Level-dependence of the relationships between amphibian biodiversity and environment in pond systems within an intensive agricultural landscape

Abstract

Wetlands, especially ponds, and their associated amphibian biodiversity are threatened by agricultural intensification. To improve conservation planning of these ecosystems, we need to understand at which scales biodiversity responds to human-induced disturbances. This study aims to assess the level-dependence of environment-amphibian biodiversity relationships in 150 ponds in an intensive agricultural landscape in Seine-et-Marne (France). Amphibian diversity surveys, site characteristic measurements and landscape descriptions are analysed. The hierarchy of the effects of local and regional variables on species richness, regional heterogeneity of species composition and species occurrences is investigated at three spatial levels: pond level, 1-, and 4-km(2) level. Species richness is negatively influenced at all levels by the fish presence. Water quality and pond density, which emphasize level-dependent effects, significantly increase species richness at the local and regional levels, respectively. With few exceptions, species occurrence analysis shows similar patterns, confirming, locally, the importance of fish avoidance, and, regionally, the need for increasing pond density. Environmental variables have no effect on the regional heterogeneity of species composition, questioning the potential existence of dispersal processes at scales above 1 km(2). This study highlights the relevance of a pond-group-centred approach compared to a pond-centred approach with regard to pond conservation in agricultural landscapes.