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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
