For animal species that form social groups, living together can have a strong effect on individuals’ chances of survival and reproduction, and ultimately on how population sizes change over time. New work, led by Dr. Andrew Bateman of the Raincoast Lab, and involving a team of researchers from Canada, the UK, and Switzerland, combines theory and data to shed light on how these considerations play out for meerkats.
While meerkats, a species of mongoose native to southern Africa, may seem far removed from Raincoast’s work in BC, they share many characteristics with a much more familiar species: killer whales. Both killer whales and meerkats are social mammals, living and breeding in family groups. Both species are matrilineal, with females usually reproducing in their group of birth. Both species share food: mostly invertebrates, in the case of meerkats, and Chinook salmon, in the case of resident killer whales. Both species’ survival and reproductive success are affected by other group members.
Whether the effects of group living are positive or negative, an individual’s prospects tend to be limited within its birth group, and eventually many individuals disperse in an effort to establish new breeding groups. As a result, understanding changes in population size for social species – several of which, such as southern resident killer whales, are endangered – requires understanding what goes on within groups and how individuals fare when they strike out on their own.
The work led by Dr. Bateman presents new tools for analysis, aimed at improving our understanding of fluctuations in the population sizes of social species. In the context of meerkats, past work had theorised that larger groups might produce more descendants each year than smaller groups (a phenomenon called the “Allee effect”). This new work indicates the opposite. Interestingly, dominant breeding females in larger meerkat groups do appear to produce each year more daughters that go on to breed. The new techniques combine such group-level patterns to paint a picture of a population as a whole. For meerkats, it appears that population growth is highest when individuals form groups of intermediate size, despite small groups producing more descendants over the short term. The results help to bridge the gap between past theory concerning Allee effects and the benefit that group living must provide, for it to exist at all.
The techniques may prove useful for understanding trends in resident killer whale populations. While northern residents have increased in number to more than 250 over the last 40 years, the southern resident population has stagnated, now numbering below 80 individuals. Dr. Bateman’s ongoing work will analyse patterns of northern resident killer whale births and deaths, within the context of social groups. Taking the same approach used with meerkats, insights gained will be able to shed light on whether different social patterns in northern and southern resident killer whales might contribute to their different population trends.
Bateman, A. W., Ozgul, A., Krkošek, M., & Clutton-brock, T. H. 2018. Matrix models of hierarchical demography: Linking group- and population-level dynamics in cooperative breeders. American Naturalist