Lecture 16 - Predation

Question 1

What are 3 effects of predators on prey?

Answer 1

1. Abundance of prey items and their distribution
2. Influence the composition of prey community.
3. Selective force to influence adaptation of prey species.

Question 2

Name 2 types of interaction between predators.

Answer 2

1. Indirect: Exploitative Competition, Apparent Competition (feeding on different prey species but those prey species are linked through a competition)
2. Direct

Question 3

What is the Discrete model formula for predators?

Answer 3

Nt+1=(1-Zt)Nt-CNtPt
where C is the predation efficiency, Pt predator @ t
Pt+1=QNt*Pt
where Q is the efficiency prey use for reproduction by predator

Question 4

What are 4 type of oscillations the Discrete model of predators can produce.

Answer 4

1. Stable oscillation in predator and prey
2. Stable equilibrium with no oscillations
3. Convergent oscillation
4. Divergent oscillation leading to extinction of either predator or prey.

Question 5

Why is the Lokta-Voltera model not realistic? How the Rosenzweig-MacArthur model different?

Answer 5

Lokta-Voltera model is very simplistic: growth of prey population depends on predators’ population (not realistic).

Rosenzweig-MacArthur model: At high prey densities, the prey start to limit themselves, don’t need as many predators to control their growth.

Question 6

Draw the two possible isoclines for predator growth when

1. Predator is only limited by food
2. Predator is limited by food and other resources

Answer 6

1. straight line down middle.

2. logarithmic growth

Question 7

Draw the equilibrium of predator-prey systems

1. Stable equilibrium
2. limit cycles

Answer 7

1. predator straight line after prey peak

2. predator straight line before prey peak

Question 8

Draw the equilibrium of predator-prey systems (ratio dependent model)

(a) Productive environments would sustain more predators
(b) Productive environment would sustain more prey and more predators

Answer 8

1. predator straight line after prey peak

2. predator sloped straight line from origin after prey peak

Question 9

What did Gauss’s paramecium and didinium experiments show?

Answer 9

Prey took refuge in sediments → prey needs refuge to survive

Question 10

What did Huffaker’s mites experiment show?

Answer 10

Mites (Huffaker): He didn’t believe Gaussian’s experiment
Scattered oranges and mites.
1st try: Was able to get oscillation but both prey and predators eventually went to extinction.
2nd try: Reproduced the oscillatory behavior by covering some of the oranges to limit feeding, adding fake oranges, adding wax on the oranges to make it more difficult to move around it, used petroleum jelly to make it sticky, etc. He was successful because he allowed immigration/emigration, and made the environment very different (environmental heterogeneity).

Question 11

Explain how and why the caribou density varied in National parks and Slate Islands.

Answer 11

Caribou density: In national park, density is low because a lot of predators, however just off-shore in the Slate Islands, density is high because no predators (haven’t been able to invade because of water barrier).

Question 12

What did the Muskrat and serengeti experiment show?

Answer 12

Muskrat and serengeti: predator NO strong impact on prey. Predators eat old and weak muskrat that have been driven out of the territory.

Question 13

Define 4 types of predator response to preys.

Answer 13

1. Functional Response: predation varies as a function of prey abundance
   ex: lynx and Hare
2. Numerical response: occurs because of reproduction of predators
3. Aggregative response: Predators will congregate where prey concentration is high
4. Developmental response: Larger predators feeds more than smaller predators. They grow and as a response, they ingest more.

Question 14

How do prey persist?

How can prey escape predation? (2 methods)

Answer 14

1. Refuges:
   Space (hiding)
   Time(ex: when predators are absent, prey come out),
   Numbers (ex: living in large groups),
   Satiation (ex: masting mechanism → flowers widespread seed, predators can’t eat them all)
   Size (ex: lion won’t prey on adult elephant)
2. Adaptation

Question 15

Give two types (with examples) of evolutionary response to prey.

Answer 15

1. Aposematic (Warning) coloration
   Butterfly larvae concentrate toxins from milkweed which are stored in adults.
   Adults are brightly colouredand visible to predators, which quickly learn to avoid these prey.
2. Batesian mimics: species mimic warning coloration of unrelated poisonous species (ex: Coral snakes)