6. Animal Behavior

a. Adaptive evolution and behavior

• proximate (immediate) causes of behavior vs ultimate (fitness, natural selection) causes of behavior

• evolutionary stable strategies: a strategy can’t be out competed by another strategy 

  • ex: prey has to be fast to escape predators 

b. Categories of animal behavior

1. social behaviors: communication, competition, cooperation 

2. reproductive behaviors: mating, courtship, taking care of young 

3. defensive behaviors: avoiding predators

4. foraging behaviors: locating, consuming, and digesting food

Foraging decisions in heterogenous environments

• where to forage?

• what types of food to forage?

• how long to forage?

Currency of foraging theory

1. Fitness: number of offsprings

2. energy gain rate: calories or amount of food per unit time

more energy = more offspring

want max fitness

Definition of optimal foraging theory

animals should make foraging decisions based on costs and benefits of feeding in particular environmental situations 

How animals respond to variation in food over space and time

1. Central place foraging

2. Risk-sensitive foraging

3. Optimal diet composition

4. Diet mixing

1. Central place foraging

• food is brought to a central place (ex: nest);

• once starting foraging in an area, the number of prey caught caught decelerates over time 

2. Risk-sensitive foraging

foraging behavior that’s influenced by presence  of predators

a. Ecology of fear

• fear of predation changes prey behavior and morphology over generations;

• need to have just right amount of fear to be able to survive, have higher fitness, and produce more offspring

3. Optimal diet composition

animals consume many different food items 

a. max ratio of energy gain to handling time

a. Maximize ratio of energy gain to handling time

prey animals vary in size

• benefit of large prey= more energy

• cost of large prey= higher handling time amount of time that a predator takes to consume prey)

4. Diet mixing

• different foods have different nutrients

• a single food is not optimal for all nutrients

• foragers often need to eat a mix of different foods

• limiting nutrients

Marginal value theorem

when an animal must spend time to forage b/w multiple different patches, the theorem states:

• a forager should leave a patch when the rate of energy gain from that patch becomes equal to the average rate of energy across all of the patches in the environment

Marginal value theorem Assumptions

• foragers don’t need to worry about risks (predators)

• everything that the forager eats is the same (no variation in energy from the food, all prey items are equally easy to get)

• all foods are equally nutritious 

• the rate of energy acquired from a patch decreases over time

• if patches have different amounts of resources, then “good” and “bad” patches are distributed randomly (and homogeneously) thru out the landscape

Giving up time

the amount of time spent in the patch before the forager decides to leave and move onto a new patch

giving up density

the food density in a patch when the animal moves onto a new patch

Interpretation of energy gain over time plots

Patch separation distance (travel time)

if patches are further apart= stay longer because want to take advantage of patch before going long distance

Patch quality

1. higher patch quality= longer forager should stay because want to take advantage of patch before going long distance

2. low quality= leave sooner