Predator-prey interactions

Question 1

In which two ways is the abundance of prey species limited?

Answer 1

Top-down: predators limit the prey

Bottom-up: food availability limits the prey

Question 2

What are the 4 forms of predation? How do they differ in lethality?

Answer 2

Carnivores: always lethal
Herbivores: generally non-lethal
Parasitoids: eventually lethal
Parasites: not lethal, but consume resources from the prey

Question 3

What are 3 positive effects of predation?

Answer 3

Keeps prey below carrying capacity, removes individuals from the prey population that aren’t contributing to the next generation (old, sick, weak), removal of competitors

Question 4

What are the direct and indirect effects of predators on prey?

Answer 4

Direct: consumptive effects of predators reducing the abundance of the prey (eating)
Indirect: non-consumptive effects just by having the predator around -> changes morphology, stress-physiology, behaviour

Question 5

What are 5 non-consumptive effects predators have on prey?

Answer 5

Vigilance, habitat selection, grouping, inducible defences (morphology changes), fear

Question 6

What are 5 assumptions of the Lotka-Volterra equations for predator-prey interactions?

Answer 6

1. without predators, prey will grow exponentially
2. predators are only limited by prey density
3. predation is random
4. all individuals are equal
5. predator mortality is density independent

Question 7

What are 4 general trends of predator-prey interactions?

Answer 7

1. response of predators lags behind prey density
2. oscillation pattern
3. predator limits prey
4. predators will eventually decrease from lack of food

Question 8

What are 6 possible outcomes of predator-prey interactions?

Answer 8

1. Predator goes extinct and the prey survive and grow
2. Prey goes extinct and the predator goes extinct too or moves
3. Oscillations that spiral into a stable point
4. Oscillations that spiral out until one goes extinct
5. Immediate stable limit cycle, reaches same maxes and mins every time
6. Immediate stable point

Question 9

How does predator-prey coexistence occur in nature?

Answer 9

Multiple predators, habitat heterogeneity, immigration, non-random predation

Question 10

Which assumptions of the Lotka-Volterra equations are violated in nature?

Answer 10

1. random predation
2. all individuals are equal -> predators and prey have different generation times
3. predators are only limited by prey density -> K may not have anything to do with prey density

Question 11

What is stability through limits?

Answer 11

Having a carrying capacity for the prey prevents extinction. K stabilizes exponential growth and creates different angles which drive the cycle in

Question 12

What are the 6 realities of predation?

Answer 12

1. Predation is not random
2. the carrying capacity of the predators may have nothing to do with the prey density
3. Prey have refuges
4. generation times are different between predators and prey
5. predators can switch prey
6. multiple equilibria may occur

Question 13

What are the 9 adapted defences of prey against predators? What is an example of each one?

Answer 13

1. Chemical (Bombardier Beetle)
2. Protective armour (clams, porcupines)
3. Batesian mimicry (Scarlet king snake)
4. Mullerian mimicry (viceroy butterfly and monarch butterfly)
5. Aposematism (poison dart frog)
6. Deimatic behaviour (the screaming frog)
7. Flashing colouration (white-tailed deer)
8. Crypsis (leaf-tailed gecko)
9. Object resemblance (katydid)

Question 14

What is the difference between Batesian mimicry and Mullerian mimicry?

Answer 14

In Batesian mimicry, a harmless species mimics the warning colours of a dangerous species. In Mullerian mimicry, both species are dangerous and the colour signals are reinforced to predators in the area

Question 15

When is herbivory considered to be predation?

Answer 15

When the plant is killed. Usually if a large amount of the shoots are eaten or the roots are eaten

Question 16

How do plants compensate for herbivory?

Answer 16

Increase photosynthesis in the remaining leaves, re-grow tissues, become herbivory tolerant

Question 17

What are some defences plants use to defend against herbivory?

Answer 17

Structural: spines, thorns, lower digestibility
Chemical: secondary compounds, chemicals that reduce digestion, toxic qualitative inhibitors that inhibit metabolic pathways of the herbivores

Question 18

What are the 5 types of refuges?

Answer 18

Spatial: areas of escape, being at low density
Temporal: altered phenology, growth rate
Large body size: large individuals usually ignored by predators, but comes at a cost of needing more energy and reproducing slower
Large groups: safety in numbers, predator satiation
Other adaptations: communication, specialized features

Question 19

What is predator satiation?

Answer 19

The predators may catch some individuals, but they can’t catch everyone because theres too many

Question 20

What were the conclusions after the 8 year study on the hare-lynx cycle about what drives the cycle?

Answer 20

1. predators decrease hare numbers at high density
2. fear of predation leads to lower birth rates in hares
3. Chemical compounds in plants increase which limits the food for the hares
4. Mostly predators drive the cycle, but food is also important

Question 21

What are trophic cascades?

Answer 21

Indirect effects of predators on lower trophic levels that they aren’t directly eating by modification of the prey behaviour

Question 22

What happens when predators are removed from a natural system?

Answer 22

Herbivores increase in abundance, which decimates the plant population and collapses the ecosystem (Wolves in Yellowstone national park)

Question 23

What 9 factors can stabilize predator-prey interactions?

Answer 23

1. immigration
2. refuges
3. habitat heterogeneity
4. non-random predation
5. less efficient predator
6. slow prey growth
7. evolution
8. density dependence of prey unrelated to predator
9. complex of predators that dampen oscillations

Question 24

What happens when predators are introduced to a natural system?

Answer 24

Can decimate the native population that don’t know how to defend themselves from the predator, extinction of the prey