Evaluation of genetic structure among black bears (ursus americanus) in Kenai Fjords National Park and the Kenai Peninsula, Alaska

Robinson, Stacie; Waits, Lisette; Martin, Ian

Black bears (Ursus americanus) represent a significant component of the fjords ecosystem in south-central Alaska. They occur throughout the coastal portions of Kenai Fjords National Park (KEFJ) and are a focal attraction for park visitors. KEFJ park managers identified resource extraction, land development, landscape fragmentation, and hunting on the Kenai as immediate threats to the coastal ecosystem and resident black bears. In 1998, KEFJ proposed a comprehensive study program on the ecology of black bears and threats to their populations. In this project we used mitochondrial DNA (mtDNA) sequencing and nuclear DNA (nDNA) microsatellite analysis to estimate the abundance of bears using park resources and evaluated phylogeography, population structure, and landscape-genetic relationships of black bears in KEFJ and surrounding areas. We used non-invasive genetic sampling and DNA-based capture-mark-recapture (CMR) analysis to provide an estimate of black bears using coastal areas within KEFJ. We used models in MARK, and DNA-specific models in Capwire and BayesN. Point estimates based on the most precise estimator (Capwire) were: Aialik 107 (95% CI 63-131); Two Arm 101 (60-154); Nuka 69 (31 132); and Harris 301 (122-750). Based on simulated CMR efforts and trap performance in this study, we recommend making more use of barbwire traps, and increasing the area covered and time period of future trapping efforts in order to achieve better recapture success and more precise abundance estimators. We analyzed mtDNA sequences, and identified 5 unique sequence variants that were closely related evolutionarily. Black bears on the Kenai and mainland showed different distributions of mtDNA lineages indicating a historical distinction between the areas. We used both aspatial and spatial Bayesian assignment tests to cluster individuals into genetically distinct groups. We identified three genetically distinct groups that clustered geographically in the Kenai Peninsula, Alaskan mainland, and Prince William Sound areas. Connectivity among genetic groups was moderate (Fst values ranging from 0.07 to 0.12), indicating that groups were separated by semi-permeable barriers across which some migrants are exchanged each generation. The definition of genetically distinct groups offers a biological basis for defining units for management. If monitored in the future, subdivision of the Kenai genetic group will provide an indicator of novel barriers or population fragmentation. To investigate spatial patterns in genetic variation we used Mantel tests to detect isolation-by distance and a Local Indicator of Spatial Association (LISA) to detect local clusters of genetic similarity. The correlation of genetic and geographic distance was weak suggesting that factors such as physical barriers or evolutionary factors exert a larger influence on genetic structure than distance alone. The LISA analysis identified spatial clusters of genetic similarity within black bears on the Kenai Peninsula. Genetic connectivity was highest within ecological zones (either western lowlands or coastal mountain forests) and lower at the interface of these ecoregions and along the Highway 1 corridor. This showed evidence that dispersing black bears may show fidelity to their natal habitat type and that anthropogenic barriers, such as highways, are likely to impede gene flow. Future monitoring of spatial genetic patterns can be used to assess impacts of novel barriers or the effectiveness of dispersal corridors.

Evaluation of genetic structure among black bears (ursus americanus) in Kenai Fjords National Park and the Kenai Peninsula, Alaska

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