Amphibian conservation in human shaped environments : landscape dynamics, habitat modeling and metapopulation analyses

Global biodiversity is experiencing a worrying decline. Habitats destruction, associated to their degradation and fragmentation are among the greatest causes. Amphibians are particularly interesting because they are more threatened and decline more rapidly than either birds or mammals. In this context, the objective of our research is to improve some methodological approaches and offer practical scientific bases for decision making in landscape management and amphibian conservation. Our study focuses on fragmented Swiss landscapes. We developed a method that uses land-cover data and expert knowledge to enable a spatially explicit assessment of 1) the temporal changes in the nature conservation value of the landscape and 2) the rehabilitation potential of the landscape. We applied this Geographical Information Systems (GIS) based approach in the Swiss Rhone plain and we used the years 1900 as the reference state. The method constitutes a helpful tool for communication, decision-making and biological conservation management in landscape planning. Effective and optimal species management strategies can only be formulated after relationships between species distribution and environmental factors have been identified. Concerning amphibians, several approaches exist but they generally suffer from two limitations: 1) the spatial autocorrelation (i.e. the dependency between two observations) in data is rarely explicitly analyzed, even if it may affect the accuracy of species-habitat relationships models. We showed how this spatial autocorrelation can be measured and included in logistic models with the example of the agile frog (Rana dalmatina) in north-eastern Switzerland. We used the Moran's I and the autologistic model (i.e. a logistic model including a measure of the spatial arrangement of the response variables). We found that if spatial autocorrelation is not considered, then conclusions on species-habitat relationships can be incorrect. 2) The effect of landscape on amphibian occurrence in ponds is often assumed to be equal in every direction (isotropic). However, barriers and inhospitable surfaces may reduce movement patterns and the area around ponds accessible to species. This implies that the ideal circular area has in reality a shape depending on the surrounding landscape. We developed a method to determine the effect of habitat variables on amphibian species distribution, considering physical barriers in their movement around ponds. We studied two amphibian species: the common toad (Bufo bufo) and the common frog (Rana temporaria) in the Rhone plain. We demonstrated that reducing the boundaries of circular area following barriers, allowed to compute landscape predictors which better explained species distribution. These results suggested that the proposed approach is more pertinent than the traditional circular buffers analysis. Our results stress the necessity to consider barriers and ecological corridors in species distribution models in o