Q: Suppose in a Lotka-Volterra system, $$r = 0.2$$, $$a = 0.01$$, $$m = 0.4$$, $$b = 2.0. $$What is the predator isocline (number of prey needed to sustain the predator population)?

$$N = \frac{m}{ba} = \frac{0.4}{2.0 \times 0.01} = 20$$

Question 1

Which of the following best distinguishes predation from parasitism and herbivory as forms of exploitation?

Accepted Answer

Predation always results in the mortality of the exploited individual, while parasitism and herbivory do not necessarily cause death.

Question 2

A caterpillar that closely resembles a twig is exhibiting which type of defense against predation?

Accepted Answer

Crypsis

Question 3

Which of the following is an example of an inducible defense in prey?

Accepted Answer

A snail developing a thicker shell in response to the presence of crab predators.

Question 4

In the Lotka-Volterra predator-prey model, what does the parameter $$a$$ represent?

Accepted Answer

Capture efficiency of the predator

Question 5

Given the Lotka-Volterra prey equation $$\frac{dN}{dt} = rN - aNP$$, what happens to the prey population when the number of predators $$P$$ exceeds $$\frac{r}{a}$$?

Accepted Answer

The prey population decreases.

Question 6

A population of sunfish begins to feed more often in vegetated areas when bass are present. This is an example of which type of prey defense?

Accepted Answer

Spatial refuge

Question 7

Which of the following is NOT an assumption of the basic Lotka-Volterra predator-prey model?

Accepted Answer

Predators have a limited capacity for prey consumption.

Question 8

If the predator isocline in a Lotka-Volterra model is given by $$N = \frac{m}{ba}$$, what does this value represent?

Accepted Answer

The minimum number of prey required to sustain a stable predator population.

Question 9

In a real-world example, the population cycles of lynx and hare in the Arctic show that:

Accepted Answer

Predator population peaks lag behind prey population peaks.

Question 10

A researcher observes that daphnia are only preyed upon by mussels when they are below a certain size. This is an example of:

Accepted Answer

Size refuge

Question 11

Which of the following best describes the evolutionary arms race between predators and prey?

Accepted Answer

Predators and prey continuously evolve adaptations and counter-adaptations in response to each other.

Question 12

Suppose in a Lotka-Volterra system, $$r = 0.2$$, $$a = 0.01$$, $$m = 0.4$$, $$b = 2.0. $$What is the predator isocline (number of prey needed to sustain the predator population)?

Accepted Answer

$$N = \frac{m}{ba} = \frac{0.4}{2.0 	imes 0.01} = 20$$

Question 13

Which scenario would most likely result in both predator and prey populations decreasing in a Lotka-Volterra phase plane?

Accepted Answer

Prey population is above the prey isocline and predator population is to the left of the predator isocline.

Question 14

A plant increases its production of phenolic compounds after being grazed by insects. This is an example of:

Accepted Answer

Inducible chemical defense

Question 15

Which of the following would violate the assumptions of the Lotka-Volterra predator-prey model?

Accepted Answer

Prey have access to refuges where predators cannot reach them.

Question 16

If a population of wolves (predators) and moose (prey) has $$R = 0.1$$, $$m = 0.3$$, $$a = 0.002$$, $$b = 1.5$$, and initial populations of 150 wolves and 200 moose, what are the values of the prey and predator isoclines?

Accepted Answer

Prey isocline: $$P = \frac{R}{a} = \frac{0.1}{0.002} = 50$$ wolves; Predator isocline: $$N = \frac{m}{ba} = \frac{0.3}{1.5 	imes 0.002} = 100$$ moose.

Question 17

Which of the following is a behavioral change in prey in response to predation risk?

Accepted Answer

Daphnia migrating to deeper water layers when fish predators are present.

Question 18

In the Lotka-Volterra model, what is the biological meaning of the prey isocline $$P = \frac{r}{a}$$?

Accepted Answer

The number of predators required to keep the prey population growth at zero.

Question 19

Which of the following real-world scenarios best illustrates the concept of lagged population cycles in predator-prey dynamics?

Accepted Answer

Lynx populations peaking several years after hare populations in the Arctic.

Question 20

A honey badger’s resistance to cobra venom is an example of which type of adaptation?

Accepted Answer

Predator chemical adaptation

6.1 Predation and Predator-Prey Dynamics: Ecological Interactions and Mathematical Models

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