Does competition drive character differences between species on a macroevolutionary scale?

Sympatric sister species generally have a degree of phenotypic differentiation that allows them to coexist. It has been well documented that phenotypic similarity results, through resource competition, in one of two major outcomes: local extinction of either competitor or character displacement. Limiting similarity suggests that there is a maximum degree of phenotypic niche overlap with which similar species may coexist. Breaching that maximum would result in exclusion. Character displacement, on the other hand, implies that the species differentiate phenotypically so that resource competition is reduced to the point where coexistence is possible. While it has been suggested that these theories have the potential to accelerate (character displacement) or limit phenotypic evolution (competitive exclusion) on microevolutionary time scales, their effects on macroevolution remain under-studied. If competition accelerates evolution on a macroevolutionary scale, one would expect that phenotypic diversity increases as novel species ‘push aside’ existing species. On the other hand, one might also expect that phenotypic evolution comes to a halt as novel species are trapped in the (ever decreasing) phenotypic space not yet occupied by existing species, except at the extremes of the phenotypic spectrum. Studying the current geographical ranges of more than 3000 extant species representing 29 mammalian families and their respective body masses, I found little evidence of competition accelerating body size differentiation between species.