Ecological theorising about the structure of communities of plants and animals has been marginalised in recent decades but may be on the brink of a revival. Despite the dominance of a Darwinian paradigm focusing on individual species as unique, independent entities, proposed ecological laws unifying the diversity of living organisms via the interplay between evolution and thermodynamic constraints have attracted enthusiasm and shown some correspondence with observation. As a critical enthusiast, I am keen to explore the nature and validity of such laws of ecology that may help bring coherence to an unwieldy science. I believe that a Christian philosophy of science should help me understand this situation and may even guide a contribution to developing community ecology.
Community ecology is the branch of ecology concerned with the coexistence of different kinds of organisms at a given geographical location, and especially with the interactions among them. In this paper I want to explore some contemporary schools of thought in this field, in which I intend to immerse myself more deeply as I seek a direction for research. The guiding questions are, does community ecology have its own laws of nature, and are we discovering them?
The search for laws in community ecology has been controversial. Early in the ecological literature of the twentieth century, the US ecologist Frederic Clements described the changes in vegetation over time in a model of succession towards a climax community. He drew an analogy with the development of animals from infancy to maturity. In Europe, analogies from human communities were evoked by research on “phytosociology”, which sought to define combinations of plant species that typically occur together.
Thus interest in community ecology pre-dates Charles Darwin, but his book On the Origin of Species (1859) is sometimes considered the seminal text for ecology as a whole, and Darwin’s broad interest in natural history gives plenty of inspiration to modern-day community ecologists. The often-quoted final paragraph of the Origin reveals how Darwin saw his theory of natural selection as describing a kind of law of nature:
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
Charles Darwin, Origin (1859)
Part of Darwin’s genius was to recognise the inevitability of a struggle for existence throughout the natural world, regardless of the appearance of harmony in pleasant gardens or of chaos in tangled hedge banks.
In the second half of the twentieth century there was a move to ground ecology more firmly in a Darwinian paradigm, especially in the work of the late British ecologist John Harper. His address to the British Ecological Society on “A Darwinian approach to plant ecology” (Harper 1967) urged a greater focus on the fitness of individual plants, viewing evolution as the principle interest of ecologists. (An aside: My PhD thesis on population ecology was examined by a notable proponent of this school and at one point in the viva he queried my interest in analysing the overall mass-per-unit-area of some plants in an experiment, rather than focusing only on the density of individual plants.) This approach puts population ecology (the study of individual species) as the key to community ecology, and may lead towards a Baconian approach, where understanding of large-scale patterns will come from amassing data on very many individuals and species through experimental studies on life-cycles and environmental responses. This, of course, lies in the tradition of natural history. The ecology of communities developed in this period with the study of “macroecology”, following MacArthur and Wilson’s theory of Island Biogeography (MacArthur and Wilson 1967), which relates the numbers of species to the location and size of habitat patches but says little about the nature of species and still less about how they may interact with each other.
In contrast to this “bottom-up” population approach, a notable proposal coming from the field of more traditional community ecology was Philip Grime’s C-S-R theory. This model claims that there are two basic factors acting on plant habitats: stress and disturbance (Grime 1974), which create four potential habitat extremes (stressed, disturbed, both stressed and disturbed, and neither stressed nor disturbed). Environments where severe stress slows down plant growth and high disturbance kills off plant material are not viable for plants to complete their life-cycle in, so the other three habitat types provide a triangular space in which to locate any habitat. Then there are expected to be three corresponding fundamental strategy types that plants will display in each habitat: “stress-tolerator”, “ruderal” or “competitor”, and thus any plant species has a home somewhere in the so-called C-S-R triangle. (Another aside: my PhD supervisor told of how he was at a symposium where one speaker introduced the species he had studied by simply presenting a triangle with a cross in it, as if this provided all the information the audience really needed – it wasn’t clear whether this was done in jest or not!) Grime’s suggestion is that behind all the complexity of biodiversity there are organising principles, or laws, that render community ecology much more independent and intriguing as a field of ecology. I was privileged to meet Prof. Grime a few weeks ago, and he explained his vision of a situation where good ecological textbooks could be much thinner than they are now. His work has included the publication of a (none-too-thin) book called Comparative Plant Ecology (Grime, Hodgson et al. 2007) that gives detailed information on many British species, the fruit of painstaking studies over several decades, and locates each one in the C-S-R triangle.
The focus on evolution as the fundamental explanatory principle in ecology puts a great emphasis on historical contingency and the particularity of species. By contrast, a search for laws of ecology at a higher level puts more emphasis on constraints upon evolution, and the concept of convergence. This has also been explored recently by Simon Conway Morris in his book Life’s Solution: Inevitable Humans in a Lonely Universe (2004). Conway Morris is a Christian who argues against the arbitrariness and reductionism of contemporary accounts of evolution.
Science since Isaac Newton has been characterised by the search for laws of nature, and it is the faith of scientists in such laws, contrasted against the notions of divine fiat (or god-of-the-gaps) and of chaos, that give science its distinctive character. Some scientists are notorious for appearing to push their faith in certain laws of nature too far, especially in the eyes of theists. I suggest that it is not so much the certainty about the laws that is the problem, but the realms in which they are supposed to apply. Laws entail reductionism, since they describe models of reality that are less than reality as we experience it. Such reductionism enables us to abstract the aspects of a situation that are important in a particular scientific perspective that offers to predict corresponding aspects of situations that are not yet observed. For example, knowing the masses, velocities and other physical features of vehicles on a road allows predictions of their stopping distances using physical models and their laws. The error of ontological reductionism is to suppose that these abstracted concepts (especially matter and energy) are more real than the vehicles and the road. The attempt to predict the reaction times of drivers using purely physical models would be recognised as far-fetched by most scientists, yet some speak as if psychology were derived from physics (perhaps via biology).
The C-S-R model has attracted enthusiasm from some quarters but has been criticised on various counts and sometimes dismissed outright. Despite decades of refinement and development, it is still seen by some ecologists as a “shot in the dark”, with neither compelling evidence for the reality of the three primary strategies it proposes nor any direct objective way to assign to species a strategy. I am less critical and believe the model needs further development. I hope to embark on an exploration of how the unifying explanatory power of the C-S-R triangle can be more directly linked to observable data and made more quantitative, aiming to help develop laws of community ecology. I share Prof. Grime’s desire to see shorter textbooks and clearly articulated ecological laws of nature.
The questions I want to pose and ponder at this stage include:
1. How reasonable is it to articulate ecological laws as distinct from evolutionary laws (especially in the light of the dissatisfaction of some biologists with the current understanding of evolutionary laws)?
2. Given that many ecological processes are observed at the limits of detectability owing to stochastic (random) processes, what kinds of ecological laws can we hope to discover, and how would they best be discerned?
3. Assuming they do really exist, for how long and how successfully might ecological laws be articulated in terms of evolutionary and physical laws? In other words, how successful can ecologists be in articulating real, free-standing community-ecology laws (if they exist) reductively, in terms of other laws? (The same question may be asked of other “higher” disciplines.)
4. Could a model that has some promise for plant communities be competent to describe the animal kingdom and other kinds of life (J.P. Grime, personal communication)? Some Reformational scientists argue that the separate creation of plants, animals and humans in the Genesis account represents a fundamental distinction that good science will not be able to ignore.
© Richard Gunton, 2010
Conway Morris, S. (2004). Life's Solution: Inevitable Humans in a Lonely Universe. Cambridge, U.K., Cambridge University Press.
Darwin, C. (1859). On the Origin of Species by Means of Natural Selection. London.
Grime, J. P. (1974). "Vegetation classification by reference to strategies." Nature 250: 26-31.
Grime, J. P., J. G. Hodgson, et al. (2007). Comparative Plant Ecology: A Functional Approach to Common British Species, Castlepoint Press.
Harper, J. L. (1967). "A Darwinian approach to plant ecology." Journal of Ecology 55(2): 247-&.
MacArthur, R. H. and E. O. Wilson (1967). The Theory of Island Biogeography. Princeton, NJ, Princeton University Press.
* This article is a modified version of a paper presented at the Christian Academic Network conference in London on 11th September 2010.