Steven W. Buskirk

HOME RANGE, TIME, AND BODY SIZE IN MAMMALS'

The relationship between home range area and body size of terrestrial mammals is reconsidered in light of the concept of biological time. Biological time is an internal, body—mass—dependent, time scale to which the durations (of rates) of biological events are entrained. These events range from purely physiological (e.g., muscle contraction time) to purely ecological (e.g., time to traverse home range). Evidence is presented that home range size scales linearly to body mass for carnivores as it does for herbivores. This scaling supports the hypothesis that animals select their home range areas to meet metabolic demands integrated over biologically critical periods. Confounding variables in the home range—body mass regression include habitat productivity and methods of location. Data on home ranges derived from telemetry studies of terrestrial carnivores are presented and used to derive allometric equations for home range area. The exponents of these equations are shown to approximate 1.0, although intercept values vary with latitude and, presumably, habitat productivity. Social organization and behavior may also influence the relationship of home range area to metabolic needs for different sex and age categories within a species.

Diet, Morphology, and Interspecific Killing in Carnivora

Interspecific killing is a key determinant of the abundances and distributions of carnivores, their prey, and nonprey community members. Similarity of body size has been proposed to lead competitors to seek similar prey, which increases the likelihood of interference encounters, including lethal ones. We explored the influence of body size, diet, predatory habits, and taxonomic relatedness on interspecific killing. The frequency of attacks depends on differences in body size: at small and large differences, attacks are less likely to occur; at intermediate differences, killing interactions are frequent and related to diet overlap. Further, the importance of interspecific killing as a mortality factor in the victim population increases with an increase in body size differences between killers and victims. Carnivores highly adapted to kill vertebrate prey are more prone to killing interactions, usually with animals of similar predatory habits. Family‐level taxonomy influences killing interactions; carnivores tend to interact more with species in the same family than with species in different families. We conclude that although resource exploitation (diet), predatory habits, and taxonomy are influential in predisposing carnivores to attack each other, relative body size of the participants is overwhelmingly important. We discuss the implications of interspecific killing for body size and the dynamics of geographic ranges.

Winter Resting Site Ecology of Marten in the Central Rocky Mountains

We investigated the resting site ecology of American marten (Martes americana) in the central Rocky Mountains during 2 winters, 1985-86 and 1986-87. We found 8 marten used 57 resting sites on 141 occasions. Marten rested primarily in subnivean sites associated with coarse woody debris, including logs and stumps. Use of spruce (Picea spp.)-fir (Abies lasiocarpa) stands by adults was greater than expected and use of lodgepole pine (Pinus contorta) stands was less than expected on the basis of spatial availability. Juveniles used stand types in proportion to spatial availability. Fidelity to individual resting sites and to subnivean sites associated with coarse woody debris was highest among adults. Type of resting site used depended on air temperature at the time of resting; above-snow sites were used during the warmest weather, and subnivean sites associated with coarse woody debris were used during the coldest weather. Marten rested for longer periods where coarse woody debris formed all or part of the resting site than they did at other sites. Log densities were higher and mean log diameters greater in spruce-fir stands than in lodgepole pine stands. Resting sites associated with coarse woody debris occurred primarily in spruce-fir stands, whereas other resting sites occurred in other stand types. Resting sites were closer to streams and lakes than expected. The importance of resting where coarse woody debris is available to provide thermal cover may explain the apparent dependence of marten on old-growth forest in the central Rocky Mountains in winter. J. WILDL. MANAGE. 53(1):191-196 Resting sites used by American marten have been described for a wide range of geographic locations and include a variety of natural and man-made microhabitats (Campbell 1979, Steventon and Major 1982, Martin and Barrett 1983, Buskirk 1984). Locations of resting sites range from the forest canopy to beneath the soil surface. Winter resting sites are often associated with coarse woody debris (CWD), including logs, stumps, and snags (Steventon and Major 1982, Martin and Barrett 1983, Spencer 1987). In summer, marten generally rest in sites above the ground, often in the canopy layer (Masters 1980, Burnett 1981, Martin and Barrett 1983). Temporal differences in resting site preferences could be explained by thermoregulatory needs of marten, or by other factors such as vulnerability to predation. Marten live where above-snow air temperatures (Ta) in winter are lower than their lower critical temperature (T,c = the temp at which an animal must increase its metabolic rate above resting levels to offset thermal losses [16 C]) (Buskirk et al. 1988) by ?50 C. Thus they would appear to pay high energetic costs to rest at or near To in winter. Marten are associated with late successional stands of conifer-dominated forest over a wide geographic area (Francis and Stephenson 1972, Koehler and Hornocker 1977, Simon 1980, Bateman 1986) and have a close and seemingly obligatory association with old-growth stands in the Rocky Mountains in winter (Campbell 1979). However, a clear understanding of why marten are associated with old-growth is lacking. Patte ns of use of resting sites may provide a better understanding of the apparently obligatory nature of this association. We report on characteristics of resting sites used by marten in the Medicine Bow Mountains, Wyoming during 2 winter field seasons. We identify environmental and behavioral correlates of resting site use and draw inferences about the importance of resting site types for thermoregulation. We also discuss the importance of CWD as a resting site component in understanding the old-growth dependency of marten during winter. L. R. Forrest provided invaluable assistance during the winter field studies. We appreciate the cooperation of R. H. Abell, for allowing use of a portion of his trapline for field work. This research was supported by the Committee for Research and Exploration, National Geographic Society, the U.S. Forest Service (USFS), Rocky Mountain Forest and Range Experiment Station, and the Office of Research, University of Wyoming. We thank the Wyoming Game and

Metrics for Studies of Resource Selection

Abstract Resource availability and resource use are 2 key concepts in studies of resource selection. Although equal accessibility to resources is one component defining resource availability, we rarely know what restricts access to resources. Consequently for spatially distributed resources, the animals use of space in association with the occurrence of resources is a frequent basis for inferring resource use and testing for resource selection. For many resources, occurrence can be defined for the population or the individual animal and requires that researchers specify the spatial extent of resources an animal might use during the time interval of study (e.g., the “choice set”). Often the occurrence of resources is defined at multiple scales, which facilitates understanding hierarchical selection patterns. We discuss numerous factors and criteria that should be considered when delineating the area an animal might use during a period of interest. New analytical approaches to resource selection, including resource utilization functions (RUF) and discrete choice modeling, help address some of the issues of defining availability and dealing with the behaviors associated with resource use. A currency of use is a measure of the investment made by an animal in securing resources, avoiding loss of resources, or otherwise optimizing fitness. Common currencies used by researchers include time spent or distance traveled in a cover type, use of event sites (e.g., nest sites, roosting sites, den sites), or amounts of different kinds of foods consumed. Less common, but potentially highly informative, are such currencies as energy expended or predation risk or other risk incurred. Simulation of animal movements interspersed with diel resting periods, through habitat types with activity-dependent energy expenditure and habitat-specific predation risk showed that choice of a currency of use strongly influences inferences about habitat selection. We argue that perhaps the most informative currency of use would be increased risk to fitness accepted by an animal. Although fairly simple conceptually, such application of risk assessment faces formidable empirical challenges and is a worthy goal for the next generation of researchers of animal resource selection.

Sex Biases in Trapped Samples of Mustelidae

Sex ratios significantly different from 1:1 usually are observed in trap captures of mustelids. Although these ratios could be caused by skewed sex ratios in wild populations, trapped samples consistently are skewed toward males. This apparent sampling bias generally has been attributed to sexual dimorphism of home-range sizes in mustelids, postulated to result in greater exposure of males to traps. The magnitude of differences in rates of capture between sexes appears to be body-size dependent because small mustelids exhibit more strongly skewed sex ratios in trap captures than do large ones. We investigated possible causes of sexual differences in rates of capture of mustelids. Mathematical equations were derived to describe the effect of trap spacing in relation to home-range diameter as a cause of these sex biases. Large trap-spacing values in relation to home-range diameter result in these biases, but this “exclusion effect” (the effect of some smaller home ranges having no traps at all) is only one consequence of sexual dimorphism of home-range size. At low trap-spacing intervals, variations in home-range size result in differential numbers of traps in male and female home ranges (the “trap number effect”), although the density of traps is the same. Computer simulations were used to examine the interaction of known and postulated body-size-dependent factors, including home-range size, rate of travel, sensory acuity, and a body-size-independent factor, dimensionality of trap arrangement, as a possible cause of sexual differences in rates of encounter with traps. Rates of encounter with traps that favor capture of males and that produce greater differences in rates of capture between sexes in small species than in large ones were observed if home ranges were sexually dimorphic, traps were arranged in grids, rate of travel was proportional to the 0.25 power of body mass, and males perceived traps at the same distances as did females. Sex-specific behaviors, either resulting from sexual differences in territory packing, or in the way that animals respond to traps that they perceive, are hypothesized to be contributing causes of differences in rates of capture between sexes.

World Distribution and Status of the Genus Martes in 2000

The genus Martes is comprised of 7 species of martens, sables and fishers, most of them forest-dwelling animals with valuable fur, distributed throughout North America, Europe and Asia. The pine marten (Martes martes) is indigenous over most of Europe, from Mediterranean biotopes to Fennoscandian taiga, and to western Siberia and Iran. It is found in insular wooded areas, shrublands, and coniferous forests. The stone marten (M. foina) occurs from Mongolia and the northern Himalayas to most of Europe. It frequents forests, woodlands and pastures, and is expanding in suburban and urban areas. The sable (M. zibellina) occurs in Russia, Mongolia, China, North Korea, and Japan. Over most of its distribution, the sable inhabits coniferous taiga forests with late seral attributes. The yellow-throated marten (M. flavigula; including the Nilgiri marten, M. gwatkinsi) occurs in sub-tropical and tropical forests from the Himalayas to eastern Russia, south to the Malay Peninsula and Sunda Shelf to Taiwan. The Japanese marten (M. melampus) occurs in forests of the main Japanese archipelago and the Korean peninsula. The American marten (M. americana) occurs in large contiguous populations in forested habitats of North America north of 35° latitude. It is associated with mesic coniferous and mixed forests with overhead cover and structural complexity near the ground. The fisher (M. pennanti) occurs in large contiguous areas across Canada, and in disjunct areas within the United States, north of 35° latitude. Whereas the distribution of Martes significantly expanded in many parts of the world over the last 20 years, largely due to several reintroduction programs, many populations are threatened by habitat loss and alteration. There is a need to develop cost-effective survey methods, monitor populations and fur-harvest activities, and assess the effects of natural and anthropogenic disturbance agents on habitat use by Martes species.

Spacing and Ecology of North American Badgers (Taxidea taxus) in a Prairie-Dog (Cynomys leucurus) Complex

We studied spacing, food habits, habitat use, and population characteristics of North American badgers (Taxidea taxus) in and around a prairie-dog (Cynomys leucurus) town in southeastern Wyoming, May 1991-October 1993. Densities of badgers varied from 0.8 to 1.1/km 2 . Prairie dogs occurred in 57% of stomach and fecal samples from female badgers, and females used prairie dog towns more than expected from spatial availability of prairie-dog towns. Ninety-five percent adaptive-kernel home ranges of females were smaller than those of males (male X = 12.3 ± 4.8 km 2 [± SD], female X = 3.4 ± 1.4 km 2 ), and occurrence of overlap and geometric mean overlap were less for females than for males. Home ranges of males were larger during the breeding season than during the nonbreeding season (breeding X = 11.1 ± 5.0 km 2 , nonbreeding X = 5.4 ± 1.7 km 2 ). Breeding home-range size of males was 2.5 times larger than that predicted (4.5 km 2 ) based on energetic demands. Spacing patterns of males were similar to those reported in other studies, but females were more territorial than reported elsewhere.

Genetic Diversity and Structure of the Fisher (Martes pennanti) in a Peninsular and Peripheral Metapopulation

Abstract Evolutionary processes can be strongly affected by landscape features. In vagile carnivores that disperse widely, however, genetic structure has been found to be minimal. Using microsatellite DNA primers developed for other mustelids, we found that populations of a vagile forest carnivore, the fisher (Martes pennanti), exhibit high genetic structure (FST = 0.45, SE = 0.07) and limited gene flow (Nm < 1) within a >1,600-km narrow strip of forested habitat; that genetic diversity decreases from core to periphery; and that populations do not show an equilibrium pattern of isolation-by-distance. Genetic structure was greater at the periphery than at the core of the distribution and our data fit a 1-dimensional model of stepping-stone range expansion. Multiple lines of paleontological and genetic evidence suggest that the fisher recently (<5,000 years ago) expanded into the mountain forests of the Pacific coast. The reduced dimensionality of the distribution of the fisher in western coastal forests appears to have contributed to the high levels of structure and decreasing diversity from north to south. These effects were likely exacerbated by human-caused changes to the environment. The low genetic diversity and high genetic structure of populations in the southern Sierra Nevada suggest that populations in this part of the geographic range are vulnerable to extinction.

Seasonal Use of Resting Sites by Marten in South-Central Alaska

Although a number of studies have dealt with the ecology of marten (Martes americana) in North America during the past decade, little attention has been directed toward the use of resting sites by this species. Marten habitat has generally been defined and evaluated in terms of food abundance or vegetation type (Koehler and Hornocker 1977). Although resting sites of marten have been described (Murie 1961, Mech and Rogers 1977, Masters 1980), seasonal variation in site preference has not been described and the importance of these sites to marten has not been considered. Resting sites may be important because they reduce thermoregulatory costs and provide protection from predators. This report describes resting sites used by marten in south-central Alaska, provides information on habitats in which resting sites occurred, and discusses the energetic importance of resting site

A PLAGUE EPIZOOTIC IN THE BLACK-TAILED PRAIRIE DOG (CYNOMYS LUDOVICIANUS)

Plague is the primary cause for the rangewide decline in prairie dog (Cynomys spp.) distribution and abundance, yet our knowledge of plague dynamics in prairie dog populations is limited. Our understanding of the effects of plague on the most widespread species, the black-tailed prairie dog (C. ludovicianus), is particularly weak. During a study on the population biology of black-tailed prairie dogs in Wyoming, USA, plague was detected in a colony under intensive monitoring, providing a unique opportunity to quantify various consequences of plague. The epizootic reduced juvenile abundance by 96% and adult abundance by 95%. Of the survivors, eight of nine adults and one of eight juveniles developed antibodies to Yersinia pestis. Demographic groups appeared equally susceptible to infection, and age structure was unaffected. Survivors occupied three small coteries and exhibited improved body condition, but increased flea infestation compared to a neighboring, uninfected colony. Black-tailed prairie dogs are capable of surviving a plague epizootic and reorganizing into apparently functional coteries. Surviving prairie dogs may be critical in the repopulation of plague-decimated colonies and, ultimately, the evolution of plague resistance.