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Population Structure in Mule Deer (Odocoileus hemionus) Across Major Highways in Southern California

Released: 2017
Fraser, D., M-B. Bourne, C. Shew, R. Wayne, E. Boydston. 2017. Population Structure in Mule Deer (Odocoileus hemionus) Across Major Highways in Southern California. International Urban Wildlife Conference, San Diego, CA. 4-7 June 2017.

Urbanization is a substantial force shaping the genetic and demographic structure of natural populations. As urban areas expand, so too do transportation corridors facilitating human movement, such as highways. Further, underpasses and overpasses are generally not designed explicitly to encourage wildlife use. It is therefore not surprising that highways have been shown to pose a major barrier to gene flow in a variety of species. Research using camera traps in our study area have shown that mule deer have highly specific requirements for utilizing such structures and are known to be sensitive to roadways. Hence, deer may be more highly impacted by the isolating effects of highways. In contrast, deer are highly mobile and less restricted by territoriality than other species such as carnivores, and so may have more opportunities for reproduction, and thus geneflow, upon successfully traversing such barriers. To determine if highways form barriers to gene flow in mule deer, we used non-invasive genetic sampling to assess how populations are structured with respect to five major highways in Southern California. We collected samples from two major regions surrounding Los Angeles and Orange Counties. We genotyped 257 unique individuals across 15 microsatellite loci and a single sex marker using DNA extracted from scat. We showed that genetic distance corresponded to the magnitude of the barrier as measured by average daily traffic volumes and surrounding urban matrix. We also found that current migration rates across highways were lower than historic migration rates as inferred from genetic data, and we used a simulation to assess how temporal and spatial features of individual highways may explain mule deer population substructure. Our results indicate that both highways and urban development can contribute to genetic structuring in mule deer and reduced gene flow relative to historic rates.
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