Range size
Hutchinsonian niche theory suggests that, apart from sinks, species’ occurrence will be constrained to sites where environmental conditions are conducive to their persistence (; that is, occurrence is spatially constrained by environmental filtering. Both island biogeography and metapopulation theories also highlight the importance of movement (dispersal), in conjunction with the geographic contingencies of habitat availability and connectivity, in determining species’ geographic distributions . As such, theory suggests that the primary mechanistic drivers of species’ distributions are environmental filtering and movement.
This importance of environmental filtering is strongly supported in the biogeographical literature. note that niche processes are among the most common explanations for interspecific variations in range size, an assertion supported by a metanalysis . Tolerance has also been invoked to explain Rapoport’s rule (the general tendency for range size to increase with increasing latitude), as species living at higher latitudes experience, and thus must tolerate, a wider range of climatic conditions than those living in lower latitude regions . In addition, the popularity and efficacy of species distribution models suggests that tolerance is an important component of range size.
Dispersal has also frequently been cited as a driver of range size , though its importance is less clear than that of environmental filtering. Empirical studies of the relationship between range size and dispersal have produced mixed results; some have found that poor dispersal capacity is common among species with restricted distributions and references therein), while others have found only a modest relationship between range size and dispersal . A recent meta-analysis found a positive relationship between range size and dispersal capacity , but noted that the relationship is complex and is mediated by factors such as taxonomy, dispersal proxy, and biogeographic realm. In addition, of our three rarity axes, range size is arguably most influenced by the effects of historical contingencies, including phylogeny and long-term environmental changes . It is possible that these influences, which operate at very broad temporal scales, may obscure or even override the role of shorter-term processes such as movement .