Neutral theory, co-occurrence and coexistence of sister taxa in damselflies

Background/Question/Methods

The communities that we study today have been shaped by the macroevolutionary mechanisms promoting speciation and extinction within component lineages and by how the resulting lineages have adapted to one another.  As a result, multiple congeneric and confamilial species can be found living together in communities.  For example, among the 135 North American damselfly species, up to 21 species in six genera can be found together in a single pond or lake, with most genera having multiple co-occurring species.  Some of these species may be coexisting in the theoretical sense of having demographic mechanisms that permit their long-term persistence in the system.  Others may not be coexisting, but rather be long-term transients that are either being driven extinct or randomly walking to extinction.  In this talk, I will explore using phylogenetic analyses, functional adaptive studies and field experimental studies where these breaks may lie among damselflies in ponds and lakes.

Results/Conclusions

Our field experimental results have shown that damselfly genera form ecologically distinct functional groups within lakes, and the genera differ in ways that are completely consistent with models of coexisting species.  In contrast, species within each genus (but that may have been separated for up to 10 million years) appear to be ecologically nearly equivalent to one another.  Two modes of speciation seem to dominate within the damselflies: (1) habitat shifts in which a lineage invaded and adapted to a new ecological environment, and (2) changes in the mechanisms by which individuals identify suitable mates.  New ecological functional groups entered these communities because of habitat shifts of lineages from outside the community.  However, changes in the mate recognition system have no discernible impact on ecological performance, and most speciation within a community occurs via this mechanism.  Thus, damselflies in North American ponds and lakes are mixtures of functional groups that originally invaded from outside the community and that are now structured by coexistence mechanisms, but with multiple ecologically very similar species embedded within each functional group.