Cooperative Breeding

Cooperative Breeding - Cooperative Breeding Alexander...

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Cooperative Breeding Alexander Skutch’s observation (1935) A curiosity until the 1970’s. Then, the field of “sociobiology” was born and research on helping in birds skyrocketed Why a hot field? Helping appears to be altruistic – a behavior that helps another individual at a cost to the helper. (Why not help itself ?)
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What is cooperative breeding? A reproductive system in which one or more members of a social group provide care to young that are not their own offspring 2 types: 1)Classic (“helper at the nest”): Mature non-breeders stay at home and help. Only one breeding pair per group 2)Communal Breeding : Young have mixed parentage. More than two individuals breed.
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Florida Scrub Jay (Glen Woolfenden & John Fitzpatrick) Very restricted in habitat A “relic” population in FL Scrub jays elsewhere do not breed cooperatively One breeding pair per group Up to 6 helpers per group. Helpers are generally sons and daughters of breeding pair
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Scrub Jays Do helpers really help? Average number of young raised in groups without helpers: 1.6 Average number of young raised in groups with helpers: 2.4 helpers can provide 80% of food to nest Experiment (Ron Mumme) # of young raised in groups with helpers removed: 0.6 # of young raised in control groups: 1.6
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Scrub Jays Territory is key Scrub Jays are non-migratory Territories are tightly delineated -- every inch taken Territorial boundaries intensively defended Bottom Line : no room for new territories & a surplus of adults waiting for opportunity to breed. These are the individuals that help.
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Scrub Jays Role of Predation Helpers help watch for predators (“sentinels”) Groups with helpers: 15% of breeders die Groups without helpers: 23% of breeders die Young are especially vulnerable to predation: Staying on a familiar territory helps reduce their risk of predation.
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How to reach breeding status? 2 routes 1) Inheritance . 20% of breeders die each year. High-ranking helpers take their role. 2) Budding . Older males of large groups start defending a piece of parents’ territory and attract females. Note : Both of these require a “home base” – being a helper
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White-fronted Bee-eaters Live in Africa Eat bees (long bill!) Nest in colonies No territories Maintain close social bonds; each bird a member of a “clan” comprised of 3-4 overlapping generations
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White-fronted Bee-eaters Breeding: Colonies consist of many monogamous pairs Older birds breed; younger are physiologically capable of breeding but often do not. When younger birds do not breed, they help Helping is common (50% of pairs have helpers) Helping is not merely a transitory stage; birds can shift status from breeding to helping.
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1) Raise your own young (direct) 2) Raise young that share your genes (indirect; full siblings share 50% of genes) How to increase one’s fitness Natural selection acts on individuals to increase the number of their genes that are passed onto the next generation. There are two routes by which this happens:
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Cooperative Breeding - Cooperative Breeding Alexander...

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