Founder takes more: interspecific competition affects range expansion of North American mammals into deglaciated areas (Q7647)

Aim I assess the impact of interspecific competition on species post-glacial range expansions into previously glaciated areas. I hypothesize that expansion of one species (the founder) after the Last Glacial Maximum (LGM) into areas that were glaciated has hindered expansion of its competitor (the successor). If true, I predict that range and niche sizes of two congeners are more disproportionate within the previously glaciated areas (i.e., the areas of postglacial expansion) than within areas that were not glaciated. I also predict that niche partitioning is reduced within previously glaciated areas. If true, range and climatic niche overlap of two congeners is smaller in the previously glaciated areas than in non-glaciated areas.  Location North America Taxon Non-volant mammals Methods I calculate species range size for 87 congeneric species pairs and climatic niche hypervolume for 71 pairs, separately for areas that were and were not glaciated during the LGM. I then compare (a) range and climatic niche size ratio and (b) range and climatic niche overlap for each species pair between areas that were and were not glaciated using a paired t-test. Results Congeneric species pairs exhibit more disproportionate range areas and climatic niche hypervolumes and smaller range and climatic niche overlap within previously glaciated areas in comparison with areas that were not glaciated during the LGM. Main conclusions Interspecific competition has likely hindered postglacial range expansion of some species into deglaciated areas. Similarly to the founder effect documented on the intraspecific level, the founder species may hinder the expansion of the successor species. Consequently, one species may expand over very large areas whereas its competitor may expand very little or not at all. Additionally, niche partitioning within the deglaciated areas may be reduced as the founder expands and fills biotopes that would otherwise be utilized by its competitor.