Lecture 7-8 community ecology

Question 1

types of species interactions

Answer 1

Predation
competition
mutualism

Question 2

intraspecific competition

Answer 2

competition amongst one species over resources

Question 3

Interspecific competition

Answer 3

Competition amongst different species for resources

Question 4

Scramble/exploitive competition

Answer 4

depletion of shared resources amongst different species
does not involve confrontation

Question 5

contest/interference competition

Answer 5

• physical fights over resources

Question 6

Lotka-Volterra Equation

Answer 6

• 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

Question 7

what does the alphas represent in the lotka-volterra model?

Answer 7

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

Question 8

what are the possible outcomes of the lotka-volterra model?

Answer 8

1. species 1 outcompetes species2
2. species 2 outcompetes species 1
3. there is an equilibrium between the two, so they are now co-existing
4. the winner depends on who had more numbers to begin with

Question 9

what do the outcomes depend on?

Answer 9

the values of K (carrying capacity) and a

Question 10

how do we reach equilibrium in the lotka-volterra model?

Answer 10

The species must inhibit their own growth more than they inhibit their competitor

Question 11

Equilibrium

Answer 11

this means that there is no change in population over time in a community, or Dn/Dt= 0

Question 12

Stability

Answer 12

the amount of time it takes for a species to return back to equilibrium following disturbance

Question 13

Co-existence

Answer 13

when two species are at non-zero population at equilibrium

Question 14

Character displacement

Answer 14

when co-existing similar species evolve differently as a way to lessen their competition against one another for resources

Question 15

What is the paradox of plankton? who came up with it?

Answer 15

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

Question 16

how is the paradox of plankton resolved?

Answer 16

• 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

Question 17

community composition

Answer 17

competition affects which and how many species live in a community
- aka species richness

Question 18

How are competitive effects manifested
in nature, compared to the lab?

Answer 18

• competition exclusion rarely goes to completion due to biological factors mixing with physical factors
• abundances and distributions in space are affected

Question 19

Antagonist co-evolution

Answer 19

-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

Question 20

how does the Seastar help reserve biodiversity

Answer 20

• to prevent mussels competitively taking over most of the species in the ocean, the starfish will eat mussels to help reserve the biodiversity

Question 21

enemy release hypothesis

Answer 21

invaders have less natural predators in the new space they are invading compared to native space

Question 22

dilution effect

Answer 22

for diseases that infect many hosts, host diversity can dilute its risks to humans and animals

Question 23

amplification effect

Answer 23

more host or vector species
can support larger populations of disease-causing
organisms, increasing risk to humans or animals

Question 24

Latitudinal gradient

Answer 24

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