Predation

Learning goals:
* Understand the determinants of diet selection of predators
* Be able to describe the assumptions and predictions of the Lotka-Volterra equations for predator and prey population growth
* Be able to describe some of the ways predators improve the efficiency of capturing prey, and the ways prey defend themselves from predators

Predator choice of food
What determines benefit (i.e. net energy gain) of prey?
How easy it is to find prey (prey abundance, amount of refugia), ability to capture and kill prey, and energy contained by the prey.

Predator-prey interactions and population cycling
modeling approach: Simple modification of the exponential growth equation (Lotka-Volterra equations)
For prey populations (N), assume growth is exponential, with mortality due to predation associated with the density of both prey and predator (P) populations and the efficiency of turning an encounter into a successful meal (a)

dN/dt = rN - aNP

Addition or loss of individuals in a prey population (dN/dt) is equal to the intrinsic growth rate (r) times the population size (N), minus the predation rate, which is equal to an estimate of the encounter rate (NP) times a coefficient that expresses the capture efficiency of the predator (a)

Predator growth rate is the balance between birth rate, which is dependent on capturing prey, and a constant deat rate:

dP/dt = faNP - dP
where P is the predator population size, t is time, f is the efficiency with which a predator converts a successful meal (aNP) into new offspring, and d is the mortality rate
Model predicts:
1) at some predator population size (r/a), the amount of predation is equal to the intrinsic rate of population growth
2) at some prey population size (d/fa), predator birth rates are equal to the death rate
3) predator and prey populations will exhibit cycles
Lag time between prey and predator population cycles occurs in Lotka-Volterra simulations

Lab experiments with predator and prey populations often result in the extinction of populations of both.
Factors that contribute to limiting predators driving prey populations to extinction include:
    1) prey switching
    2) refugia
    3) evolution of defense mechanisms

Prey defense: Avoidance of being eaten by other animals
Physical defenses- e.g. spines, shells, significantly increase handling time, lowering benefit for predator
Mimicry (resembling an inedible object), including camoulflage (Crypsis)- blending in with background
Chemical defense- includes production of toxins by prey, as well as uptake from plant sources
Behavioral defense-

Predator strategies- increasing efficiency of prey capture
Use of multiple senses- sight, smell- helps to overcome prey crypsis
Crypsis- wait undected until prey come by, often associated with rapid burst of speed to capture prey
Cooperative behavior-