Community Ecology Flashcards
What is an ecological community?
A group of populations of different species that occur together in space and/or time and generally share the same resources.
Idea of competition is important.
Example of how diversity is hugely variable
In a single hectare in Brazil - 400 different tree species
In USA and Canada - 700 different tree species in total
What is Gause’s principle of competitive exclusion?
Two species cannot coexist on a single limiting resource if other ecological factors remain constant.
Example of competitive exclusion
Gause’s paramecium. Both P. aurelia and P. bursaria eat bacteria. When grown together in a well stirred mixture, P.aurelia outcompetes P.bursaria. If the mixture isn’t stirred, both species persist, but P. bursaria is confined to the bottom of the beaker. This is because anoxia sets in at the bottom of the beaker, and P. bursaria with its photosynthetic symbionts can generate oxygen internally.
Tilman’s diatoms?
Photosynthetic, planktonic organisms. Diatom cells are contained within a unique silica cell wall. Can be grown in culture such that silica is the limiting factor.
What happens if you add diatoms to a culture that has initially got plenty of resources?
Population grows and reaches a steady state if the populations are alone.
R* is the level of resource at which the population growth rate is zero. Synedra has a lower R* level than Asterionella so can predict this will be the winner.
Define the R* theory?
R* is the minimum resource concentration a species requires for positive population growth.
The species with the lowest R* for the limiting resource is predicted to be the superior competitor.
Assumptions made for R* theory
The species are competing for a single limiting resource.
The resource is labile and the system is well mixed.
Minnesota example of R*?
Lack of nitrogen for grasses.
Assumptions: species are competing for a single limiting resource and nitrogen is the most mobile molecule in soil.
Measure the R* levels and predict the winner.
The theory correctly predicted a number of 2 species competitions.
Single species population model including density dependence formula?
dN1 / dt = r1N1 ( [K1 - N1] / K1 )
What is the population model including interspecific competition?
dN1 / dt = r1N1 ( [K1 - N1 - a12n2] / K1 )
𝛼12 is the competition coefficient.
Interspecific competitors are N2.
What outcomes does the 2 species Lotka-Volterra competition model have?
Many, including a stable coexistence.
Coexistence occurs when
𝐾1 > 𝐾2𝛼12 AND 𝐾2 > 𝐾1𝛼21
When is interspecific competition likely to be weaker than intraspecific competition?
When each species has its own ecological niche.
If species use different food or prefer different habitats, this concentrates competition onto members of their own species.
Interspecific
Between different species
What is neutral theory?
States that all species are identical. Not just similar but really and truly identical. This means that all species have identical per capita birth and death rates.
Probability of dying and being born isn’t to do with what species you are.
Hubbell 2001.