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showing how greenbeard loci can perturb the outcomes expected under pedigree relatedness alone.

After the social insects, cooperative birds and mammals have attracted the most attention. Many bird species have helpers at the nest, usually offspring from previous broods who have remained at their natal site (Cockburn, 2006). Kinship is important here too. Helping systems usually evolve from monogamous ones, and discrimination evolves in systems that show variation in relatedness (Cornwallis et al., 2010). But the story is more complicated, for two reasons. First, although, some helpers gain kin-selected benefits through helping close kin, others may gain direct benefits. Compared with the social insects, more research on birds has addressed the particular benefits of remaining at home and on the ecological constraints that may limit independent breeding. Variance in reproductive success has played a role in these discussions, but in Chapter 4, Dustin Rubenstein moves it to a more central position. He suggests that cooperative breeders may be bet hedgers, gaining advantage from a more uniform reproductive output in cooperative groups. Rubenstein draws on many years of his field data on starlings in Africa, where there is much variation in both time and space, and he finds support for several predictions of this hypothesis.



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