topic 9 functional responses

Question 1

• Factors that stabilize predator-prey interactions- the simplest predators-prey interactions are not very stable. solutions?

Answer 1

he solution: other kinds of biology can help stabilize these interactions
1. Interference from outside the system (e.g., immigration)
2. Escape from predation - partial prey refuge
3. Positive density-dependence in prey populations (increasing d or declining b with increasing prey density)
– Intraspecific competition among prey for limiting resources
– Can be caused by certain functional responses of predators

Question 2

what arw functional responses of predators? lv assumptions?

Answer 2

• Describes how predators respond to variations in prey density (amount of prey consumed per unit time)
• lotka-Volterra Assumptions
• Predators consume prey at a constant rate, proportional to prey population density
• No satiation of predators
Unlimited functional response

Question 3

how does the unlimited functional response impact prey death rate?

Answer 3

○ Prey death rate is density independent
§ Prey death rate does not vary with prey population density
§ Does not aid in stabilizing populations (need positive density dependence)

Question 4

what types of predator functional responses are observed in nature

Answer 4

• Types I, II, AND III, observed in nature

Question 5

when do preds have a type 1 response?

Answer 5

• Occurs when:
	• # eaten increases LINEARLY as a
	CONSTANT function of
	(proportionate to) prey density
	(until satiation)
	• Only search time is important
		• Relatively rare in nature 
	• Seen in passive predators: 
	– Filter feeders: aquatic organisms
	(zooplankton, whales, some fish, etc.)
	– Spiders

Question 6

What is the effect of increasing prey population density on prey mortality rate (from predation)?

Answer 6

• Decline in prey mortality rate

* Negative/inverse d-d = no stabilizing effect (bc only happens with positive d-d)

Question 7

describe type II func resp of preds

Answer 7

• Asymptotic
  
  • Increases at declining rate
  • Most common
  • Search and handling time important

Question 8

describe search time

Answer 8

• Search time
• How long it takes a predator to find prey
• Function of prey density
• Limits predators at low prey densities
(similar to Type I

Question 9

describe handling time

Answer 9

• Handling time
• How long it takes to capture, kill & consume prey
• Limits predators at high prey densities (little
search time)
• Max. predation rate defined by handling time

Question 10

• What is the effect of increasing prey population density on prey
mortality rate?

Answer 10

• Negative/inverse D-D

Question 11

describe type iii response in pred

Answer 11

• Sigmoid/ S shape
• Predation rate initially increases with
increasing prey abundance (slope increases)
•
• Predation rate eventually declines
(limited by handling time - similar Type II)

Question 12

type iii mechaisms (low and intermediate densities)?

Answer 12

• Three mechanisms that cause type iii functional responses

1. Predator learning
2. Prey switching
3. Prey refuges

Question 13

describe predator learning - how does it affect consumption rates

Answer 13

• When prey are rare, it is difficult for predators to learn to hunt effectively
• learn where to find prey:
• Search time declines as prey become more familiar to predators (increase in abundance)
• Search image formation difficult at low prey
abundances
• Learning how to catch & kill (handle) prey:
• Predator may have special techniques
depending on prey
• Efficiency increases with familiarity (handling
time reduced)

Question 14

describe prey switching. look at shrimp ex

Answer 14

• Optimal foraging theory: predator should focus on the most profitable prey
• Rare prey often ignored (high search time)
• If prey become abundant, predator may switch
(more profitable – reduced search time)

Question 15

how can prey refuge impact predators

Answer 15

imited # safe places for prey to hide
	• As prey abundance increases, more
	are unprotected
	• Search time would decline with
	increases in prey abundance
	• Results in an increase in consumption
	rate of predators at low prey densities

Question 16

what sets type iii apart?

Answer 16

• Only functional response with
positive density dependence
• Prey mortality rate (predation rate) initially increases with prey population size

Question 17

Prey d-d arising from predator functional response- type i - what does it need to regulate prey

Answer 17

needs postitive dd to regulate /stabilize

Question 18

what dd does type ii have

Answer 18

positive d-d - increase in prey death rate w increasing prey abundance

Question 19

type i and type ii vs type iii d-d - stabilizing or destabilzing

Answer 19

type i - destab - as prey density increases, mortaility declines (negative d-d)
type ii - same
type iii - stabilizing - prey death rate initially increases w prey density

Question 20

•

Type III functional response - regulation, inflection point?

Answer 20

• Regulating (stabilizing) effect of predators is limited to prey population densities where mortality increases
  
  • After inflection point no longer stabilizing