How does selection work in communities?

Species living in diverse natural communities have to interact with lots and lots of other species during their lifetimes. Community ecologists have done a pretty good job of accounting for these multi species interactions. In addition to the direct effects of many species, there are also indirect effects, which may often be weaker, but also far outnumber the possible direct effects in a community. Collectively, these indirect effects can be really important for the ecology of a community.

Because ecology ultimately drives evolution, it behooves us to also look at the evolutionary effects of complex direct and indirect species interactions. Evolutionary biologists are just starting to get a handle on this complexity. Two recent publications from the lab highlight this.
In a recent paper in Molecular Ecology, Jen Lau and I highlighted some of the reasons why invasive species may fail to adapt to their new environment during or following invasion. Diffuse selection from multiple species in their new habitat is one important reason why adaptation may fail to occur.

In a paper that just came out this week, a group of us spent a lot of time thinking about how one could measure selection in response to indirect effects. The way to do so is relatively easy in terms of experimental design. Well, maybe not easy, but something that lots of community ecologists are doing already. The ideal experimental design is a multifactorial experiment. In other words, manipulate the abundance of Potential Selective Agent A and the abundance of Potential Selective Agent B. Many of us commonly do these 2 x 2 (or even 3 x 3) factorial experiments and typically measure some component of fitness, even if it’s just biomass. In this paper, we’re encouraging ecologists to also measure traits and fitness in individuals in these experiments, which would allow for estimates of selection in response to indirect ecological effects that can be compared across studies.

Our hope is that when people start to estimate fitnesses and traits in these experiments (or go back to old experiments for which people might already have data to re-analyze in this respect), we can start to get a general sense of whether selection in response to indirect ecological effects is pervasive in natural communities, and whether the strength is comparable to selection imposed by direct effects of competitors, predators, herbivores, pollinators, etc. Given the prevalence and importance of indirect ecological effects in communities, we expect that the evolutionary consequences could be important as well.


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