The effect of group size on reproduction in cooperatively breeding gray wolves depends on density

• Published in: Animal conservation 2021-12, Vol.24 (6), p.994-1000
• Main Authors: Ausband, D. E., Mitchell, M. S.
• Format: Article
• Language: English
• Subjects: Animal reproduction; Breeding; Breeding success; Canis lupus; Communal breeding; competition; cooperative breeding; gray wolves; Group size; Litter size; Litters (births); National parks; Parturition; Polygamy; Population density; Puppies; radio telemetry; Reproduction; Survival; Wolves; Yellowstone National Park
• ISSN: 1367-9430; 1469-1795
• DOI: 10.1111/acv.12701

In cooperatively breeding species, large group size is often positively related to reproductive success and group persistence. We have a poor understanding, however, of how group sizes within a population affect reproduction particularly as density varies. We hypothesized that at low densities, wolves in both small and large groups would have similar reproductive rates. At high densities, however, wolves in small groups would have lower reproductive rates compared to those in large groups. Using empirical data from radio‐collared wolves in Idaho and Yellowstone National Park, WY, USA (1996–2012), we compared reproductive rates (i.e. proportion reproducing, litter size, pup survival) among small and large groups of wolves as density fluctuated within the populations. Reproductive rates were generally lower for individuals in small groups compared to those in large groups, particularly as density increased. Pup survival, however, was slightly higher for wolves in small groups compared to large groups except at very high densities. Polygamy increased with density regardless of group size, suggesting a polygamy threshold for wolves. Large group size resulted in less parturition failure, more breeding females per group, larger litter sizes, and ultimately more pups recruited per group. Large group size appears advantageous for several, but not all, aspects of reproduction particularly when population density is high. In cooperatively breeding species, large group size is often positively related to reproductive success and group persistence. We have a poor understanding, however, of how group sizes within a population affect reproduction particularly as density varies. We found that group size has a marked effect on reproduction in gray wolves, but only at above average population density. At such densities, small groups had smaller litter sizes and more parturition failure. Large group size therefore appears advantageous for several, but not all, aspects of reproduction particularly when population density is high.