Lecture 7-8 community ecology Flashcards
types of species interactions
Predation
competition
mutualism
intraspecific competition
competition amongst one species over resources
Interspecific competition
Competition amongst different species for resources
Scramble/exploitive competition
depletion of shared resources amongst different species
does not involve confrontation
contest/interference competition
- physical fights over resources
Lotka-Volterra Equation
- this builds upon the logistic model of population growth, but adds an additional variable to account for a second species effect on species 1 population
- the equation is Dn/Dt= rN(1- n/k -a12-N2/K1)W
what does the alphas represent in the lotka-volterra model?
the alphas convert the number of species two into an equivalent number of species 1
eg. squirrels can eat more seeds than sparrows, a12 will represent how many sparrows it takes to eat all the seeds a single squirrel can eat
what are the possible outcomes of the lotka-volterra model?
- species 1 outcompetes species2
- species 2 outcompetes species 1
- there is an equilibrium between the two, so they are now co-existing
- the winner depends on who had more numbers to begin with
what do the outcomes depend on?
the values of K (carrying capacity) and a
how do we reach equilibrium in the lotka-volterra model?
The species must inhibit their own growth more than they inhibit their competitor
Equilibrium
this means that there is no change in population over time in a community, or Dn/Dt= 0
Stability
the amount of time it takes for a species to return back to equilibrium following disturbance
Co-existence
when two species are at non-zero population at equilibrium
Character displacement
when co-existing similar species evolve differently as a way to lessen their competition against one another for resources
What is the paradox of plankton? who came up with it?
hutchinson brought up the fact that large numbers of co-species plankton, which are relatively the same and all need the same resources to survive are able to co-exist in an unstable environment with little competition
how is the paradox of plankton resolved?
- the reality is that competitive exclusion rarely goes to completion because species are usually kept under the carrying capacity by means of weather, disease and predators
community composition
competition affects which and how many species live in a community
- aka species richness
How are competitive effects manifested
in nature, compared to the lab?
- competition exclusion rarely goes to completion due to biological factors mixing with physical factors
- abundances and distributions in space are affected
Antagonist co-evolution
-generally referred to as an “arms race”
- this is where prey develop evolutionary defences to compete with prey but at the same time predators develop evolutionary adaptations to overcome the preys defenses
how does the Seastar help reserve biodiversity
- to prevent mussels competitively taking over most of the species in the ocean, the starfish will eat mussels to help reserve the biodiversity
enemy release hypothesis
invaders have less natural predators in the new space they are invading compared to native space
dilution effect
for diseases that infect many hosts, host diversity can dilute its risks to humans and animals
amplification effect
more host or vector species
can support larger populations of disease-causing
organisms, increasing risk to humans or animals
Latitudinal gradient
much more species at the equator than at the poles
maybe because they haven’t experienced glaciation and they defrosted already whereas at the poles things are still frozen
- or climate primary productivity may explain why species are at equator
