Ecological bases of philopatry and cooperation in Ethiopian wolves
Marino J., Sillero-Zubiri C., Johnson PJ., Macdonald DW.
Ecological reasons for philopatry and cooperation are frequently invoked when kin selection is an insufficient explanation. The Ethiopian wolf (Canis simensis) is a specialised rodent hunter that forms family groups with cooperative breeding but also lives as monogamous pairs in suboptimal areas. Given the apparent absence of fitness gains to helpers from cooperative breeding, we set out to explore the benefits accrued by communal territorial defence measured as the acquisition and retention of habitats with more and most preferred rodent prey. Pairs defended relatively large territories to encompass critical amounts of key habitats within a matrix poor in rodents. Groups in optimal areas had relatively small territories and were expansionist, such that wolves in larger packs benefited per capita from increased good-quality foraging habitat. The fitness benefits of philopatry became evident after a rabies epizootic, when philopatry and expansionism prevailed in under-saturated conditions, until large groups split or provided dispersers that established locally. This study shows that high concentrations of prey can shift the balance of costs and benefits towards group living and cooperation in long-lived territorial carnivores, in so far as this dictates immediate rewards accrued from a given increment in territory size, namely greater foraging area per animal, leading to group enlargement and eventual inheritance of breeding space. © 2012 Springer-Verlag.