Owing to our recent interest in different approaches to modelling extinction risk, and because climate change impacts on biodiversity and conservation is always one of our key interests, we discussed a paper by Barbet-Massin et al. (2010). The authors state that considering the full range of a species is essential for modelling future climatic suitability within a region of interest. For evidence, they provide a comparison of using species occurrence data only within Europe versus considering the full Western Palearctic region. The loss of climatic suitability is decreased when the input data for modelling consists of a larger area. The authors show that extending the geographical space also tends to extend the environmental space which is suitable for the species according to the input data, which makes it more likely for a species to maintain suitable climate space in the course of climate change.
The immediate response from those of us who are not working with species distribution modelling was: but isn’t that obvious? Indeed, the conclusion may not come as a big surprise, considering that climatic variables tend to have clear spatial patterns, and that species distribution models build on statistical association between climatic variables and species occurrences. Yet, because activities to map out biodiversity are often carried out within regions (such as Finland, European Union or Europe) which are defined politically rather than biogeographically, the consideration of the full extent of a species range has been ignored in many, if not most, applications. In this respect, the study of Barbet-Massin et al. was a welcome reminder of the necessity to comply with theory when predicting the climatical suitability of species into the future.
One might think that considering those parts of the distribution which are restricted by dispersal barriers such as the Mediterranean Sea would only make sense with species able to overcome such barriers (which most bird species are able to do). However, Barbet-Massin et al. also note that “accounting for all populations within the species range or within an extended biogeographic area allows one to consider the full extent of the species potential climatic adaptations, and so doing, the potential adaptability of European populations”.
The vulnerability of a particular species to climate change depends on a number of other factors, including the availability and quality of suitable habitat, degree of local adaptation, dispersal behaviour, and ecological interactions. Predictions of future species distributions with climatic suitability models often do not consider these additional filters – we tend to take terminological shortcuts and talk about “future distributions” instead of “future spaces of potential climatic suitability”, but should not forget about this limitation. Nevertheless, improved practices for modelling climatic suitability – the coarsest filter – is important for getting the first step right.
For reference, see