Anuran abundance and persistence in agricultural landscapes during a climatic extreme

Climate change in concert with habitat loss and degradation are major threats to global biodiversity. As part of climate change, the occurrence of extreme climatic events is expected to increase. Agricultural intensification has led to the increased homogeneity of agricultural habitats and declines in farmland species diversity. We investigated the abundance of common frog Rana temporaria populations in boreal farmlands in relation to multiple scales of landscape structure during years 2002-2003, and the effect of habitat structure on R. temporaria population persistence during a severe drought. On average, 113 and 24 egg clutches were observed per site in years 2002 and 2003, respectively. This dramatic decline was synchronized over the entire study area (ca. 320 km(2)), with some local variations. Population persistence was higher in sites where ground water levels decreased less but it was also positively correlated with the heterogeneity of the adjacent landscape. Under normal weather conditions, local habitat characteristics had a dominating role on R. temporaria population abundance, as it was positively correlated with the amount of ditches and ponds within the study sites. After the drought, however, population abundance was related to landscape and regional level factors. The results indicate that landscape homogenization can have negative effects on population persistence during climate change. They also show that the scale at which landscape characteristics affect populations can be strongly dependent of processes functioning at large scales, such as weather. In summary, heterogeneous landscapes may lower the risk of regional amphibian population declines under extreme weather perturbations and serve as sources of recovery in postdisturbance recovery phases. Thus, maintaining such areas should be promoted in long-term biodiversity conservation.