Predation

Question 1

What effect does predation have on sp 1 vs sp 2?

Answer 1

Sp1- Negative

Sp2- Positive

Question 2

Whats predation?

Answer 2

-Interaction between consumers (predators) and resources (victims, prey)

Question 3

What increases predator population growth?

Answer 3

Reduction in prey population

Question 4

What does the Lotka-Volterra predator-prey model assume? Is it realistic? What effect of predators is it trying to see?

Answer 4

• Specialist predator on single prey (narrow range of conditions)
• Victim pop is limited by predators
• Predator/prey regulate one another’s populations
• No; As soon as predator feeds on prey using energy to go into reproduction
• How much predator population will decrease per capita growth rate of prey

Question 5

What does alpha stand for?

Answer 5

Every time predator captures a victim- how many times will they be successful?
-Capture efficiency

Question 6

How does the equilibrium for V depends on P?

Answer 6

Only few predators wont be able to control prey population- prey pop increase and vice versa

Question 7

What does predator growth depend on?

Answer 7

Prey abundance

Question 8

Whats neutral stability?

Answer 8

Will cycle with different amplitude if perturbed (unsettled)

Question 9

1 way to increase realism of Lotka-Volterra model? What does the victim isocline produce? Why more stable?

Answer 9

• Victim carrying capacity
• Density Dependence
• Can run out of resources
• Damped oscillations
• Victim pop is regulated by another factor besides predator

Question 10

Whats a basic functional response?

Answer 10

• Rate of victim capture by predator as a function of victim abundance
• Type I
• Increases realism

Question 11

Explain Type II functional response. What does it arise from?

Answer 11

-At high prey
predators get full
time needed to consume victims (handling time)
- Handling time- Time needed to “handle” prey reduces overall consumption rate

Question 12

Explain Type III functional response.

Answer 12

-At high prey: predators get full
time needed to consume victims (handling time)
-At low prey: Poor search image, Prey refugia (hiding places), and Switch to other prey

Question 13

What is type I fractional response?

Answer 13

Linear horizontal line

Question 14

What is type II fractional response?

Answer 14

• Fractional consumption rate decreases with population increase
• Predator is having smaller impact on victims pop growth
• More realistic model for how quick predators can feed upon victims.
• More victims- predators consume less share of pop; less effective in regulating size of victims.

Question 15

What is type III fractional response?

Answer 15

Fraction consumed increase initially- but will plateau- victims go up more but smaller impact

Question 16

What does the victim isocline with a type II functional response produce?

Answer 16

• Increasing unstable oscillations

- Not stable because predator is less effective at regulating victim pop

Question 17

Whats the Rosenzweig-Macarthur model?

Answer 17

• Combines prey density-dependence with Type II predator functional response
• Simplest “realistic” model of 
predator-prey systems

Question 18

Rosenzweig-Macarthur model victims isocline. What does the stability depend on?

Answer 18

• Parabola

- Predator isocline

Question 19

Whats the Paradox of Enrichment?

Answer 19

• As CC increases, victim pop destabilizes because predator is more responsible for its suppression
• Lower CC- stable
• Increase CC- limit cycles
• very high cc- intersect predator isoline; unstable pop; 1 or 2 species will go extinct

Question 20

Why might predator isocline not be vertical?

Answer 20

Predator interference
→ must defend territory or fight other predators

Predator density-dependence
→ regulated by other factors when excess victims

Alternative prey sources
→ switch to other prey when few victims

Victims have density-dependent effects
→ stable ratio of predators to victims

Question 21

3 considerations for each potential item in the optimal foraging theory.

Answer 21

• Energy (Ei) = net calories obtained
• Encounter rate (λi) = # found per unit search time
• Handling time (hi) = time needed to consume

Question 22

Diet preference is based on?

Answer 22

The profitability of each item:
-Profitability = Ei/hi
(rate of energy gain once prey has been located)

• The most profitable items should always be included in diet
• Less profitable items may or may not be included

Question 23

What is energy intake?

Answer 23

E/T

Question 24

Should profitability or energy intake be more?

Answer 24

Profitability

Question 25

What are some predictions from optimal foraging?

Answer 25

Inclusion of less-preferred items
does not depend on their encounter rate
does depend on encounter rates of more-preferred items

Foragers should broaden their diet as preferred items become less abundant

Question 26

How to determine rate of food depletion?

Answer 26

Can use functional response to predict rate of food depletion (assume a single consumer)
Intake rate decreases over time

Question 27

How to decide when to relocate?

Answer 27

-Cost of travel time not spent foraging
-Weighed against higher intake rate of new patch
-Maximize-
Food consumed/ foraging time + travel time

Question 28

How do travel time and food availability affect foraging decisions?

Answer 28

1. Give-up times: time spent in patch before moving

2. Give-up density: amount of food remaining upon leaving

Question 29

How do longer travel times affect give up times and densities?

Answer 29

• increased give-up times

- decreased give-up densities

Question 30

How do more food in patches affect give up times and densities?

Answer 30

• increased give-up times

- increased give-up densities

Question 31

Whats the marginal value theorem?

Answer 31

• Describes behaviour in a patchy system where food and resources vary in resource density and are some distance apart.
• Helps predict the optimum time for the organism to stay in the patch gathering resources before moving on