APS209 Animal Behaviour
Cooperative Breeding
Aims
1. To present the
two-stage ecological constraints model for the evolution of cooperative
breeding
2. To explain the role of ecological
and demographic factors in constraining reproduction
3. To examine the potential direct and
indirect sources of inclusive fitness for helpers
Objectives
1. To understand the
principles underlying the ecological constraints hypothesis
2. To understand how
predictions of the ecological constraints hypothesis have been tested
3. To understand the
alternative routes to fitness for helpers
Cooperative breeding - Some individuals forego personal
reproduction and spend all or part of their lives helping others to breed. The
great majority of cooperative systems are kin-based and these breeding systems
are therefore likely to provide examples of kin-selected behaviour. The social
organisation of cooperative breeders varies widely, with a continuum of social
organisation encompassing: 'helpers-at-the-nest' where breeding pairs are aided by one or more
helpers, usually offspring of previous
broods, and 'plural breeders' where communal nests have several breeders of one
or both sexes.
Evolution of cooperative breeding - The ecological constraints
hypothesis (aka the habitat saturation hypothesis) envisages the evolution of
cooperative breeding as a 2-stage process:
Stage 1. Ecological factors (no
suitable breeding territories available) and/or demographic factors (no
breeding partners available) constrain independent breeding causing grown young
to delay dispersal and 'stay at home' on their natal territory. Observational
evidence provides some support, but the best evidence comes from removal
experiments: e.g. superb fairy wren Pruett-Jones & Lewis 1990, Nature
348:541-542). However, reproductive constraints are widespread, comparative
studies have been inconclusive, and other factors may be important, e.g.
phylogeny.
Stage 2. Fitness benefits of helping
exceed those of not helping, so young who have delayed dispersal help relatives
to raise later broods.
What are the fitness benefits of
helping?
(a)
Direct fitness
- fitness component resulting from personal reproduction.
- increased survival of helpers through
group benefits – ‘group augmentation’, e.g. reduce predation risks, share
resources
- increased probability of future
breeding, e.g. territory or mate acquisition/ inheritance
- increased experience of parental care
('skills' hypothesis)
- direct reproduction
(b) Indirect fitness - fitness
component from increased production of non-descendant kin.
- increased reproductive success of
relatives (genetic benefits through raising siblings which share 50% of genes)
- increased survival of related breeders
through reduced reproductive costs
The
relative importance of indirect or direct fitness benefits in the evolution of
helping behaviour is still debated
References
See Chapter 13 in Alcock’s Animal Behavior (2009). See also
more detailed accounts in Cockburn A (1998) Evolution of helping behaviour in
cooperatively breeding birds, Annual Review of Ecology & Systematics 29:
141-177. Emlen S.T. (1991). Evolution of cooperative breeding in birds and
mammals; in J.R. Krebs & N.B. Davies (eds), Behavioural Ecology, 3rd
edition.
Comments
Post a Comment