“Patterns of local community composition are linked to large-scale diversification and dispersal of clades”
John J. Wiens (Feb 2018)
Local communities are dominated by clades with rapid rates of global-scale diversification and dispersal
New study uses snakes to reveal a fundamental pattern in the biodiversity of communities
What determines which groups of organisms will have the most species at any location on Earth? Few studies, if any, have addressed this fundamental question. A new study suggests there is a simple explanation for these patterns of diversity.
A new paper in The American Naturalist addresses the question of which groups dominate local communities, by analyzing data from snakes. The study used data from 166 local sites around the world and an evolutionary tree of 1,262 snake species. The results reveal that those groups that evolve new species most rapidly and spread most quickly are those that dominate most local communities around the world. On the other hand, groups that are present in a region longer than others rarely dominate local communities, despite having more time to build up species diversity.
The results also reveal that most snake communities around the world are surprisingly similar to each other. Specifically, most communities are dominated by members of one family (Colubridae), which includes garter snakes and kingsnakes. Most communities also have dangerously venomous species from the viper family and the cobra family. Remarkably, these venomous groups have spread around the world almost as much as the highly successful Colubridae have, but generally have few species in local communities. The results suggest that these dangerously venomous snakes may be weaker competitors relative to species of the mostly harmless Colubridae.
The tendency for local communities to be dominated by a few groups that proliferate and spread rapidly may apply to many other organisms besides snakes. For example, plants, frogs, mammals, and birds are each dominated by a rapidly proliferating group that has spread around the world. The new study proposes that there may be simple explanation for patterns of local species diversity across organisms and around the world.
At any location, a group of organisms may be represented by several clades. What determines which clades will dominate local communities in terms of their species richness? Here, this relatively neglected question is addressed by analyzing 166 local assemblages of snakes distributed globally. For most regions, local assemblages are dominated by clades with higher global-scale diversification rates and more frequent dispersal into each region, and not by clades that have been present in that region longer. This result contrasts with many other studies of local richness (in other organisms), which show strong impacts of regional colonization time on overall local species richness of clades. Furthermore, even though local assemblages are assembled independently on different continents, most regions have converged on similar patterns of proportional richness. Specifically, a few rapidly diversifying clades dominate most communities around the world. The high diversification rates of these clades are then linked to their high dispersal rates. Similar patterns may occur in many groups, such as plants, frogs, salamanders, birds, and mammals.