The superpopulation approach for estimating the population size of 'prolonged' breeding amphibians: Examples from Europe

Abstract

Individual members of a population of 'prolonged' breeding amphibian species are asynchronously present at their breeding sites. Therefore, population size estimates can be misleading when based on commonly used closed or open-population capture-mark-recapture approaches. The superpopulation approach, a modified Jolly-Seber model, has been successfully applied in taxa other than amphibians with distinct migratory behaviour and where individuals are asynchronously present at the sampling site. In this paper, we suggest that the superpopulation approach is a useful population size estimator for 'prolonged' breeding amphibian species. Two case studies on European anurans show that superpopulation estimates are much higher than simple population counts. A simulation study showed that superpopulation estimates are unbiased but that accuracy can be low when either survival or detection probabilities (or both) are low. We recommend the superpopulation approach because it matches the natural history and phenology of amphibian species with prolonged breeding seasons.

Estimating roadkill rates while accounting for carcass detection and persistence using open-population capture–recapture models

“…Low recapture rates are known to cause subestimation of persistence probabilities and consequently decrease precision (Pollock et al 1990). As other studies with capture-recapture models suggest, field effort should be maximised to increase both amount of data and detection probabilities in order to estimate parameters with confidence (Wagner et al 2011). The low precision we observed for some scenarios is linked to a low number of roadkill observed: if we compare Stretch 2 and 3 for the opossum in the data subset analysis (the one with highest and lowest number of captures, respectively; Figs 4e, f ), the precision in carcass detection and persistence is a lot higher in Stretch 2 (Fig.…”

“…This is probably because more occasions result in a greater number of marked carcasses, allowing for a greater number of recaptures and longer capture histories that contain more information on carcass detection and persistence (Pollock et al 1990). For example, in Wagner et al (2011), when both persistence and detection were high (≥0.8), precision in superpopulation increased, but even if just one of these parameters was low, precision was affected. Most of our detection or persistence estimates were low or presented high uncertainty.…”

“…1990). As other studies with capture–recapture models suggest, field effort should be maximised to increase both amount of data and detection probabilities in order to estimate parameters with confidence (Wagner et al . 2011).…”

No evidence for effects of infection with the amphibian chytrid fungus on populations of yellow-bellied toads

“…Count data often underestimate true population sizes, especially of so-called 'prolonged breeding' amphibian populations (Wagner et al 2011). 'Prolonged breeding' sensu Wells (2007) means that the reproductive part of the population is asynchronous ly present at the breeding sites (where sampling takes place).…”

“…The POPAN model furthermore estimates the number of individuals present during a capture occasion and then estimates the number of individuals that enter the population between this and the following occasion. Thus, the total or cumulative population size is additionally estimated (super population approach [N], for details see Schwarz & Arnason 2007, Wagner et al 2011. For each data set, we tested whether models with constant or time-varying detection probabilities (p) provided a better fit to the data.…”