Cooperative Breeding Diversity and consequences Why not disperse? Why provide help? Conflict over reproduction (reproductive skew theory)

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