The species we’ve neglected

Species in last 3 months' papers in Ecology Letters.
"Multiple species" tended to be meta-analyses.

Browse the abstracts of a high profile ecological journal (for example, Ecology Letters, right) and one pattern you’ll notice is that high impact, hypothesis-driven ecology usually involves a small pool of focal species. Plants, for example, dominate any discussion of community ecology and have since Clements’ and Gleason’s arguments. It is not that hard to see why – plants don’t move, for one, live in speciose groups, and often complete a full lifecycle in a matter of months. They are also the lowest trophic level and so pesky multiple trophic level interactions can be omitted.

Other groups of species also show up frequently. Insects are popular for some studies of herbivory (again, it is easy to estimate damage to species that can’t move), mutualisms, and predation. Butterflies and birds, being pretty and easy to count, make a nice model for species populations and climate change studies. And while it is easy to sound critical of this kind of system-based myopia, it exists for perfectly good reasons. Immobile plants, after all, are a major source of experimental knowledge upon which much of modern ecology relies. They are easy to work with and manipulate, and their responses are relatively easy to measure (phenology, fitness, biomass, herbivory). Further, once an experimental system is established, using that system becomes increasingly attractive. You have a growing literature to base decisions on, to put your results into context, and against which to prove the novelty or importance of your work. In contrast, if you do your work on the rare bunny-toed sloth-monkey, the novelty of the system may overwhelm the generality of the work. And so the short-term limitation is that established systems allow immediate in-depth studies, while novel systems, though necessary to broaden ecological knowledge, may (initially) relatively be shallow in their returns.

Establishing a new system may be a time-consuming activity with the possibility of failure. But these under-utilized species have something new to tell ecology. This is not to say that the popular systems of species have nothing to tell us anymore – not at all, given all the complexities of ecological dynamics – but they bias the story. The ecological processes at play are not likely much different between novel systems and traditional ones. But the same processes interact in different ways and differ in importance across systems, and so we may have unrealistic expectations about the importance of, say, competition, if we only focus on 1 or 2 systems. To follow Vellend’s (2011) framework, the processes of selection, drift, speciation, and dispersal are part of any ecological system. What differs is their importance, and their importance differs for reasons related to the ecological context and evolutionary history a species experiences. This is the reason that comparing Mark McPeek’s work on neutrality in damselflies with Jonathan Losos’ findings about adaptive radiation in anoles is so interesting. No one questions that adaptive radiations may drive one set of species and neutrality another, the real question is what about their contexts produces to this result. Unfortunately, if our current set of focal species is small, we are limited in our ability to make such informative comparisons.

Many of the limitations on species have been methodological: popular systems tend to involve amenable species. Other species may be very small, very mobile, very difficult to identify, or highly specialized in their habitats. This creates difficulties. But when we overcome them, the results are often revolutionary. For example, consider the current burst of interest in belowground interactions, once their incredible importance to plant community interactions became clear (e.g. Klironomos 2002, Nature). Further, techniques are continually improving in ways which make new systems tenable.

So we should continue to focus on a few well-understood systems, attempting to perfect our understanding and predictive abilities. There is much value in understanding a system as completely as possible. But on the other hand, we can limit ourselves by focusing too much. It seems like one of the big areas for growth in modern ecology is simply to expand into novel ecological systems.

(**It's probably too general and a bit unfair to refer to all plants and all insects as though they are monolithic groups, since they are each large and varied (which is part of the reason they've been useful thus far). And some of their great representation may in fact relate to the number of species available to study. But I do think the general point about the problem of focusing too much holds.**)