Understanding what drives the vast variability in species range size is
still an outstanding question. Among the several processes potentially
affecting species ranges, dispersal is one of the most prominent
hypothesized predictors. However, the theoretical expectation of a
positive dispersal-range size relationship has received mixed empirical
support. Here, we synthesized results from 84 studies to investigate in
which context dispersal is most important in driving species range size.
We found that dispersal traits -- proxies for dispersal ability --
explain range sizes more often in temperate and subtropical regions than
in tropical regions, when considering multiple components of dispersal,
and when investigating a large number of species to capture dispersal
and range size variation. In plants, positive effects of dispersal on
range size were less often detected when examining broad taxonomic
levels. In animals, dispersal is more important for range size increase
in ectotherms than in endotherms. Our synthesis emphasizes the
importance of considering different aspects of the dispersal process
-departure, transfer, settlement-, niche aspects and evolutionary
components, like time for range expansion and past
geological-environmental dynamics. We therefore call for a more
integrative view of the dispersal process and its causal relationship
with range size.