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Nordic Society Oikos Patterns in Ecology Author(s): John H. Lawton Source: Oikos, Vol. 75, No. 2 (Mar., 1996), pp. 145-147 Published by: Blackwell Publishing on behalf of Nordic Society Oikos Stable URL: http://www.jstor.org/stable/3546237 . Accessed: 19/10/2011 19:44 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Blackwell Publishing and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Oikos. http://www.jstor.org OIKOS75: 145-147. Copenhagen1996 JohnLawton'sViewfromthe Park 15 Patterns in ecology Without bold, regular patterns in nature, ecologists do not have anything very interesting to explain. Patterns can exist at various scales in time and space, ranging from population abundances, through communities, ecosystems, biomes and the entire biosphere. Robert MacArthur understood this very clearly. In 1972, in the Introduction to GeographicalEcology he wrote: 'To do science is to search for repeated patterns... The best person to do this [in ecology] is the naturalist who loves to note changes in bird life up a mountainside, or changes in plant life from mainland to island, or changes in butterflies from temperate to tropics.' Yet despite the obvious importance of patterns, ecology twenty years after MacArthur is still ambivalent about pattern seeking. I sense that things are changing (James Brown's Macroecology, University of Chicago Press, 1995 captures this changing mood as well as any), but there are still too many people who believe that the only way to do science is to experimentally manipulate nature. It is a curious fact, for example, that ecological scientists have not gathered together in one place a database of the significant, interesting, patterns that we seek to explain, still less a compendium of patterns linked to theoretical explanations in a hierarchy ranging from 'reasonably well understood' to 'there are several possible explanations, none very satisfactory', to 'fascinating, but what does it mean?' Some text books document some of the patterns, more specialised monographs describe others (for instance, for all that I like what Brown is trying to do, Macroecology is economical with the literature). The result is that there is no one place to send a new graduate student, from which they can get a sense of the main empirical framework of our OIKOS 75:2 (1996) subject. Compiling such a database will be a difficult task, but it needs doing. Paradoxically, ecology's obsession with manipulation experiments over the last two decades springs, at least in part, from a reaction against simplistic, selective and uncritical use of patterns to support (rather than test) theory; Hutchinson's supposedly constant body-size ratios in guilds of coexisting predators provides a good example. The need to avoid 'just so stories', and to impart some rigour into field tests of theory was a healthy and timely development for our subject, but in the process the search for patterns worth explaining got side-tracked. It didn't stop, but it was certainly hard to get funded - which slows things down somewhat! I gather from Jim Brown, for instance, that although he has had considerable grant support for his pathbreaking field manipulation experiments, he has never had significant grant support for any of his work on largescale ecological patterns. I know of other similar cases, and it is a disgrace. Field manipulation experiments, like any approach to a difficult problem, have both advantages and disadvantages. One rarely discussed disadvantage, pointed out to me by Clive Jones, is the problem of the scale of human perception. Very simply, and generalising wildly but with some justification, human beings operate on the wrong spatial and temporal scales to discover, by doing field manipulation experiments, many of the major patterns and rules that determine how assemblages of 'large' multicellular organisms (higher plants, insects, fish, birds, etc.) are put together. We find it difficult to see the wood when trying to manipulate trees. Consider a fanciful analogy. Imagine you are a fairy, a bit larger than an atom, sitting in a world made up of 145 a mixture of gasses. You would see balls (molecules) of different sizes and colours whizzing about, occasionally colliding, and sometimes combining to.yield differentsized balls. Being a curious fairy, with an experimental bent, you attempt to manipulate the molecules by building fences in a very local part of this imaginary world, to keep out the big red balls which appear to be attacking the smaller blue ones. The grant application to the king of the fairies says that you wish to: 'Understand and predict the role of large red balls in structuring the assemblage of other balls.' Does it sound familiar? The problem, put like this, is obvious. The really important things determining the behaviour of this hypothetical, gaseous world, operate at scales either much bigger, or much smaller than the unaided fairy can perceive. As scientists we are adept at peering into smaller scales using a microscope, or some equivalent piece of clever technology; no doubt the fairy will quickly realise that he or she needs to study sub-atomic particles, and devise a means of doing so. It is rather harder to stand back and realise that the gaseous world has macroscopic properties, pressure for example, and predictable, long-term chemical equilibria, when you are surrrounded by a mass of whizzing, coloured balls, the individual, local behaviours of which are mainly random and largely irrelevant. The fairy lacks a macroscope, and has basically posed the wrong question, at the wrong scale. Ecologists, too, lack a macroscope - a machine that reveals big patterns that emerge from a mass of local fuzz, and which operates on time-scales orders of magnitude longer than a three-year research grant. But we can search for large patterns in nature, and they are the next best thing to a macroscope. Let me suggest a real-life example. The ecological literature is full of small-scale (each replicate is typically a few square metres) field manipulation experiments characterising interspecific interactions between pairs or a handful of species (usually competitors, or predators and their prey). Sometimes, and least interesting, the manipulations last less than a generation of the key organisms; luckier, or more thoughtful, investigators (Jim Brown, for instance) manage to continue the experiment for several generations. The aim of the experiment is usually to discover how species A influences the presence, absence, or abundance of species B, C, etc. Properly designed and run for long enough, such experiments are important - this is not diatribe against good field experiments. But they do not answer the larger question. For example, why are there 2 species in the system I am interested in at one locality, 20 at another and 200 at a third? This bigger question is highly unlikely to be answered by small-scale manipulation experiments. One of the boldest amd most interesting patterns to emerge in ecology over the last decade is the fact that in many systems (a large majority, it would appear, but 146 not quite all), local species richness (2, 20, or 200 species in the above example) is linearly related to the number of species in the regional pool, with a slope less than 1. That is, local assemblages are a 'proportional sample' of the regional pool (e.g. Ricklefs, R. E. and Schluter, D. 1993 (eds), Species Diversity in Ecological Communities. Chicago University Press). Under these circumstances, small-scale field manipulation experiments that seek to 'explain the structure' or 'understand the processes controlling diversity' are simply looking at second, even third-order, phenomena - the noise round the main regression line. They most certainly do not say anything very interesting about the processes (which is what we write in grant proposals) structuring particular assemblages; they look at the fine tuning. Many readers will disagree with this view. Good. Treat it as an hypothesis, and let there be a debate about the problem. To make it constructive, we might ask, for example, how the size of the regional pool of species is determined. The answer will certainly involve geology, evolution and some very large-scale, slow processes. But what part, if any, do local species' interactions play? If the answer, again, is very little, why do we pay so much attention to them, at the expense of the big patterns? A key question in ecology, rarely asked explicitly, is which local processes amenable to field manipulation experiments, scale up and have a significant influence on, patterns in species' distributions and ecosystem processes across landscapes, biomes and the biosphere? To search for patterns in nature, is not, of course, the same as stamp collecting. It is, as MacArthur realised only too well, central to the scientific enterprise. And to offer, and test, hypotheses to explain patterns, even though the tests will not usually involve controlled, experimental manipulations is also to do science. As I and others have said repeatedly, if you doubt this, then astronomy is not a science. One more thought about patterns is worth articulating. Too often, ecologists seem obsessed with finding a single explanation for some process or pattern of interest. 'My explanation is right, yours is wrong' may get papers published (and even grants funded), but for many of the ecological phenomena I am familiar with, such polarisation is unwise and unhelpful. For many phenomena, there are likely to be several contributory mechanisms, and the question is not so much about which mechanism is correct, but about the relative contributions of a plurality of mechanisms. Species-area relationships, one of the boldest and most robust patterns in ecology, have several explanations, all of them now known to be valid, but operating with different force in different systems and on different scales (see Michael Rosenzweig's Species Diversity in Space and Time. Cambridge University Press, 1995). One interesting hypothesis worth considering, is that like species-area relationships, the most consistent and OIKOS 75:2 (1996) clearest ecological patterns will almost invariably have several explanations, with the various mechanisms all pulling in the same direction. A corollary is that where patterns are weak, inconsistent or non-existent, either nature in these cases is indeed mainly fuzz, or (and more interesting), conflicting mechanisms are at work, pulling the patterns in different directions. There is also a more philosophical message underlying the idea of alternative processes creating the strongest patterns when they work together. There is no one correct way to do ecology. Mathematical models, model ecosystems, field manipulation experiments and the search for large-scale patterns are all valid approaches, and all have their strengths and weaknesses. OIKOS 75:2 (1996) They are simply tools to help us understand nature; like all tools, each approach does some things well, some things badly and other things not at all. And all tools can be used badly by dumb practitioners. Ecology is likely to be the stronger if it recognises and values a plurality of approaches to understanding the biosphere, and if practitioners skilled at using different tools all pull in the same direction. John H. Lawton NERC Centrefor PopulationBiology ImperialCollege SilwoodPark Ascot SL5 7PY, UK 147