Evolution of social organization: phylogenetic analyses of ecology and sexual selection in weavers

Crook published a landmark study on the
social organization of weavers (or weaverbirds, family
Ploceidae) that contributed to the emergence of sociobiology, behavioral
ecology, and phylogenetic comparative methods. By comparing ecology,
spatial distribution, and mating systems, Crook suggested that the spatial
distribution of food resources and breeding habitats influence weaver
aggregation, both during the breeding season (colonial vs solitary
breeding) and non-breeding season (flocking vs solitary foraging), and
the food resources distribution and breeding aggregation of
individuals in turn impact mating systems and sexual selection.
Although Crook’s study stimulated much follow-up research, his conclusions
have not been scrutinized using phylogenetically
controlled analyses. We revisited Crook’s hypotheses using modern
phylogenetic comparative methods and an extended dataset of 107 weaver
species. We showed that both diet
and habitat type are associated with spatial
distribution and the latter predicts mating
system, consistent with Crook’s propositions. The best
supported phylogenetic path model (PPA) also supported Crook’s arguments,
and uncovered a direct relationship between non-breeding distribution and
mating system. Taken together, our phylogenetically corrected
analyses confirm Crook’s conjectures on the roles of ecology in social
organizations of weavers; however, our analyses also uncovered an
association between non-breeding distributions and mating systems, which
was not envisaged by Crook.