Are locally rare species abundant elsewhere in their geographical range?

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Abstract

Abstract  Ecologists have long sought to understand why some species are rare and others common. For the most part, inconsistent relationships between local rarity and underlying mechanisms have emerged. One possibility for this inconsistency is that locally rare species may not always be rare. However, it is largely unknown whether most locally rare species in a community possess the capacity to become abundant elsewhere in their geographical range. Here, we identified 57 locally rare plant species of open forest in south-eastern Australia. We found that most of these species (91%) occurred in higher abundance at other sites within their geographical range (somewhere-abundant species), while the remaining small percentage of locally rare species were consistently rare (everywhere-sparse species). Somewhere-abundant species had significantly smaller seeds on average than everywhere-sparse species in cross-species regression analysis. This pattern was not maintained when the influence of other life-history attributes was controlled for, or when phylogenetic relatedness among species was considered explicitly in phylogenetic regression analysis. In both cross-species and phylogenetic regressions, somewhere-abundant and everywhere-sparse species did not differ significantly with respect to growth form, height, regeneration-after-fire strategy, or dispersal. Our findings provide further evidence for the notion that theories to account for local rarity which are couched in terms of within-community interactions alone are incomplete for the majority of species, because they need to account for different outcomes in different places.

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