Cooperative Breeding Diversity and consequences Why not disperse? Why provide help? Conflict over...
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Transcript of Cooperative Breeding Diversity and consequences Why not disperse? Why provide help? Conflict over...
Cooperative Breeding
• Diversity and consequences
• Why not disperse?
• Why provide help?
• Conflict over reproduction (reproductive skew theory)
Diversity
• 220 species of birds have helpers at the nest
• 120 species of mammals have some form of alloparental care, e.g. communal nursing
Consequences
Conclude: Helpers invariably increase offspring production
Why not disperse?
• Group living advantage
• Ecological constraints: habitat or mate saturation– Dispersal is difficult or risky– Species defend year-round all purpose territories– Residency improves competition for territories
Habitat saturationSeychelles warblers Acorn woodpeckers
Mate or nest limitation
• Superb blue fairy wren1.8 breeding males/female; 1.5 helpers/nest
Male dispersal Yes No
Male removed and transplanted 31 1
Male and female removed 0 7
• Red-cockaded woodpeckers Occupied next year Yes No
New nest boxes in old territories 18 2
New nest boxes in similar habitat 0 20
Why provide help?
• Nonadaptive result of parental care
• Increase own survival– Improving survival of offspring increases group size
• Increase fecundity– Through practice - no evidence
• Enhance breeding opportunities
• Increase inclusive fitness
Why provide help?• Enhance breeding opportunities
– Helpers recruit offspring to join coalitions - green woodhoopoes
– Gain access to mates - stripe-backed wrens
Open = intact familiesFilled = families with female replacements
Why provide help?
• Increase inclusive fitness by decreasing parental feeding rate– WIF = WH + rBHWB
– Increased breeding• Grey-crowned babblers
– Enhanced survival• Florida scrub jays
Why provide help?
• Increase inclusive fitness by improving offspring survival– Reproductive success
must correlate with helper number (independent of territory quality)
– Must preferentially help close relatives
Is the benefit of helping independent of territory quality?
Test by removing helpers then compare RS before vs after removal
Conclude that helpers make a difference in babblers and scrub jays but not moorhens
Helpers are usually related
Florida scrub jay
Seychelles warbler
White-fronted bee-eater
Bee-eaters help closest relatives
When male breeding attempts fail
Helping increases inclusive fitness in
pied kingfishers
Males either help at home (primary helper), help elsewhere (secondary helper) or delay breeding for a year
Total
0.990.840.29
Conflicts over reproduction
• Requirements– Ecological constraints
limits dispersal– Group breeding
enhances individual RS– Individuals in group
vary in social dominance
– Individuals in group are related
Reproductive skew theory
W = fitness of dominantW = fitness of subordinate
Reproductive skew predictions
• If group is unrelated, subordinates should do no worse than if they left the group
• If group members are related, then subordinates should permit more skew and allow the dominant to reproduce for them
Reproductive skew evidence: paper wasps