Dirk H. Van Vuren

Detectability, philopatry, and the distribution of dispersal distances in vertebrates

Dispersal is of central importance to population biology, behavioral ecology and conservation. However, because field studies are based on finite study areas, nearly all dispersal distributions for vertebrates currently available are biased, often highly so. The inadequacy of dispersal data obtained directly by traditional methods using population studies of marked individuals is highlighted by comparing the resulting distributions with dispersal estimates obtained by radio-tracking and by using genetic estimates of gene flow.

The Ecology and Macroecology of Mammalian Home Range Area

Although many studies employ allometric relationships to demonstrate possible dependence of various traits on body mass, the relationship between home range size and body mass has been perhaps the most difficult to understand. Early studies demonstrated that carnivorous species had larger home ranges than herbivorous species of similar mass. These studies also argued that scaling relations (e.g., slopes) of the former were steeper than those of the latter and explained this in terms of the distribution of food resources, which are more uniformly distributed for most herbivores than for carnivores. In contrast to these studies, we show that scaling relations of home ranges for carnivorous mammals do not differ significantly from those of herbivorous and omnivorous species and that all three exhibit slopes that are significantly steeper than predicted on the basis of energetic requirements. We also demonstrate that home range size is constrained to fit within a polygonal constraint space bounded by lines representing energetic and/or biophysical limitations, which suggests that the log‐linear relationship between home range area and mass may not be the appropriate function to compare against the energetically predicted slopes of 0.75 or 1.0. It remains unclear, however, why the slope of the relationship between home range area and body mass, whether based on raw data or on constraint lines, always exceeds that predicted by the energetic needs hypothesis.

Behavioral responses of bobcats and coyotes to habitat fragmentation and corridors in an urban environment

We examined the behavior of bobcats and coyotes in a fragmented urban area northwest of Los Angeles, California, from July 1998 to October 1999. Activity patterns of bobcats and coyotes were crepuscular with no apparent shift to nocturnality, but activity was somewhat lower during daylight hours than in an unfragmented reference area, implying some avoidance of humans. Home ranges were not significantly larger in fragmented than in unfragmented habitat, probably because unproductive development within a home range may have been balanced by availability of human-related food, such as fruit, garbage, and pets. Female bobcat home ranges were generally within a single fragment, while male bobcats and coyotes of both sexes included more than one fragment. Both species tended to cross over roads rather than use culverts. Culverts were more likely to be used earlier in the night, during heavier traffic, and if they contained less water. Bobcats and coyotes used corridors as habitat and, less often, for travel. Both species also crossed development to move between fragments, but seemed to prefer corridors when available. Our results indicate that bobcats and coyotes persisting in an urban environment adjust behaviorally to habitat fragmentation and human activities, in part through temporal and spatial avoidance. Both species appeared willing to cross well-travelled roads despite the availability of culverts; consequently, vehicular collision is an important cause of mortality (50%) and needs attention.

DIFFERENTIAL COSTS OF LOCATIONAL AND SOCIAL DISPERSAL AND THEIR CONSEQUENCES FOR FEMALE GROUP·LIVING PRIMATES

Individuals that disperse may leave familiar conspecifics (social dispersal), a familiar home range (locational dispersal), or both. Social and locational dispersal are not necessarily coincident in group-living animals. Here we differentiate among some potential costs of both social and locational dispersal in group-living mammals, including aggression from strangers and unfamiliarity with new habitats. As an example of the utility of distinguishing between social and locational dispersal, we examine patterns of female transfer in Old and New World anthropoid primates. The results suggest that in Old World primates, female transfer is more likely to be frequent in populations without female aggression between groups. In anthropoid primates, female transfer is more likely to be frequent in populations in which home ranges of groups overlap extensively with those of other groups. Female transfer between groups in Old World, but not New World, primates appears to be more common when females suffer few or no costs of social and locational dispersal. We suggest that when there are few, if any, costs of social and locational dispersal (inferred from moderate to extensive home range overlap and the absence of aggression between groups of females), female transfer in Old World anthropoids will be obligate when groups of females cannot be monopolized by a single male and conditional upon the behavior of individual males when groups of females can be monopolized by a single male. When costs of social and locational dispersal exist (inferred from minimal home range overlap and aggression between groups of females), female transfer will be conditional upon competition with other females in their groups.

Survival of Dispersing and Philopatric Yellow-Bellied Marmots: What Is the Cost of Dispersal?

Understanding the evolution of dispersal has been hindered by a lack of reliable measures of the cost of dispersal. We report that survival of dispersing yellow-bellied marmots (Marmota flaviventris) (0.73) was only 16% less than survival of philopatric marmots (0.87). A cost-benefit analysis reveals that the survival cost of dispersal may be less than some other costs of philopatry; thus, dispersal is explicable as a tactic to improve individual fitness

Effects of urbanization on carnivore species distribution and richness

Abstract Urban development can have multiple effects on mammalian carnivore communities. We conducted a meta-analysis of 7,929 photographs from 217 localities in 11 camera-trap studies across coastal southern California to describe habitat use and determine the effects of urban proximity (distance to urban edge) and intensity (percentage of area urbanized) on carnivore occurrence and species richness in natural habitats close to the urban boundary. Coyotes (Canis latrans) and bobcats (Lynx rufus) were distributed widely across the region. Domestic dogs (Canis lupus familiaris), striped skunks (Mephitis mephitis), raccoons (Procyon lotor), gray foxes (Urocyon cinereoargenteus), mountain lions (Puma concolor), and Virginia opossums (Didelphis virginiana) were detected less frequently, and long-tailed weasels (Mustela frenata), American badgers (Taxidea taxus), western spotted skunks (Spilogale gracilis), and domestic cats (Felis catus) were detected rarely. Habitat use generally reflected availability for most species. Coyote and raccoon occurrence increased with both proximity to and intensity of urbanization, whereas bobcat, gray fox, and mountain lion occurrence decreased with urban proximity and intensity. Domestic dogs and Virginia opossums exhibited positive and weak negative relationships, respectively, with urban intensity but were unaffected by urban proximity. Striped skunk occurrence increased with urban proximity but decreased with urban intensity. Native species richness was negatively associated with urban intensity but not urban proximity, probably because of the stronger negative response of individual species to urban intensity.

ENERGETIC CONSTRAINTS AND THE RELATIONSHIP BETWEEN BODY SIZE AND HOME RANGE AREA IN MAMMALS

Recent theoretical developments to explain the unimodal and asymmetric distribution of body sizes among species in higher taxa have yielded predictions for related demographic and life history traits. In particular, it has been predicted that there is an energetically optimal body size (M*) for terrestrial mammals at ∼100 g, and that the relationships of many biological characteristics will change slope or even sign at this point. We reanalyze a well-known data set on the relationship between home range size and body size in mammals. If the distribution of home range sizes as a function of body size is energetically constrained, then it is reasonable to assume that the lower size limit of a home range for a given body mass will also be constrained. To evaluate this hypothesis, we predicted that the relationship between minimal home range size and body size is nonlinear, and that the smallest home ranges should correspond to species in the vicinity of M*. Our data tentatively support both hypotheses but constitute a clear call for more comprehensive analyses with larger data sets.

Range expansion, population sizes, and management of wild pigs in California

The introduction and spread of nonnative organisms to new regious can disrupt ecosystems by causing declines or extinctions of native species. Widely mtroduced wild pigs (Sus scrofa ) have contributed to declines and extinctions of numerons species on oceanic islands and can have pronounced negative ecological effects on mainland areas when population densities are high. Although range expansion by introduced wild pigs has ceased in many regions of the United States, it has increased significantly since the 1950s in California. Our analyses of data from annual hunter survevs and mapped locations of hunter-killed wild pigs shows that the distribution of wild pigs increased from around 10 coastal connties in the early 1960s to parts of 49 of Californias 58 counties by 1996. An index to density based on locations of hunter-killed wild pigs plotted in a Geographic Information System (GIS) indicated that within the 79,550 km 2 (25%) of the total land area of the state now occupied by wild pigs populations are most abundant in the central and north-coast regions. By stratifying each county into 1 of 3 relative abundance classes and assigning density values based on research at multiple sites, we estimated tbere were around 133.106 (range = 106,485-159,727) wild pigs in California in 1996. The recent increase in the range of wild pigs in California was facilitated by a combination of multiple hunting-related introductions, deliberate releases of domestic pigs, and, possibly, increased forage availability associated with agricultural development. Natural range expansion also has occured, however, and the dynamics of the spread of wild pigs in California appear typical of invasions observed among other organisms. Forage and water availability are important factors influencing the dist ribution and abundance of wild pigs in California. and predation may be important to an unknown extent. Up to 40% of Californias wild pigs are removed from the population annually hich may control populations in some areas but not others. Wild pigs may be cansing ecological damage in some coastal regions where population densities are very high, and detailed studies are needed in those areas to help mitigate potential problems with this increasingly widespread mammal in California.

Home range and parasite diversity in mammals.

Parasite diversity among and within host species is not solely the result of random processes; rather, it depends on a suite of physiological or ecological host traits as well as environmental factors. Because most macroparasites exhibit life cycles that include infective stages off the definitive host and that rely on host movements for dissemination, parasite acquisition by a host depends largely on hosts being present in a given area where and when infective stages are present. Consequently, host ranging pattern may have a major influence on parasite diversity. Larger home range size is hypothesized to be associated with higher parasite species richness because hosts living in large home ranges should encounter a greater diversity of habitats and other host individuals, which in turn may favor infection by a great diversity of parasite species. By focusing on helminths in wild mammals, we show that an increase in home range area does not lead to an increase in parasite diversity in ungulates and, moreover, that it is associated with a decrease in parasite species richness in carnivores and in glires (rodents and lagomorphs). We also show that home range size is negatively correlated with host density in mammals after correcting both variables for host body mass. We discuss these results from an epidemiological perspective.

Habitat Associations of Small Mammals at Two Spatial Scales in the Northern Sierra Nevada

Abstract Effective management strategies require an understanding of the spatial scale at which fauna use their habitat. Toward this end, we sampled small mammals in the northern Sierra Nevada, California, over 2 years at 18 livetrapping grids among 5 forest types. Forest types were defined by overstory tree composition, and 19 microhabitat variables were measured at all trap stations. Forest type and year explained 93% of variation in abundance of North American deermice (Peromyscus maniculatus), whereas only 40% was explained by microhabitat and year. Similarly, variation in abundance of long-eared and shadow chipmunks (Neotamias quadrimaculatus and N. senex) was better explained by forest type and year (67%) than by microhabitat and year (30%). Red fir (Abies magnifica) forests supported more P. maniculatus and Neotamias species than mixed-conifer and pine–cedar forests, and more Neotamias species than mixed-fir forests. Five of 6 uncommon species were significantly associated with forest type; golden-mantled ground squirrels (Spermophilus lateralis), northern flying squirrels (Glaucomys sabrinus), and long-tailed and montane voles (Microtus longicaudus and M. montanus) were captured almost exclusively in red fir forests, whereas dusky-footed woodrats (Neotoma fuscipes) and California ground squirrels (Spermophilus beecheyi) were found in pine–cedar, mixed-fir, and mixed-conifer forests. The first 2 axes of a canonical correspondence analysis on microhabitat variables explained 71% of variation in combined small mammal abundance. Microhabitat associations varied among species but were driven primarily by canopy openness, shrub cover, and shrub richness. Although much of the small mammal fauna appeared to select habitat at both spatial scales studied, canonical correspondence analysis using forest type as a covariate revealed that microhabitat explained much less variation in small mammal abundance than did forest type.