energetics:

Some of the photons that reach plants are transformed into photochemical energy used in photosynthesis. That energy, stored in the chemical bonds of carbohydrates and other carbon-based compounds, becomes the source of energy for other living organisms. In this way, the story of energy within an ecosystem is in large part a story of carbon in the form of organic matter - the living and dead tissues of plants and animals. All ecological processes involve the transfer of energy, and ecosystems are no different from physical systems such as the atmosphere because they are subject to the same physical laws. As energy is transferred from one organism to another in the form of food, a portion is stored as energy in living tissue, whereas a large part of that energy is dissipated as heat and entropy increases. Living systems, however, are open systems with a constant input of energy in the form of solar radiation, providing the means to counteract entropy.

The physical environment also directly affects the rate of decomposition:

Temperature and moisture greatly influence microbial activity. Low temperatures reduce or inhibit microbial activity, as do dry conditions. The optimum environment for microbes is warm and moist, resulting in higher decomposition rates. Alternating wet and dry conditions tend to reduce microflora activity.

The distance of the island from the mainland and the size of the island both affect equilibrium species richness:

The greater the distance between the island and the mainland, the less likely that many immigrants successfully complete the journey. The result is a decrease in the equilibrium number of species. On larger islands, extinction rates, which vary with area, are lower because a greater area generally contains a wider array of resources and habitats. For this reason, large islands can support more individuals of each species as well as meet the needs of a wider variety of species. The lower rate of extinction on larger islands results in a higher equilibrium number of species.

_____ ecosystems are characterized by low NPP and high energy flow through the detrital food chain primarily from dead organic matter inputs from neighboring ecosystems.

Stream

Landscape connectivity permits movement between patches:

The degree to which the landscape facilitates or impedes the movement of organisms among patches is referred to as landscape connectivity.

Disturbance on the formation of landscape patterns:

The distinct patterns of communities that we see in the landscape, as well as the species inhabiting them, are heavily influenced by both past and present natural disturbances. A disturbance is any relatively discrete event (such as fire, windstorm, flood, extremely cold temps or drought) that disrupts community structure and function. Disturbances both create and are influenced by patterns on the landscape.

Primary production...

The flow of energy through an ecosystem starts with the harnessing of sunlight by green plants through a process referred to as primary production. The total amount of energy fixed by plants is gross primary production. The amount of energy remaining after plants have met their respiratory need is net primary production in the form of plant biomass.

Explain how energy allocation may influence NPP:

The greater the rate of photosynthesis, the greater the allocation of carbon (energy) to photosynthetic tissues (leaves) relative to nonphotosynthetic tissues (stems and roots), the greater the net carbon gain and plant growth. Reduced moisture conditions result in an increased allocation to roots at the expense of leaves, thus reducing leaf area and rates of net carbon gain, thus reducing NPP.

Nutrients in organic matter are mineralized during decomposition:

The higher the nitrogen content of the dead leaf, the higher the nutrient value for the microbes and fungi that feed on the leaf.

The two food chains are linked:

The initial source of energy for the detrital food chain is the input of dead organic matter and waste materials from the grazing food chain. The distinction between the two food chains is often blurred at the higher trophic levels (carnivores) because predators rarely distinguish whether their prey draw their resources from primary producers (plants) or detritus.

Key ecosystem processes influence the rate of nutrient cycling:

The internal cycling of nutrients through the ecosystem depends on the processes of primary production and decomposition. Primary productivity determines the rate of nutrient transfer from inorganic to organic form (nutrient uptake), and decomposition determines the rate of transformation of organic nutrients into inorganic form (net mineralization rate). Therefore, the rates at which these two processes occur directly influence the rates at which nutrients cycle through the ecosystem.

Define decomposition and describe processes involved in decomposition:

The key process in the recycling of nutrients within ecosystems is decomposition. Decomposition is the breakdown of chemical bonds formed during the construction of plant and animal tissues. Decomposition involves the release of energy originally fixed by photosynthesis, carbon dioxide, and water, and ultimately the conversion organic compounds into inorganic nutrients. Decomposition is a complex of may processes, including leaching, fragmentation, changes in physical and chemical structure, ingestion, excretion of waste products, and mineralization.

Allochthonous inputs of carbon are important to small streams...

The relative importance of allochthonous sources of carbon varies widely among different aquatic ecosystems... In most marine ecosystems, AUTOchthonous inputs of organic carbon dominate because of the high NPP of resident populations of phytoplankton. In contrast, in small stream ecosystems flowing through forested catchments derive most of their organic carbon from dead plant materials deposited into the water from the surrounding forest ecosystem - ALLOchthonous.

Interpret data from litterbag experiments:

The mass of litter remaining in the bags decreases continuously as time progresses. Decomposition is expressed as the percentage of the original mass remaining at different times during the experiment. It is important to note that as time passes, the mass of organic matter remaining in the litterbag includes the original plant material as well as the bacteria and fungi (microbial decomposers) that have colonized and grown on the plant.

Energy fixed in the process of photosynthesis is primary production:

The rate at which carbon dioxide in the atmosphere or water is converted into organic compounds by autotrophs is referred to as primary productivity because it is the first and basic form of energy storage in ecosystems. With the exception of chemotrophs, the flow of energy through an ecosystem starts with the harnessing of sunlight in the process of photosynthesis.

Several factors influence the rate of decomposition:

The rate of decay (mass loss) is related to: (1) the quality of plant litter as a substrate (food source) for microorganisms and soil fauna active in the decomposition process. (2) features of the physical environment that directly influence decomposer populations, namely soil properties, (texture and pH) and climate (temperature and precipitation).

Net primary production (NPP):

The rate of energy storage as organic matter after respiration is net primary production (NPP). NPP is described as: Gross primary productivity (GPP) - Respiration by autotrophs (R).

Production efficiency (P/A):

The ratio of production to assimilation (P/A), the production efficiency. This is a measure of how efficiently the consumer incorporates assimilated energy into secondary production.

Explain the Theory of Island Biogeography:

The theory of island biogeography provides a framework to understand how size and connectivity can interact to influence patterns of species richness on patches within the landscape. The theory was first developed to explain patterns of species richness on islands... On islands, a 10 fold increase in land area leads to doubling of the number of species. The theory of island biogeography is quite simple: the number of species established on an island represents a dynamic equilibrium between the immigration of new colonizing species and the extinction of previously established ones. The rate at which one species is lost and a replacement species is gained = the turnover rate.

Identify components of landscape connectivity:

There are two components to landscape connectivity: structural and functional. Structural connectivity relates to the physical arrangement of habitat patches on the landscape; that is, the degree to which patches are contiguous or physically linked to one another. Functional connectivity describes the degree to which the landscape facilitates the movement of organisms and is a function of both the physical structure of the landscape as well as the behavioral responses of organisms to the structure. Functional connectivity is therefore both landscape AND species specific. It requires a species centered approach that considers factors such as a species' mode and range of dispersal and its ability to move through different types of habitat.

We typically refer to decomposers as organisms that feed on dead organic matter or detritus.

These organisms include: microbial decomposers - a group made up primarily of bacteria and fungi (microflora). detritivores - animals that feed on dead organic matter (detritus), including dung. microbivores - feed on the microflora.

As the phytoplankton go deeper into the water column, the photosynthetic rate declines as the light intensity decreases until at some point the rate of photosynthesis (gross production) is equal to the rate of respiration, and NPP is 0.

This zone is referred to as the compensation depth and corresponds to the depth at which the availability of light is equal to the light compensation point.

Describe landscape ecology in terms of patches and matrix communities:

We have defined a community as a group of potentially interacting species occupying a given area. Although by definition, ecological communities have a spatial boundary, they likewise have a spatial context within the larger landscape. This patchwork of different types of land cover is called a mosaic. The land mosaic is a product of the boundaries defined by the changes in the physical and biological structure of the distinct communities that forms its elements. Patches and their boundaries - the structural and functional components of the landscape - interact in a variety of ways depending on their size and spatial arrangement, and they change through time. The study of the composition, structure, and function of landscapes is called landscape ecology.

Productivity can be expressed in units of dry organic matter:

g/m^2/yr

Which of the following may have an impact on NPP?

light availability limiting nutrients water availability temperature

Energy flows through trophic levels can be quantified:

n = the energy available to a given trophic level This is a result of the level below thus trophic level, designated as (n-1).

One main way to simplify food webs is to aggregate species into trophic levels:

A basic food web is aggregated into 3 trophic levels: primary producers, herbivores, and carnivores. The arrows point in the direction of energy flow, from the autotrophs to herbivores, and from the herbivores to the carnivores.

Rank-abundance diagram:

A common method for examining patterns of relative abundance within communities involves plotting the relative abundance of each species against rank, where rank is defined by the order of species from the most to least abundant. Thus, the most abundant species is plotted first along the x-axis, with the corresponding value on the y-axis being its relative abundance value. The resulting graph is called a rank-abundance diagram.

Describe a community:

A community is a spatial concept - the collective of species occupying a place within a defined boundary. Because ecologists generally do not study the entire community, the term community is often used in a more restrictive sense. It refers to a subset of species, such as a plant or fish community. This use of community suggests relatedness or similarity among the members in their taxonomy, response to the environment, or use of resources.

Biological structure:

A community is the group of species (populations) that occupy a given area and interact either directly or indirectly. The biological structure of a community is defined by its species composition, that is, the set if species present and their relative abundances.

Trophic cascade:

A type of top-down control. A trophic cascade occurs when a predator in a food web suppresses the abundance of their prey (the intermediate species) such that it increases the abundance of the next lower trophic level (basal species) on which the intermediate species feeds.

Succession involves heterotrophic species:

Although our discussion and examples of succession have thus far focused on temporal changes in the autotrophic component of the community (plant succession), associated changes in the heterotrophic component also occur. As plant succession advances, changes in the structure and composition of the vegetation result in changes in the animal life that depends on the vegetation as habitat.

Explain the structure of a food CHAIN:

An abstract representation of feeding relationships within a community is the food chain. A food chain is a descriptive diagram - a series of arrows, each pointing from one species to another, representing the flow of food energy from prey to predator. ex. grass --> grasshopper --> sparrow --> hawk.

In other cases, however, heterotrophic succession can be a product of autogenic changes in the environmental conditions brought about by the heterotrophic organisms themselves:

An example is decomposition... Dead plant tissues, animal carcasses, and droppings form substrates on which communities of organisms involved in decomposition exist. Within these communities, groups of fungi and animals succeed one another in a process of colonization and replacement that relates to changes in the physical and chemical properties of the substrate through time. These changes of substrate are a direct function of the feeding activities of the decomposer organisms.

Top predators:

Are not subject to predators; they prey on intermediate and basal species.

Zonation is spatial change in community structure:

As one moves across the landscape, the biological and physical structure of the community changes. Often these changes are small, subtle ones in the species composition or height of the vegetation. However, as we travel farther, these changes often become pronounced. These changes in the physical and biological structures of communities as one moves across the landscape are referred to as zonation.

Environmental heterogeneity:

As we have seen, the biological structure (species composition) of a community reflects both the direct response (survival, growth, and reproduction) of the component species to the prevailing abiotic environmental conditions, as well as their interactions (direct and indirect) with other species. In turn, as environmental conditions change from location to location, so will the set of species that can potentially occupy the area and the manner in which they interact. However, environmental conditions are typically not homogenous even within a given community.

Explain autogenic environmental change and the role it plays in succession:

Autogenic environmental change is a direct result of the presence and activities of organisms within the community. For example, the vertical profile of light in a forest is a direct result of the interception and reflection of solar radiation by the trees. This is a common feature in plant succession. In both primary and secondary succession, colonization alters environmental conditions. In all cases, the role of temporal, autogenic changes in environmental conditions and the differential response of species to those changes are key features of community dynamics. Some types of autogenic change = organic matter, nutrients, and soil development.

Simpson's Index of Diversity:

Because the greater the value of D, the lower the diversity, D is often subtracted from 1 to give: Simpson's index of diversity = 1 - D The value of this index also ranges from 0 to 1, but now the value increases with species diversity. In this case, the index represents the probability that two randomly selected individuals will belong to different species. ***As diversity increases, the probability that two randomly selected individuals belong to different species increases.

Terrestrial communities:

The forms and structures of terrestrial communities are defined primarily in terms of their vegetation. Plants can be tall/short, evergreen/deciduous, herbaceous/woody... Such characteristics can describe growth forms. Ecologists often classify and name terrestrial communities based on the dominant plant growth forms and their associated physical structure: forests, woodlands, shrublands, or grassland communities.

Species within a community can be classified into functional groups:

The grouping of species into trophic levels is a functional classification; it defines groups of species that derive their energy in a similar manner. Another approach is to subdivide each trophic level into groups of species that exploit a common resource in a similar fashion; these groups are termed guilds. Guilds are used to describe groups of functionally similar species in a community. (example: hummingbirds and other nectar-feeding birds form a guild of species that exploits the common resource of flowering plants in a similar fashion).

Like zonation, the process of succession is generally common to all environments, both terrestrial and aquatic.

The initial, or early successional species (pioneer species) are usually characterized by high growth rates, smaller size, high degrees of dispersal, and high rates of population growth. In contrast, late successional species (climax species) generally have lower rates of dispersal and colonization, slower per capita growth rates, and are larger and longer-lived. The colonizing species ameliorate the environment, and thus pave the way for invasion of other species.

In contrast to the inverse relationship between soil fertility (nutrient availability) and plant species richness observed in terrestrial plants, the pattern between nutrient availability and species richness of autotrophic organisms in aquatic communities is quite different...

Unlike the pattern of decreasing species diversity in terrestrial plant communities, fertilization results in an increase in the species richness of autotrophs in both freshwater and marine communities.

Dominance:

When a single or a few species predominate within a community, they are referred to as dominants, The dominants are often defined as the most numerically abundant; however, in populations or among species in which individuals can vary widely in size, abundance alone is not always a sufficient indicator of dominance.

Dominance:

When a single or few species predominate within a community, those species are referred to as dominants. Dominance is the converse of diversity. Dominant species are usually defined separately for different taxonomic or functional groups of organisms within the community. Because dominant species typically achieve their status at the expense of other species in the community, they are often the dominant competitors under prevailing environmental conditions.

Compare the 3 models of succession:

(1) The facilitation model - states that early successional species modify the environment so that it becomes more suitable for later successional species to invade and grow to maturity. In effect, early-stage species prepare the way for late-stage species, facilitating their success. (2) The inhibition model - involves strong competitive interactions. No one species is completely superior to another. The first species to arrive holds the site against all invaders. It makes the site less suitable for both early and late successional species. (3) The tolerance model - holds that later successional species are neither inhibited nor aided by species of previous stages. Thus, later-stage species can invade a newly exposed site, establish themselves, ad grow to maturity independently of the species that proceed or follow them.

Two distinct vertical layers (in aquatic environments) are also recognized based on light penetration through the water column:

(1) upper layer, the photic layer, where the availability of light supports photosynthesis. (2) deeper layer, the aphotic layer, an area without light. *The bottom layer of sediments, where decomposition is most active, is referred to as the benthic layer.

Types of indirect interactions:

(a) Species 1 affects Species 2, which affects species 3. (b) Species 1 indirectly affects Species 3.

Describe the changes in community structure of North American forest over geologic time:

- An ice sheet covered North America - Canada was under ice - Boreal forest, dominated by spruce and jack pine, covered most of the eastern and central US - As the climate warmed and the ice sheet retreated northward, plant species invaded the glaciated areas - 4 major tree genera advanced after the retreat of the ice sheet - Subsequently, over the past 18,000 years, the distribution and abundance of species and the subsequent structure of forest communities in eastern North America have changed dramatically

Which species occupies a given vertical layer may change during the day or season - such changes reflect daily and seasonal variations in the physical environment such as:

- Humidity - Temp - Light - Oxygen concentrations (in water) - Shifts in abundance of resources - Different requirements for organisms necessary for the completion of their life cycles Ex. zooplankton migrate vertically in the water column during the course of the day in response to varying light and predation.

Example of environmental heterogeneity...

- Spatial variation in soil nitrogen and moisture across an abandoned agricultural field. - Considerable spatial variation in soil moisture and nitrate - Similar studies show comparable patterns of fine-scale environmental variation within forest, intertidal, and benthic communities.

Example of diffuse interaction...

11 of the 12 predators within a community prey on snowshoe hares... Any single predator species may have a limited effect on the snowshoe hare population, but the combined impact of multiple predators can regulate the hare population.

Physical structure:

Communities are characterized by physical structure. In terrestrial communities, structure is largely defined by the vegetation. Vertical structure on land reflects the life-forms of plants. In aquatic environments, communities are largely defined by physical features such as light, temp, and oxygen profiles.

Communities have a characteristic physical structure:

Communities are characterized not only by the mix of species and by the interactions among them - aka their biological structure - but also by their physical features. The physical structure of the community reflects abiotic factors, such as the depth and flow of water in aquatic environments. It also reflects biotic factors, such as the spatial arrangement of the resident organisms. For example, the size and height of the trees and density and spatial distribution of their populations help define the physical attributes of the forest community.

Describe diversity changes during succession:

During the early phases of succession, diversity increases as new species colonize the site. However, as time progresses, species become displaced, replaced as dominants by slower-growing, more shade-tolerant species. The peak in diversity during the middle stages of succession corresponds to the transition period, after the arrival of later successional species but before the decline (replacement) of early successional species.

Discuss the role of environmental heterogeneity on community structure:

Environmental heterogeneity within a community can influence patterns of diversity. As an environment becomes more diverse, the species will also become more diverse. Just as an increase in the diversity of potential habits within a community results in an increase in the number of animal species that can be supported, an increase in the diversity of food resources within a community can likewise potentially increase the diversity of consumers that depend on those food resources.

Relative abundance:

Expressed as the proportion each species contributes to the total number of individuals of all species within the community. Relative abundance is calculated as: Pi = ni/N Where pi is the proportion of individuals in the community belonging to species I. ni is the number of individuals belonging to species I, and N is the total number of individuals of all species in the community.

Intermediate species:

Feed on other species AND are prey for other species.

Food webs:

Feeding relationships can be graphically represented as a food chain: a series of arrows, each pointing from one species to another that is a source of food. Within a community, many food chains mesh into a complex food web with links leading from primary producers to an array of consumers. Species that are fed on but do not feed on others are termed basal species

Explain the structure of a food WEB:

Feeding relationships in nature, are not simple, straight-line food chains. Rather, they involve many food chains meshed into a complex food web with links leading from primary producers through an array of consumers. Such food webs are highly interwoven, with linkages representing the complex interactions of predator and prey. Each circle represents a species, and the arrows from the consumed to the consumer are termed "links." The species in a food web are distinguished by whether they are basal species, intermediate species, or top predators -- these terms refer to the structure of the web, rather than to strict biological reality.

Identify indirect interactions in a food web and the role these interactions play in community structure:

Food webs illustrate a second important feature of species interactions within the community: indirect effects. Indirect interactions occur when one species does not interact with a second species directly, but instead influences a third species that does directly interact with the second. For example, in the food web, lynx do not indirectly interact with white spruce. However, by reducing snowshoe hare and other herbivore populations that feed on white spruce, lynx's predation can positively affect the white spruce population. The key feature of indirect interactions is that they may arise throughout the entire community because of a single direct interaction between only two component species.

Community structure is an expression of the species' ecological niche:

For a species to be a component of an ecological community at a given location, it must first and foremost be able to survive... The environmental conditions must fall within the range under which the species can persist - its range of environmental tolerances. The range of conditions under which individuals of a species can function are the consequences of a wide variety of physiological, morphological, and behavioral adaptations. As well as allowing an organism to function under a specific range of environmental conditions, these same adaptations also limit its ability to do equally well under different conditions.

Predators often function as keystone species within communities:

For example, sea otters (Enhydra lutris) are a keystone predator in the kelp bed communities found in the coastal waters of the Pacific Northwest. Sea otters eat sea urchins, which feed on the kelp.

The simplest quantitative measure of community structure is the index of species richness (S). However, species richness does not account for differences in the relative abundance of species within the community.

For example, two communities may both be inhabited by the same number of species and therefore have the same value of species richness, yet in one community the vast majority of individuals may be of a single species, whereas in the other community the individuals may be more evenly distributed among various species.

Characteristic organisms inhabit each available vertical layer, or stratum, in a community.

In addition to the vertical distribution of plant life described, various types of consumers and decomposers occupy all levels of the community (however, decomposers are typically found in the greatest abundance at the forest floor and sediment (benthic) layer).

Secondary succession:

In contrast, secondary succession occurs on previously occupied sites (previously existing communities) after disturbance. In these cases, disturbance is defined as any process that results in the removal (either partial or complete) of the existing community.

Resource availability can influence plant diversity within a community:

In general, increased availability of nutrients can support higher rates of photosynthesis, plant growth, and a higher density of plants per unit area. HOWEVER, a variety of studies have shown an INVERSE relationship between nutrient availability and plant diversity in communities. There is an inverse relationship between species richness and a composite index of soil fertility.

The biological structure of a community is first constrained by the species' environmental tolerances - aka the fundamental niche.

In turn, the fundamental niche is modified through interactions with other species - the realized niche. Influence of species interactions on community structure: Ex. competitors and predators can restrict a species from a community; conversely, mutualists can facilitate a species' presence and abundance within a community.

Discuss the role of resource availability on community structure:

Increased resource availability can positively influence diversity within a community. A greater number of food resources and more consistent food sources can increase the diversity of a community.

Describe keystone predation and give examples:

Keystone predation is a type of indirect interaction in which the predator enhances one or more less competitive species by reducing the abundance of the more competitive species. Ex. in the rocky intertidal zone, mussels, barnacles, limpets, and chitons are all preyed upon by starfish. The removal of starfish from the community reduces the diversity of prey species as a result of increased competition among them. Thus, in the absence of predation, the superior competitors will become more abundant and can exclude resources from other less competitive species, reducing the overall diversity in the community.

Keystone species:

Keystone species are species that function in a unique and significant manner, and their effect on the community is disproportionate to their numerical abundance. Their removal initiates changes in community structure and often results in a significant loss of diversity. Their role in the community may be to create or modify habitats or to influence the interactions among other species.

Explain the significance of keystone species and provide examples:

Keystone species function in a unique and significant manner, and their effect on the community is disproportionate to their numerical abundance. Their removal initiates changes in community structure and often results in a significant loss of diversity. Their removal in the community may be to create or modify habitats or to influence the interactions among other species. In some cases, keystone herbivores may modify the local community through their feeding activities. An excellent example is the role of the African elephant in the savanna communities of southern Africa.

One organism that functions as a keystone species by creating habitat is the coral, Oculina arbuscula, which occurs along the eastern coast of the US.

More than 300 species of invertebrates are known to live among the branches of it, and many more are reported to complete much of their life cycle within the coral.

Discuss the organismic concept of a community:

Organismic concept of communities: The thought that associations implied processes that might be responsible for structuring communities... The existence of clusters or groups of species that repeatedly associate was direct evidence for either positive or neutral interactions among them. Such evidence favors a view of communities as integrated units... This concept likens associations to organisms, with each species representing an interacting, integrated component of a whole. Development of the community through time (succession) was viewed as development of the organism. - suggests a common evolutionary history and similar fundamental responses and tolerances

Species diversity changes during succession:

Patterns of plant species diversity change over the course of succession. Species diversity increases into the late herbaceous stages and then decreases into shrub stages. Species diversity than increases again in young forest, only to decrease as the forest ages. Colonization by new species increases local species richness. Species replacement typically results from competition or an inability of a species to tolerate changing environmental conditions. Species replacement over time acts to decrease species richness.

Explain zonation:

Patterns of spatial variation in community structure (aka zonation) are common to all environments - both aquatic and terrestrial. Ex) Salt marsh along the northeastern coastline of North America... These differences can result from various environmental changes across a spatial gradient, including micro topography, water depth, sediment oxygenation, and salinity. The changes are marked by distinct plant communities that are defined by changes in dominant plants as well as structural features such as height, density, and spatial distribution of individuals.

Systematic changes in community structure are a result of allogenic environmental change at a variety of time scales:

Purely abiotic environmental (allogenic) change can produce patterns of succession over timescales ranging from days to millennia or longer. Environmental fluctuations that occur repeatedly during an organism's lifetime are unlikely to influence patterns of succession among species with that general lifespan. In contrast, shifts in environmental conditions that occur at period as long as or longer than the organism's life span are likely to result in successional shifts in species dominance.

Species evenness:

Refers to the equitability in the distribution of individuals among the species. The maximum species evenness would occur if each species in the community was equally abundant.

Ways environmental heterogeneity can influence diversity...

Soil moisture and nutrients Light environments (gaps in the canopy) Vegetation structure (can influence habitat suitability for bird species) etc. (ex. heterogeneity in the light environment of the forest floor caused by the death of canopy trees (gap formation) has been shown to increase tree species diversity in forest ecosystems... The increase in available light below canopy gaps would allow for the survival and growth of shade-intolerant species that would otherwise be excluded from the community.) Another example of the influence of environmental heterogeneity comes from the link between vegetation structure and bird species diversity.

The rank abundance diagram illustrates two features of community structure:

Species richness (number of species) and species evenness (relative abundance). The greater species richness is reflected by a greater length in the rank abundance curve. A more equitable distribution of individuals among the species is indicated by a more gradual slope. If each species was equally abundant, the curve would be a straight line, parallel to the x-axis.

Describe succession:

Succession is the gradual and seemingly directional change in community structure through time (ex. field to forest). Succession, in its most general definition, is the temporal change in community structure... Unlike zonation, which is the spatial change in community structure across the landscape, succession refers to changes in community structure at a given location on the landscape through time.

ALL communities have an autotrophic and a heterotrophic layer.

The autotrophic layer carries out photosynthesis. The heterotrophic layer uses carbon stored by the autotrophs as a food source. Vertical layering provides the physical structure in which many forms of animal life live.

Biological structure of community defined by species composition:

The biological structure of a community is defined by its species composition, that is, the set of species present and their relative abundance.

The upper layer, the canopy, is the primary site of energy fixation through photosynthesis.

The canopy structure has a major influence on the rest of the forest. If the canopy is fairly open, considerable sunlight will reach the lower layers. If ample water and nutrients are available, a well-developed understory and shrub strata will form. If the canopy is dense and closed, light levels are low, and the understory and shrub layers will be poorly developed.

Defining boundaries between communities if often difficult:

The community is a spatial concept involving the species that occupy a given area. Ecologists typically distinguish between adjacent communities or community types based on observable differences in their physical and biological structures: the different species assemblages characteristic of different physical environments. Ecologists use various sampling and statistical techniques to delineate and classify communities. Generally, all employ some measure of community similarity or difference.

Null model of community structure:

The null model assumes that the presence and abundance of the individual species found in a given community are solely a result of the independent responses of each individual species to the prevailing abiotic environment. Interactions among species have no significant influence on community structure. The null model is based on the fundamental niche of a species, or the environmental conditions they could potentially occupy- independent from interactions with other species (based ONLY on environmental conditions).

Diversity:

The number of species in the community defines species richness. Species diversity involves two components: species richness and species evenness, which reflect how individuals are apportioned among the species (relative abundances).

Niche and community structure...

The range of environmental conditions tolerated by a species defines its fundamental niche. These constraints on the ability of a species to survive and flourish will limit their distribution and abundance to a certain range of environmental conditions. Species differ in the range of conditions they tolerate. As environmental conditions change in both time and space, the possible distribution and abundance of species also changes. This framework provides a null model against which to compare observed community patterns. Community structure reflect the species' realized niches, which are the fundamental niches modified by species interactions.

Describe the physical structure and associated vertical structure of aquatic communities:

The strata of aquatic ecosystems such as lakes and oceans are determined largely by the physical characteristics of the water column. Open bodies of water (lakes and oceans) have distinctive profiles of temperature and oxygen. In the summer, well stratified lakes have a surface layer of warm, well mixed water that is high in oxygen, the epilimnion; a second layer, the metalimnion, which is characterized by a thermocline (steep and rapid decline in temp relative to waters above and below); and the hypolimnion, a deep, cold layer of dense water, often low in oxygen.

Bottom-Up Control:

The structure of food chains suggests that the productivity and abundance of populations at any given trophic level are controlled (limited) by the productivity and abundance of the populations in the trophic level below them. Thus, plant population densities control the abundance of herbivore populations, which in turn control the densities of carnivore populations in the next trophic level.

One of the simplest and most widely used indices of species diversity is the Simpson's index.

The term "Simpson's diversity index" can actually refer to any of three closely related indexes.

In recent years, ecologists have expanded the concept of guilds to develop a more broadly defined approach of classifying species, based on function rather than taxonomy:

The term "functional type" is now commonly used to define a group of species based on their common response to the environment, life history characteristics, or role within the community.. For example, plants may be classified into functional types based on their photosynthetic pathway.

Because species within a guild draw on a shared resource...

There is a potential for strong interactions, particularly interspecific competition, between the members, but weaker interactions with the remainder of the community.

Each set of adaptations enable a species to succeed (survive, grow, and reproduce) under a given set of conditions, and conversely, restricts or precludes success under different conditions.

These adaptations determine the fundamental niche of a species. The concept of a species' fundamental niche provides a starting point to examine the factors that influence the structure of communities. We can represent the fundamental niches of various species with bell-shaped curves along an environmental gradient (such as the mean annual temp or elevation). The response of each species along the gradient is defined in terms of its population abundance.

Like a population, a community has attributes that differ from those of its components and that have meaning only within the collective:

These attributes include the number of species, their relative abundance, the nature of their interactions, and their physical structure (defined primarily by the growth forms of the plant components of the community). Community attributes: Number of species Relative abundance of each species Physical structure Nature of interactions

The definition of community also recognizes that species living in close association may interact:

They may compete for a shared resource, such as food, light, space or moisture. One may depend on the other as a food source. They may also provide mutual aid, or they may not directly affect one another at all.

There is a general trade-off between a species' stress tolerance and its competitive ability along gradients of resource availability.

This trade-off can result in patterns of zonation across the landscape where variations in resource availability exist. The relationship between stress tolerance and competitive ability is more complex along gradients that include both resource and nonresource factors, such as temp, salinity, and water depth.

Communities on soils with lower nutrient availability supported a greater number of tree species than those communities on more fertile soil.

Under low nutrient availability, plant growth rate, size, and density are low for all species... Competition primarily occurs belowground and therefore is symmetric. Competitive displacement is low and diversity is maintained. As nutrient availability increases, growth rate, size, and density increase. Species that maintain higher rates of photosynthesis and growth exhibit a disproportionate increase in size. As faster-growing species overtop others, creating a disparity in light availability, competition becomes strongly asymmetric. Species that achieve high rates of growth and stature under conditions of high soil fertility eventually outcompete and displace those that are slower-growing, smaller-stature species, thus reducing the species richness of the community.