Predicting the Persistence of Amphibian Populations with the Help of a Spatial Model

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Applied Ecology. Summary 1. We have used a stochastic population model with immigration to calculate extinction rates for two amphibian species: the common toad, Bufo bufo, and the crested newt, Triturus cristatus. 2. Population models for amphibians are difficult to parameterize. It was not possible to measure all the relevant parameters for the model. The other parameters were obtained from other studies or estimated on the basis of similar species. 3. Contour maps for persistence were generated using the model. The persistence of populations associated with a pond is affected both by the pond's internal dynamics and its proximity to a source pond. On a 20-generation time scale, toad ponds that were initially occupied were relatively unaffected by the proximity of a source. Persistence was almost certain (> 95%) when the average carrying capacity of a pond was greater than 30 adult females. Initially unoccupied toad-ponds were equally likely to persist if they lay within 4 km of a source and could support more than 50 adult females. Initially occupied newt ponds were likely to persist if they supported more than 40 females or lay within 0 5 km of a typical source pond. Initially unoccupied newt ponds were mainly dependent upon immigration rates. Very small ponds (Nk < 10) could persist if they lay within 0 75 km of a source pond, while large ponds (Nk >> 10) only needed to be within 1 5 km of a source pond. 4. This model allows us to use the data available, to make predictions about the criteria which must be met by a landscape to ensure the survival of amphibian populations. It offers the possibility of better predictions when the data is refined. The model also suggests directions for further research such as the statistical study of environmental variation, the nature of minimum viable populations for toads and the statistics of long-range dispersal.

Contrasting population structures in two sympatric anurans: implications for species conservation

“…Long-term variations in population size are the most important determinants of N e , but again there is no reason to suppose that these differ systematically between the two species. Both R. temporaria and B. bufo can experience substantial fluctuations in N c over long time periods (Halley et al, 1996;Meyer et al, 1998). A more likely explanation of our results is that the definitions of populations as breeding assemblages, and thus the N c estimates, were inappropriate surrogates of N e in one or both species.…”

The problem of spatial fit in social-ecological systems: detecting mismatches between ecological connectivity and land management in an urban region

“…Previous research in Stockholm Municipality has used 2 km as a maximum spring migration distance for the common toad (Löfvenhaft et al 2004;Mörtberg et al 2006). A third amphibian species of conservation interest in Stockholm County is the crested newt Triturus cristatus, for which Halley et al (1996) used 1 km as maximum dispersal distance in a population viability study. Recent restorations of wetlands in southern Sweden have improved the situation of previously regionally endangered amphibians (Nyström & Stenberg 2006;.…”

Strategies for Assessing the Implications of Malformed Frogs for Environmental Health

“…Although it is important to explore the implications of a variety of possible influences on amphibian survival and reproductive rates, ecologists are constrained by a lack of high-quality quantitative analyses of amphibian population processes. In particular, priority should be placed on obtaining a more detailed understanding of minimum viable population sizes, the influences of behavioral and competitive factors on population sizes, and more reliable data concerning population growth and replacement rates (32). Without these data, it will not be possible to generate predictions of population persistence or to determine how damaging different levels of malformation may be to amphibian populations in the long term.…”