Behavioral Ecology Study Guide test 2

Behavioral Ecology Study Guide test 2 - Behavioral Ecology...

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fitness Behavioral Ecology Study Guide test 2 Chapter 6: Living in Groups *Two main environmental influences on group size for costs and benefits 1. food 2. predation Living in Groups and Avoiding Predation *predators success depends on surprise * many eyes are better than one *hawks are less successful in attacks on large flocks of pigeons mainly because the birds in a large flock take to the air when the hawk is still some distance away *the way vigilance changes with flock size depend on how individuals in a group spend their time * ostriches: each individual spends less time scanning when in a group but that the overall vigilance of the group increases with group size; each bird in the group has more time to feed; each bird raises its head independently of others, random so predators cannot detect it * cheating: why would it pay for an individual to just spend all its time feeding when it knows others are looking out for predators occasionally? How is cheating prevented from evolving? -even when there is an overall benefits of being in a group, each individual will be expected to try to get more benefit than the others (by scanning for himself) * gazelles: the scanning individual gets a higher pay off because he is able to get away first most likely; so there is a direct benefit to the scanning individual so there is no selection for cheating Dilution and Cover *by living in a group, the ostrich dilutes the impact of a successful attack because there is a good chance that another bird will be the victim * antelope : if the herd is more vigilant it may pay the predator to concentrate attacks on small groups and solitary individuals
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* monarch butterfly : (benefits of groups living from diluation): they live in communal roosts in trees; predation rate is inversely related to colony size, so the advantage of dilution seems to outweigh any disadvantage of greater conspicuousness in a large roost * stealing young: ostriches and goosanders: when two females meet, each appears to try and steal the others young and incorporate them into their own brood; predation pressure is severe so it might outweigh the effects of caring for more young because of dilution * horses and flies: horses in large groups are less likely to be attacked by flies; an experiment in which horses were transferred from large to small groups and vice-versa confirmed living in a group gives protection by the dilution effect * cicada cyles: they come out at 13 and 17 yr cycles (prime numbers); predators die or switch to other prey, (evolutionary race in which cicadas and predators extended their life cycles until cicadas won) and the predators cannot fall into synchrony with their cycle; cicadas that come at the middle of the cycle have a less chance of predation than ones at the beginning or end * individuals in the middle of the group may be safer than those at the edge; predators attack the edge of a group * Confusion effect: predators suffer from confusion when attacking a dense group of prey of
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This note was uploaded on 04/07/2008 for the course BIOS 337 taught by Professor Itzkowitz during the Spring '08 term at Lehigh University .

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Behavioral Ecology Study Guide test 2 - Behavioral Ecology...

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