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

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.