Factors Influencing Population Performance and Tradeoffs Associated with Reproduction of a Large Herbivore

Abstract

Large herbivores are commonly reliant on sources of nutrition to maximize survival and reproductive output and thus, fitness. Moreover, large herbivores exhibit slow-paced life histories where, throughout a long lifespan, those nutritional reserves are allocated to adult survival and reproduction. Because survival of adults is relatively constant, juvenile survival is more variable and responsive to changes in resource availability. Therefore, juvenile survival and recruitment typically influence population performance the most. Maternal females must maintain a balance of nutritional plane and allocating resources to reproduction resulting in potential tradeoffs when choosing to invest in current or future reproductive effort. With changing climate forecasted to strongly affect arid environments via drought, I focused on testing how environmental factors influence a mule deer (Odocoileus hemionus) population in an arid region. I investigated variables influencing juvenile survival and potential tradeoffs of habitat use that maternal females make throughout various stages of the reproductive cycle. I used 3 study areas on the Mojave National Preserve, California, USA to characterize the heterogeneous landscape features exhibited in the area. Adult and neonatal mule deer were captured and equipped with GPS radio collars from 2013 to 2016. I found that juvenile survival was highly influenced by forage availability to maternal adults after precipitation events that occurred between January and April (mid-pregnancy). Additionally, I found that juveniles born at a larger structural size had a higher probability of survival to recruitment. Lastly, I identified a tradeoff in resource selection by maternal females between the provisioning young and post-juvenile mortality periods of the reproductive cycle. Females exhibited anti-predator behavior by choosing more rugged terrain while provisioning young, thereby investing in current reproductive output. Post-juvenile mortality, females increased selection of higher forage quality thus investing in future reproduction.