Abstract
Behavior represents one of the primary mechanisms by which animals overcome environmental constraints on survival and reproductive success. Females in particular often exhibit plastic behavioral strategies for coping with the different nutritional demands and degrees of susceptibility to predation imposed by gestation, parturition and lactation. Previous studies have demonstrated a link between space-use behavior and important correlates of fitness and have highlighted the value of mechanistic nutritional approaches for understanding the fitness consequences of behavior. However, the mechanisms by which individual responses to variation in the nutritional landscape scale up to influence population performance remain unclear. We quantified relationships among the nutritional landscape (i.e., spatiotemporal variation in forage biomass), dam behavior, and neonatal survival in bighorn sheep (Ovis canadensis). We conducted intensive vegetation sampling and used generalized additive modeling to map the nutritional landscapes available to sheep during summer (May–September) in three population ranges in Idaho: Owyhee River, East Fork of the Salmon River, and Lost River Range. We used GPS collars and lamb surveys to monitor ewe behavior and lamb survival in each study area, and used known-fate survival modeling to test for behaviorally mediated effects of nutrition on lamb survival. Relationships among the nutritional landscape, ewe behavior, and lamb survival were context dependent and varied among study sites. In the Lost River, where lamb survival was highest (83.9%), probability of lamb survival increased when ewes traded access to rugged terrain for access to higher forage biomass. We observed the opposite pattern in the East Fork (i.e., probability of lamb survival increased when ewes traded access to forage for access to rugged terrain), however, and in the Owyhee no metric of ewe behavior was significantly related to the probability of lamb survival. We also observed a strong, positive relationship between spring nutritional condition and probability of lamb survival across study sites. Our research helps to establish mechanistic links among habitat heterogeneity, individual space-use behavior, and reproductive success in bighorn sheep, and underscores the fundamental importance of nutrition as a driver of ungulate performance. Continuing to improve our understanding of such relationships will provide valuable insights for managers and conservationists, and will aid in accurately parameterizing models of population dynamics. Maximizing the usefulness of such models requires knowledge of the mechanisms that underpin variation in population demographics, and nutritional-ecological approaches like those used in our study shed important light on those mechanisms.