Vital rates of large herbivores normally respond to increased resource limitation by following a progressive sequence of effects on life‐history characteristics from survival of young, age at first reproduction, reproduction of adults, to adult survival. Expected changes in life‐history characteristics, however, should operate through changes in nutritional condition, which is the integrator of nutritional intake and demands represented primarily by the deposition and catabolism of body fat. Elucidating seasonal patterns of nutritional condition and its relative influence on individual and population performance should improve our understanding of life‐history strategies and population regulation of ungulates, provide insight into the capacity of available habitat to support population growth, and allow assessment of the underlying consequences of mortality on population dynamics. We acquired longitudinal data on individual female mule deer (Odocoileus hemionus), and linked those data with environmental and population characteristics. Our goal was to provide a nutritional basis for understanding life‐history strategies of these large mammals, and to aid in the conservation and management of large herbivores in general. We studied a migratory population of mule deer that overwintered in Round Valley on the east side of the Sierra Nevada, California, USA, and was subject to a highly variable climate and predation from a suite of large carnivores. We intensively monitored nutritional and life‐history characteristics of this population during 1997–2009 as it recovered from a population crash, which occurred during 1985–1991. Deer in Round Valley migrated to high‐elevation summer ranges on both sides of the crest of the Sierra Nevada (Sierra crest), where a rain shadow resulted in a mesic and more forested range on the west side compared with xeric conditions east of the Sierra crest. Average survival of neonatal mule deer to 140 days of age during 2006–2008 was 0.33 (SE = 0.091), but was lower for neonates on the west side (0.13, SE = 0.092) compared with those on the east side (0.44, SE = 0.11) of the Sierra crest. Birth mass and nutritional condition of mothers had a positive effect on survival of young; however, those effects were evident only for neonates born east of the crest where predation pressure was less intense compared with the west side. Black bear (Ursus americanus) predation was the main cause of mortality for west‐side young (mortality rate = 0.63, SE = 0.97) compared with canid and felid predation for east‐side young (0.29, SE = 0.076). Mean autumn recruitment of young during 1997–2008 was lower for females on the west side (0.42, SE = 0.037) than for females on the east side (0.70, SE = 0.041) of the crest, and was affected positively by March ingesta‐free body fat (IFBFat) of individual females. At the level of the population, ratios of young‐to‐adult females (1991–2009) were highly variable and strongly related to March IFBFat of adult females during the current and preceding year. Repro...

Abstract. Phenological events of plants and animals are sensitive to climatic processes. Migration is a life-history event exhibited by most large herbivores living in seasonal environments, and is thought to occur in response to dynamics of forage and weather. Decisions regarding when to migrate, however, may be affected by differences in life-history characteristics of individuals. Long-term and intensive study of a population of mule deer (Odocoileus hemionus) in the Sierra Nevada, California, USA, allowed us to document patterns of migration during 11 years that encompassed a wide array of environmental conditions. We used two new techniques to properly account for interval-censored data and disentangle effects of broad-scale climate, local weather patterns, and plant phenology on seasonal patterns of migration, while incorporating effects of individual life-history characteristics. Timing of autumn migration varied substantially among individual deer, but was associated with the severity of winter weather, and in particular, snow depth and cold temperatures. Migratory responses to winter weather, however, were affected by age, nutritional condition, and summer residency of individual females. Old females and those in good nutritional condition risked encountering severe weather by delaying autumn migration, and were thus risk-prone with respect to the potential loss of foraging opportunities in deep snow compared with young females and those in poor nutritional condition. Females that summered on the west side of the crest of the Sierra Nevada delayed autumn migration relative to east-side females, which supports the influence of the local environment on timing of migration. In contrast, timing of spring migration was unrelated to individual life-history characteristics, was nearly twice as synchronous as autumn migration, differed among years, was related to the southern oscillation index, and was influenced by absolute snow depth and advancing phenology of plants. Plasticity in timing of migration in response to climatic conditions and plant phenology may be an adaptive behavioral strategy, which should reduce the detrimental effects of trophic mismatches between resources and other life-history events of large herbivores. Failure to consider effects of nutrition and other life-history traits may cloud interpretation of phenological patterns of mammals and conceal relationships associated with climate change.

Summary1. Body reserves of numerous taxa follow seasonal rhythms that are a function of temporal patterns in food availability and life-history events; however, tests of the theory underlying the allocation of somatic reserves for long-lived organisms are rare, especially for free-ranging mammals. We evaluated the hypothesis that allocation of somatic reserves to survival (i.e., metabolic processes) and reproduction should be sensitive to current nutritional state relative to seasonal thresholds in those reserves. 2. Our goal was to reveal the linkages between nutrition and life-history traits to understand how long-lived, iteroparous organisms balance the allocation of somatic reserves to reproduction, while retaining reserves as insurance for survival in unpredictable environments. Our evaluation was based on seasonal dynamics in fat (measured as ingesta-free body fat; IFBFat) and protein reserves (measured as ingesta-free, fat-free body mass; IFFFBMass) of 136 female mule deer (Odocoileus hemionus) over 8 years. 3. Although mean changes in fat and protein reserves were positive over summer and negative over winter, accretion and catabolism of those reserves was not consistent among individuals. Over winter, both lipid and protein stores available in autumn were catabolized in proportion to their availability above a post-winter threshold (5Á8% IFBFat, 33 kg IFFFBMass); however, lean body tissue was spared at the expense of lipid reserves. 4. Female deer mostly synthesized lean body tissue over summer and committed post-winter fat reserves to reproduction relative to their availability above an autumn threshold (>8Á6% IFBFat), which was lowered by 2Á8 percentage points (pp) for each additional young recruited. Mothers reduced their autumn fat threshold to secure current reproductive investment and, thereby, endured a cost of reproduction at the expense of fat accumulation. 5. Allocation of somatic reserves occurred in a risk-sensitive framework; females allocated reserves relative to their availability above seasonal thresholds. In contrast to current notions of summer accretion and winter catabolism of body reserves, some individuals deposited reserves over winter and catabolized reserves over summer, mainly because regulation of individual condition was state-dependent. Consequently, behaviour and life-history strategies may be as much a function of nutritional contributions of the previous season as of the current one.