Density-independent predation affects migrants and residents equally in a declining partially migratory elk population

Migration is expected to benefit individuals through exposure to higher quality forage and reducing predation rates more than non-migratory conspecifics. Previous studies of partially migratory ungulates (with migrant and resident individuals) have focused on bottom–up factors regulating resident and migrant segments, yet differential predation between strategies could also be a density-dependent regulatory mechanism. Our study tested for density-dependence in mortality, as well as mechanisms of bottom–up or top–down regulation in the resident and migrant portions of the partially migratory Ya Ha Tinda elk population. We tested for density dependence in adult female and juvenile survival rates, and then discriminated between predator- and food-regulation hypotheses by testing for density-dependence amongst mortality causes for adult female elk. Notably, the population declined almost 70% from near previously published estimates of carrying capacity over 10 years, providing ideal conditi...