Ecology Exam 3

Competition

the struggle between organisms to survive in a habitat with limited resources (both expend energy and both risk being injured)(i.e. lion and hyena fighting over carcass)

What is niche breadth?

the variety of resources used and the range of conditions used.

What is the -3/2 self-thinning rule

thinning of plant populations due to intraspecific competition. (Plot plant density on x-axis and plant weight on y-axis and slope will be -3/2).

predation

an animal killing another animal and consuming it

Parasitism

an organism that lives on another living organism causing it harm

Can you describe the differences between a community and an assemblage of species?

assemblage: may occur together but are not structured into a community by species interactions

Can you describe what the geometric model's niche-preemption hypothesis means?

assumes the most dominant species preempts some % of a critical resource, the next most dominant get some % of what is left, and so on (niche preemption hypothesis). If random variation in these percentages (or variation of arrival time) is considered then the result is a log series model of species abundance.

What is an ecological community? What is meant by the term community structure?

community: a group of interacting species that occur together in a common area community structure: various attributes that describe a community such as the number of species and relative abundance of species

interspecific competition

competition between members of different species

Intraspecific competition

competition between members of the same species

What is the difference between connectedness webs, functional webs, and energy flow webs?

connectedness: shows feeding relationships among organisms functional: emphasizes the influence of populations on growth rates in other populations energy flow: shows connections quantified as energy flow

What is niche modeling? Can you give an example of it?

creating a model of niches. the lone star tick's niche has been modeled in the United States to show that potential habitat does not mean current occupation, but it does mean there is potential for tick range expansion.

What did Joseph Connell mean when he wrote of "the ghost of competition past".

current evidence for past competition is not present because it has been eliminated by past coevolutionary divergence between those species.

What are 4 characteristics/metrics used to describe food webs and can you explain what they are?

1. Food Chain Length - Number of trophic links in the longest chain in a food web 2. Connectance (C)= percentage of possible links that exist. (number of links / (number of species(number of species -1 )) 3. Compartmentalization - Large food webs are actually comprised of multiple compartments with strong links within compartments and weak links among them. 4. Stability - Ability to persist or likelihood of persistence over time (Affected by food chain length, connectance, compartmentalization)

Why might connectance be lower in food webs from fluctuating environments versus constant environments?

Consumers rely on more brief and intense feeding bouts so connections are ephemeral and would also be weaker

What is an ecological indicator and what would be the characteristics of a good indicator? What can they be used for?

A measurement used to synthesize and monitor information about the status of the environment. Must be: Indicative of ecosystem function Applicable to multiple species or characteristics of an ecosystem Readily repeatable in order to track environmental quality over time Applicable over large spatial areas

If I describe a species as having displayed a niche shift, what does that mean and why might it occur?

A niche shift is a change in resource use, this is usually induced by the presence of a competitor or changes to the biotic environment.

What is eutrophication? Can this occur in both aquatic and terrestrial ecosystems?

A process by which nutrients, particularly phosphorus and nitrogen, become highly concentrated in a body of water, leading to increased growth of organisms such as algae or cyanobacteria.

Commensalism

A relationship between two organisms in which one organism benefits and the other is unaffected (orchid growing on a tree)

Mutualism

A relationship between two species in which both species benefit (pollination)

Can you define disturbance?

A relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability or the physical environment

What is a keystone species? Are they always top predators?

A species that exerts great control over the structure of a community even though that species may not be the most abundant. Not always top predators.

What are some characteristics of species that occur high in a food chain compared to species low in a food chain?

Lower biomass Lower abundance Often larger relative size Often more susceptible to extinction Control trophic cascades

What are the environmental conditions and species characteristics thought to produce the lognormal rank-abundance curves?

Biologically the lognormal applies to stable many-species communities interacting along many niche dimensions, or sets of rapidly-reproducing opportunistic species - and appears to be the most commonly applicable model.

Are bottom-up or top-down controls more important in ecosystems?

Bottom-up effects have primacy Top-down effects real & important

What is character displacement and how is it related to competition?

Character displacement is a situation where two species will differ more in places where they both occur than where they do not overlap. This is because two two species occupy similar niches, and must adapt to slightly different niches.

Ecosystems such as the Serengeti grasslands have a long co-evolutionary history between grazers and grasses. In examining this interaction, what is compensatory growth?

Compensatory growth is the phase of rapid growth that allows individuals that have suffered a period of growth depression to achieve approximately the same size for age as continuously fed contemporaries. (Biomass increases in grazed areas.)

How can resource dynamics and density-independent factors alleviate competition?

Density independent factors (i.e. climate, natural disasters) can decreases population size, decreasing competition. Resource dynamics (change in resource availability over time) can increase resources, decreasing competition.

What is the difference between direct and indirect interactions in food webs?

Direct - Predation & herbivory Competition w/ a trophic level Indirect - One species affects another through an intermediary third species (indirect commensalism)

What is a trophic cascade, and can you describe how populations in a food chain would change in abundance if the top predator were removed, or if a new top predator was added?

Effects of top predators/consumers that cascade down a food chain to influence all lower trophic levels Impacts on population size and abundance alternate for each successive trophic level

In examining the conditions for population cycles, Lotka wrote of "spatially structured populations" and the need for the capture/consumption rate of predators to vary in order for population cycles to occur. What did he mean by these statements?

For a spatially structured population, the value of p (capture/consumption rate of the predator) may vary rather than be a constant even for a single species.Thus p may be constant within a patch or habitat but its value should vary as a function of differences in the habitats or an underlying environmental gradient.

Can you give one example why top down control may not be characteristic of a food chain?

Forest productivity predicts invertebrate biomass and ovenbird reproduction in appalachian landscapes

What does it mean if I say that "species diversity is usually greater in more complex environments" and provide an example?

In essence, a more complex environment can be partitioned in more ways so that competition is lessened and coexistence can occur. (MacArthur's warblers) These species often share the same breeding grounds in mature coniferous forests Originally thought to occupy the same niche - and thus were an exception to competitive exclusion MacArthur demonstrated partitioning of space and food resources, and increasing bird richness with more complex forest structure

Can you define, graph and explain grazing optimization? How does it relate to compensatory growth of grasses?

Intermediate intensity of grazing increases the rate of primary production because of compensatory processes, without overgrazing.

Is intraspecific or interspecific competition more common and intense?

Intraspecific

Can you graph and explain the intermediate disturbance hypothesis?

Low levels of disturbance allow competition to reduce diversity. High levels of disturbance reduces diversity. The intermediate disturbance hypothesis suggests that intermediate levels of diversity are best for diversity.

why is niche overlap important to the intensity of competition?

More niche overlap results in more competition for resources, with no niche overlap there would be no competition.

Can you define/describe "apparent competition"?

Negative impacts result from two species sharing a predator or herbivore, Or when one species increases the population of another species' predator

How does niche partitioning help alleviate competition?

Niche divided so that different species use different resources within niche, less competition because less overlap.

What does it mean if I say that nutrient and water often interact to influence primary production?

Nutrients are often dissolved in water so terrestrial ecosystems with more moisture often have higher nutrient content.

Can you generally describe Huffaker's experiments with mites and the conditions he found necessary to produce predator-prey cycles?

Patches of habitat (oranges) used in different spatial configurations, sometimes with rubber balls between them, and with barriers to dispersal made from petroleum jelly. More complex spatial environments more likely to produce predator-prey osscilations.

Can you describe the classical experiments carried out by Dave Tilman and colleagues on the effect of species diversity on ecosystem productivity? What is the difference between species diversity and functional diversity? How important is each to primary production?

Planted species in combinations with different species diversities and different functional diversity(functional groups). Determined species diversity/richness and functional group richness were of about equal importance.

Your text describes changes in the rank abundance curves for a European field over a long time period of continued fertilization? What does the pattern in curve change indicate? Why would fertilization cause this to happen?

The ectomycorrhizal fungi declined as nitrogen increased so the plant diversity declined. Fetilization increases nitrogen

Mutualisms with mycorrhizal fungi are integral for many plant species. What do both species gain from this mutualism? How does this mutualism aid nutrient uptake by plants?

The fungus gains carbon compounds (energy) from the tree and facilitates tree uptake of water and minerals. Fungi may also (1) defend against parasites, predators (such as nematodes), and soil pathogens, and (2) protect against toxic effects of high soil metal concentrations

What is the importance of terrestrial-aquatic linkages when it comes to food chain energetics of small first order streams?

The initial contributions of energy to headwater streams are leaves and other coarse particular organic matter)

Community structure can be created by many factors. What are some of them that we have talked about?

predation, mutualism, commensalism. competition, feeding interactions

Why is spatial heterogeneity viewed as an important driver of biological diversity? Why would this be the case? How is spatial heterogeneity related to disturbance? What "things" can be spatially heterogeneous?

There need to be different microhabitats (due to disturbances) within a certain space to support various animals with different niches. Soil type, soil depth, concentration of nutrients, types and number of plants, etc can be examples.

What are the environmental conditions and species characteristics thought to produce the geometric rank-abundance curves?

These models apply to species poor communities, e.g. early successional communities, degraded communities, or those in very harsh environments.

What can a tree ring core tell you about a tree's growing environment?

Thinner rings = years with less growth. More herbivory results in less tree growth. More predation results in more tree growth.

What are the environmental conditions and species characteristics thought to produce the broken stick rank-abundance curves?

This model seems most applicable to communities of a few taxonomically very similar species, in a homogenous environment, between which a single overriding survival requirement is divided with little/no overlap of use.

Trophic cascades are characterized by top-down control. What does that mean and can you contrast that with bottom-up control? How does this relate to Mary Power's assertion that plants have "primacy" in food webs?

Top Down Control (Keystones) Effects of consumers on food web and community structure Bottom Up Control (Dominants) Effects of nutrient availability or primary production on food web and community structure (Consumers that exert top-down control over food webs would not exist without primary production) Mary Powers found: Bottom-up effects have primacy Top-down effects real & important

Raymond Lindeman is the "father" of the trophic-dynamic aspects of ecology. What are trophic dynamics and ecological efficiencies? What is the likely range of ecological efficiencies in ecological food chains?

Trophic dynamics is the basic process of transference of energy from one trophic level to the next in an ecosystem.Ecological efficiency describes the efficiency with which energy is transferred from one trophic level to the next. (5-20%, more for parasites.

What is the competitive exclusion principle and how does it relate to niche concept

Two species with identical niches cannot coexist indefinitley. (Two species cannot occupy the same niche)

The "ecology of fear" is an overrated term, but it is used quite often. What does it mean and can you give an example?

Under threat of predation, elk decreased foraging in riparian areas, where vegetation has since grown back, altering the interaction of riparian forest with stream ecosystems

If bottom-up control is important, why is spatial heterogeneity of primary production an important thing to be able to describe? Think in terms of food webs along a productivity gradient.

differences in primary production will lead to different amounts of all members of the food web above producers as well.

What is the difference between a food web and a food chain?

food chain: one path of energy and nutrient flow within the web food web: consists of many interconnected chains

faculative mutualism

form of symbiosis where both organisms benefit, but is not required for survival of the species involved

ecotomycorrhizal fungi

fungi grow fungal sheath on outside of the root and also form a network of hyphae around cortex root cells

arbuscular mycorrhizal fungi

fungi produce arbuscules, associated hyphae, and vesicles within the root cortex cells

What is a guild of species?

group of species that have similar means of feeding, are closely related taxonomically, or have similar life forms

In a Lotka-Volterra isocline graph, when the either species population goes to zero, the other species...

has "won" the competition, population size is equal to carrying capacity.

In some cases, predator and prey populations can "cycle". Why might this occur and could you graph those cycles over time as well as in terms of species populations?

increase in predator populations leads to increased predation which lowers prey density leading to less food for predators which causes predator density to decline which induces an increase in prey density.....over and over again

Secondary production = Ingestion - Egestion - Excretion - Respiration. Can you describe these terms and how they relate to assimilation?

ingestion-eating egestion- excreting undigestable material from cells excretion-waste respiration-energy used in cellular respiration Assimilation in biology is defined as the process in which living organisms integrate the nutrients from various external resources to their body and utilizes them to satisfy the energy demands required to stay alive. The above must be balanced to assimilate well.

What is symbiosis?

interaction between two different organisms living in close physical association, typically to the advantage of both.

herbivory

interaction in which one animal (the herbivore) feeds on producers (such as plants) but does not kill it

Exploitative Competition

involves differential efficiencies in resource use that can lead to resource limitation (using a resource so that it is unavailable to competitors).

Interference competition

involves direct interactions between individuals (i.e. fighting, allelopathic chemical production.

What is the difference between a keystone species and a dominant/foundation species?

keystone species are those whose influence on a community is disproportionate to their biomass dominant species are ones that have a significant influence on communities by virtue of high biomass

For competition to occur, resources must be...

limited

Ecologists have used the different shapes of rank-abundance curves to interpret the factors that structure ecological communities. Which model is thought to most commonly represent real communities?

lognormal model

mycorrhizal fungi

mycorrhizal fungi live in a mutualistic relationship with plants

What does NPP = GPP - R mean?

net primary productivity is equal to gross primary production minus plant cellular respiration

Which two nutrients are usually the most limiting in natural ecosystems? Do these differ between terrestrial and aquatic ecosystems?

nitrogen and phosphorous. nitrogen more so in terrestrial, phosphorous more so in aquatic ecosystems

obligate mutualism

one species cannot survive without the other

pathogen

organisms that induce disease and reduce fitness of hosts, may or may not kill them.

What is secondary production?

production of biomass by heterotrophic organisms feeding on plants, animals, fungi, detritus, etc. over a specified period of timeThus, all production by all trophic levels above plants

What does a rank-abundance curve tell you about a community? Can you compare two curves and define the differences in the two communities?

rank abundance curves are best suited to comparing different communities richness (abundance rate) and evenness( (proportional abundance), greater evenness indicated by lower slope.

Why is Preston's lognormal distribution of species abundance graph often "truncated" in empirical studies? If the lognormal is a community representation of species abundances, what does it say about the relative abundance of species in ecological communities?

rarer species are not catalogued which causes graph truncation

What are the two components of species diversity and how are they related to rank-abundance curves?

species richness(number of species) and diversity (number of species and evenness of representation)

What are strong interactions vs. weak interactions within a food web?

strong links are connections that most strongly influence community structure weak links are opposite

Lynn Margulis put forth the important evolutionary concept of endosymbiosis. What is it?

symbiosis in which one of the symbiotic organisms lives inside the other & may evolve into an organelle

What are three factors that limit NPP in terrestrial ecosystems?

temperature, moisture, and nutrients

Can you describe the ant-plant mutualism found in African savannas with Acacia drepanolobium and Crematogaster mimosae?

whistling thorn acacia allows ants to live inside of swollen thorns and in return the ants protect the tree from herbivory