Kenneth R. Wilson

IDENTIFYING GAPS IN CONSERVATION NETWORKS: OF INDICATORS AND UNCERTAINTY IN GEOGRAPHIC‐BASED ANALYSES

Mapping of biodiversity elements to expose gaps in conservation networks has become a common strategy in nature-reserve design. We review a set of critical assumptions and issues that influence the interpretation and implementation of gap analysis, including: (1) the assumption that a subset of taxa can be used to indicate overall diversity patterns, and (2) the impact of uncertainty and error propagation in reserve design. We focus our review on species diversity patterns and use data from peer-reviewed literature or extant state-level databases to test specific predictions implied by these assumptions. Support for the biodiversity indicator assumption was varied. Patterns of diversity as reflected in species counts, coincidence of hot spots, and representativeness were not generally concordant among different taxa, with the degree of concordance depending on the measure of diversity used, the taxa examined, and the scale of analysis. Simulated errors in predicting the occurrence of individual species indicated that substantial differences in reserve-boundary recommendations could occur when uncertainty is incorporated into the analysis. Furthermore, focusing exclusively on vegetation and species distribution patterns in conservation planning will contribute to reserve-design uncertainty unless the processes behind the patterns are understood. To deal with these issues, reserve planners should base reserve design on the best available, albeit incomplete, data; should attempt to define those ecological circumstances when the indicator assumption is defensible; should incorporate uncertainty explicitly in mapped displays of biodiversity elements; and should simultaneously consider pattern and process in reserve-design problems.

MOVEMENT PATTERNS OF RIPARIAN SMALL MAMMALS DURING PREDICTABLE FLOODPLAIN INUNDATION

Abstract We monitored movements of small mammals resident on floodplains susceptible to spring floods to assess whether and how these animals respond to habitat inundation. The 2 floodplains were associated with 6th order river segments in a semiarid landscape; each was predictably inundated each year as snowmelt progressed in headwater areas of the Rocky Mountains. Data from live trapping, radiotelemetry, and microtopographic surveys indicated that Peromyscus maniculatus, Microtus montanus, and Dipodomys ordii showed different responses to inundation, but all reflected a common tendency to remain in the original home range until “forced” to leave. The reluctance of Dipodomys ordii to abandon the home burrow often resulted in death in situ, whereas individual P. maniculatus and M. montanus moved to nearby higher ground but not necessarily toward upland. This behavior could lead to occupancy of an island that disappeared as floodwaters rose. Peromyscus maniculatus climbed into sapling cottonwood, but the quality of such arboreal refuges was unclear. We found only weak support for the hypothesis that displacement was temporary; most floodplain residents, including P. maniculatus, disappeared over the flood period. No secondary effect from flooding on adjacent upland small-mammal assemblages was detected. Our data suggest populations of facultatively riparian, nonarboreal small mammals such as M. montanus and D. ordii generally experience habitat inundation as a catastrophy. Terrestrial species capable of using an arboreal refuge, such as P. maniculatus, face a more variable risk, determined in part by timing and duration of the flood event. River regulation can affect both sets of risks.

CHANGES IN THE LANDSCAPE STRUCTURE OF A SOUTHEASTERN WYOMING RIPARIAN ZONE FOLLOWING SHIFTS IN STREAM DYNAMICS

Throughout western North America, flood regimes have been altered as a result of large-scale water impound- ments and diversions, yet the effects on riparian land- scape structure have not been quantified. Using aerial photographs and a GIS, we examined changes in the Rawhide Wildlife Management Area in southeastern Wyoming between 1937 and 1990 after shifts in the frequency and intensity of flooding of the North Platte River. The river declined in wetted area by 75% between 1937 and 1990. Also, the areal proportion occupied by cottonwood (Populus spp.) stands with 70% canopy closure decreased during this period.. indicating a shift from young, dense stands to older, more open stands. Some traditional measures of landscape structure (i.e. richness, diversity, dominance, average patch perimeter length, average patch shape), however, appeared insensitive to these changes. Finally, the proportion of the landscape that changed land types declined with increasing distance from the river. We expect further modification of the land-

Spatiotemporal Distribution of Black Bear-Human Conflicts in Colorado, USA

Abstract Management and conservation of large carnivores increasingly includes conflicts with humans. Consequently, a greater understanding of spatiotemporal trends of conflicts is needed to efficiently allocate resources and apply targeted management. Therefore, we examined spatial and temporal distribution of American black bear (Ursus americanus; hereafter, bear)–human conflicts in Colorado, USA, related to 3 conflict types (agriculture operations, human development, and road kills). We used the Getis–Ord spatial clustering statistic to describe location and assess magnitude of bear–human conflicts in Colorado during 1986–2003 and investigated temporal trends of bear–human conflicts by type. Bear–human conflicts showed distinct spatial clustering by type, and areas of high clustering overlapped conflict types. Clustering for agriculture operations conflicts had the largest overall value and overlapped counties with high sheep production. Both human development and road-kill conflict clusters were high in areas of high-quality oak (Quercus spp.)–shrub habitat in the central and southern portions of Colorados Front Range region and near the city of Durango in southwestern Colorado. Bear–human conflicts varied by year and type but overall increased during the 18 years. Summed across years, most conflicts were related to agriculture (32%), followed by road kills (27%) and human development (24%). The greatest proportion of agriculture operations–related conflicts (76%), human development–related conflicts (36%), and road kills (47%) occurred in 1988, 1999, and 2003, respectively. Considering that bear–human conflicts in Colorado increased over time and will likely continue to increase, we suggest wildlife managers improve data collection by obtaining detailed location data, categorizing conflict types uniformly, and applying conflict regulations consistently to strengthen inference of similar analyses. We also suggest that managers target efforts to mitigate damage by focusing on areas with high clustering of conflicts.

AUTUMN MIGRATION AND SELECTION OF ROCK CREVICES AS HIBERNACULA BY BIG BROWN BATS IN COLORADO

Abstract Movements, distribution, and roosting requirements of most species of temperate-zone bats in autumn are poorly understood. We conducted the 1st radiotelemetry study of autumn migrations and prehibernation roost selection of bats in western North America. Big brown bats (Eptesicus fuscus, n = 55) in the Poudre River watershed, Colorado, moved from low-elevation summer ranges to high-elevation locations in autumn, where they roosted in rock crevices during the period leading up to winter hibernation. We characterized rock crevices used as roosts in autumn at these higher elevations at microhabitat and landscape scales. We used logistic regression combined with an information theoretic approach to determine which variables were most important in roost selection. At the microhabitat scale, autumn roosts were higher to the ground above and below the exit point and were in deeper crevices that had more constant temperatures than randomly selected crevices. At the landscape scale, aspect of the hillside was important, with autumn roosts typically facing north–northwest. Autumn roosts fell into 2 categories: those used for a few days (transient roosts) and those used for ≥7 days and presumed to be hibernacula. Temperature regimes in the presumed hibernacula appear to provide optimal conditions for use of winter torpor, whereas transient roosts may offer passive rewarming and energy savings for bats still active in early autumn. Elevational segregation of sexes also was documented in our region, with a preponderance of females found at lower elevations and males at higher elevations in summer. Sex ratios at higher elevations became even in autumn. Use of short elevational migrations and selection of hibernation sites in rock crevices may be a common overwintering strategy of insectivorous bats of western North America.

Interfacing models of wildlife habitat and human development to predict the future distribution of puma habitat.

The impact of human land uses on ecological systems typically differ relative to how extensively natural conditions are modified. Exurban development is intermediate-intensity residential development that often occurs in natural landscapes. Most species-habitat models do not evaluate the effects of such intermediate levels of human development and even fewer predict how future development patterns might affect the amount and configuration of habitat. We addressed these deficiencies by interfacing a habitat model with a spatially-explicit housing-density model to study the effect of human land uses on the habitat of pumas (Puma concolor) in southern California. We studied the response of pumas to natural and anthropogenic features within their home ranges and how mortality risk varied across a gradient of human development. We also used our housing-density model to estimate past and future housing densities and model the distribution of puma habitat in 1970, 2000, and 2030. The natural landscape for pumas ...

Stochasticity in Natural Forage Production Affects Use of Urban Areas by Black Bears: Implications to Management of Human-Bear Conflicts

The rapid expansion of global urban development is increasing opportunities for wildlife to forage and become dependent on anthropogenic resources. Wildlife using urban areas are often perceived dichotomously as urban or not, with some individuals removed in the belief that dependency on anthropogenic resources is irreversible and can lead to increased human-wildlife conflict. For American black bears (Ursus americanus), little is known about the degree of bear urbanization and its ecological mechanisms to guide the management of human-bear conflicts. Using 6 years of GPS location and activity data from bears in Aspen, Colorado, USA, we evaluated the degree of bear urbanization and the factors that best explained its variations. We estimated space use, activity patterns, survival, and reproduction and modeled their relationship with ecological covariates related to bear characteristics and natural food availability. Space use and activity patterns were dependent on natural food availability (good or poor food years), where bears used higher human density areas and became more nocturnal in poor food years. Patterns were reversible, i.e., individuals using urban areas in poor food years used wildland areas in subsequent good food years. While reproductive output was similar across years, survival was lower in poor food years when bears used urban areas to a greater extent. Our findings suggest that bear use of urban areas is reversible and fluctuates with the availability of natural food resources, and that removal of urban individuals in times of food failures has the potential to negatively affect bear populations. Given that under current predictions urbanization is expected to increase by 11% across American black bear range, and that natural food failure years are expected to increase in frequency with global climate change, alternative methods of reducing urban human-bear conflict are required if the goal is to prevent urban areas from becoming population sinks.

Urban Maternity‐Roost Selection by Big Brown Bats in Colorado

Abstract Despite prevalent use of anthropogenic structures by bats and the associated implications for public health, management, and bat conservation, very little quantitative information exists about urban roost characteristics and their selection by bats. During the summers of 2001 to 2004 we conducted fieldwork in Fort Collins, Colorado, USA, situated on the northern end of Colorados Front Range, to address questions of roost selection by the big brown bat (Eptesicus fuscus). The city has experienced its greatest growth in the past half century, with its population increasing by 30% in the last decade. Similar growth in new buildings has occurred, with the number of new housing permits issued annually doubling in the past decade. We located 142 roosts using radiotelemetry or by citizen calls in response to a newspaper article and flyers. To determine characteristics of roost selectivity by bats, we compared variables for known maternity roosts and randomly selected buildings at microhabitat and landscape scales using logistic regression; we used an information theoretic approach to determine which variables were most important. We considered 44 and 100 buildings in the microhabitat and landscape scale analyses, respectively. At the microhabitat scale maternity roosts had exit points with larger areas that were higher from the ground and had warmer average temperatures than randomly selected buildings. At the landscape scale distances to similarly categorized roosts were smaller, and urbanization variables such as lower building density, higher street density, and lower traffic count density were most important. Results for variables important to urban-roosting big brown bats were often analogous to studies that characterized maternity roosts found in tree snags and rock crevices. In addition, changes in the landscape, not only in the form of anthropogenic structures but also in water availability and vegetation structure such as riparian forests, may have led to population increases and range expansions of the big brown bat. Because big brown bats appear to selectively choose specific combinations of characteristics found at maternity roosts, not all available structures can be considered suitable and exclusion from established maternity roosts may negatively impact bat populations.

Evaluation of a Density Estimator Based on a Trapping Web and Distance Sampling Theory

A new density estimation technique using a trapping web and distance sampling theory was evaluated using Monte Carlo methods. A sophisticated computer algorithm simulated movement of small mammals according to four different home range utilization distributions. Trapping of small mammal populations was simulated with four spatial patterns, two population densities, and three realistic average capture probabilities; in total, 8151 replications were evaluated. Percent relative bias of the estimator of density ranged from -4 to 29% for average capture probabilities (p) of .16 and .24, and from - 17 to 30% at p = .09. Average coefficients of variation were 7.8-9.8% at a density (D) of 100 individuals/ha and 15.1-19.1% at D = 25 individuals/ha. Achieved confidence interval coverage for the density estimator ranged from 32 to 94%, under the assumption of a 95% nominal level. An improved variance estimator for the trapping web was developed that should improve the confidence interval coverage. The trapping web approach appears very promising in aiding the manager or researcher to obtain reliable density estimates for small mammal populations. The statistical theory underlying this estimation method is well developed and is based on relatively few assumptions.

Patterns of Small Mammal Density and Survival Following Ski-Run Development

Abstract We investigated short-term effects of ski-run development on the dynamics of small mammal populations at Vail Ski Area, Colorado. We compared a new ski run, an experimental ski run with added woody debris, a forest adjacent to a new ski run, and a control forest outside ski development by estimating density and survival of common small mammals using Pollocks robust design. In 4 summers (1998–2001), 16,800 trap nights resulted in 1,276 captures of 668 individuals. Before ski-run development, Clethrionomys gapperi was most abundant in forested areas, but after, density was greatest in the forested site adjacent to a new ski run and next highest on the experimental ski run. C. gapperi survival was similar across sites and years. Peromyscus maniculatus and Tamias minimus densities were greatest on the ski run without woody debris and lowest on the forested control site. Estimated survival of T. minimus varied more by year than by site. Greatest densities of Phenacomys intermedius occurred on the 2 ski runs in years following development, and densities were low on forested sites. Peromyscus maniculatus and Phenacomys intermedius captures were insufficient to estimate survival. Our results suggest that C. gapperi, in the short term, will inhabit ski runs with tree islands and woody debris. Additional studies on impacts of ski-run development are needed to understand small mammal responses and to promote effective management strategies for maintaining populations of forest-dwelling animals.