Lecture 19 Flashcards
Outcome of competition
hurts both species
Outcome of predation
benefits predators, but hurts prey
Outcome of host-parasite and plant herbivore interactions
same as predation - positive and negative
Outcome of mutualism
helps both species
Interactions between species are often classified by
their outcome (+ or -)
Two main foci of study in ecology and evolution of species interactions
- population dynamics and effects on community structure (how species interactions affect these two things)
- evolutionary dynamics (adaptation and co-evolution)
Intra-specific competition
competition among the members of the same species (i.e. among conspecifics) for resources
Inter-specific competition
competition among members of different species (ie among heterospecifics) for resources
Scramble/exploitative competition
depletion of a shared resource
Contest/interference competition
direct interactions, such as battles over territory
Give an example of interference competition
- Invasive Argentine ants fight a harvester ant in California
- Invasive ants (superior competitors) often drive down populations of native ants
Exploitative competition
- two species do not need to directly interact or even to be active at the same time to compete
- if one consumes a resource, leaving less resource for the other, then they compete
Example of exploitative competition
squirrels and birds, and bird feeders
- squirrel eats food from the feeder and leave no seeds left from the birds
- squirrel is competing successfully with birds by consuming a lot of shared resources
model for inter-specific competition for resources
Lotka-Volterra equations for two species competing for resources
- is a simple outgrowth of logistic equation
- logistic already has a breaking term for intra-specific competition
- Just add a second braking term for
inter-specific competition
give the 4 steps for arriving at the Lotka-Volterra model from a logistic model
- Start with the logistic model for population growth
- Rewrite the logistic model with subscripts to indicate species 1
- Add a term to show effect of species 2 on species 1
- Write matching equation for species 2
give the equation for Lotka-Volterra model
α(ij) =
α(ji)
per-capita effect on i by j
per capita effect on j by i
=> competition coefficient
describe the competition coefficients (α’s)
- fixed for a particular pair of species
- α(12)N(2) converts individuals of species 2 into an equivalent number of individuals of species 1
- eg a squirrel can eat a lot more seeds than a sparrow; a measures how many sparrows-worth of seeds a single squirrel eats
four possible equilibria outcomes of Lotka-Volterra competition
- the two species may stably coexist
- species 1 may always win (N1 = K1, N2 = 0)
- species 2 may always win (N2 = K2, N1 = 0)
- identity of winner may depend on starting N’s
meaning of Equilibrium for Lotka-Volterra competition
N’s are no longer changing
what do the outcomes of the Lotka-Volterra competition depend on?
values of K’s and α’s
coexistence requires
both species to inhibit their own growth more than they inhibit each other’s
define equilibrium
- for a population: size not changing over time (dN/dt = 0)
- for a community: a community not changing over time (in a strict sense: all populations in a community at equilibrium. more generally: constant species composition)
define stability
the ability of a system to return to equilibrium following a perturbation or disturbance