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14 Cards in this Set

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Optimality models
-do animals make the "right" decisions according to our understanding of the factors important to fitness?
-trade offs
-cost-benefit ratios
major point of optimality modeling isn't to learn if animals behave 'perfectly', but to see if one has correctly identified the factors that influence behavior.
Foraging decisions
1.habitat selection:optimal habitat to settle in, with respect to food availability
2.patch selection:what are the optimal foraging sites? how long should the animal forage in a particular patch before moving on? if the resource is renewable, what is the best interval between repeat visits?
3.Diet selection:what food items should be eaten and what should be ignored?
Optimal "choice" is the one that is the best (in terms of fitness) from among the available options. Simplist foraging and diet models define fitness in terms of energy intake.
2 categories of foragers
energy maximizers
time minimizers
energy max: fitness increases in proportion to the toal calories eaten

Time minimizers:extra food is not as important as extra time for non-foraging activities
whether energy maximizer or time minimizers, the important pt is to maxmize NET RATES OF ENERGY INTAKE (a cost benefit ration:energy eaten/energy used in foraging)
Optimal diet
Which of a choice of prey should be eaten and which should be ignored
-Average amount of time needed to locate, capture, and eat the prey
3 rules of optimal diet
1.always eat the prey(type 1) with the lowest time per joule gained
2.other types(type 2,3)are eaten ONLY if the animal has a net gain greater than if it ignored type 2 and looked instead for another of type 1. This rule is followed for other prey types down the line.
-as food abundance increases, the optimal diet shrinks and vice versa
-presence of competitors leads to an expanded diet, beacuse competitors reduce prey density. This is opposite to what happens over evolutionary time, when competing species evolve to minimize resourve overlap
Example of optimal diet
Bluegill sunfish
bulegill sunfish feeding on Daphnia
-3 prey sizes(small medium large)
-3 dentsities(low, medium, high)
-figure out search and handling times of each prey size
-calculated the optimal "switch points"(in terms of search time)
-Real fish matched predctions
high densitiy:only eat large prey
medium density:eat large and medium
low density:eat all sizes
Example of optimal diet
Great tits
-select worm sizes from a moving conveyor belt
-crows eating clams
-oystercatchers eating mussles
Criticisms of optimal foraging theory
-hard t see how animals could be optimal unless they accurately assess prey density; difficult in a complex changing environment. but knowledge comes with experience
Failed optimality prediction
Adelie penguins
-adelie penguins eat krill
-how much time spent at depth vs at surface?
-spend about 1/3 of their time on the surface and stay under for a max. 3min.
-The deeper they go, less time they can spend chasing prey(bottom line)
-PREDICTION:they should maximize ratio of bottm time/(surface time+travel Time+bottm time)
-But they do not do this. They spend less time underwater than would be "optimal" under initial assumptions
-maybe improves energy efficiency, or perhaps krill are so abundant in swarms that optimality isn't important to fitness
Things besides prey energy content that could influence the fitness of diet choice and foraging behavior?
1.nutrients:a diet optimal for energy intake may not provide adequate nutrients
2.Toxic compounds:may have to compromise between toxicity and nergy or nutrition
3.Predation:many species modify foraging if predators are a ris
4.overall physiological condition:a very lean or hungry animal will often modify foraging behavior (with respect to predation exposure)
Ex of max. effectiveness of foraging by "optimizing" use of space

south american army ant Eciton
-live in huge colonies that move around the forest floor and make temporary "camps" called bivouacs
-bivouacs are a bit ball of ants with the queen and young inside
-every day a "raid" of ants fans out radially from the bivouac and gathers prey and brought back tot he bivouac

Problem:a riad will essentailly clean out a piece of forest of all available prey. How do colonies avoid wasting time and energy foraging in depleted areas?
-every day, raids go out in a different direction(130 from previous day) this min. raid overlap around a bivouac
-when bivouacs move(every week or two) they avoid places where they or other colonies have recently foraged