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Neuchâtel, Switzerland

Schmidt B.R.,KARCH | Schmidt B.R.,University of Zurich | Ursenbacher S.,KARCH | Ursenbacher S.,University of Basel
Zeitschrift fur Feldherpetologie | Year: 2015

Environmental DNA (or eDNA) is a novel method to detect the presence of species in lentic and lotic aquatic environments. Small volumes of water (15 ml) can be sufficient to detect a species in a pond. In the laboratory, PCR is used to detect the DNA of the study species. Several studies compare detection probabilities of eDNA and methods commonly used by field herpetologists. Using the Crested newt (Triturus cristatus) as a model species, these studies showed that eDNA has higher detection probabilities than other methods. Environmental DNA is often cheaper than other methods when all costs of a survey are considered. Because there is a relationship between the concentration of eDNA and abundance, eDNA may in the future be used to estimate abundance. © Laurenti-Verlag, Bielefeld. Source

Wagner N.,University of Trier | Pellet J.,KARCH | Lotters S.,University of Trier | Schmidt B.R.,KARCH | And 2 more authors.
Amphibia Reptilia | Year: 2011

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. © 2011 Brill Academic Publishers. Source

Werner P.,University of Trier | Lotters S.,University of Trier | Schmidt B.R.,KARCH | Schmidt B.R.,University of Zurich
Journal of Zoology | Year: 2014

Parapatry is a remarkable distributional pattern where the ranges of two species come into contact but only narrowly overlap. Theory predicts and empirical data suggest that parapatric range margins are most likely to form along environmental gradients when there is interspecific competition. Here, we study the ecology of the narrow contact zones of two parapatric European land salamanders, Salamandra salamandra and Salamandra atra. Previous research showed that abiotic conditions determine parapatric range margins of these two species. However, in contrast to other parapatric salamander species and theoretical predictions, there is no evidence for competitive interactions in the two Salamandra species. To study whether competition restricts these species' ranges and to understand local syntopic co-occurrence within their contact zones, we used site-occupancy models (1) to assess species-habitat relationships and (2) to test whether there is evidence for competition. We found that the two salamanders show dissimilar species-habitat relationships. The slope of the site positively affected the site-occupancy probability of S.salamandra, while none of the habitat characteristics explained the occupancy probability of S.atra. The local presence of one species had no effect on the occupancy probability of the other, suggesting that there is no effect of competition on local occurrence or that competition does not lead to spatial segregation. To fully understand the mechanisms that determine the parapatric range margins between the salamander species and to unravel the role of interspecific interactions, it is necessary to further study species' functional traits. © 2013 The Zoological Society of London. Source

Schmidt B.R.,KARCH | Schmidt B.R.,University of Zurich | Kery M.,Swiss Ornithological Institute | Ursenbacher S.,KARCH | And 4 more authors.
Methods in Ecology and Evolution | Year: 2013

The use of environmental DNA (eDNA) to detect species in aquatic environments such as ponds and streams is a powerful new technique with many benefits. However, species detection in eDNA-based surveys is likely to be imperfect, which can lead to underestimation of the distribution of a species. Site occupancy models account for imperfect detection and can be used to estimate the proportion of sites where a species occurs from presence/absence survey data, making them ideal for the analysis of eDNA-based surveys. Imperfect detection can result from failure to detect the species during field work (e.g. by water samples) or during laboratory analysis (e.g. by PCR). To demonstrate the utility of site occupancy models for eDNA surveys, we reanalysed a data set estimating the occurrence of the amphibian chytrid fungus Batrachochytrium dendrobatidis using eDNA. Our reanalysis showed that the previous estimation of species occurrence was low by 5-10%. Detection probability was best explained by an index of the number of hosts (frogs) in ponds. Per-visit availability probability in water samples was estimated at 0·45 (95% CRI 0·32, 0·58) and per-PCR detection probability at 0·85 (95% CRI 0·74, 0·94), and six water samples from a pond were necessary for a cumulative detection probability >95%. A simulation study showed that when using site occupancy analysis, researchers need many fewer samples to reliably estimate presence and absence of species than without use of site occupancy modelling. Our analyses demonstrate the benefits of site occupancy models as a simple and powerful tool to estimate detection and site occupancy (species prevalence) probabilities despite imperfect detection. As species detection from eDNA becomes more common, adoption of appropriate statistical methods, such as site occupancy models, will become crucial to ensure that reliable inferences are made from eDNA-based surveys. © 2013 British Ecological Society. Source

Werner P.,University of Trier | Lotters S.,University of Trier | Schmidt B.R.,KARCH | Schmidt B.R.,University of Zurich | And 2 more authors.
Ecography | Year: 2013

Abrupt range limits of parapatric species may serve as a model system to understand the factors that determine species' range borders. Theory suggests that parapatric range limits can be caused by abiotic conditions along environmental gradients, biotic interactions or a combination of both. Geographic ranges of the parapatric salamanders, Salamandra salamandra and S. atra, meet in small contact zones in the European Alps and to date, the cause of parapatry and the restricted range of S. atra remain elusive. We combine multivariate approaches and climatic data analysis to explore niche differentiation among the two salamanders with respect to the available climatic environment at their contact zones. Our purpose is to evaluate whether climatic conditions explain the species' sharp range limits or if biotic interactions may play a role for range delimitation. Analyses were carried out in three contact zones in Switzerland to assess possible geographic variation. Our results indicate that both species occur at localities with different climatic conditions as well as the presence of a strong climatic gradient across the species' range limits. Although the species' climatic niches differ moderately (with a wider niche breadth for S. atra), interspecific niche overlap is found. Comparisons among the contact zones confirm geographic variation in the species' climatic niches as well as in the conditions within the geographically available space. Our results suggest that the change in climatic conditions along the recognized gradient represents a determining factor for species' range limits within contact zones. However, our analyses of geographic variation in climatic conditions reveal that both salamander species can occur in a much wider range of conditions than observed within contact zones. This finding and the interspecific climatic niche overlap within each contact zone provides indirect evidence that biotic interactions (likely competition) between the two species may also determine their range limits. © 2013 The Authors. Source

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