- Helpers at the nest
Helpers at the nest is a term used in
behavioural ecologyand evolutionary biologyto describe a social structure in which juveniles, of one or both sexes, remain in association with their parents and help them in raising subsequent broods or litters, instead of dispersing and beginning to reproduce themselves. This phenomenon was first studied in birds, and is found, for example, in the Common Moorhen, also species of woodpeckers-(example Acorn Woodpecker), but it is now known in animals of many different groups. It is a simple form of co-operative breeding.
Three explanations for the occurrence of helpers at the nest have been put forward; they are not mutually exclusive, and in any particular species an investigation of the exact benefits and costs will be needed to see what combination of these factors may have driven the evolution of helping. [Dickinson, JL & BJ Hatchwell (2004) "Fitness consequences of helping" In Ecology and evolution of cooperative breeding in birds By Walter D. Koenig, Janis L. Dickinson. Cambridge University Press. ISBN 9780521530996]
*Advantage to the helpers, who may be protected from predation, or gain skills that they will need when they subsequently reproduce, as a result of staying in the parental nest.
Kin selection: since subsequent litters or broods from the same parents will be full siblings to the helpers, they are as closely related genetically as their own offspring would be. Helping their parents is therefore as productive for the juveniles as reproducing themselves would be, and if their parents are better able to reproduce, the balance of advantage may be greater.
*Delayed advantage to the helpers, in particular because they stand to inherit their parents' territory; this explanation is particularly compelling if suitable territories are in short supply, but requires specific quantitative conditions to be met, favouring a stable queue of potential heirs. [Wiley, R. H., & Rabenold, K. N. (1984). The evolution of cooperative breeding by delayed reciprocity and queuing for favorable social positions. Evolution 38:609-621]
Although it is frequently assumed that helpers are non-breeders, molecular evidence suggests that this may happen and the term "secondary helper" is sometimes used in this case to indicate helpers that mate with or are not related offspring of the pair being assisted. The term "primary helper" being used for the commoner case of the helper being offspring of the pair and not involved in mating. [Ligon, JD & DB Burt (2004) "Evolutionary origins" In Ecology and evolution of cooperative breeding in birds By Walter D. Koenig, Janis L. Dickinson. Cambridge University Press. ISBN 9780521530996] Juveniles living in association with their parents cannot automatically be regarded as helpers; it is necessary to demonstrate that the reproductive success of their parents is increased by their presence (in the
Percula Clownfish, for example, it is notFact|date=August 2008). However the delayed advantage explanation for the juveniles' association with their parents can still work in the absence of effective helping, whereas the kin selection explanation cannot.
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