Predator-prey dynamics between mountain lions and mule deer: Effects on distribution, population regulation, habitat selection, and prey selection

Abstract

Mountain lions (Puma concolor) and mule deer ( Odocoileus hemionus), which share a winter range in the Eastern Sierra Nevada in Round Valley, California, USA, were fitted with radio-telemetry collars and tracked to determine their movements and cause of mortality. The mountain lion population of Round Valley refers to a group of individuals that lived in close proximity to one another, essentially isolated from similar groups during the winter, and fed on the migratory herd of mule deer that overwinter in Round Valley. Mountain lions migrated seasonally with the deer population, and two distinct patterns for coping with variability in abundance of prey were observed. The unique migratory behavior identified for the mountain lions in this study indicates a more flexible social system for mountain lions than previously described. Tests of whether the presence of another mountain lion affected where individuals to killed deer indicated that social interactions had no effect and that social behavior was not regulating the population of mountain lions via spatial partitioning of prey. Examination of habitat selection by mule deer and mountain lions revealed that mule deer selected habitat at higher elevations (P < 0.001) with more bitterbrush ( Purshia tridentata) and less rabbitbrush (Chrysothamnus nauseosum ) than random locations. Mountain lions killed deer in relatively open areas with more desert peach (Prunus andersonii) than locations in which deer foraged. Those results indicated that deer were not confronted with a tradeoff in terms of habitat selection on the winter range because habitat with the best forage (e.g. bitterbrush), also provided the least predation risk. Comparisons of mule deer killed by mountain lions, coyotes, and automobiles indicated that mountain lions selected young (<1 year old) deer and both predators selected older age classes among adults. Furthermore, there was no selection by either predator for animals in poor condition. Among mountain lions in different social categories, female mountain lions with kittens selected more young deer than did other social categories. This study indicated that ambush predators (mountain lions) may be as selective for prey as coursing predators (coyotes) and that lactation in mountain lions may play a role in determining prey selection. ion.