VL 6

Question 1

Definition of predator

Answer 1

A predator consumes all / most of its prey and needs many prey to reach maturity

Inter-trophic relationship

Predators affect abundance and distribution of prey and vice versa

Important selection pressure on both sides for more effective predators and less vulnerable prey

Question 2

Predator feeding

Answer 2

Specialized or generalist, depending on number of species they feed on - specialist may have adapted traits to overcome defenses

e.g. ground beetles (Scaphinotus) have evolved long head and mandibles to feed selectively on mollusks (get inside snail shells)

Question 3

Intraguild predation

Answer 3

Big eyed bugs (Geocoris spp) are preyed upon by fire ants which they compete with for herbivorous insect prey
-> intraguild predation

Question 4

Cannibalism

Answer 4

consume other predators competing for same prey, but they are members of the same species

Big eyed bugs become cannibalistic of their eggs when specific population densities are reached

Mechanism to avoid overpopulation, or to eat competitor’s eggs

Question 5

Manipulation of populations

Answer 5

Accidental introduction of cottony cushion scale insect (Icerya purchasi) to California from Australia

Used predacious ladybird (Rodolia cardinalis) to control scale insect

Introduction of insect growth regulators toxic to Rodolia in 1990s caused re-emergence of cottony cushion scale

-> introducing a novel predator as biocontrol isn’t always effective:
p. 10

Removing an existing predator doesn’t always lead to an increase in the prey population, due to compensatory mortality
(-> other limiting factors like space or nutrients, competition)

Question 6

Predator responses to changes in prey density

Answer 6

Numerical response: change in predator population size in response to changes in prey density

Functional response:
How an individual predator responds to changing density of prey

Question 7

Numerical response

Answer 7

As prey density increases, the predator population will also increase, both through aggregation and reproduction

Aggregation:

Reproduction:

Question 8

Type II functional response

Answer 8

limited by density and handling time until saturation due to handling time. Most invertebrate predators (e.g. ladybugs, praying mantis) and parasitoids

Question 8

Functional response - what affects an individual predator’s effectiveness in catching prey?

Answer 8

Physical properites, efficiency
Time
How likely you are to see / find prey
Prey density
how long it takes to catch and eat prey

Question 9

Type III functional response

Answer 9

At low prey densities, consumption rate rises slowly, at high prey densities consumption rises rapidly to saturation. Can be due to learning or prey switching

Question 10

p. 16 - 17

Answer 10

p. 16 - 17

Question 11

Functional response to defended prey

Question 12

Predator dependent functional response

Answer 12

(How other predators affect a predator’s effectiveness)

Prey may adapt behaviour when more predators present - refuge use or lower acitvity

Mutual interference / intraguild predation amongst predators

All of these factors complicate real life food webs and functional responses by predators - prey density, prey defenses and predator density / competition

Question 13

Multiple predator species impact on prey - additive effect

Question 14

Multiple predator species impact on prey - antagonistic effect

Question 15

Multiple predator species impact on prey - synergistic effect

Answer 15

predator species enhances predation of another species -> commensalism

Frequently involves one predator taking advantage of strategy of another. Prey may escape one species to be captured by the second

Question 16

Prey diversity

Answer 16

Presence of one prey species can have a negative impact on another by increasing the population of a shared predator