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Open Access Publications from the University of California

The John Muir Institute of the Environment supports innovative interdisciplinary research, teaching and outreach activities which respond to problems in the environment and strengthen the scientific foundation for environmental decision making.

The John Muir Institute of the Environment champions research and service at the University of California, Davis which benefits the biological, physical and human environment. The institute provides campus-wide leadership, hosts centers and projects, and seeds research and educational initiatives to solve environmental problems. Their activities link traditional academic and administrative units by providing the intellectual setting for interaction between researchers, regulatory agencies, policy-makers and the public to find solutions to complex environmental problems.




Habitat and population fragmentation as a result of human disturbance in the form of human transportation and settlement corridors is affecting the viability of wildlife populations worldwide. I studied dispersal, inter-population movement and population fragmentation of grizzly bears near the southern extent of their North American range in southwestern Canada and northwestern U.S.A. This area represents the interior portion of the southern edge of grizzly bear distribution following 100 years of range contraction. I address whether anthropogenic fragmentation has affected grizzly bear populations in this vulnerable area. Human attitudes toward grizzly bears, and large carnivores in general, have experienced a paradigm shift from active persecution towards tolerance and respect. However, major forces underpinning range contraction, including human-caused mortality and fragmentation, may be still operating, albeit, more subtly and less intentionally. Checking further range contraction requires specific knowledge of the processes at work. Improvements have been made in managing and monitoring human-caused mortality; however, besides the obviously isolated populations (e.g., Yellowstone National Park), the status of fragmentation in this region was largely unknown. My goals were to use genetic analyses to explore bear movement and dispersal within and between the relictually inhabited mountain ranges in southwestern Canada and test whether or not the human environment associated with linear transportation and settlement corridors is fragmenting grizzly bear populations. I genetically sampled and generated 15-locus microsatellite genotypes for 835 bears across approximately 100,000 km2 in immediately adjacent geographic areas separated by various levels of human disturbance associated with highways and associated human development. I used population assignment techniques, parentage analysis, cluster analysis, multiple linear regression and several matrices of population genetics. I found evidence of natural and human-caused fragmentation, identified fragmenting forces, established population and sub-population boundaries in the region, identified small vulnerable sub-populations, and discussed these in relation to factors that make bears susceptible to fragmentation. Female movement was restricted by human transportation and settlement corridors, and male movement appeared to be reduced in some areas. Fragmentation by north/south-oriented human-settled valleys and by major east/west transportation corridors has resulted in a partially fragmented set of local sub-populations varying in size and intensity of fragmentation. I found one small isolated population (n 300). Through multiple linear regression, I implicated human settlement patterns, human-caused mortality, and highway traffic volume as inhibiting inter-population movement. Because several fragmented sub-units are small, maintaining regional connectivity may be necessary to ensure long-term persistence. Despite grizzly bear vagility, their conservative dispersal behaviour and difficulty in living close to humans makes maintenance of regional connectivity challenging. This work demonstrates, at a regional scale, the impact that transportation corridors and their associated settlements can have on movements of animals, and highlights the ultimate effect this may have on populations. The historical mechanisms of range contraction (fragmentation and human-caused mortality) appear to still be operating and require mitigating management strategies. My results suggest that these strategies must focus on linkage zone development and highway crossing structures, as well as mortality management beyond the roadway and within adjacent populations.




Studies from different continents have proved amphibians to be the most frequently killed vertebrates on roads. In Central-Europe their ratio is between 70 and 88 percent. Local populations are known to become extinct or genetically isolated, and avoidance is also recognised, especially where the road network is dense and the traffi c is intensive. Besides ecological and conservation considerations, amphibian road kills also present a hazard for motorists when amphibians migrate in large numbers. Mitigation measures for amphibians have been applied since the 1960s. In Central-Europe the fi rst amphibianrelated culvert modifi cation occurred at Parassapuszta, Hungary, in 1986. A number of amphibian-oriented mitigation measures have been made in the region under roads and motorways since then, especially after 1995. The aim of this paper is to describe the main features of these constructions, overview the different designs, and make suggestions for their improvement as well as for future amphibian-oriented mitigation measures in general. A total of 31 road sections was monitored. Besides amphibian tunnels, game passages and game bridges were also investigated. Both the detailed characterisation of the technical solutions and the survey of amphibian populations and habitats were included in the methodology. The investigation of the tunnel systems showed a great diversity, e.g., in tunnel and fence material, their position in relation to the road, and connections between them. For economical reasons concrete tunnels were the most common. Both circular and square cross-section tunnels were in place. The accessibility of the entrance was a possible problem, especially in areas where erosion is considerable. Plastic mesh and concrete fences were both applied with a height fl uctuating between 45 and 70cm. Plastic fences are usually fi xed to wooden poles, which need to be checked before the migration period starts. However, the advantage of such fencing is fl exibility, which makes possible, e.g., the turning back of its ends to prevent amphibians from getting on the road. Some systems did not work because certain elements (usually fences) were in bad condition. Elsewhere lack of maintenance reduced the effi ciency of mitigation measures. Missing elements should be replaced immediately, even if the amphibian migration period is over, because other animals, e.g., small mammals, also use these systems. The lowest distance between tunnels in amphibian mitigation systems is 40m in the region (Kudowa Zdrój, Poland). Usually, amphibian tunnels were placed 50-100m from each other, which is an acceptable distance. In case of adequate fencing, game passages and game bridges would also be appropriate for the crossing of amphibians as well as reptiles and small mammals, similar to slightly modifi ed existing culverts under high road mortality sections, and there would be a need for such conservation improvements at several sites. As a result of this work, several recommendations on the maintenance of amphibian tunnels and fences were also developed. Further cooperation among different agencies and organisations was urged, nationally as well as internationally. The improvement of public relation activities on fauna passages also seems to be needed for the effective protection of wildlife on roads.