3. Predator-prey relationships and responses of predators to the changes of prey populations.

Question 1

Predator-prey relationship

Answer 1

Predation is the interaction between two trophic levels.

One species is feeding on the other.

Prey - animal being eaten
Predator - animal doing the eating

Predator regulate prey densities and prey can regulate predator densities.

Predator prey relationship is an important one:
- Plays role in structure of ecological communities
-predators influence the dynamics of their prey that cascades through ecosystems
to affect processes including:
=productivity
=biodiversity
=nutrient cycling
=disease dynamics
=carbon storage, etc

As predator decrease prey populations, lack of food resources decrease predator abundance > lack of predation allows prey populations to rebound

Illustrated by a food chain/ food web

If an organism is removed from a food chain/web all together (overhunting) it can have a catastrophic effect on the other organisms in the chain/web

Question 2

Predator- prey relationship (responses)

Answer 2

Prey population experience exponential or logistic growth

Predation rate is influenced by functional or numerical response

-functional response: # of prey successfully attacked per predator as functional of prey density. Describes the way a predator responds to the changing density of its prey.

• Numerical response: The change in predator density as a function of the change in prey density. Associated with functional response.
• Aggregation response: The change in predator population due to immigration into an area with increased prey population

Question 3

Effects of predators

Answer 3

Top-down regulation:
-prey density is low when predators are present
-prey can reach high densities when predators are culled

Bottom-up regulation:
-predators depend on prey density

Question 4

Regulatory effects of predators

Answer 4

Complete regulation: prey population is completely regulated by predator population

Partial regulation: prey population is regulated by food and other resources and can’t reach higher numbers even when predator density decreases
- multiple stable points develop - prey population is regulated differently depending on the time of the year

Question 5

Behavior of prey

Answer 5

Migration: Moving away from predators and to look for more resources

Herding: Walking in large groups decrease predation risk - difficult to select and catch

Spacing: Females hide young while grazing

Birth synchrony: All members of a group will have young at the same time to increase population survival (only part of young are eaten)

Question 6

Management

Answer 6

Predator-prey relationship is one of great interest in wildlife management

Predator management is mostly used today to benefit threatened/ endangered species and game species.

Predator control is very controversial - it’s hard to predict actual outcomes:
- Rare prey species: presence of predators can make the difference between survival and extinction, especially in the case of invasive or introduced predator (Coyote and rodents in North America)
-Pest prey species: predators are necessary for biological control
-Hunting ground: the offtake by natural predation should be taken into account, else there will be overharvesting, causing a collapse of prey population

When creating a management plan, think of:
-Will the prey survive?
-Can habitats support more prey?
-predators out of control area will migrate back
-Predator control has little effect if population is near K