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 .