Irina Levinsky:
Species distributions and climate change - linking the past and the future

Date: 15-05-2010    Supervisor: Carsten Rahbek

Climate change is predicted to have a marked impact on biodiversity, and changes in the distributions of numerous species have already been correlated with ongoing climate change. Climatic oscillations, however, were also the rule during the Pleistocene. A look to the past may therefore shed light on the impact of future climate change. In this thesis, I relate past climatic changes and their impact on biodiversity to future climate change.
I first revisit the role of refugia as areas where African birds and mammals survived adverse climatic conditions. I use bioclimate envelope models to reconstruct climatically suitable ranges of the two taxa during the Last Glacial Maximum, and find that these congregated in the same areas, lending support to the refugia hypothesis. I then focus on one taxonomic group of birds, the African starlings, and explore surrogates for their dispersal ability in relation to range size and range filling.
Next, I take a critical view of the tools I use and the assumptions behind them. Bioclimate envelope models are the most widely used tool to forecast the impact of climate change on species distributions, and species that are predicted to have reduced or no climatically suitable range in the future are considered at risk. However, by hindcasting bioclimate envelope models, I find that that several extant species are modelled to have no climatically suitable range in the Last Glacial Maximum, even though we know they existed in that period and persisted until today. This cautions against interpreting uncritical forecasts of reduction in bioclimate envelopes as strong evidence for species extinction due to future climate change. Finally, I discuss how our perception of species’ abilities to cope with future climate change is altered by novel geophysical findings of abrupt climatic changes in the past. Climatic changes in the Pleistocene have generally been regarded as gradual, and therefore not detrimental for  biodiversity, while the current rapid climate change is assumed to pose a marked threat. The new studies support the view that abrupt climatic changes were more common in the past, yet species have nevertheless managed to persist. Although this may imply that current climate change may not impose a big threat to biodiversity, habitat fragmentation doubtless alters this view.