Properties of species in the tail of rank-abundance curves: The potential for increase in abundance

It has recently been shown that most low-abundance species at a location are substantially more abundant somewhere else within their geographical range (somewhere-abundant). Fewer than 10% are everywhere-sparse. Here, two everywhere-sparse species from dry sclerophyll woodland were compared with phylogenetically contrasted somewhere-abundant species, at sites where both were at low abundance. In each pair, everywhere-sparse species produced approximately ten-fold fewer seeds per area of canopy cover than the somewhere-abundant species, consistently across replicate sites. Around individuals, a significantly larger proportion of the immediately colonizable neighbourhood was already occupied by the same species, for the everywhere-sparse compared to the somewhere-abundant species, in each pair and across replicate sites. Together, these differences amount to a much lower potential rate of increase in everywhere-sparse species compared with somewhere-abundant species, and are consistent with their having low capacity for opportunistic increase to high abundance. Our findings suggest novel differences between species that differ in local abundance patterns across geographical ranges, and provide a basis for further exploration of life-history and demographic differences between everywhere-sparse and somewhere-abundant species.