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20 Cards in this Set

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- one organism benefits at the expense of another

examples: parasites, parasitoids, pathogens

Two ways to understand possible outcomes of predation

1. observation (natural history)

2. experimentation

Results of laboratory populations of host and parasite

- reciprocal oscillations

Results of algae and caddisfly experiment

- algal biomass increased quickly

- caddisfly colonized and algal biomass declined

Foxes, mange, and hares

- as mange reduced the fox population, the hare population increased dramatically

Three features of lynx/hare cycles

1. 10 year cycle

2. hares feed on shrubs and small trees

3. lynx is the predator

Lotka-Volterra for host population


dNh/dt: rate of host population change

r: host per capita rate of increase

N: number of host (h) or predator (p)

(p): predation rate

Lotka-Volterra for predator population


dNp/dt: rate of predator population change

c: host to predator conversion rate

p: predation rate

N: number of predator (p) or host (h)

d: death rate

What are the predator/prey oscillations a result of?

- predators increasing when prey are abundant

- predators decreasing as prey populations become depleted

- when pressure on prey population is lessened, prey can recover and cycle repeats

Consequences of herbivory

- can alter allocation of energies

- can affect timing and amount of reproduction

- can affect transmission of disease

Why may predators not be very efficient in low prey densities?

- refuges

- lack of reinforcement of learned behavior

- low rate of prey encounters reduces hunting efficiency

- predators may switch to alternative prey

What happens in the absence of refuges and immigration?

- both prey and predator populations go extinct

What happens when refuge is added?

- prey population persists

- predators go extinct

What happens when immigration from source populations is maintained?

- oscillations are maintained

Vulnerability to predation

- organisms that are larger in size may escape predation due to their large size

example: mussels and starfish

What does the Lotka-Volterra model suggest?

- predator population changes in direct proportion to the number of prey

- response may not be immediate

- predator reproductive output is less than prey and life span usually longer than prey

What five features dampen out predicted predator/prey population cycles?

1. predator inefficiency

2. density dependent limitation of either population by external factors

3. alternative food sources for predator

4. prey refugia

3. time lags in predator response to prey abundance

What do we expect natural selection to do?

- increase predator efficiency for food capture

- increase capability of prey to escape

When are evolutionary pressures reduced?

- if predators do not control the abundance of prey

What are three big benefits of group living?

1. many lookouts: spend more time feeding

2. if size difference is not that large, several prey acting together may deter predator

3. fleeing in confusion may distract predator