Mapping Occupied Habitat for Forest Carnivores in the American West and Estimating Their Conservation Status. (Habitat Issues)

Article excerpt

Abstract

Conservation concerns are escalating due to the small numbers, reduced range, and increasingly fragmented distribution of wide-ranging forest carnivores in the American West--specifically the lynx (Lynx canadensis), wolverine (Gulo gulo), and fisher (Mattes pennanti). Observation data from the U.S. Forest Service and state natural heritage programs were compiled and mapped. Occupied habitats and population centers for the three species were identified and population sizes estimated based upon recorded densities and distribution. The results indicate small, isolated populations well below what may be necessary for long-term viability.

Introduction

Some of the smaller forest carnivores of the American West--the lynx (Lynx canadensis), wolverine (Gulo gulo), and fisher (Mattes pennanti)--have not yet grabbed headlines like bears (Ursus spp.) and wolves (Canis lupus). Yet mounting concerns about their viability indicate that large carnivores are not the only species in jeopardy because of past and ongoing habitat loss and fragmentation, and excessive human-caused mortality. While these lesser known species were never persecuted like the wolf, grizzly bear (Ursus arctos), and other species that pose a risk to livestock, their conservation status is now suffering due to neglect.

Critical information about the habitat requirements and population sizes of these animals is lacking, leaving conservationists ill-informed at where and how to initiate conservation strategies. Existing range maps are too coarse to prioritize specific areas for protection, such as individual mountain ranges or watersheds. There are few published population estimates, and they are limited to specific study areas and fail to address the conservation status of each species throughout its range.

We can no longer take for granted the survival of wide-ranging, low-density forest carnivores. As we have done for the grizzly bear and the wolf, we should make conscious decisions about where in the western U.S. we will maintain and restore forest carnivores, and protect them and their habitat in these areas accordingly. The capacity of these areas to support forest carnivores should be assessed to ensure that sufficient habitat is protected to provide for their long-term survival and recovery. Given the forest carnivores' large ranges and low densities and the fragmented nature of suitable habitat that remains, a conservation strategy will likely require restoration and maintenance of a connected network of population centers across the western U.S. and Canada (e.g., McKelvey et al. 2000a). The objective of this paper is to identify occupied habitats and population centers for the lynx, wolverine, and fisher based on available presence/ absence data, and to estimate population sizes within these areas based upon recorded densities, as a first step toward devising a long-term conservation strategy for these species.

Mapping occupied habitat

To identify occupied habitats and population centers for the lynx, wolverine, and fisher, observation data from the U.S. Forest Service and the natural heritage programs of eight western states were gathered (Maj and Garton 1994; McKelvey et al. 2000b). These data were not collected through standardized survey techniques but include observations made by workers in the field, trapping records, and museum specimen records. State natural heritage programs maintain this data and attempt to filter out unreliable observations.

GIS software was used to highlight parcels of public lands where the observations were located. Private land was excluded from this analysis, because of the difficulty delineating borders around point locations on private lands. Administrative boundaries were convenient for this purpose on public lands, and though they have no biological basis they serve the purpose of delineating the large landscape features relevant to this scale of analysis. …