Showing papers in "Journal of Mammalogy in 1999"

The Ecology of Fear: Optimal Foraging, Game Theory, and Trophic Interactions

Abstract: Mammalian predator-prey systems are behaviorally sophisticated games of stealth and fear. But, traditional mass-action models of predator prey dynamics treat individuals as behaviorally unresponsive “molecules” in Brownian motion. Foraging theory should provide the conceptual framework to envision the interaction. But, current models of predator feeding behavior generally envision a clever predator consuming large numbers of sessile and behaviorally inert prey (e.g., kangaroo rats, Dipodomys , collecting seeds from food patches). Here, we extend foraging theory to consider a predator-prey game of stealth and fear and then embed this game into the modeling of predator-prey population dynamics. The melding of the prey and predator's optimal behaviors with their population and community-level consequences constitutes the ecology of fear. The ecology of fear identifies the endpoints of a continuum of N-driven (population size) versus μ-driven (fear) systems. In N-driven systems, the major direct dynamical feedback involves predators killing prey, whereas μ-driven systems involve the indirect effects from changes in fear levels and prey catchability. In μ-driven systems, prey respond to predators by becoming more vigilant or by moving away from suspected predators. In this way, a predator (e.g., mountain lion, Puma concolor ) depletes a food patch (e.g., local herd of mule deer, Odocoileus hemionus ) by frightening prey rather than by actually killing prey. Behavior buffers the system: a reduction in predator numbers should rapidly engender less vigilant and more catchable prey. The ecology of fear explains why big fierce carnivores should be and can be rare. In carnivore systems, ignore the behavioral game at one's peril.

A Comparison of Acoustic Versus Capture Techniques for the Inventory of Bats

Abstract: To evaluate the efficacy of the Anabat II ultrasonic detector and analysis system for use as a tool for conducting inventories, we compared results of acoustic versus capture techniques in the southwestern United States. We sampled 57 locations using standard methods (mist nets and double-frame harp traps) and simultaneously with an ultrasonic detector (Anabat II). Assuming total number of species obtained by both methods equaled a complete inventory, captures accounted for 63.5% and acoustic sampling 86.9% of the combined species present. Acoustic sampling was capable of sampling bats that routinely flew outside the sampling capabilities of nets and traps. We found no statistical difference between capture and acoustic sampling with respect to species that use low-intensity echolocation. Acoustic sampling of bat communities is a powerful tool but should be used with various capture techniques to perform the most accurate inventory.

Optimal Foraging and Risk of Predation: Effects on Behavior and Social Structure in Ungulates

Abstract: Optimal foraging theory predicts that animals will either attempt to maximize energy gained or minimize time spent to obtain a fixed amount of energy. A time-minimizing approach implies that an animal is attempting to maximize time spent in other behaviors such as reproduction or to minimize its exposure to temperature extremes, predators, or some other factor in the environment while foraging. Indeed, many ungulates must balance the need to obtain sufficient energy and other nutrients required for maintenance, growth, and reproduction while avoiding predation. Adopting social behavior that results in the formation of herds confers several advantages to the individual because of the difficulty a predator has in approaching large groups, or in capturing individuals in the confusion caused by a fleeing herd. Such behavior is often seen in ungulates occurring in open habitats where coursing predators are common. The problem becomes more acute, however, for ungulates living in closed habitats year-round, where predators commonly hunt by stealth, or for those sex and age classes such as females with young that exhibit solitary behavior. Such species or sex and age classes would be expected to exhibit a time-minimizing strategy at least seasonally. Use of linear-programming models of dietary choice have been successful in predicting classes of forages consumed by ungulates and other generalist herbivores and indicate that they often follow an energy-maximization strategy. Nonetheless, overwhelming evidence indicates that ungulates modify their behavior in the presence of predators. I suggest that decisions about when and how to forage are being made at different scales, and these differences may account for observed discrepancies between models and empirical evidence. Finally, new analytical techniques such as stochastic dynamic programming may allow development of more realistic models of foraging behavior and may better incorporate observed behaviors in ungulates.

Qualitative Identification of Free-Flying Bats Using the Anabat Detector

Abstract: A variety of ultrasonic (bat) detectors have been used over the past 3 decades to identify free-flying bats. Analyses of recorded echolocation calls were slow and typically restricted to few calls and at a resolution obscuring details of call structure. The Anabat II detector and associated zero-crossings analysis system allows an immediate examination, via a laptop computer, of the time-frequency structure of calls as they are detected. These calls can be stored on the hard drive for later examination, editing, and measurement. Many North American bats can be identified to species by qualitatively using certain structural characteristics of calls, primarily approximate maximum and minimum frequencies and morphological aspects of calls (e.g., linearity and changes in slope). To identify calls precisely, it is important to use a continuous sequence of calls from an individual in normal flight rather than from single isolated calls. All calls are not equally useful, and many fragmentary calls must be discarded before making a determination. Each sequence of calls must be examined to ensure that multiple bats have not been simultaneously recorded, which confounds correct identification. We found the percentage of non-usable calls within usable vocal sequences to be highest in vespertilionids (20–40%), whereas for other families this was frequently <10%. Active rather than passive collection of data maximizes quality and quantity of diagnostic calls and provides a contextual base for the investigator.

Sexual Segregation in White-Tailed Deer: Density-Dependent Changes in Use of Space, Habitat Selection, and Dietary Niche

Abstract: Sexual segregation, defined as the exclusive use of different areas by males and females at specified spatial and temporal scales, is common among polygynous ruminants and in cervids in particular. Underlying mechanisms for such segregation are not understood fully, and reports have included female cervids segregating into habitats of both poorer and better quality than those used by males. Furthermore, two competing hypotheses of sexual segregation (body-size hypothesis, reproductive-strategy hypothesis) predict different responses to changes in population density; an increase in degree of sexual segregation with increasing density in the former and a decrease in segregation in the latter. We examined patterns of sexual segregation among white-tailed deer (Odocoileus virginianus) on the Welder Wildlife Refuge in south Texas at moderate (39 deer/km 2 ) and high (77 deer/km 2 ) population densities during 1974-1977. At moderate density, females with young made greater use of chaparral-mixed grass habitat with dense cover than did males, where preferred herbaceous forage was less abundant, presumably for reasons of predator avoidance. At high density, which was a result of predator control, sexual segregation among male and females decreased during all seasons (P < 0.05). Males that otherwise used more open habitats increased their use of the chaparral-mixed grass as levels of intraspecific competition increased. As spatial segregation between males and females decreased at the high population density, diets of both sexes shifted toward more graminoids and browse, and shifts were more pronounced among males. The result was decreased dietary overlap between sexes when measured by principal-component analysis. Measures of fat reserves suggested that although both females and males were in poorer condition at high density, females were affected to a greater extent than were males. This outcome suggested that females were not driving patterns of spatial segregation by being better able to compete with males for closely-cropped forages. Rather, predator avoidance by females with young related to the reproductive-strategy hypothesis best explained patterns we observed, and competition between sexes was rejected as a cause of sexual segregation.

Genetic Consequences of Mammalian Social Structure

Abstract: Populations of social mammals are characterized by several demographic features that may increase the magnitude of genetic drift relative to other evolutionary forces. In particular, polygynous mating and socially mediated constraints on gene flow have been proposed to foster random genetic differentiation among social groups, thereby accelerating rates of evolutionary change. To evaluate this hypothesized link between sociality and genetic sub-division, I examined results of published studies of mammalian populations in which genetic structuring was assessed at the level of social groups. Population genetic data from a taxonomically diverse array of social mammals revealed low to moderately high levels of genetic differentiation among social groups ( F st = 0.006–0.227), coupled with consistently high levels of within-group heterozygosity indicated by negative F is -values. Relatively higher levels of genetic structuring were observed in populations in which sampling effects associated with polygynous mating were reinforced by female philopatry. The degree of genetic subdivision observed in several taxa, most notably black-tailed prairie dogs ( Cynomys ludovicianus ) and red howler monkeys ( Alouatta seniculus ), indicated that social organization can have a profound impact on population genetic structure. However, in most cases, social barriers to gene flow are likely insufficient to promote the degree of genetic subdivision and inbreeding envisioned by models of rapid drift-induced speciation. It appears that social mammals generally are characterized by a dynamic non-equilibrium mode of population structure in which local demes are characterized simultaneously by small variance effective sizes and large inbreeding effective sizes.

Annual Cycle of Body Composition and Hibernation in Free-Living Arctic Ground Squirrels

Abstract: We monitored a natural population of arctic ground squirrels ( Spermophilus parryii kennicottii ) on the North Slope of Alaska for seasonal changes in body mass and composition and dates of immergence into and emergence from hibernation. Yearlings and adult females were at the lowest body mass of their active season at emergence in spring. Their mean body mass did not increase for 1 month after emergence and peaked in July (adult females) and August (yearlings). Body mass of adult males was near the highest of the active season when they emerged from hibernation and decreased by 21% over the subsequent 10-day mating season. Juveniles gained body mass during their active season, except for significant losses associated with dispersal. During hibernation, females lost >30% of their body mass, but adult males emerged in spring without significant decreases in body mass, fat, or lean. Yearling and nonreproductive males were significantly lower in fat but not lean mass at emergence than immergence, and females were significantly lower in fat and lean mass. Arctic ground squirrels entered hibernation over a >1 -month interval beginning in early August; females entered before males, and adults of each sex immerged before juveniles. Reproductive males emerged before females, and fatter females emerged significantly earlier than leaner females. Vaginal estrus was maximal at 3 days post-emergence. Nonreproductive males emerged last from hibernation. Mean ± SE days in hibernation was 240.1 ± 12.1 for adult females (69% of the year), 235.8 ± 10.3 for juvenile females, 230.3 ± 4.2 for nonreproductive males, 220.3 ± 12.5 for adult males, and 214.7 ± 6.5 for juvenile males. Timing of immergence into and emergence from hibernation for arctic ground squirrels did not differ significantly from sciurid populations in temperate latitudes.

Birth-Site Selection by Alaskan Moose: Maternal Strategies for Coping with a Risky Environment

Abstract: We studied birth-site selection in Alaskan moose ( Alces alces gigas ) from 1990 to 1994 in Denali National Park and Preserve in interior Alaska. Twenty percent of preparturient females made extensive movements (≥5 km) immediately before giving birth. Females selected (use was greater than availability) sites for giving birth ( n = 39) that were on southerly exposures with low soil moisture and high variability in overstory cover. Moose selected birth sites based on micro-site characteristics rather than on broad types of habitat, which were used in proportion to their availability. Spatial distribution of birth sites did not differ significantly from random locations. We hypothesize that such unpredictable behavior by females is a strategy to avoid predators. Parturient females also selected sites with high visibility that were located at high elevation, which ostensibly allowed them to see and then hide from approaching predators. We rejected the hypothesis, however, that moose in this population spaced themselves away from predators or avoided habitat types favored by large carnivores. Likewise, we rejected the hypothesis that moose gave birth close to human developments to avoid predators; random sites were >100 m closer to human developments than were birth sites. Cover of forage, especially willows ( Salix ), was more than twice as abundant at birth sites than random sites. Forage quality, as indexed by nitrogen content and in vitro dry matter digestibility, was slightly but significantly higher at birth sites. An inverse relationship between visibility and availability of forage indicated that female moose made tradeoffs between risk of predation and food in selecting sites to give birth. Thus, maternal females coped with a risky environment; they gave birth at sites that helped them minimize risk of predation but exhibited risk-averse behavior with respect to the forage necessary to support the high cost of lactation. We hypothesize that risk of predation prevented moose from seeking birth sites with more forage and, hence, a greater nutritional reward, which reduced the variance in forage availability at birth sites.

Bats are not birds- a cautionary note on using echolocation calls to identify bats: a comment

Abstract: Monitoring and identifying echolocating bats in the field has been used extensively for many years, and O'Farrell et al. (1999) present an updated "qualitative" method for identifying species from their echolocation calls. However, they make the assumption that, like bird songs, echolocation calls of bats are species-specific. There is no reason to expect that natural selection favored incorporation of this information. Although identification of some species of bats by their calls is possible, variation at several levels makes other species indistinguishable. Monitoring echolocation in the field and identifying species can be useful in determining presence or absence of species and factors influencing activity of bats. However, limitations and degree of reliability of the technique must be recognized. Only by more explicitly defining how the method is used and quantifying characteristics that define calls of recognizable species will the method be scientifically sound and repeatable. I suggest a number of guidelines for use of the method in field studies.

Responses of small mammals to coarse woody debris in a southeastern pine forest

Abstract: The importance of coarse woody debris (CWD) to small mammals in a managed pine forest in South Carolina was tested experimentally during summer and autumn 1990 and winter and spring 1991–1994. Abundance and demographics of small mammals were compared between plots with abundant CWD created by a tornado (unsalvaged plots) and plots where tornado-created CWD had been removed (salvaged plots). Species composition was similar between unsalvaged and salvaged plots, but more small mammals were captured on unsalvaged plots. Cotton mice ( Peromyscus gossypinus ) were the most abundant species captured in all plots and were significantly more abundant in unsalvaged plots in every trapping period. Adult female P. gossypinus in unsalvaged plots had greater survival and were more likely to be in reproductive condition than adult females in salvaged plots. Southern short-tailed shrews ( Blarina carolinensis ) and cotton rats ( Sigmodon hispidas ) tended to be more abundant in unsalvaged plots. Fox squirrels ( Sciurus niger ), the second most abundant species in salvaged plots, were never captured on unsalvaged plots. Large amounts of CWD improve habitat quality of pine forests for P. gossypinus , and CWD is probably an important habitat component for other species.

Bat Activity in the Boreal Forest: Importance of Stand Type and Vertical Strata

Abstract: We examined habitat use by bats in the boreal forest of central Saskatchewan during summer 1995 by monitoring echolocation calls across forest types and through the canopy of mature forest. We sampled bat activity in mature aspen ( Populus tremuloides )-white spruce ( Picea glauca ) mixedwood, aspen, and jack pine ( Pinus banksiana ) stands and recorded passes from little brown ( Myotis lucifugus ), northern long-eared ( M. septentrionalis ), big brown ( Eptesicus fuscus ) or silver-haired bats ( Lasionycteris noctivagans ), and hoary ( Lasiurus cinereus ) bats. There were significantly more bat passes per night in the aspen-white spruce mixedwood forest than in aspen or jack pine forest. There was no difference in the proportion of feeding buzzes recorded from aspen-white spruce mixedwood and aspen forest. In aspen forest, mean number of hoary bat calls per night was higher above than below the canopy, whereas number of Myotis calls was higher within and above the canopy than below the canopy. There was no difference in the number of feeding buzzes recorded among the three canopy heights. Bat activity peaked toward sunset below the canopy but was more uniform within and above the canopy. Our results highlight the importance of mature aspen-white spruce mixedwood and aspen forest as habitat for boreal forest-dwelling bats and demonstrate for the first time that insectivorous bats are active both within and above canopy levels of the boreal forest.

Roosting ecology of the Northern bat (Myotis septentrionalis) and comparisons with the endangered Indiana bat (Myotis sodalis)

Abstract: During 1993 and 1994, we radiotracked 11 adult female and juvenile northern bats ( Myotis septentrionalis ) to 32 roost trees: 18 silver maples ( Acer saccharinum ), 1 red maple (A. rubrum ), and 13 green ashes ( Fraxinus pennsylvanica ). Fifty-three percent of the trees were living; 52% of the roosts were in crevices or hollows, and the rest were under exfoliating bark. Northern bats did not use American elms ( Ulmus americana ) in proportion to their abundance, but in general, characteristics of roost trees were similar to a random sample of apparently suitable trees. Northern bats changed roosts every 2 days, and distance between roosts varied from 6 to 2,000 m. As many as 60 adults were found in a single tree, making this the largest summer aggregation ever reported for the species. Compared with Indiana bats ( M. sodalis ) separately studied at the same site, northern bats moved greater distances between roosts and roosted more often in maples, cavities, living trees, and areas with high canopy cover.

Effects of Climate and Food Availability on Four Rodent Species in Southeastern Brazil

Abstract: Seasonal reproduction of small mammals in the tropics usually is related to annual cycles of rainfall. We examined effects of weather and food availability on reproduction and population ecology of Nectomys squamipes, Oryzomys intermedius, Akodon cursor and Trinomys iheringi . Each species was studied monthly from February 1993 to January 1995 using mark-recapture methods at Ilha do Cardoso, Sao Paulo State, Brazil. Average capture rate for each month was used as an index of population size, and survival rate was estimated by the Jolly-Seber method. Direct effects of food availability and rainfall were related to female reproductive activity and survival rate. Path analyses were used to describe quantitatively the hypothesized causal relations among the variables. N. squamipes reproduced seasonally, and O. intermedius, T. iheringi , and A. cursor reproduced all year with peaks during the rainy season. Species responded differently to the environmental factors; however, food availability seems to be the main factor determining reproduction. Abundance of rains appears to diminish survival rate of O. intermedius . Survival rate of N. squamipes increases with increases in fruit availability.

Density Dependence and Life-History Strategies of Ungulates

Abstract: Due to their large sizes and long life spans, ungulates typically exist in populations close to environmental carrying capacity (CC), and this has had a strong influence on evolution of life-history traits. I review models describing the relationship of ungulate populations to CC. The shape of the functional relationship of density dependence (DD) on population size (N) determines the response of N relative to CC and the tendency of N to come to equilibrium at CC. Environmental, and to a lesser extent demographic, stochasticity determine the realized relationship of N to CC in nature. It is difficult to distinguish DD signals from noise in environments with high stochasticity or with populations at or near CC. Life-history strategies of ungulates evolved in the context of DD and CC. Sexual selection has resulted in asymmetry of reproductive success between sexes and consequent evolution of dimorphism in body size with males being larger than females. Because males have larger bodies, greater absolute nutrient and energy costs, and higher rates of mortality than females, their reproductive fitness strategies tend to skew the population sex ratio towards females. Females are less costly to produce and maintain, so increased skew in the sex ratio of the population should, in theory, result in greater N (higher CC) relative to a given resource base. Sexual selection should lead to increasingly skewed sexual dimorphism and sex ratio up to some constraint set by the male's physical ability to sequester females or physiological limits to impregnate females. This suite of life-history traits in ungulates has led to resource partitioning between sexes and sexual segregation outside of the rut in most species. Female-female competition also complicates the relative value of sex of offspring to individual females, which varies with female age, size, and social position.

Mitochondrial DNA Phylogeography of the New World Flying Squirrels (Glaucomys): Implications for Pleistocene Biogeography

Abstract: Cytochrome- b sequence data of mitochondrial DNA (mtDNA) were used to infer evolutionary and biogeographic histories of the New World flying squirrels, Glaucomys sabrinus and G. volans . Two distinct mtDNA lineages were recovered within G. sabrinus: a western lineage consisting of populations from western California, Oregon, and Washington, and a much larger “eastern” lineage comprised of populations from the remainder of the species ' range (North Carolina, West Virginia, Michigan, Utah, Alaska, eastern Washington, British Columbia, and Alberta). In contrast, only one major mtDNA lineage was recovered within G. volans . Little sequence variation was observed among populations of G. volans (≤0.6%), but sequence variation within G. sabrinus was much higher (2.3% and 2.6% within the eastern and western clades, respectively, and 4.3–7.2% between the two clades). The level of sequence divergence observed between the eastern and western mtDNA clades of G. sabrinus (4.3–7.2%) was slightly greater than that observed between the two species, G. sabrinus and G. volans (4.0–6.1%), suggesting the possibility of an unrecognized species within G. sabrinus . Minimum levels of sequence divergence among the three mtDNA clades were nearly equal (ca. 4% in all pairwise comparisons), suggesting that Glaucomys underwent a relatively rapid diversification in the early-to-middle Pleistocene. The mtDNA discontinuity in the Pacific Northwest within G. sabrinus is congruent with similar disjunctions in a variety of vertebrate taxa, suggesting that an ancestral North American boreal ecosystem may have been divided into two distinct communities at this time.

Evolution of Sociality in Marmots

Abstract: The 14 species of marmots (Marmota) can be placed in one of four social systems: solitary; female kin matriline; adult male with two females and immature offspring; and a family group consisting of a territorial pair, subordinate adults, and immature offspring. Body size and hibernation are two critical features of marmot biology from which sociality evolves. The high correlation (r = 0.91) between immergence mass and mass loss suggests that species are heavier because they require more mass to survive the hibernation period. Marmots increase mass either by having a larger frame or by increasing the amount of mass per frame. Emergence and immergence mass are linearly related to body length; but change in mass is curvilinearly related to body length: large species use relatively more mass. An analysis of mass:length ratios reveals that species with a relatively high immergence mass use considerable mass during the hibernation period whereas species with a relatively high emergence mass use considerable mass after emergence. The consequence of large body size and a short growing season is that young in all but one species require two or more growing seasons to reach reproductive maturity. All species reach a maturity index for dispersal by age one; however, only two species disperse by that age and several species delay dispersal beyond the age of first reproduction. All species are reproductively mature by age two, but many species delay reproduction for one or more years. Delayed dispersal produces social groups of high relatedness. A cost of sociality is reproductive suppression; reproductive loss is partially compensated by increased survivorship and alloparental care. Subordinate adults also may reproduce or succeed to territorial status. Alloparental care occurs during hibernation when subordinate adults assist in social thermoregulation of closely related young. Thus, marmots have the characteristics of cooperative breeding. The following sequence of events is hypothesized to have occurred in the evolution of marmot sociality. Large size and a short growing season required the retention of offspring in their natal group for one or more additional years to reach maturity. Habitat saturation led to delayed dispersal, which in turn, increased survivorship. When subordinate adults remained in the social unit, they could participate in social thermoregulation and alloparental care.

Use of Roosts by the Long-Tailed Bat, Chalinolobus tuberculatus, in Temperate Rainforest in New Zealand

Abstract: Patterns of roost-switching behavior and roost reuse were investigated in the threatened New Zealand long-tailed bat ( Chalinolobus tuberculatus ) in temperate rainforest. A total of 371 roosts was monitored for 503 roost-days after radiotracking 58 bats. Bats were solitary (37.3%) or communal (62.7%). Colonies were small, averaging 34.7 bats ± 23.4 SD . Reproductive females dominated colonies, and males roosted more often by themselves. C. tuberculatus differed from other species of bats because roost-site lability was extremely high (70% of sites occupied for only 1 night), bats did not cycle around a small number of preferred roosts, females carried their young to a new roost each day, and individuals abandoned each roost simultaneously as a group. Rates of reuse were low, with 301 new roost trees found >3 years of study. All sex and age classes switched frequently between solitary and communal roosts. Solitary roosts were occupied for longer times than colonial roosts. Reproductive females predominately (although not exclusively) used colonies during pregnancy and lactation but were more often solitary during post-lactation. Ratio of communal to solitary roosts in nonreproductive bats remained the same throughout summer, but adult males switched to communal roosts more often during post-lactation, presumably to mate. We suggest that suitable roosts were abundant allowing C. tuberculatus to move frequently in response to social and thermoregulatory requirements. If the pool of suitable trees were reduced, population viability may be affected.

Perception of Scale and Resource Partitioning by Peccaries: Behavioral Causes and Ecological Implications

Abstract: Two herds of white-lipped ( Tayassu pecari ) and two herds of collared ( T. tajacu ) peccaries were monitored by aerial and ground radiotelemetry in rainforest and rainforest-savanna-wetland edge vegetation from January 1992 to January 1993 (total locations = 194) in the northern Brazilian Amazon. Small- and large-scale patterns of vegetation in their ranges were quantified and described, and dietary items were noted. One herd of white-lipped peccaries was radiotracked in the dry and wet-flood seasons and the other herd was followed only for the wet-flood season. Considering the total area of ranges of the four herds as available habitat, white-lipped peccaries used palm ( Mauritia flexuosd ) wetlands and savanna wetlands more than expected, whereas collared peccaries used terra-firme forest more often than expected. White-lipped peccaries did not show seasonal differences in habitat use. One herd of white-lipped peccaries spent more time in riverine vegetation and savanna-wetlands than the other, which preferred palm-wetlands and terra-firme forest. Collared peccaries occurred almost exclusively in terra-firme forest; they did not enter savanna-wetlands and rarely used riverine vegetation. Each species may be responding to different levels of organization of the vegetation. Collared peccaries partitioned their habitats at finer scales of resolution than white-lipped peccaries, and the two species may have different habitat requirements due to differences in body size, morphology, and behavior. Apparent requirements of white-lipped peccaries for a large-scale landscape-level mosaic of vegetation types and collared peccaries for a single large-scale vegetation type may explain the higher susceptibility of white-lipped peccaries to extirpation by anthropogenic disturbance.

Temperatures of hibernacula and changes in body composition of arctic ground squirrels over winter

Abstract: Soil temperatures near hibernacula of free-living arctic ground squirrels (Spermophilus parryii) were recorded over 3 winters (October-April 1993-1996) at Toolik Lake, Alaska. Means and minima of soil temperature at 20 burrows averaged -8.9 and -18.8°C, respectively. Soil temperatures were 5 months, which represented the duration of winter that hibernating arctic ground squirrels were actively thermogenic. Individual burrows did not differ significantly in mean soil temperature over 3 years, but significant differences in mean and minimum soil temperatures were observed among burrows. Sites of burrows with shrubby vegetation accumulated more snow and had significantly higher soil temperatures over winter than windswept sites in non-shrubby vegetation. Female ground squirrels hibernated in burrows that had significantly higher mean and minimum soil temperatures than burrows of males, and adults hibernated in burrows with significantly higher soil temperatures than burrows of juveniles. Although ground squirrels occupying colder burrows were predicted to lose more body mass during hibernation than those in warmer burrows, changes in body, fat, and lean masses over winter were not correlated with soil temperature for any sex or age. Relationships between change in body composition of hibernating arctic ground squirrels and temperatures of their hibernacula may be confounded by use of food caches, differing thermal conductance of nests, or differences in individual's energetics of hibernating not related to the gradient between body and soil temperatures.

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

Abstract: 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.

Migratory patterns of mountain lions : Implications for social regulation and conservation

Abstract: We studied movements of mountain lions ( Puma concolor ) in the southern Sierra Nevada of California from 1992–1997. We observed two distinct patterns, which likely represent strategies of mountain lions for coping with variability in abundance of their primary prey, mule deer ( Odocoileus hemionus ). Some mountain lions migrated together, often slowly, following movements of mule deer from winter range toward the summer range of their prey. Those mountain lions remained together on the eastern scarp of the Sierra Nevada and overlapped in distribution throughout the year. Other mountain lions exhibited rapid movements to disjunct summer ranges, on the western side of the Sierra Nevada, shared with mountain lions that did not occur on their winter range. Mountain lions that moved more slowly and overlapped in distribution had large annual home ranges (95% adaptive kernel; X = 817 km2), whereas mountain lions with distinct summer ( X = 425 km2) and winter ( X = 476 km2) distributions had smaller home ranges. Such disparate patterns of movement may lead to difficulties in sampling population size for mountains lions. Moreover, maintaining corridors that would allow for both patterns of movement may be critical for the conservation of these large felids. Finally, extensive overlap in the distribution of mountain lions, especially the association of one group of individuals on winter range and another on summer range for mountain lions with disjunct distributions, indicates a more flexible social system than previously described.

Does Moonlight Change Vertical Stratification of Activity by Forest-Dwelling Insectivorous Bats?

Abstract: We hypothesized that bats would not change total nightly activity in response to the lunar cycle but would exhibit a shift in habitat among vertical levels (different degrees of spatial complexity and light penetration) of temperate rainforest with changing levels of lunar light. As predicted, we found no evidence that activity of bats varied directly with intensity of moonlight. However, activity changed depending on height within the forest, and there was a significant interaction between moonlight and height. The shift between vertical levels was not expected if risk of predation was an important selective pressure, because activity was highest in the canopy and lowest at the level of shrubs on bright nights. The most likely explanation for interaction between height and moonlight is that bats adjust use of microhabitats to match distribution of prey.

Subpopulation Structure and Dispersal in Two Populations of Chamois

Abstract: Subdivision of a population into reproductive units and rates of exchanges among them may influence population dynamics. Unfortunately, subpopulation units and flows of immigration and emigration are difficult to estimate because of the lack of data on spatial behavior of individuals. By studying two populations of chamois ( Rupicapra ), 244 marked animals, and a 10-year monitoring program, we determined that subpopulation units were related closely to topographic limits in which >90% of the females were philopatric. Males had a greater tendency to disperse than females, especially before reproduction, but females did more exploratory movements. We found no difference in sex-specific dispersal rates between sites, despite differences in densities and sex-ratio. The relatively high dispersal rate of males and the lack of effects of sex-ratio and density on dispersal rates support the inbreeding-avoidance hypothesis as a main cause of dispersal. High rates of exploratory movements, especially among females, indicates that local resource competition within female groups also may play a role. Dispersal patterns have to be explained in the context of possible different motivations between sexes, related to social and spatial segregation. Moreover, we argue for an effect of topography, which determines where dispersal is possible. Accordingly, dispersal occurred at a site with continuous connections with favorable habitat. Colonization of new areas from protected reserves is limited by low dispersal rates of females and increasing isolation between favorable areas in mountains. Management and conservation policies have to take these aspects into account to predict distribution of chamois on a large scale and cope with high local densities resulting from female philopatry.

Sex-Specific Differences in Activity Patterns and Fattening in the Gray Mouse Lemur (Microcebus murinus) in Madagascar

Abstract: The gray mouse lemur ( Microcebus murinus ) is a small, nocturnal primate endemic to Madagascar and has evolved specific activity patterns to survive the dry season, a period of low food availability and low ambient temperatures. These patterns are sex-specific. I determined seasonal fluctuations of body mass and tail circumference in M. murinus under natural conditions in a dry deciduous forest of western Madagascar in 1994–1995. I compared those variables among individuals during different activity patterns. Based on mark-recapture and monitoring of sleeping sites, 73.1% of adult females but only 18.9% of adult males remained inactive for the several weeks to 4—5 months throughout the cool dry season. Inactive females stored fat before the onset of the inactive phase and lost 31.7% of their mass during the dry winter, but inactive males hardly stored fat, and their body mass did not change between onset and end of the period of inactivity. Duration of inactivity was significantly longer for females than males, due to earlier emergence of males. At the end of inactivity and activity periods, respectively, body masses and tail circumferences did not differ between inactive and active males and females. Thus, M. murinus has evolved two different strategies to survive the cool dry season: being generally active but combined with daily torpor of <24 h, and remaining inactive for days to several weeks, which might be associated with prolonged bouts of torpor.

Sex ratios in extant ungulates: products of contemporary predation or past life histories?

Abstract: Variation in mammalian adult sex ratios (ASR) is striking both within and among species. Darwin (1871) originally suggested that causes of variation included competition among males for females and predation. He also recognized that intensity of competition might be greater in species adorned with secondary sexual traits. Assuming that sexual dimorphism is a reasonable indicator of intrasexual competition, we predicted that ASR would become increasingly skewed among dimorphic species and this pattern would be exacerbated by the intensity of predation. With effects of common ancestry removed by computing phylogenetically independent contrasts, we failed to detect strong relationships between ASR and either sexual dimorphism or body mass of males or females. Presence of predators also had no consistent effect on these broader patterns, and even within Cervidae and Bovidae, there was not a solid relationship between dimorphism and ASR. The only generalized pattern that emerged was that males were killed disproportional to their abundance (74% of 31 species). However, differences between live and killed sex ratios in a population were not correlated with female or male body mass or sexual dimorphism. Our results suggest that relationships between sexual dimorphism and mortality are not as straightforward as presumed. Nevertheless, at a proximate level, predation directly affects patterns of sex ratio variation among adult ungulates, but differences in survival of sexes may arise as a direct consequence of greater age-specific mortality among males, for which the ultimate cause is likely to be selection operating differently on males and females. A challenge for the future lies not so much in the separation of proximate from ultimate factors but in evaluating what, if any, life-history traits predispose sexes to differential mortality and the extent to which predation may shape these characteristics.

Post-Breeding Distribution and Diving Behavior of Adult Male Southern Elephant Seals from Patagonia

Abstract: Seven post-breeding adult male southern elephant seals, Mirounga leonina, were tracked using satellite-relay data loggers (SRDL) in 1994-1996. Two animals also were instrumented with a time depth recorder(TDR). Animals were monitored for 31-112 days at the end of the breeding season as they left Peninsula Valdes, Argentina. Males traveled ≤1,300 km from the breeding rookery but remained in temperate waters of the SW Atlantic Ocean, between 42°S and 55°S. The maximum travel distance recorded for the entire trip for any one seal was >4,500 km. Five males swam across the continental shelf in 3-11 days and stayed along the shelf margin or break where travel rates decreased markedly and remained low, suggesting that they may have reached foraging grounds. The other two males remained on the continental shelf during the entire time that they were tracked at sea. One of them was tracked for 66 days and concentrated his activity only 6-10 km off the coast of Patagonia in two areas located 700-800 km S of Peninsula Valdes. He never dived deeper than 94 m. The diving behavior sampled by one working TDR and several SRDL were similar. Dives over the continental shelf were mostly down to the seabed. Some dives over the shelf break were to the seabed (down to 1,500 m) but most were mid-water (300-600 m) and were deeper during the day. Previously studied post-breeding and post-molt adult females from the same colony spent virtually all their time over deep water off the shelf in the latitudinal range of 36-50°S. Their movements were less localized than those of males and dives did not take them to near the ocean bottom.

Cohort Affects Growth of Males but Not Females in Alpine Ibex (Capra ibex ibex)

Abstract: We studied long-term cohort effects on chest girth and horn length in a recently established population of alpine ibex ( Capra ibex ibex ). Environmental conditions of the year of birth affected chest girth and first-annual increment of horns of males but did not affect chest girth and horns of females. Females compensated for a slow horn growth during their 1st year of life, whereas males did not. Level of polygyny of the species and environmental conditions experienced by the population could account for the occurrence of long-term cohort effects in male growth and its absence in female growth. Abundance of food resources throughout the study period allowed females to show compensatory growth. However, evolutionary constraints on growth that may exist in males of polygynous species may have prevented males from showing compensatory growth.

Relationships between Seed Fall of Three Tree Species and Peromyscus leucopus and Clethrionomys gapperi during 10 Years in an Oak-Pine Forest

Abstract: We analyzed live-trapping data from 10 years (1983-1992) of a long-term study of forest ecosystems in southern Maine to investigate relationships between seed fall of red oak (Quercus rubra), white pine (Pinus strobus), and red maple (Acer rubrum), and populations of Peromyscus leucopus and Clethrionomys gapperi. Spring populations of Peromyscus were correlated positively with crops of both red oak and white pine in the previous autumn; summer populations were correlated only with the acorn crop of red oak in the previous year. Populations of Clethrionomys were not correlated with either red oak or white pine in spring or summer. The increase from spring to summer in Peromyscus was associated positively with the magnitude of seed fall from red maple in the current year. Following years of above average acorn production of red oak, adult male and female Peromyscus weighed more than in years following low acorn production. Following 2 years of high acorn production, captures of Peromyscus were associated positively with the number of live red oaks >10 cm diameter at breast height per 0.25-ha quadrat. Group-selection logging also was associated with increased summer captures of Peromyscus per quadrat for 2 of 4 years, probably due to an increase in both herbaceous cover and fruit production of shrubs.

Food Preferences of Kinkajous (Potos flaws): A Frugivorous Carnivore

Abstract: The diet of the kinkajou ( Potos flavus ) is described from analyses of feces and observations of habituated individuals. Ripe fruit was the primary food comprising 90.6% of feeding bouts and present in 99% of feces. Leaves and flowers made up <10% of the diet. No animal prey was eaten. Seventy-eight species of fruit from 29 families were detected. Moraceae was the main plant family in the diet and Ficus was the most important plant genus. Kinkajous preferentially fed in large fruit patches. Selection indices were calculated for 37 fruit species. Compared with other large mammalian frugivores in central Panama the diet of kinkajous is most similar to the spider monkey ( Ateles geoffroyi ).

Mechanisms of Coexistence of Optimal Foragers as Determinants of Local Abundances and Distributions of Desert Granivores

Abstract: Foraging theory can be applied to the study of ecological communities. We developed and tested several local mechanisms of species coexistence based on foraging theory for a desert granivore community in a heterogeneous landscape in the Negev Desert, Israel. The most common species were Allenby's gerbil ( Gerbillus allenbyi ), Wagner's gerbil ( Gerbillus dasyurus ), and crested lark ( Galerida cristata ). Allenby's gerbils were most abundant on sandy substrates; Wagner's gerbils were most abundant on cobble and loess substrates; crested larks occurred across all three. To test among predictions of the different mechanisms of coexistence, we used live-trapping and counts to census rodents and birds, recorded spoor in sand-tracking plots to determine habitat-specific activity patterns, and measured giving-up densities in depletable food patches to estimate relative foraging efficiencies on different substrates and within different habitats. Allenby's gerbil had an advantage in habitat selection by being the most efficient forager (lowest giving-up densities on seeds in feeding trays) in the sandy habitat. The crested lark was the tolerant forager. Its foraging abilities were affected little by escape substrate, foraging substrate, or food type. As a result, the crested lark had three advantages: it was the most efficient forager in the loess habitat, it was a better insectivore than the gerbils, and its diurnal habit allowed it first access to seed patches that renew in the afternoon in the sandy habitat when winds typically arise. In response to our measures of foraging aptitude, Wagner's gerbil revealed no advantage over the other species, and factors promoting its success eluded our proposed mechanisms of species coexistence. Foraging ecology and community ecology can be integrated to understand local species distributions, abundances, and community structure and organization. Uniform conceptual and methodological techniques can be applied across taxa and communities. We were able to relatively quickly test which mechanisms of coexistence apply. In the community we studied, there were two species whose presence we feel we understood and one species whose presence remained an enigma.