A multiplicity of communities for community ecology

Community ecologists have struggled with some fundamental issues for their discipline. A longstanding example is that we have failed to formally and consistently define our study unit – the ecological community. Textbook definitions are often broad and imprecise: for example, according to Wikipedia "a community...is an assemblage or associations of populations of two or more different species occupying the same geographical area". The topic of how to define the ecological community is periodically revived in the literature (for example, Lawton 1999; Ricklefs 2008), but in practice, papers rely on implicit but rarely stated assumptions about "the community". And even if every paper spent page space attempting to elucidate what it is we mean by “community”, little consistency would be achieved: every subdiscipline relies on its own communally understood working definition.

In their 1994 piece on ecological communities, Palmer and White suggested “that community ecologists define community operationally, with as little conceptual baggage as possible…”. It seems that ecological subdisciplines have operationalized some definition of "the community", but one of the weaknesses of doing so is that the conceptual basis for these communities is often obscured. Even if a community is simply where you lay your quadrat, you are making particular assumptions about what a community is. And making assumptions to delimit a community is not problematic: the problem is when results are interpreted without keeping your conceptual assumptions in mind. And certainly understanding what assumptions each subfield is making is far more important than simply fighting, unrealistically, for consistent definitions across every study and field.

 

Defining ecological communities.

Most definitions of the ecological community vary in terms of only a few basic characteristics (figure above) that are required to delimit *their* community. Communities can be defined to require that a group of species co-occur together in space and/or time, and this group of species may or may not be required to interact. For example, a particular subfield might define communities simply in terms of co-occurrence in space and time, and not require that interactions be explicitly considered or measured. This is not to say they don't believe that such interactions occur, just that they are not important for the research. Microbial "communities" tend to be defined as groups of co-occurring microbes, but interspecific interactions are rarely measured explicitly (for practical reasons). Similarly, a community defined as "neutral" might be studied in terms of characteristics other than species interactions. Studies of succession or restoration might require that species interact in a given space, but since species composition has or is changing through time, temporal co-occurrence is less important as an assumption. Subdisciplines that include all three characteristics include theoretical approaches, which tend to be very explicit in defining communities, and studies of food webs similarly require that species are co-existing and interacting in space and time. On the other hand, a definition such as “[i]t is easy to define local communities where in species interact by affecting each other’s demographic rates” (Leibold et al. 2004) does not include any explicit relationship of those species with space – making it possible to consider regionally coexisting species.

How you define the scale of interest is perhaps more important in distinguishing communities than the particulars of space, time, and interactions. Even if two communities are defined as having the same components, a community studied at the spatial or temporal scale of zooplankton is far different than one studied in the same locale and under the same particulars, but with interest in freshwater fish communities. The scale of interactions considered by a researcher interested in a plant community might include a single trophic level, while a food web ecologist would expand that scale of interactions to consider all the trophic levels. 

The final consideration relates to the historical debate over whether communities are closed and discrete entities, as they are often modelled in theoretical exercises, or porous and overlapping entities. The assumption in many studies tends to be that communities are discrete and closed, as it is difficult to model communities or food webs without such simplifying assumptions about what enters and leaves the system. On the other hand, some subdisciplines must explicitly assume that their communities are open to invasion and inputs from external communities. Robert Ricklef, in his 2008 Sewall Wright Address, made one of the more recent calls for a move from unrealistic closed communities to the acceptance that communities are really composed of the overlapping regional distributions of multiple organisms, and not local or closed in any meaningful way.

These differences matter most when comparing or integrating results which used different working definitions of "the community". It seems more important to note possible incompatibilities in working definitions than to force some one-size-fits-all definition on everything. In contrast to Palmer and White, the focus should not be on ignoring the conceptual, but rather on recognizing the relationship between practice and concept. For example, microbial communities are generally defined as species co-occurring in space and time, but explicit interactions don't have to be shown. While this is sensible from a practical perspective, the problem comes when theory and literature from other areas that assume interactions are occurring is directly applied to microbial communities. Only by embracing this multiplicity of definitions can we piece together existing data and evidence across subdisciplines to more fully understand “community ecology” in general.

Speaking the language: is jargon always bad?

You hear mostly about the evils of jargon in science. Undeniably jargon is a huge barrier between scientific ideas and discoveries and non-scientists. Translating a complex, nuanced result into a sound bite or recommendation suitable for consumption by policymakers or the public can be the most difficult aspect of a project (something Alan Alda, as part of his Center for Communicating Science, is attempting to assist scientists with). But sometimes the implication in general seems to be that scientific jargon is always undesirable. Is jargon really always a bad thing?

Even between scientists, you hear criticism about the amount of jargon in talks and papers. I have heard several times that community ecology is a frequent offender when it comes to over-reliance on jargon (defn: “words or expressions that are used by a particular profession or group and are difficult for others to understand”). It is fun to come up with a list of jargon frequently seen in  community ecology, because examples are endless: microcosm, mesocosm, niche, extinction debt, stochastic, trophic cascades, paradigm shift, priority effects, alternate stable states, or any phrase ending in ‘dynamics’ (i.e. eco-evolutionary, neutral, deterministic). Special annoyance from me at the usage of multidisciplinary, trans-disciplinary, and inter-disciplinary to all express the exact same thing. I don’t think, despite this list, that jargon is necessarily problematic.

If the meaning implied by the word or phrase is more than the sum of its parts it is probably jargon. Ideally, jargon is a shared, accurate shorthand for communicating with colleagues. A paper published without any jargon at all would be much longer and not necessarily clearer. Instead of saying, “we used protist microcosms”, it would have to say, “we used a community of protist species meant to encapsulate in miniature the characteristic features of a larger community”. (And arguably ecology is still relatively understandable for a newcomer, compared to disciplines like cell and systems biology, where an abstract might seem impenetrable: “Here, we report that, during mouse somatic cell reprogramming, pluripotency can be induced with lineage specifiers that are pluripotency rivals to suppress ESC identity, most of which are not enriched in ESCs.”)

Jargon is useful as a unifying tool: if everyone is using the same nicely defined label for a phenomenon, it is easier to generalize, contrast and compare across research. Jargon is many pieces of information captured in a single phrase: for example, using the term 'ecophylogenetics' may imply not only the application of phylogenetic methods and evolutionary biology to community ecology, but also the accompanying subtext about methodology, criticism, and research history. At its best, jargon can actually stimulate and unify research activities – you could argue that introducing a new term (‘neutral dynamics’) for an old idea stimulated research into the effects of stochasticity and dispersal limitation on community structure.

That’s the best case scenario for jargon. There are also consequences to developing a meaning-laden dialect unique to a subdiscipline. It is very difficult to enter a subdiscipline or move between subdisciplines if you don’t speak the language. New students often find papers difficult to penetrate because of the heavy reliance on jargon-y descriptions: obtaining new knowledge requires you already have a foundation of knowledge. Moving between subdisciplines is hard too – a word in one area may have completely different meaning in another. In a paper on conservation and reserve selection, complementarity might refer to the selection of regions with dissimilar species or habitats. In a biodiversity and ecosystem functioning paper, a not-very distant discipline, complementarity might refer to functional or niche differences among co-occurring species. Giving a talk to anyone but the most specialist audience is hampered by concerns about how much jargon is acceptable or understandable.

Jargon also leads to confusion. When using jargon, you can rely on understood meaning to delimit the boundaries of your meaning, but you may never specify anything beyond those boundaries. Everyone has heard a 30-second spiel so entirely made of jargon that you never develop a clear idea of what the person does. The other issue is that jargon can quickly become inaccurate, so laden with various meanings as to be not useful. The phrase ‘priority effect’, for example, has had so many particular mechanisms associated with it that it can be uninformative on its own. And I think most ecologists are well aware that jargon can be inaccurate, but it’s a difficult trap to get out of. The word “community”, essential to studying community ecology, is so broadly and inconsistently defined as to be meaningless. Multiple people have pointed this out (1, 2, 3) and even suggested solutions or precise definitions, but without lasting impact. One of the questions in my PhD defense was “how did I define an ecological community and why?”, because there is still no universal answer. How do we rescue words from becoming meaningless?

Something interesting, that you rarely see expressed about jargon is that linguists tells us that language is knowledge: how we understand something is not independent of the language we use to describe it. The particular language we think in shapes and limits what we think about: perhaps if you have many ways of finely delineating a concept you will think about it as a complex and subtle idea (the 100-words-for-snow idea). On the other hand, what if you have to rely on vague catch-alls to describe an idea? For example, a phrase like ‘temporal heterogeneity’ incorporates many types of differences that occur through time: is that why most researchers continue to think about differences through time in a vague, imprecise manner? Hard to say. It is hard to imagine where community ecology would be without jargon, and even harder to figure out how to fix all the issues jargon creates.