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86 2.0 Conclusions Males: Females highway n=126 powerline n=161 1.5 Jaeger et al.133 suggested four ways that roads might influ- 1.0 ence the persistence of animal populations. One important 0.5 parameter includes a decrease in habitat amount and quality 0.0 near roads. If habitat quality decreases, the animals that in- ROW 50 300 600 habit areas near roads would be expected to decrease in di- Transect versity, density, and/or abundance. The results from the dry, Figure 29. Sex ratios of deer mice, compared arid Intermountain West sagebrush country of Utah and the among transects for each treatment. mesic, coniferous forests of southern British Columbia found no consistent patterns to suggest that habitat quality differed abundance closer to the road in 2005. These conflicting trends beyond the ROW verge. The research team found no consis- suggest that roads per se do not have a direct effect on small tent pattern that small mammals were impacted close to the mammal distribution. Other factors clearly have a more road and conclude that, at least on these study sites, roads did decisive influence. Abundance and density seem to be primarily not impact habitat quality beyond the ROW. The research influenced by the presence of suitable habitat and resource team suggests other factors may be responsible for the differ- availability. Desert habitat quality is very often dependent on ences in small mammal species diversity, density, and abun- precipitation levels, which were very different in 2004 (wet) and dance that were documented. 2005 (dry). In 2004, the general habitat quality appeared to be good throughout the range. In contrast, during a drier year such 3.5 Restoring Habitat Networks as 2005, green vegetation and suitable habitat appeared to be with Allometrically Scaled limited to areas adjacent to the road, which may have acted as a Wildlife Crossings water collector and perhaps was responsible for the higher con- centration of individuals and species near the road. Introduction Similarly in British Columbia, there were no consistent pat- The placement of crossings has been a relatively hit-or-miss terns to indicate small mammal abundance or densities proposition lacking solid ecological theory to underpin the changed consistently within the forest as distance from the decision, in part because the idea of landscape permeability ROW increased. If there were demonstrated demographic ef- has not been traditionally viewed from an animal perspective. fects caused by this relatively low-volume, two-lane highway Permeability refers specifically to the ability of species of all other than those due to the simple shift in habitat type from kinds to move relatively freely across the roaded landscape. By forest to graminoid (grass) cover in the ROW, they were less this definition, landscape permeability differs from the term evident than were the effects of site or microhabitat conditions connectivity. Connectivity refers to the human perception of in the ROW. Similarly, the 60 m wide highway or transmission- how connected the landscape matrix is, irrespective of organ- line ROWs that dissected mesic coniferous forest appeared to ism scaling. Permeability implies free movement by organisms be negative for most species and potentially neutral to positive across the landscape. Stevens et al.'s224 use of the term "func- for others, with total species diversity lower in the ROW than tional connectivity" (i.e., the ability of an animal to cross a forest. This is not to suggest that impacts due to the highway landscape) is roughly equivalent to this definition of perme- itself may not exist for some species, but that large samples, ability, but relies on the concept of relative resistance of matrix highly consistent habitat conditions, and correctly focused habitat separating habitat patches. Relative resistance refers to transplant experiments may be required to detect them. the degree to which boundary conditions between habitats as well as habitat physical structure allow or impede animal movement. Animal vagility (i.e., the capacity or tendency of % Sample Juveniles 60 highway n=126 powerline n=161 50 an organism or a species to move about or disperse in a given 40 environment) differs from species to species, and with age and 30 sex class in many species. An animal's movement capabilities 20 10 define in large part its abilities to find resources necessary for 0 survival. The development of allometric equations that relate ROW 50 300 600 the home range sizes of species to movement ability allows the Transect calculation of scaling properties for individual species. Allom- Figure 30. Juveniles as a percentage of total etry is a fundamental concept in biology. It began with deer mouse sample, compared among tran- considerations of the relation between the size of an organism sects for each treatment. and the size of any of its parts; for example, between brain size