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Food Web Structure - Principles of Ecology - Lecture Slides, Slides of Ecology and Environment

These are the lecture slides of Ecology. Key important points are: Food Web Structure, Stability of Communities, Environmental Perturbation, Functioning of Community, Resilience of Communities, Alternative Stable States, Trophic Structure of Community

Typology: Slides

2012/2013

Uploaded on 01/22/2013

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15.4 Food web structure influences the
stability of communities
Some consumers are keystone species and play an important role
in community structure.
How about the food web structure on stability of communities?
Stability: constancy and resilience
Constancy: a measure of ability of a system to resist change in
the face of outside influences (resistance)
Resilience: ability of system to return to some reference state
after a disturbance.
Resilience means that system may have internal processes that
can compensate for disturbance-induced changes. For
example, increase in birth rate can help population move back
after a population size decreases.
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15.4 Food web structure influences the

stability of communities

Some consumers are keystone species and play an important role

in community structure.

How about the food web structure on stability of communities?

Stability: constancy and resilience

Constancy: a measure of ability of a system to resist change in

the face of outside influences (resistance)

Resilience: ability of system to return to some reference state

after a disturbance.

Resilience means that system may have internal processes that

can compensate for disturbance-induced changes. For

example, increase in birth rate can help population move back

after a population size decreases.

Environmental perturbation can cause a delayed response in the functioning of a community

Suttle and Thomsen (Mary Power lab at UC Berkeley)

Spring watering:

Enhanced biomass, especially in the beginning

How about species richness?

Any extension of the rainy season resulting from climate change is likely to lead to a reduction of specie richness.

15.6 Communities can switch between

alternative stable states

Resiliency means that a system is able to return to a “reference”

state following a perturbation. Sometimes, however, a system

can have more than one stable reference state.

Predation and prey: upper and lower equilibrium states of prey

population

Stable state: small perturbations are followed by return to the

reference state

Biological community might have multiple stable states:

Two keystone species respond differently to climate change:

Global warming may shift the community to species favors

warming climate

Rainfall  fire  grassland community structure.

Remove of organisms in a New England rocky intertidal zone community resulted in replacement by one of several possible new community

Northern facing site dominated by barnacles

Southern facing site by algae

Replaced original ones and did not recover over five years

Trophic structure of a community may be

determined by bottom-up or top-down control

Cases for bottom-up, top- down control or both

Mathew Leibold, Uni. Of Chicago 1997, Survey

Remove or add herbivore will influence primary production

But consumer production is related to primary production

Leibold et al. 1997

Change in nutrient level can switch a marine

community between alternate state

Fish have indirect effects on the populations of several species in and around ponds

Knight et al. 2005, Nature

Compared ponds contain fish compared to ponds without fish

4 control (no fish) 4 treatment (within fish)

Another nice example to demonstrate the

indirect interactions

Keystone species

Keystone species: a species that has a

disproportionate impact on the community

relative to its abundance.

Remove of keystone species initiates changes

in community structure and results in

significant diversity loss.

Role in community: create or modify habitats,

or influence interactions with others.

Keystone species examples

Coral (Oculina arvbuscula) in the eastern coast

of US

This coral has complex branch and provide

shelter of more than 300 species of

invertebrates

African elephants in the

savannas of southern

Africa

Elephants are destruct

feeders, damage trees,

reduce density of shrubs,

but increase grass

growths. Docsity.com