Groups and Mortality: Their Effects on Cooperative Behavior and Population Growth in a Social Carnivore

PhD Dissertation, David Ausband (2011-2015)

Cooperative breeding refers to the cooperative care of related, or even unrelated, young. Helpers can increase the survival or reproduction of the breeders in the group which increases helper fitness indirectly. We have a poor understanding of how mortality, particularly human harvest, affects cooperative breeders. Given their complex social structures, territorial defense that relies on group size, and persistent harvest regimes, gray wolves (Canis lupus) are an ideal species for studying the ecological relationships between mortality, group size and composition, and population growth in a cooperative breeder. This research comprised four parts: 

  • How does group size affect vital rates of individuals and population growth? Furthermore, how do density and immigration of individuals into groups influence the effect of group size on population growth? I used historic data from Idaho and Yellowstone National Park as well as the scientific literature to populate a metapopulation model and explore the simultaneous influences of group size, density, and immigration on population growth.
  • What is the effect of harvest on recruitment in a cooperative breeder? Are there both direct (i.e., mortality from harvest) and indirect effects (i.e., reduced survival because of breeder turnover, reduced group size) of harvest on recruitment? I used a natural experiment and genetically sampling to assess the influence of harvest on pup recruitment. I compared genotypes of sampled pups to harvested pups to determine whether harvest had both direct and indirect effects on recruitment.
  • How does mortality, in the form of persistent public harvest, affect group size, composition, and ultimately recruitment in a cooperative breeder? I genetically sampled wolves across a broad range of human-caused mortality in western North America. I used the resulting data to assess the influence of harvest on group size, group composition, breeder turnover, and ultimately recruitment.
  • How do individual, group, and environmental factors influence helping behavior in a cooperative breeder? I used location data from satellite-collared wolves in western North America to explore the influences of sex, individual status within a group, group size, and predation risk on pup-guarding behavior.