Biotic Interactions Part III

Prey density model

Doesn’t ALWAYS result is straight forward increase in predator population size

IDEA or Theory Attemps to model what

How organisms feed as an optimizing process.

• Attempts to predict what consumers eat, when and where they feed. 

IDEA or Theory

Natural selection is likely to favour individuals in the population who are highly effective at acquiring energy. 

Optimal foraging studies attempt to predict 

• How lang predator forage in area 

• Influence of prey density on time predator will forage 

• Influence of prey variety predator choice of acquired prey. 

Functional Response

Refers to predator varies its consumption of food (prey) according to abundance of resource (prey) 

Key concept underling prey/predator and energy flow in ecosystems 

Types of Predation (graph) 

1) Type 1 - Linear 

2) Type 2 -  Curve up and flat (carry capacity) 

3) Type 3 - Flat, same linear curve, and then flat. 

Type II (predation)

Predators searching time decreases with increasing prey density. Predators’ handling time of prey remains constant. Propation of prey eaten declines linearly. Limited by handling time (Most common). 

# of prey taken rises at decreasing rate to  max level 

Type II (characteristics)

• Deceleration phase in consumption rate

• Predators handling time determined by physiology/ecology of organism and remains constant.

• Handling time and search efficiency determine plateau 

Type II (examples) (predation) 

Spiders (handling time: spend time capturing, subduing, consuming prey)(Satiation: Feeding rate slows approach satiation) 

Type 1 (Predation)

Rate of prey capture increases linearly with food density

• Time required for consumer to process food is minimal, or eating doesn’t disrupt search for food. 

Type III (Predation)

Prey switching. More efficient for predators to catch prey which is abundant, compared to rare ones

*High densities prey consumption limited: handling time and search efficiency.

• Prey consumption starts low, gradually increases (reaching plateau)

• Predators turn to alternate, more abundant prey.

Ex: Vertebrates

Three types of behaviour

1) alternative prey offers better choice

2) Predators ignore preys that are rare 

3) Concentrating search on more rewarding areas 

Type III (Predation)

High Prey Densities

• Similar to type II

Low Prey Densities

• Accelerating phase where increase in density leads to more linear increase in consumption.