The influence of forest fragmentation and landscape pattern on American martens and their prey.

摘要

Habitat fragmentation occurs when large tracts of an original habitat are replaced by smaller patches of two or more habitat types, largely through human activities. I studied the behavior of six measures of landscape pattern that seemed appropriate for quantifying fragmentation, and used these measures to investigate the effects of forest fragmentation on American martens (Martes americana) and their prey. The measures I selected were edge density, contagion, mean nearest neighbor distance between patches, mean proximity index, perimeter-area fractal dimension, and mass fractal dimension. To test the behavior of these measures with a variety of landscape patterns, I used a computer program to create nine series of increasingly fragmented landscapes that differed in the size and shape of patches, and in the way fragmentation was allowed to increase.; Patch size changed the range of attainable values for all measures examined, and patch shape affected all measures except nearest neighbor distance and mean proximity index. The method in which fragmentation increased within each landscape series also affected all measures. None of the measures was able to differentiate between different spatial distributions of patches.; To investigate the effects of forest fragmentation on martens and their prey, I selected 18 areas of mature forest habitat in Utah that differed in the amount of landscape heterogeneity due to natural openings and timber clearcuts. I conducted a live-trap survey of martens within each site over three summers from 1991-1993, and a 7-week snap-trap survey of small mammals within 12 of the sites in 1992.; Martens were negatively correlated with increasing fragmentation, and mean proximity index was the strongest correlate with reductions in marten captures across sites {dollar}(chisp2=9.48,{dollar} df = 1, {dollar}P=0.04).{dollar} Capture rates of red-backed voles (Clethrionomys gapperi) also declined with increasing fragmentation {dollar}(chisp2=4.66,{dollar} df = 1, {dollar}P=0.03),{dollar} while deer mice (Peromyscus maniculatus) capture rates increased {dollar}(chisp2=6.12,{dollar} df = 1, {dollar}P=0.01).{dollar} Martens and voles both appeared sensitive to landscape pattern, with low numbers in areas having large, closely spaced patches of unforested habitat.