Niche breadth, competitive strength and range size of tree species: a trade-off based framework to understand species distribution.

Understanding the mechanisms causing latitudinal gradients in species richness and species range size is a central issue in ecology, particularly in the current context of global climate change. Different hypotheses have been put forward to explain these patterns, emphasizing climatic variability, energy availability and competition. Here we show, using a comparative analysis controlling for phylogeny on 234 temperate/boreal tree species, that these hypotheses can be included into a single framework in an attempt to explain latitudinal gradients in species range size. We find that species tend to have larger ranges when (i) closer to the poles, (ii) successionally seral, (iii) having small and light seeds, and (iv) having short generations. The patterns can simply be explained by energy constraints associated with different life-history strategies. Overall, these findings shed a new light on our understanding of species distribution and biodiversity patterns, bringing new insights into underlying large-scale evolutionary processes.