Christian Hof:
Species distributions and climate change: current patterns and future scenarios for biodiversity

Date: 15-02-2010    Supervisor: Carsten Rahbek

How does climate change affect biodiversity? - Answering this question is one of the most important tasks in current ecological research. Earth has been warming by 0.7°C during the last 100 years, and the consequences are already apparent in biotic systems. For example, species are responding by shifts of their distributional ranges, which affects the spatial patterns of species richness and turnover. Global temperatures are projected to rise by 1.8 - 4°C until the end of the century; hence climate change will most likely leave further imprints on species and ecosystems. This PhD thesis aims to contribute to a better understanding of the impacts of climate change on species distributions and spatial patterns of biodiversity.

Contemporary climate change is assumed to be one of the major future threats for biodiversity, due to its supposedly unprecedented velocity. On the contrary, recent studies suggest that climatic changes during and after the Pleistocene may have been much faster than commonly assumed. In one of the studies of this thesis I discuss the consequences of these findings for species and ecosystems. Since these rapid climate change events did not cause a broad-spectrum mass extinction, one might assume that most species may also be able to successfully cope with contemporary climate change. However, current ecosystems are heavily modified by humans. Among other factors, habitat destruction and fragmentation caused by anthropogenic land-use changes negatively affect species’ strategies to cope with climate change. Therefore, although we need to rethink species’ abilities to cope with rapid climate change, the interactions of different threats impose severe challenges for biodiversity. In a global assessment of future threats for amphibian diversity, I investigate the geography of climate change, land-use change and the fungal pathogen Batrachochytrium dendrobatidis (Bd). Results indicated that the regions with highest projected climate and land-use change impacts show a strong tendency of congruence, but show little overlap with regions of high Bd prevalence. Overall, two-thirds of the areas harboring the richest amphibian faunas may be heavily impacted by at least one of the major threats by 2080.

The stability of the climatic niche influences the need for a species to track climate change via dispersal, or its potential to adapt to novel climatic conditions. I therefore explore the phylogenetic signal in climatic niches of the world’s amphibians, which serves as a surrogate quantification of niche stability. Results indicate an overall tendency of phylogenetic signal to be present in realised climatic niches, but signal strength varies across biogeographical regions and among amphibian orders.

The ability to successfully track climatic changes depends on dispersal, which is in turn influenced by ecological adaptations, such as the affiliation with a certain habitat type. A common hypothesis is that species adapted to less persistent habitats have evolved stronger dispersal abilities. Two studies of my thesis provide evidence for this hypothesis: (1) geographical distributions of dragonflies adapted to less persistent habitats show higher degrees of equilibrium with climatic conditions; (2) spatial patterns of European freshwater species richness and turnover differ strongly among habitats, indicating a faster post-glacial re-colonization of northern Europe by species adapted to habitats of lower persistence.