Eco - Behavioral Ecology

proximate causes

immediate explanation of behaviors; how the behavior occurs

ultimate causes

why the animal behavior occurs; the evolutionary and historical reasons

optimal foraging theory

animals will maximize the amount of energy gained per unit of feeding time, and minimize the risks involved

• assumes that natural selection acts on the foraging behavior of animals to maximize their energy gain

what do optimal foraging and dietary preferences depend on?

• encounter rate

• handling tim

encounter rate

if low, predators (carnivores) should be generalists

handling time

if prey are easy to find but handling time is long (i.e., immobile but less nutritious plants) then predators (herbivores) should be specialists

what does profitability of a food item depend on?

depends on how much energy the animal gets relative to amount of time it spends searching for and handling the food

monophagous vs oligophagous vs polyphagous

monophagous - feeding on one food type

oligophagous - feeding on a few food types

polyphagous - feeding on many food types

optimal diet model

foragers choose food items to maximize net energy gained per unit of time; foods are ranked by profitability, calculated as energy content divided by handling time

assumptions of the optimal diet model

• foragers encounter food at random

• different food types are encountered independently

• encounter one food at a time

• searching and handling are exclusive

• no depletion

• foragers can estimate encounter rates with food, profitability, and can rank foods, instantaneously

• food are selected according to their constant profitability

• no constraints on foraging

predictions of the optimal diet model

1. if 2 types of prey are available and 1 is more profitable:

   1. always accept more profitable

   2. if more profitable has a high encounter rate (ow search time), ignore less profitable, even if the less profitable prey is very abundant

   3. accept less profitable prey only if more profitable prey is scarce (rare, longer search time)

2. if handling times are short relative to search times, forager should add more items to diet

3. if longer handling times relative to searching, add fewer items to diet

4. if an unproductive environment prey can be scarce, expect more generalists

marginal value theorem

• model that predicts when an organism should leave a depleted resource patch to maximize its overall rate of resource intake

• an animal should stay in a patch until the rate of energy gain has declined to match the average rate for the whole habitat (giving up time)

assumptions of the marginal value theorem

1. food is patchily distributed throughout the habitat - some patches contain more food than others

2. animals maximize energy intake (benefit/cost)

3. time is divided into two stages - no food in encountered when moving between patches

   1. searching for food inside a patch

   2. traveling between patches

4. animals encounter patches randomly and don’t revisit them in one foraging bout

5. food is depleted as it is consumed

6. foragers can measure their instantaneous rate of energy intake

7. foragers can measure and remember the average rate of energy intake among patches and compare this value to instantaneous rate to decide whether to stay in a patch

predictions of the marginal value theorem

• animals should stay longer in better patches

• the longer the travel time between food patches, the longer an animal should spend in a patch

• animals should ignore patches below average quality

• because of depletion, foragers gradually bring all the patches down to an average patch quality

ideal free ditribution

model that explains how animals spread themselves across different resource areas to maximize their survival and reproductive success

assumptions of ideal free distribution

• patches of different profitability in habitat

• profitability decreases with increased competition

• individual forages are free to move among patches

• all individuals have the same competitive ability

predictions of the ideal free distribution

• the density of foragers present in a patch is proportional to profitability

• all foragers obtain the same feeding rate over all patches

benefits of group living

• higher reproductive success - especially when males hold high quality territories

• group members may share feeding and care of young

• reduced risk of predation - individuals can band together to prevent attacks; predators may be detected sooner

costs of group living

• as group size increases, available food is depleted faster

• more time may be spent in moving between feeding sites

• competition for food can be more intense

• in groups with a dominance hierarchy, subordinate members can spend much time and energy on interacting with group members

• group members may live close together or come into contact more often than in a small group; parasites and diseases often spread more easily

cost/benefit principle of group size

group size should be where net benefits exceed costs

• but unless group members can prevent other individuals from joining once optimal size is reached, observed group size may be larger than the optimal

sexual selection

individuals with certain characteristics gain an advantage over others of the same ex solely with respect to mating success

anisogamy

female invests more to produce a large egg, and often continue to invest more in the offspring (incubating eggs, caring for young, etc.)

what factors can alter mate choice?

• number and locations of potential mates

• mate quality

• food availability

• presence of predators or competitors