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Cooperative Breeding

VIEWS: 10 PAGES: 24

  • pg 1
									 Cooperative Breeding
 Non-breeding adult helpers assist in caring
  for young produced by the breeders
 The breeding unit is a group, consisting of
  breeders + helpers
 Occurs in 200+ species, most common in
  Australia and Africa
 Has evolved many times, is the norm in
  some families (shrikes, wrens, corvids and
  their Australian relatives)
Cooperative breeding is
most common in Australia
Simplest, most common system: young
remain as helpers on their natal territory
More complex: helpers attempt to participate in
reproduction (Acorn Woodpeckers)
Most complex: multiple breeding pairs lay in same
nest (Ostrich) or different nests (Mexican Jay)
Evolution Cooperative Breeding
 Apparent altruism of helpers an interesting
  evolutionary issue
    Helpers sacrificing themselves for others?

 Breeders benefit from help
    Reproduction, survival breeders increased

 Clear costs of helping
    Time and energy expended

    Forego breeding
 Two separate questions:
     (1) why stay?
      (2) why help

Helpers do not stay in order to help
Benefits of group living apply, but do not
offset costs of sharing reproduction, let alone
foregoing reproduction
Reasons To Stay
 Poor reproductive capacity at young ages
  (due to lack of foraging skill perhaps)
 Ecological constraints – good territories are
  unavailable
    Territories are physically restricted
     (islands: Seychelles Brush-Warbler)
    Great variation in territory quality, best to
     wait for a good one
Florida Scrub Jay: Variation depends on habitat
quality (scrub habitat)
Red-cockaded Woodpecker: Variation depends
on special resource, cavities excavated live pines
Acorn Woodpecker: Variation depends on a
special resource (acorn storage granaries)
Staying is a strategy to become a
breeder on a good territory
 Delayed dispersal and reproduction,
  dispersal restricted to neighborhood
 Helpers become breeders by inheriting natal
  territory or dispersing to neighboring one
 Make up for years of lost reproduction by
  high levels of reproduction once acquire
  good territory
Why Help?
 Kin selection: benefit by perpetuating own
  genes through relatives
    Only count extra reproduction of related
     breeders due to help
 Direct benefits
    Present but small compared to kin
     selection benefit in many cases
    Larger in cases where help provided to
     non-relatives
Direct Benefits of Helping
 Inherit mates (rare: Pied Kingfisher)
 Acquire territory through budding
  (common: Florida Scrub Jay)
 Recruit allies and future helpers (common:
  Acorn Woodpeckers)
 Caring for own young if helpers participate
  in reproduction (occurs in complex systems:
  Acorn Woodpecker)
 Pay-to-stay (a theoretical possibility)
Ostrich system:
dominant pair
cares for entire
brood; winner
takes all when
broods meet
Ani system: females toss eggs until begin to
lay; contribution depends on dominance
because females lay in reverse rank order;
subordinates lay a late egg to increase success
Florida Scrub Jay Example
 Illustrates acquisition of breeding positions
  by helpers
 Illustrates budding
 Illustrates importance of relatedness (kin
  selection) to helping
 Mate choice evident in effects of age and
  dominance on pairing
 Illustrates social complexity
Acorn Woodpecker Example
 Illustrate alliances among brothers to
  acquire breeding position (power struggle)
 Dominance among allies determines
  breeding status, helpers attempt participate
  reproduction, move up when allies die
 Birds related to opposite-sex breeders are
  strictly helpers (inbreeding avoidance)
 Females behave similarly: form alliances,
  subordinates attempt reproduce (lay, toss
  eggs), avoid mating with relatives
White-fronted Bee-eater Example
 Clan defends feeding territory, breeds in
  pairs in colonies with other clans
 Birds whose nest fails or do not attempt
  nesting help at other clan nests
 Birds help relatives, those who helped them
 Will split with mate temporarily to help
    Find mate outside clan (avoid inbreeding)

								
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