title: How much gene flow is needed to avoid inbreeding depression in wild tiger populations?
abstract: The number and size of tiger populations continue to decline owing to habitat loss, habitat fragmentation and poaching of tigers and their prey. As a result, tiger populations have become small and highly structured. Current populations have been isolated since the early 1970s or for approximately seven generations. The objective of this study is to explore how inbreeding may be affecting the persistence of remaining tiger populations and how dispersal, either natural or artificial, may reduce the potentially detrimental effect of inbreeding depression. We developed a tiger simulation model and used published levels of genetic load in mammals to simulate inbreeding depression. Following a 50 year period of population isolation, we introduced one to four dispersing male tigers per generation to explore how gene flow from nearby populations may reduce the negative impact of inbreeding depression. For the smallest populations, even four dispersing male tigers per generation did not increase population viability, and the likelihood of extinction is more than 90% within 30 years. Unless habitat connectivity is restored or animals are artificially introduced in the next 70 years, medium size wild populations are also likely to go extinct, with only four to five of the largest wild tiger populations likely to remain extant in this same period without intervention. To reduce the risk of local extinction, habitat connectivity must be pursued concurrently with efforts to increase population size (e.g. enhance habitat quality, increase habitat availability). It is critical that infrastructure development, dam construction and other similar projects are planned appropriately so that they do not erode the extent or quality of habitat for these populations so that they can truly serve as future source populations.
authors.affiliation: Department of Fisheries, Wildlife and Conservation Biology, University of Minnesota, St Paul, MN 55108, USA kenn0005@umn.edu.
authors.forename: John
authors.initials: J
authors.lastname: Kenney
authors.affiliation: Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.
authors.forename: Fred W
authors.initials: FW
authors.lastname: Allendorf
authors.affiliation: International Trust for Nature Conservation, 3c Gunnersbury Avenue, Ealing Common, London W5 3NH, UK.
authors.forename: Charles
authors.initials: C
authors.lastname: McDougal
authors.affiliation: Department of Fisheries, Wildlife and Conservation Biology, University of Minnesota, St Paul, MN 55108, USA.
authors.forename: James L D
authors.initials: JL
authors.lastname: Smith
mesh_terms: D000818:Animals; D003247:Conservation of Natural Resources; D017753:Ecosystem; D005260:Female; D051456:Gene Flow; D005828:Genetics, Population; D007178:Inbreeding; D008297:Male; D008957:Models, Genetic; D009390:Nepal; D011156:Population Density; D046010:Tigers / Q000235:genetics*
keywords: conservation; extinction probability; gene flow; inbreeding depression; risk analysis; tigers