Selective foraging

What is optimal foraging theory?

Predators can adjust their behaviour to maximize energy gain

What are 2 ways that predators impact prey?

• Consumptive effects

• Nonconsumptive effects

What are consumptive effects?

Lethal effects

What are nonconsumptive effects?

• Changes in morphology/allocation to defense

• Changes in behaviour

• Changes in life history

• Changes in stress levels

What are 2 examples of predator-related changes in morphology/allocation to defense?

• Paramecium exhibit decreased swimming speeds and increased body widths in the presence of flatworms

• Acacia exhibit increased spine length and cyanide with high levels of giraffe browsing

What is an example of predator-related changes in behaviour?

Mice and gerbils exhibit decreased foraging and increased giving-up densities with increased owl abundance

What is an example of predator-related changes in life history?

Mayflies exhibit decreased foraging activity, size at maturity, and population growth in the presence of fake predators (plastic fish)

What is an example of predator-related changes in stress levels?

The sensitive hare: hares exhibit increased cortisol levels and decreased litter size and mass in the presence of dogs

What do negative values of Paine’s index indicate?

Species x reduces the abundance

What % of prey show a positive response to predator removal?

60%

What % of predators depress prey density by > 50%?

45%

In what % of cases do prey do better in the presence of predators?

25%

What determines how predators influence community structure?

• Predator preferences

• Competitive ability of prey

How do changes induced by predators involve trade-offs?

• Investment in defenses cannot be used for reproduction

• Changes in behaviour that reduce predation risk incur foraging costs

Why might prey do worse when a predator is removed?

If the predator preferentially forages on a dominant competitive species, removal of the predator will allow this species to increase in abundance, reducing the abundance of other prey species