Abstract
The spatial distribution of species is affected by dispersal barriers, local environmental conditions and climate. However, the effect of species dispersal and their adaptation to the environment across geographic scales is poorly understood. To investigate the distribution of species from local to broad geographic scales, we sampled termites in 198 transects distributed in 13 sampling grids in the Brazilian Amazonian forest. The sampling grids encompassed an area of 271 500 km2 and included the five major biogeographic regions delimited by Amazonian rivers. Environmental data for each transect were obtained from local measurements and remote sensing. Similar to previous studies, termite species composition at the local scale was mostly associated with measures of soil texture and chemistry. In contrast, termite species composition at broad geographic scales was associated with soil nutrients, and the geographic position of the transects. Between 17 and 30% of the variance in termite species composition could be attributed exclusively to the geographic position of the transects, but could not be attributed to measured environmental variables or the presence of major rivers. Isolation by distance may have strong effects on termite species composition due to historic processes and the spatially structured environments along distinct geological formations of Amazonia. However, in contrast to many taxa in Amazonia, there is no evidence that major rivers are important barriers to termite dispersal.
Highlights
Recommended Citation Dambros CS, Morais JW, Azevedo RA, Gotelli NJ
When all variables were included in the regression model, twenty two percent of the variation in termite species richness could be explained either by spatial variation at broad geographic scales or by environmental variables with broad scale spatial autocorrelation
Despite the association of environmental variables with termite species richness, 27% of the variation in species richness could be explained only by spatial predictors associated with geographic distance (MEMs), but not accounted for by the environment or by biogeographic regions delimited by major rivers (Fig. 2A)
Summary
Recommended Citation Dambros CS, Morais JW, Azevedo RA, Gotelli NJ. Isolation by distance, not rivers, control the distribution of termite species in the Amazonian rain forest. Other taxa with higher dispersal ability, such as plants (Tuomisto et al 2003, Kristiansen et al 2012, Pomara et al 2014) and many insects (Penz et al 2015), are unlikely to be limited in their dispersal by rivers These taxa should be more strongly associated with local environmental conditions than with geographic distance or the presence of barriers. Several studies of Amazonian plants (Tuomisto et al 2003, Costa 2006, Kristiansen et al 2012) and animals (Menin et al 2007, Tarli et al 2014) have found that the similarity in species composition between sites is correlated with differences in soil texture and chemistry Most of these studies are conducted at relatively small spatial scales, and do not encompass multiple geological formations or the major rivers of Amazonia. No single study was able to associate the distribution of species with geography and environmental conditions across multiple scales, and to demonstrate in which scale niche and neutral processes are more important for species distribution
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