Predator-prey relationships

Question 1

What are the types of predator-prey cycles?

Answer 1

• Stable limit cycles
• Stable-point cycles
• Unstable cycles
• Extinction

Question 2

What do we mean by a ‘stable’ cycle?

Answer 2

Where a pair of populations (predator, prey) have a return tendency to a particular density. There is a regular identifiable pattern of population sizes over time.

Question 3

What is a stable limit cycle?

Answer 3

Both predator and prey go through similar cycles, the predator lags behind the prey and populations never reach equilibrium. - oscillation

Question 4

What is a stable point cycle?

Answer 4

Both predator a prey populations settle at a fixed number no or only small oscillations.

Question 5

What happens when predators are introduced?

Answer 5

• There can be extinction
• The ecosystem can be destabilised
• over evolutionary time there is coexistence.

Question 6

Do predators cause commonly observed population cycles?

Answer 6

Evidence suggests that this system is not as simple as it initially seems. In the hare and lynx example, there are several other factor influencing the 10 year cycle of hare and in areas where lynx are absent the cycle still occurs.

Question 7

What are indirect interactions between predator and prey?

Answer 7

Reduced quality/quantity of food results in a poorer condition and greater stress. The prey must search further to find food and is less able to avoid predation.
Higher predation risk results in greater chronic stress and lower reproductive output.

Question 8

What are the limitations of predator-prey models?

Answer 8

• Prey usually have a refuge of some sort where they are free from predation.
• The models assume predation is random when it is rarely random.
• Models assume similar generation times for prey and predators.
• predators may be generalists and can switch prey which may stabilise populations.

Question 9

Can predator prey interactions drive species diversity?

Answer 9

There is evidence from the fossil record that predation events shown in fossils correlated with predator and prey diversity. High predation pre-dates diversification. This could occur as if there is speciation, predators may have to adapt to new prey or speciation could occur to avoid predators.

Question 10

What is an example of predators driving diversity?

Answer 10

The Bahamas Mosquitofish. Predated by the bigmouth sleeper. There was a repeated natural experiment in the Bahamas in which some pools had no predators. In pools with no predators there was no speciation. In the other pools the mosquitofish diverged and speciated in response to predation. Predators take prey with certain traits leave others to survive. This is a by-product of predator-prey interactions over a large time-scale. couples with sexual sixe dimorphism, sexual traits and sexual selection, where big fish only mate with big fish, there is reproductive isolation and speciation.