Friday, December 10, 2010

Biodiversity and ecosystem functioning – without fungi?

Different subfields of ecology have a propensity to remain remarkably isolated – researchers in aquatic systems independently develop hypotheses that already exist in some form in other systems, and vice versa. Population ecology and community ecology, despite their obvious relevance to each other, are rarely integrated. There is a tendency – resulting from limits on our time, experience, and possibly imagination – to stay within whatever box we’ve defined for ourselves.

Historically, it seems that biodiversity and ecosystem functioning has lost sight of the progress made in classical ecology in understanding the mechanisms behind species coexistence (and all the functional implications that follow). Studies of ecosystem functioning often vaguely reference concepts such as “niche partitioning”, which would hardly be explicit enough for most papers on coexistence. Fortunately, there are periodically attempts to unifying ecological knowledge.

One of the most important contributions to understanding coexistence is Chesson’s (2000) framework of equalizing and stabilizing effects. Unlike previous approaches to species interactions, which tended to reference these vaguely-defined “niche differences”, Chesson proposed that species interactions depended on both fitness differences (differences in absolute growth rates after niche differences are controlled for) and niche differences (ecological differences between species which cause intraspecific competition to exceed interspecific competition). He also suggested rigorous methods to quantify these concepts. This framework has been applied both to the obvious questions of species coexistence and diversity maintenance, as well as predator-prey relationships (2008) and the phylogenetic structure of communities (2010).

In a recent paper, Ian Carroll et al. apply this framework to the search for the mechanisms behind biodiversity and ecosystem functioning. They point out that the questions in studies of ecosystem functioning are directly analogous to Chesson’s concepts – selection effects result from fitness or competitive differences between species, while complementarity relates to the partitioning of resources, or niche differences between species. The added benefit is that Chesson has provided clear definitions for these concepts.

While this may not be world-altering, it’s encouraging. Anytime different areas of ecology intersect, both benefit. Of course there are difficulties – no doubt the question of how to measure niche differences and fitness differences will be contentious (as attempts to translate ecological theory into ecological methodology often are) - but the possibility that a few general ecological concepts explain diverse observations is worth pursuing.