Scaling population density and spatial pattern for terrestrial, mammalian carnivores

Abstract

A large part of ecological theory has been developed with the assumption that intra- and inter-specific patterns of density and spatial distribution can be consistently and reliably compared, and that these patterns have represented populations across nonstudied landscapes. These assumptions are erroneous. We found that log population density estimates consistently decreased linearly with log spatial extent of study areas for species of terrestrial Carnivora. The size of the study area accounted for most of the variation in population estimates, and study areas increased with the female body mass of the study species. But study sites consistently had higher densities than can be expected for nonstudy sites, regardless of the size of the study area, because study sites are typically chosen based on a priori knowledge of high density. Inter-specific comparisons of density and distribution might provide more insight into community organization after intra-specific density estimates have been scaled by the study areas, and related to the nonstudied landscapes within each species' geographic range.

The Demography and Dynamics of an Expanding, Managed African Wild Dog Metapopulation

“…Comparative data from larger, unmanaged populations were obtained from published literature (Fuller et al, 1992;Creel et al, 2004) and in many cases were derived from study areas comprising just a small proportion of the population. Such data are susceptible to selection biases, as field studies tend to be conducted in areas where study populations are at higher densities (Smallwood & Schonewald, 1996). As a result, density estimates in these populations are likely to be overestimates for the unmanaged populations they represent.…”

Animal Burrowing Attributes Affecting Hazardous Waste Management

“…Animal density can range Ͼ100-fold from low to high density (Smallwood and Schonewald 1996), whereas the average burrow volume might range 10-fold from low to high volumes among studies for a single species. If animal density of a species reportedly varies from 1 to 100 individuals/ha, and if burrow volume per individual varies from 0.05 to 0.5 m 3 /yr, then the product of density and burrow volume can yield 0.05-50 m 3 /ha/yr, a 1000-fold range of uncertainty mostly due to the uncertainty in density.…”

“…A conspicuous absence of a burrowing animal species could indicate that the environmental impact of the site has already occurred. Alternatively, animal species are naturally clustered across their range (Smallwood and Schonewald 1996), and these clusters shift locations through time (Koford 1958, Taylor and Taylor 1977, Boer 1981. The species population that should occur at a hazardous waste site according to range maps might occur nearby just because the population shifted locations a few years previously.…”

“…The number of individuals per unit area is one of the most important influences on estimates of annual burrow volume per unit area and percentage of ground covered by excavated soil mounds. However, animal density is meaningless without being defined on spatial and temporal scales (Smallwood and Schonewald 1996). In addition to resolving density to the spatial scale of interest and season of the year, density needs to be predicted separately for mechanically unaltered soils, backfilled soils, and edge conditions.…”

“…McKenzie and others (1986) also averaged one to three density estimates per species. Averaging density was inappropriate because density can increase Ͼ1000-fold from low to high as the spatial extent of the study area is reduced from the largest to smallest reported in the literature (Smallwood and Schonewald 1996). Not all the resident burrowing species were included, and no distinctions were made in burrow parameters among soil conditions such as backfill, edge, and overlying vegetation.…”