Chapter 14 - Predation and Herbivory

Question 1

What are the two populations of predators?

Answer 1

Mesopredators and top predators.

Question 2

What are mesopredators? Provide examples.

Answer 2

Relatively small carnivores that consume herbivores. Feral cats, coyotes, weasels.

Question 3

What are top predators? Provide examples.

Answer 3

Predators that typically consume both herbivores and mesopredators. wolves, mountain lions, sharks.

Question 4

Why is it not usually beneficial to remove a top predator?

Answer 4

Enables mesopredators to increase in abundance, nothing controlling that population makes them eliminate herbivores they prey upon.

Question 5

How do herbivores affect species abundance?

Answer 5

If herbivore populations are not controlled, they can eat plants to extinction from their community. OR if herbivores are removed, plants may grow exponentially.

Question 6

What enables predators and prey to coexist?

Answer 6

Suitable refuges for the prey.

Question 7

What are the two types of time delays that cause predator-prey populations to cycle?

Answer 7

1. Predators dispersing more slowly between food patches and prey
2. Time needed for predators to reproduce

Question 8

What is the Lotka-Volterra model?

Answer 8

A model of predator-prey interactions that incorporates oscillations in the abundances of predator and prey populations and shows predator numbers lagging behind those of their prey.

Question 9

What does the Lotka-Volterra model tell us about the population growth of prey?

Answer 9

Growth rate of prey population depends on the rate of individuals being added to the prey population minus the number of individuals being killed by predators.

Question 10

Define the variables in the Lotka-Volterra model of prey population growth:
dN/dt = rN - cNP

Answer 10

rN = exponential growth of population
cNP = loss of individuals to predation

Question 11

What does the Lotka-Volterra model assume about predation rate?

Answer 11

It is determined by the probability of a random encounter between predators and prey (NP) and the probability of such an encounter leading to a prey’s capture.

Question 12

What does the Lotka-Volterra model tell us about the population growth of predators?

Answer 12

Depends on the birth rate of predators and the death rate of predators.

Question 13

Define the variables in the Lotka-Volterra model of predator population growth:
dP/dt = acNP - mP

Answer 13

cNP = number of prey consumed
a = efficiency of converting prey into predator offspring
m = mortality rate
P = number of predators

Question 14

What does this indicate: rN = cNP

Answer 14

Prey population becomes stable when the addition of prey is balanced out by the consumption of prey.

Question 15

What does this equation imply: P = r/c?

Answer 15

Prey population will be stable when number of predators equals the ratio of the prey’s growth rate and the predator’s capture efficiency.

Question 16

What does this equation indicate? rN > cNP

Answer 16

Prey population will increase when addition of prey exceeds the consumption of prey.

Question 17

What does this equation imply? acNP = mP

Answer 17

Predator population becomes stable when the addition of predators is balanced by the mortality of predators.

Question 18

What is an equilibrium isocline?

Answer 18

The population size of one species that causes the population of another species to be stable.

Question 19

What do numbers above the equilibrium isocline mean?

Answer 19

There are relatively few predators and the prey population increases.

Question 20

What do numbers below the equilibrium isocline of prey mean?

Answer 20

Predators remove prey faster than prey can reproduce; prey population decreases.

Question 21

What do numbers on the right of the predator equilibrium isocline mean?

Answer 21

Increased abundance of prey; predator population increases.

Question 22

What do numbers on the left of the predator equilibrium isocline mean?

Answer 22

Not enough available prey; predator population decreases.

Question 23

What is joint population trajectory?

Answer 23

The simultaneous trajectory of predator and prey populations.

Question 24

What is the joint equilibrium point?

Answer 24

The point at which the equilibrium isoclines for predator and prey populations cross.

Question 25

Explain what is happening in each quadrant of this image.

Answer 25

Upper left: both predator and prey populations are declining.
Lower left: Predators have declined, allowing prey to increase.
Lower right: Further increase in prey enables increase in predator
Upper right: Increase in predator results in decrease in prey

Question 26

Do the predator-prey models cycle due to time delays? If not, what causes their cycling?

Answer 26

No; cycling is result of each population responding to changes in size of the other population.

Question 27

What is a predator’s functional response?

Answer 27

The relationship between the density of prey and an individual predator’s rate of prey consumption.

Question 28

What is a type I functional response?

Answer 28

Predator’s rate of prey consumption increases in a linear fashion with an increase in prey density until satiation occurs.

Question 29

What is a type II functional response?

Answer 29

Predator’s rate of prey consumption begins to slow down as prey density increases and then plateaus when satiation occurs.

Question 30

What is a type II functional response?

Answer 30

Predator’s rate of prey consumption begins to slow down as prey density increases and then plateaus when satiation occurs.

Question 31

Why does consumption slow down in type II functional response?

Answer 31

As predators consume more prey, they need to spend more time handling said prey.

Question 32

What is a type III functional response?

Answer 32

Low prey consumption under low prey densities, rapid consumption under moderate prey densities, slowing consumption under high prey densities.

Question 33

Identify the functional response of each line.

Answer 33

Purple = type I
Orange = type II
green = type III

Question 34

What is a numerical response?

Answer 34

A change in the number of predators through population growth or population movement due to immigration or emigration.