Vernon C. Bleich

Sexual Segregation in Ungulates: New Directions for Research

We reviewed the literature on sexual segregation in polygynous ungulates in an effort to clarify terms and concepts, summarize recent information that supports or discredits three broadly defined hypotheses, and suggest directions for future research that should help resolve when and why the sexes segregate in these large mammals. The hypotheses discussed include those based on intersexual differences in energetics and security (reproductive-strategy hypothesis), body size dimorphism and dietary requirements (sexual dimorphism-body size hypothesis), and social mechanisms (social-factors hypothesis). These hypotheses represent ecological, physiological, and social perspectives and are not mutually exclusive. Most evidence reviewed supported the reproductive-strategy hypothesis. Less support was available for either the sexual dimorphism-body size hypothesis or the social-factors hypothesis. Nonetheless, most available evidence is provided by field studies that contend with many confounding variables. We suggest several areas of future study that may serve as critical tests and are likely to be productive in resolving why sexual segregation occurs in polygynous ungulates.

HABITAT SELECTION BY MULE DEER: FORAGE BENEFITS OR RISK OF PREDATION?

Abstract Risk of predation may affect individuals in prey populations by limiting their use of high-quality habitat. Predation risk, however, cannot be implicated as a factor in habitat selection by prey without data comparing quality of selected and avoided habitats, along with the predation risk associated with those habitats. If forage benefits and predation risk are not positively correlated among habitat types, then predation risk may have little influence on the habitat selected by prey. We evaluated habitat selection by mountain lions (Puma concolor) and mule deer (Odocoileus hemionus) in the eastern Sierra Nevada, California, USA, from 1994 to 1997, to determine how forage benefit or risk of predation by mountain lions affects habitat selection by mule deer. Mountain lions were the primary predator of mule deer in our study area. Stands of bitterbrush (Purshia tridentata) in the Great Basin provided more cover for mule deer than surrounding patches of rabbitbrush (Chrysothamnus nauseosum) or desert peach (Prunus andersonii). Bitterbrush also was important forage for mule deer during winter. We hypothesized that mountain lions would be more successful at stalking and killing mule deer in habitats with more concealment cover than in habitats with less cover, and therefore mule deer would choose between foraging on bitterbush and avoiding predation by mountain lions. We collected data on habitat characteristics in 3 types of locations: random locations (n = 180), deer foraging locations (n = 179), and locations where mountain lions killed deer (n = 41). Mule deer selected habitat at greater elevations (P < 0.001) with more bitterbrush (P < 0.001) and less rabbitbrush (P = 0.033) when compared with random locations. Logistic regression indicated that mountain lions killed deer in relatively open areas with more desert peach (P < 0.001) than at locations in which deer foraged. Therefore, deer were not confronted with a trade-off when selecting habitat on winter range, and they minimized the ratio of predation risk to forage benefit by selecting habitat with more bitterbrush. Changes in diet among seasons, which occur for herds of migratory deer, lead to individuals experiencing changing predation risk to forage benefit ratios throughout the year. Hence, migratory populations of mule deer likely adopt different strategies of habitat selection among seasons.

Mountain Sheep and Coyotes: Patterns of Predator Evasion in a Mountain Ungulate

I used retrospective analyses to investigate relationships among terrain type, reactions of prey, and age and sex of prey and outcomes of encounters between mountain sheep ( Ovis canadensis ) and coyotes ( Canis latrans ). Adult females fled from coyotes more often when in open terrain and young always fled regardless of type of terrain. Young were less likely to survive encounters with coyotes than were adults, and no adult females were killed by coyotes. When types of terrain were pooled, females were more apt to flee than were males, but no difference existed in proportion of females and young that fled. When terrain type and sex of adults were pooled, no difference in survival existed between adults that fled and those that did not. When coyotes were encountered in open terrain, female mountain sheep fled more frequently than did female mule deer ( Odocoileus hemionus ). Ungulates less dependent on terrain for predator evasion than are mountain sheep may employ a more plastic strategy than artiodactyls inhabiting precipitous terrain.

Timing of seasonal migration in mule deer: effects of climate, plant phenology, and life‐history characteristics

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.

Landscape genetics of California mule deer (Odocoileus hemionus): the roles of ecological and historical factors in generating differentiation

Landscape genetics is an emerging discipline that utilizes environmental and historical data to understand geographic patterns of genetic diversity. Niche modelling has added a new dimension to such efforts by allowing species–environmental associations to be projected into the past so that hypotheses about historical vicariance can be generated and tested independently with genetic data. However, previous approaches have primarily utilized DNA sequence data to test inferences about historical isolation and may have missed very recent episodes of environmentally mediated divergence. We type 15 microsatellite loci in California mule deer and identify five genetic groupings through a Structure analysis that are also well predicted by environmental data. We project the niches of these five deer ecotypes to the last glacial maximum (LGM) and show they overlap to a much greater extent than today, suggesting that vicariance associated with the LGM cannot explain the present‐day genetic patterns. Further, we analyse mitochondrial DNA (mtDNA) sequence trees to search for evidence of historical vicariance and find only two well‐supported clades. A coalescence‐based analysis of mtDNA data shows that the genetic divergence of the mule deer genetic clusters in California is recent and appears to be mediated by ecological factors. The importance of environmental factors in explaining the genetic diversity of California mule deer is unexpected given that they are highly mobile species and have a broad habitat distribution. Geographic differences in the timing of reproduction and peak vegetation as well as habitat choice reflecting natal origin may explain the persistence of genetic subdivision.

SELECTION OF MULE DEER BY MOUNTAIN LIONS AND COYOTES: EFFECTS OF HUNTING STYLE, BODY SIZE, AND REPRODUCTIVE STATUS

Abstract Predation on mule deer (Odocoileus hemionus) by mountain lions (Puma concolor) and coyotes (Canis latrans) was examined to test effects of hunting style and body size, and for mountain lions reproductive status, on selection of prey. Mountain lions, which hunt by stalking, selected ≤1-year-old mule deer as prey. Body condition of mule deer did not affect prey selection by coyotes or mountain lions, and both predators preyed upon females and older adult deer more often than expected based on the percentage of these groups in the population. Female mountain lions selected female deer, but male mountain lions did not. Female mountain lions without offspring, however, did not differ from male mountain lions in prey selection. Coyotes did not select for young deer. Female mountain lions with kittens were selective for young deer in late summer.

Genetics and the conservation of mountain sheep ovis canadensis nelsoni

Abstract Recent hypotheses have proposed that mountain sheep were suffering from inbreeding depression. Here we present an alternative hypothesis. We have examined sheep migration abilities, the distances required for migration, and sheep mating patterns to challenge the inbreeding hypothesis and conclude that the sound application of more traditional wildlife management techniques will likely preclude short- and long-term genetic problems.

Recruitment Dynamics in a Southern California Mountain Sheep Population

Lamb: ewe ratio data spanning the years 1953-82 for mountain sheep (Ovis canadensis) in the Santa Rosa Mountains of southern California were analyzed by multiple regression to investigate hypothesized controlling factors. Precipitation during November, January, and February as independent variables each showed a significant positive influence on recruitment rate, in accord with expectations for this desert environment. Between 1962 and 1976, an unidentified 4th factor (probably rising population density) caused a slow decline in recruitment ratio. This ratio plummeted in 1977 and averaged about 25% of the ratio predicted from precipitation alone for 1977-82, a period coincident with a suspected disease epizootic. A similar period of depressed lamb recruitment was found for the 1953-61 period, suggesting the possibility of a recurrent phenomenon. Data needs and various hypotheses concerning factors potentially underlying the observed and future population dynamics are discussed. J. WILDL. MANAGE. 51(1):86-98 Multiple factors potentially underlie the dynamics of wild ungulate populations. The partitioning of the relative magnitude of the influence of different factors in different species and ecological settings is one of the primary objectives of research related to wildlife management. This understanding is crucial if management activities are to be focussed on factors whose manipulation will produce a population response (Leopold 1933). California currently has mountain sheep populations in approximately 50 mountain ranges, mostly in desert regions (Weaver 1975, 1982). Adequate data existing for a small number of these populations indicate recent dynamics varying from rapid population increases to disappearance (DeForge et al. 1981; Weaver 1982; Bleich 1983; Holl and Bleich 1983; Wehausen 1983a,b). Weaver (1975) considered the mountain sheep population of the Santa Rosa Mountains to be one of the 2 largest populations in California. Recently it has come to the forefront as a major population suggested to be declining rapidly due to excessive lamb mortality that began in 1977 (DeForge and Scott 1982). Blood samples from mountain sheep in this range have yielded titers to 4 viral diseases: parainfluenza-3 (PI-3), bluetongue (BT), epizootic hemorrhagic disease (EHD), and contagious ecthyma (CE) (DeForge et al. 1982; Turner and Payson 1982a,b). PI-3 and BT have been suggested as factors predisposing lambs to fatal bacterial pneumonia. This paper attempts to quantify the influence of the purported disease epizootic and other variables on lamb recruitment through statistical analyses of lamb:ewe ratio data spanning 30 years. In addition to the expected depressing effects of diseases on lamb recruitment, it was hypothesized that precipitation and population density also should influence recruitment rate through their influence on nutrition. The Santa Rosa Mountains are a desert ecosystem of low and variable precipitation (Ryan 1968). Consequently, variance in precipitation was expected to strongly affect nutrition and survival of lambs through its influence on vegetative growth (Monson 1960). Work in the nearby Mojave Desert has indicated that the timing of precipitation is of particular importance to subsequent plant growth (Beatley 1974). Specifically, fall precipitation is a crucial determinant of whether annual and perennial forb growth will be present the following spring and strongly influences spring growth of shrubs and perennial grass species. Winter and early spring precipitation also can trigger growth in shrubs and perennial grasses. Turner (1973) found that mountain sheep in the Santa Rosa Mountains consumed a mixture of browse, forb, grass, and cactus species that varied seasonally and yearly with availability of succulent growth. Particularly noteworthy relative to nutrition of lambs was an increase in consumption of forbs and green grasses during spring in years when these were available.

Rainfall, El Nino, and dynamics of mule deer in the Sonoran Desert, California

We used long-term El Nino southern oscillation (ENSO), rainfall, and deer harvest records to investigate effects of ENSO and rainfall on mule deer (Odocoileus hemionus) population trends in the Sonoran Desert, southeastern California, USA. We found significant relationships between the southern oscillation index and rainfall (R 2 = 0.38, P≤0.001), and between rainfall and annual deer harvest (R 2 = 0.25, P ≤ 0.001). We also found that deer harvest (i.e., an index of deer abundance) in any year was related to accumulations of rainfall >5 years before that hunting season (R 2 = 0.34), whereas the change in harvest between years (i.e., an index of rate of population change) was most related to rainfall the year immediately prior to that hunting season (R 2 = 0.15). Fluctuations in deer populations in the deserts of California ultimately may be caused by ENSO events.

Factors Affecting Habitat Use and Distribution of Desert Mule Deer in an Arid Environment

Abstract We studied habitat use by desert mule deer (Odocoileus hemionus eremicus) in the Sonoran Desert to understand the relative importance of vegetation, terrain characteristics, human disturbances, and water sources in determining their distribution. We located 44 radiocollared female mule deer weekly over 5 years. In spring, when water was most scarce, deer were in areas with lower elevations, shallower slopes, and greater normalized difference vegetation index (NDVI) rates, when compared to random locations. Use of water developments (i.e., catchments) during spring was evident but their effect on deer distribution was small relative to other factors, and their importance varied by animal. More deer locations were recorded in areas of higher NDVI rate in spring, summer, and autumn, but they were also further from washes in autumn. The deer we monitored used lower elevations in spring and higher elevations during the rest of the year. The effect of slope was strong in all seasons. However, deer tended to select shallow slopes in spring and steep slopes during the rest of the year. Deer avoided roads in summer and autumn but were closer to them in winter. They avoided rivers or canals in summer but were closer to those features in autumn. Our results suggest that terrain characteristics in all seasons (slope and elevation), as well as forage quality in 3 of 4 seasons (as indexed by NDVI rate) were most important in determining distribution of deer. Concomitantly water catchments had a measurable, but minor, role during hot, dry conditions. We recommend investigators continue to evaluate the importance of water developments relative to other habitat factors, particularly via the use of multivariate studies, global positioning system technology, adaptive management, and temporary closure of water developments known to be used by radiocollared deer.