Cascading effects of habitat on maternal condition and life-history characteristics of neonatal mule deer

Abstract

The condition of maternal female mammals greatly influences life-history characteristics of their young, but interactions between habitat and maternal condition and their combined influences on birth characteristics and survival of neonates are less well understood, especially in free-ranging populations. We monitored survival of neonatal mule deer (Odocoileus hemionus) inhabiting 2 contrasting ecotypes in Idaho: aspen woodlands (Populus tremuloides) in southeast Idaho (Caribou Mountains) and mixed-conifer grasslands (lodge-pole pine, Pinus contorta; Douglas-fir, Pseudotsuga menziesii) in central Idaho (Salmon River Mountains). We expected the Caribou Mountains to offer better forage and greater concealment cover than the Salmon River Mountains. We tested for an array of maternal influences on neonatal deer inhabiting those dissimilar ecosystems. We monitored 96 neonates from date of capture to 5 months of age (n = 44 in the Caribou Mountains, 2010; n = 52 in the Salmon River Mountains, 2011). Survival and birth characteristics consistently diverged between study areas, whereas timing of births was similar. Female deer from the Salmon River Mountains exhibited poor maternal condition and small litter sizes compared with females from the Caribou Mountains. Young from the Salmon River Mountains exhibited lower rates of growth, occupied bedding sites with less concealment cover, and subsequently experienced lower survival from birth to 5 months of age, compared with neonates from the Caribou Mountains. Cause of deaths for young mule deer on both study sites was mostly from predation. Our findings emphasize the potential role that habitat plays in the population dynamics of mule deer via cascading effects on physical condition, reproduction, and survival. Changes in habitat, potentially associated with changing climate, fire regimes, and land uses, probably have contributed to the widespread declines in populations of mule deer during recent decades.