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- High dispersal in a frog species suggests that it is vulnerable to habitat fragmentation

4. Discussion

Our study shows that current and historical rates of dispersal are exceptionally high in Rana luteiventris. Other studies have also shown high dispersal rates in some amphibians (Alford & Richards 1999; Marsh & Trenham 2001), but this is the first study, to our knowledge, to quantify amphibian dispersal using formal capture-recapture analysis in replicate basins and to confirm that current dispersal patterns are representative of historic patterns with genetic analysis. Moreover, this is the first study, to our knowledge, to document high dispersal rates between low and high elevation populations of amphibians, suggesting that populations in these different habitats are connected demographically. The negative relationship between return rate and the number of toes clipped in Marten Creek indicates that capture, survival, and/or movement probabilities are negatively affected by toe-clipping in this basin, and we are currently investigating the effects of toe-clipping on each of these parameters in more detail. The general agreement between the capture-recapture and microsatellite data, however, suggests that any effects of toe-clipping on movement rates are subtle.

High dispersal rates in R. luteiventris and other amphibians suggest that dispersal plays an important role in the population dynamics of some amphibians and that isolation of these populations through habitat fragmentation may increase extinction rates. Dispersal of amphibians can be impeded by roads, urbanization and clear-cutting of forests (Hitchings & Beebee 1997; Johnston & Frid 2002) and several studies indicate that dispersal is important for amphibian population persistence. For example, extinction probability is correlated with population isolation in pool frogs (Sjögren 1991) and the dispersal of stream salamanders from downstream to upstream sections increases population growth rates of upstream sections (Lowe 2003). The maintenance of habitat connectivity should therefore be a high priority for amphibian conservation. It seems likely that other amphibian species also have high dispersal rates, but this can only be verified by studies designed to quantify dispersal over large distances. We feel that capture-recapture and genetic analyses should be applied more widely for estimating amphibian movement rates to determine whether high dispersal rates are more common in amphibians than was previously recognized.


This project was funded by the US Department of the Interior's Amphibian Research and Monitoring Initiative and a seed grant from the Declining Amphibian Populations Task Force to W.C.F.; W.C.F. was also funded by an NSF Graduate Research Fellowship, the NSF Training-WEB, and Bertha Morton Scholarships from the University of Montana. We thank S. Adams, R. Benson, B. Bentz, G. Brownworth, C. Crowder, R. Greene, N. Johnson, P. Lizon, C. Richey, and several volunteers for help with capture-recapture field work and Rodd Gallaway and Jill Davies for field accommodations. We thank P. DeVries, B. Maxell, S. Mills, A. Sheldon, M. Schwartz, and D. Tallmon for comments on earlier versions of this manuscript. We also thank Mark Lindberg for advice on multistate capture-recapture analysis. This project was approved by the Animal Care and Use Committee at the University of Montana. This is publication number 72 of the Yanayacu Natural History Research Group.

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