Interactions among populations II: Dynamics of competition between species Flashcards
Define ecological community
group of species that occur together in space and/or time and compete for the same limiting resources
Give Gause’s principle of competitive exclusion
two species cannot coexist on a single limiting resource if other ecological factors remain constant.
Discuss Connell’s barnacles
- Chthamalus is competitively excluded from the lower shore by Balanus
- persists in the upper shore because it is more tolerant towards dessication
Discuss Gause’s Paramecium
- both Paramecium aurelia and Paramecium bursaria eat bacteria
- when grown together in a well-stirred mixture, P. aurelia outcompetes P. bursaria
- if the mixture is not stirred, both species persist (P. bursaria mostly confined to the anoxic bottom of the beaker)
- P. bursaria, with its photosynthetic symbionts, generates oxygen internally
- P. aurelia outcompetes P. bursaria under aerobic conditions, but P. bursaria can persist in anoxic conditions where P. aurelia cannot
Describe Fenchel’s snails (Hydrobia)
- Hydrobia ulvae and Hydrobia ventrosa
- most places you only find one species or the other; appear almost indistinguishable
- when they are sympatric, there is character displacement
- H. ulvae becomes significantly larger than H. ventrosa
Describe Tilman’s diatoms
- photosynthetic, planktonic organisms
- unique silica cell wall
- can be grown in culture such that silica is the limiting factor
R*
concentration of resource at population equilibrium
Describe R*
- theory of competition for a single limiting resource: R*
- level to which the concentration of a limiting resource is reduced by an equilibrial monoculture of a species
- minimum resource concentration a species requires for positive population growth
What are the assumptions of R*?
- species compete for a single limiting resource
- resource is labile and the system is well-mixed
Give an example of a well mixed system
nitrogen in soil
Describe the R* prediction
species with the lowest R* for the limiting resource is the superior competitor
How to measure R*?
- a variety of ways
- individuals against each other
- seed v seed
- ability to invade a monoculture of the other species
Give a two-species population model that includes both the density of intra (N1) and interspecific (N2) competitors
- dN1/dt = r1N1(K1-N1-alpha12N2)/K1
- interspecific competitors are weighted by a competition coefficient (α12).
“alpha values”
specify the effect of interspecific competition.
When does Lotka-Volterra coexistence occur
𝐾1>𝐾2 𝛼12
𝐾2>𝐾1 𝛼21
- if K1 = K2, when interspecific competition coefficients are < 1 (interspecific competition is weaker than intraspecific competition)