Topic 7 - Organisms & Predation (BIOL 2300)

what does behavioral ecology increase our understanding of

how biotic factors influence distribution/abundance of organisms

to maximize fitness, organisms require

• suitable environmental conditions (abiotic factors)

• sufficient energy resources(abiotic and biotic factors) → acquire appropriate quantities of energy, acquire energy efficiently (gain>loss)

behavioral strategies have _______ under these selection pressures to maximize ______

evolved, fitness

predation

consumption of prey animals by a predator, where prey is alive when attacked

predator consumption rate depends on.. (3)

1. search efficiency for prey (search time, s)

2. time to pursue, subdue  & ingest prey (handling time, h)

3. prey abundance per unit area (prey density) - all prey species

functional response

relationship between prey density and predator consumption rate

functional response - type 1

Linear

• rarely observed

• search time varies w/ prey density

• handling time is constant but near zero

• e.g. passive predators (spiders, filter feeders), herbivores - occurs if prey densities do not become high enough for satiation

• as prey density increases, encounter rates increase, search time decreases. s > > h

functional response - type 2

Linear

• most common

• search time varies with prey density

• handling time is constant but above zero → consumption rate levels off at high prey densities (limited by handling time)

• as prey density increases, encounter rates increase, search time decreases s > > h

• where is starts to plato: as prey density increases, search time is zero but handling remains constant (above zero) h > > s

functional response - type 3

Exponential

• rarely observed

• search time and handling time vary w/prey density → consumption rate is lower at low prey densities

• as prey density increase, h > s (same as type 2)

• at low prey density, search time increases, and handling time = pursue, subdue & ingest prey

why is handling time lower at low prey densities then increase - type 3

1. search time: few prey encounters → have not learned high capture efficiency

2. refuge: high availability of cover for prey at low densities → low capture

compare and contrast 3 functional responses

specialist

an individual takes one or few prey types

generalist

an individual takes many prey types

preference

proportion of a prey type in the diet is higher than its proportion in the envr. (“selectivity)

what doe preferences depend on

• nutritional content of prey (e.g. vitamins, minerals)

• energy**content of prey - more energy → more offspring → higher fitness

*preferences can be switched - switch may depend on the abundance of different prey types

foraging theory - goal

predict the optimal (or best) foraging strategy under certain conditions

• based on math. models derived from economics 

• offers powerful way to understand foraging decisions of predators

foraging theory - assumptions

1. foraging behavior enhances fitness (i.e. foraging strategy is a behavioral trait favored by natural selection in the past)

2. animals maximize net energy gain (ensures high fitness) → predators must expend energy to forage: energy loss - searching & handling time, energy gain - consumption *efficiency depends on energy: energy gain - energy loss = net energy

diet model - specialists and generalists

if predator knows the energy content of each prey type:

• specialists - consume more profitable prey, more energy searching

• generalists - consume less profitable prey, less energy searching

*predators switch between these 2 strategies depending on conditions

diet model - predictions

1. if searching time > > handling time → generalists

2. if handling time > > searching time → specialists

*a predator should consume all prey types when overall prey abundance is low

what type of envr. should predators be generalists in

in a low productive envr

underlying diet model assumptions

• predators know everything about their foraging envr.

• predators perform complex mathematics to determine the profitabiliti’s of a variety of prey types