How biological communities form and are maintained is a complex and fascinating area of molecular ecology. Gerhold et al. offer up an interesting take on community phylogenetics in a recent Functional Ecology paper that argues against the use of phylogenetic dispersion as a proxy for the mechanisms behind community assembly.
The authors take the time to work through some of the assumptions made in these proxy analyses and weigh their real support in the literature. This list of assumptions includes:
- (i) phylogenetic dispersion reflects trait dispersion
- (ii) a given ecological function can be performed only by a single trait state or combination of trait states
- (iii) trait similarity causes enhanced competition;
- (iv) competition causes species exclusion
- (v) communities are at equilibrium with processes of assembly having been completed
- (vi) assembly through habitat filtering decreases in importance if assembly through competition increases, such that the relative balance of the two can be thus quantified by a single parameter
- (vii) observed phylogenetic dispersion is driven predominantly by local and present-day processes.
The lack of support for some of these isn’t that surprising (such as ii and vii), but I was surprised to find some of the concepts that I consider well-supported (such as iv) might not be so accepted after all.
Gerhold et al. suggest the way forward is to incorporate more evolution into the first steps of forming questions:
Despite an increasing number of pictures of Charles Darwin in conference presentations of community ecologists, the questions asked in many of these studies do not concern any evolutionary processes.
It turns out that these same assumptions that the authors criticize make for fantastic hypotheses to test using the same types of data. This context shift in how community assembly questions are asked is the true purpose of this paper, and makes it well worth the read:
Phylogenetic dispersion of communities is of limited value for understanding ecological assembly processes, but of high value to address other questions in eco-evolutionary research. The links between ecological assembly processes and trait patterns, and between trait patterns and phylogenetic dispersion of communities, might be too complex and weak. Instead, information on phylogenetic community structure is a potentially valuable tool to answer evolutionary questions, where community ecology can be seen as macroevolution in action.
Gerhold P., Cahill J.F., Winter M., Bartish I.V. & Prinzing A. (2015). Phylogenetic patterns are not proxies of community assembly mechanisms (they are far better), Functional Ecology, n/a-n/a. DOI: http://dx.doi.org/10.1111/1365-2435.12425