The conservation of Allegheny woodrats in Indiana

Timothy J Smyser, Purdue University

Abstract

Allegheny woodrats are a native rodent of the eastern deciduous forest ranging from New York in the north, Tennessee in the south, and extending as far west as Indiana. Allegheny woodrats have declined dramatically over the last 40 years with dwindling abundance and the extirpation of populations noted throughout much of the species' range, although declines have been most pronounced among peripheral populations. Three interrelated and synergistic factors have been identified as potential causes for the range-wide decline, including: (1) habitat fragmentation, (2) reduced hard mast availability, and (3) increased exposure to raccoon roundworm. Within the context of the Indiana Allegheny woodrat metapopulation, examination of habitat attributes associated with these hypotheses across both extirpated and extant populations revealed site-specific factors which likely contributed to the extirpation of some populations. Specifically, this analysis revealed habitat fragmentation and associated heightened levels of raccoon roundworm exposure likely contributed to the extirpation of the woodrat population at Noe's Park Bluff. Alternatively, the woodrat population at The Narrows appears to suffer in response to a lack of diversity among mast producing species which would make this population susceptible frequent mast failures. Declines and extirpations among other populations (Bull's Point Bluff, Indian Hollow, Tobacco Landing, and Rabbit Hash Ridge) may be attributable to spatial isolation in combination with small population sizes and a history of population bottlenecks, a context in which genetic diversity would be lost rapidly through genetic drift and allow inbreeding depression to contribute to local declines. To quantify the potential for a loss of genetic diversity to impact local population dynamics I used 11 microsatellite markers developed for Allegheny woodrats to characterize patterns of genetic diversity for both the declining Indiana Allegheny woodrat metapopulation and a robust woodrat metapopulation in southwestern Pennsylvania. I documented significantly lower levels of genetic diversity among the Indiana metapopulation with allelic richness across subpopulations ranging from 1.18 to 2.36 and levels of heterozygosity ranging from 7% to 47% relative to allelic richness values of 2.09 to 3.91 and heterozygosity values of 35% to 58% among the subpopulations of the robust Pennsylvania metapopulation. This analysis revealed the loss of genetic diversity threatens the persistence of the Indiana Allegheny woodrat metapopulation. Additionally, I conducted an experimental translocation of Allegheny woodrats to gain a greater understanding of the role raccoon roundworm exposure played on population dynamics and to evaluate the potential for genetic rescue of genetically impoverished populations. Specifically, I released wild-caught woodrats into 6 disjunct populations in Indiana with 3 of the populations receiving treatment to mitigate woodrat exposure to raccoon roundworm and 3 remaining as unmanipulated controls. To evaluate the potential for genetic rescue effect, 2 of the 6 translocated populations reflected the release of individuals into occupied sites (supplementations) while individuals among the remaining 4 translocated populations were released into previously occupied habitats (reintroductions). In sum 4 of the 6 populations persisted over the subsequent 2 year period with local abundance at these 4 sites approaching historic highs. Raccoon roundworm exposure appears to have contributed to the failure of 1 population. The failure of the other translocation was likely attributable other deleterious effects associated with raccoons (predation or competition for denning resources) or demographic stochasticity. The raccoon roundworm mitigation I conducted successfully reduced local roundworm exposure levels. Additionally, the strong demographic response associated with the genetic recovery of the supplemented populations suggests the release of a limited number of individuals was sufficient to elicit a genetic rescue effect.

Degree

Ph.D.

Advisors

Rhodes, Purdue University.

Subject Area

Ecology|Genetics|Conservation biology

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