Population Dynamics, Distribution,
William R. Clark, Ph.D. & Todd Gosselink, Ph.D.
IOWA STATE UNIVERSITY
Iowa Department of Natural Resources
A major emphasis of our project has been on population and landscape genetics, evaluating the genetic similarity of the Iowa population in relation to other bobcat populations in the Midwest. Genetic methods have increasingly become an integral component of conservation of wild animal populations. By examining DNA we can identify "population structure" that reveals how factors such landscape barriers (such as roads, rivers, mountains, cities, or unsuitable habitat) or simply geographic distance influences animal movement and the potential for individuals to settle in new areas and interbreed. Understanding how and why bobcats are structured into populations will help conservationists to anticipate how they might respond to habitat loss, recover from local extinction, spread disease, or even evolve in response to long-term trends like global climate change. Dawn Reding just completed a Ph.D. dissertation in which she used DNA analysis to investigate the patterns and mechanisms of population structure for bobcats within Iowa, around the Midwest, and across the entire United States.
Within Iowa, we analyzed tracking data from 23 radio-collared animals along with genetic markers from 625 individuals. Consistent with our other data on habitats, the tracking data indicated that bobcats prefer forest and grassland habitats when moving across the landscape and thus, many parts of Iowa pose a high level of "resistance" to bobcat movement (in figure to right note the sparse number of potential paths across row crop landscapes linking bobcats in southern Iowa with those in northeastern Iowa; in contrast there are lots of linkages across southern Iowa). Somewhat surprisingly we did not find that these distinct habitat preferences translated into differentiated genetic structure among individuals within Iowa. In practical terms this means that where habitat exists in Iowa bobcats have the potential to disperse and interbreed.
But preference for forest and avoidance of cropland did affect how Iowa bobcat populations are genetically linked with bobcats in surrounding states. We analyzed DNA in 1447 tissue amples contributed by cooperators from 15 Midwestern states. We identified 6 genetic populations separated by both physical barriers (large expanses of row crop agriculture and a major waterway) and cryptic boundaries (zones of sharp changes in habitat type) (map right shows the 6 color-coded genetically identifiable populations; it also shows the areas in tan where bobcats could legally be harvested at the time of this study). Recently-established populations in Iowa and northern Missouri, places where 30 years ago bobcats were virtually absent, were closely linked with bobcats to the southwest (eastern Kansas and southern Nebraska), but they showed little genetic input from populations to the north and east. Thus, large scale habitat fragmentation is influencing how bobcats are rebounding in the Midwest. The results at the regional scale emphsize the importance of understanding how wildlife management actions in surrounding states may impact Iowa's expanding bobcat populations, and vice versa.
Once we had uncovered the population structure evident within the Midwest, we became even more interested in whether landscape barriers had led to genetic divergences among bobcats that might correspond to the previously delineated subspecies across the range. We analyzed DNA data for 1704 samples from across the entire United States, including samples from 9 of the 12 recognized subspecies. We found that although genetic patterns were loosely congruent with subspecific designations, the genetic data supported only two historically independent eastern and western groups of descendants which adjoin along the Great Plains in the central United States. The data support two distinct refugia during the Pleistocene (the period of repeated glaciations that began about 2.5 million years ago; in the figure below the range of bobcats is tan and currently recognized subspecies are delineated by white lines; the Eastern group (mitochondrial DNA subclade) are in red, the Western group in green and yellow, and the blue group is ancestral to both). The groups were separated by the relatively arid and treeless conditions in the center of the continent during the Pleistocene and bobcat populations likely expanded since the glaciers receded about 11,000 years ago. The distinct genetic sequences that we discovered in the few Mexico samples we analyzed suggests that unique genetic characteristics of Mexico's bobcat population should be further investigated.
As a carnivore and furbearer, the bobcat is a species of ecological and economic importance, and the understanding of population structure that we have gained through this study is fundamental to properly managing and conserving them. Bobcat populations do not correspond to political boundaries, as both the regional and national analyses demonstrated. Given that bobcats are an internationally regulated species under CITES these findings could become integral to management decisions. The study emphasizes that large scale landscape changes, whether caused by glaciers or human activities, have ecological and evolutionary effects that have influenced populations of bobcats in the past and will continue to do so for a long time into the future.
of Ecology, Evolution, and Organismal Biology
Ecology and Evolutionary Biology