General patterns
Most of the studies assessing the dispersal-range size relationship have
focused on marine and terrestrial systems (48 and 31 studies,
respectively), whereas freshwater systems have received much less
attention (only 7 studies; Fig. 1,2). Regarding taxa, most of studies
have focused on vascular plants, fishes, and insects (24, 17 and 14
studies respectively; Fig. 1), whereas dispersal-range size
relationships in bryophytes (liverworts), diatoms, trematodes and
mycorrhiza fungal (all with a single study) have barely been studied.
The majority of studied relationships (55%) showed a neutral effect of
dispersal on range size, 40% of relationships were positive and only
few (5%) were negative (Fig. 2). While for most of the taxa we did not
find a consistent positive association between range size and dispersal,
for molluscs, amphibians and birds we found more often positive effects
of dispersal on range size than neutral effects (Fig. 1). Marine,
terrestrial and freshwater realms showed similar proportions of positive
and neutral relationships (Chi-squared test = 0.078, p = 0.67, Fig. 1).
Interestingly, plants showed a lower proportion of positive
relationships than animals (Chi-squared test = 10.72, p = 0.001, Fig.
1).