Ecosystem theory and conservation
Timothy Moulton, Ecologia, Universidade do Estado do Rio de Janeiro. E-mail: firstname.lastname@example.org
Conservation of aquatic systems has broadened tremendously over the years. The original motives still stand: we conserve for a large number of utilitarian reasons – water supply for domestic, agricultural and industrial uses, fisheries and other natural resources, recreation, navigation, hydroelectricity and many more. The broadening has come about principally in terms of how the questions are viewed, and particularly how multiple issues need to be analysed and resolved. Thus the concept of ecosystem is invoked as a general framework in which the multiple factors interact. The framework is obviously important for this journal, which has ‘ecosystem’ in its title. We invoke ‘ecosystem health’ and a variety of ecosystem properties, like resilience, resistance and stability, in our rhetoric, and we imply that these concepts can be assessed and incorporated into conservation and management.
Because our modern practice of conservation invokes ecosystem I consider it interesting and important to review its theoretical basis. In other words, how does ecosystem theory inform us about conservation practice?
For my arguments we need to make a distinction between ‘community’ and ‘ecosystem’. There are good reasons for not doing this, as pointed out by many ecologists (e.g. Begon et al., 1986), but the artificial separation of the biological components (community) from their context within the environment (ecosystem) will illustrate some important phenomena. I will allocate all questions of energy and materials flow to ecosystem, and biodiversity, food webs and biotic interactions to community.
Historically, ecology of communities and ecology of ecosystems have developed separately, and for some authors this separation marks a major divergence within ecology (Golley, 1993). Not only has there been this separation, but when we look at the development of theory within ecology, we see a large and burgeoning literature in community ecology, and relatively little in ecosystem ecology. Exactly why this should be is not the theme of this paper, but I suspect that it has to do with the amenability of biotic interactions to mathematical analyses, so that we see the early work in niche theory (MacArthur and Levins, 1967) and community matrix (May, 1973) opening up into network analysis (Rayfield et al., 2011), application of information theory, etc. There are important applications in this area for aquatic conservation and biodiversity, for instance in riverine networks (Brown et al., 2011). Here, however, I will concentrate on the application of ecosystem concepts.
The word ‘ecosystem’ has entered the common parlance and is bandied around in a loose way in the popular literature. It is used widely in the scientific literature and not always in a strict sense. This need not be of concern as long as we recognize that the term has this general connotation. However, when we use ‘ecosystem’ in a more strict sense, and particularly when we invoke ‘ecosystem health’, ‘ecosystem functioning’ and ‘ecosystem properties’, such as persistence and stability, I feel that we should examine the foundations of our concepts.
The ecosystem concept has come under quite an amount of scrutiny. Robert O'Neill, one of the founding fathers and productive practitioners of ecosystem analysis, chose to address the Ecological Society of America with ‘Is it time to bury the ecosystem concept?’ (O'Neill, 2001), although his criticisms of the concept were relatively light. Kristin Shrader-Frechnette has questioned ecosystem and other concepts in the context of conservation and application of ecological knowledge to policy and decision-making (Shrader-Frechette and McCoy, 1993). The concept of ecosystem health has come under fire from various sources (Calow, 1992). One of the most cogent criticisms comes from Mark Sagoff, who questions the basis of holistic ecosystem science and contests its application to environmental questions – ‘Although ecosystem theory has been a burgeoning academic industry since the 1950s … many ecologists believe it has failed to provide any basis or guidance for management’ (Sagoff, 2003). The alternative for Sagoff is a case-study based science (his ‘bottom-up’ approach) that is also fraught with difficulties.
There have been many attempts at formulating the ‘new’ approach to conservation; for instance the book The Ecological Basis of Conservation: Heterogeneity, Ecosystems, and Biodiversity came out of the 1995 Carey Conference at The Institute of Ecosystem Studies, but in the opening chapter the editors state quite openly that ‘the new approach of ecosystem management does not have a foundation of well-developed theory to guide it’ (Pickett et al., 1997).
The community of ecologists and environmental scientists have adopted different attitudes to this general question of working with ecosystems and particularly with respect to the questions of managing and conserving environment. I will classify these attitudes broadly into three classes: (1) work with ecosystems without recourse to holistic principles (the ‘bottom-up’ approach): (2) incorporate ecosystem-level properties as the guiding principles (the ‘top-down’ approach); (3) work with properties such as ecosystem health without recognizing or invoking holistic principles. It is a complex question and I will necessarily distort and omit much of it here in my brief essay, but I will expand on these three attitudes below.
ECOSYSTEMS WITHOUT HOLISTIC PROPERTIES
Much research and environmental management progresses without the practitioners using ecosystem-level theory. Such work sometimes explicitly rejects the models of top-down control of the system and claims that the system can be explained entirely by the interactions of the biota among themselves and with the physical and chemical factors of the environment with the ever-present force of evolution selecting organisms and adapting populations.
At other times, the field can be seen as not particularly rejecting the holistic approach, but patiently accumulating the large body of work that goes towards the ‘bottom-up’ approach mentioned above – the accumulation of case histories and intensively-studied situations, which can then inform problems as they arise. Ecology, like many other branches of applied science, treasures its stock of information of this sort. This approach has its counterpart in medicine, where case histories are used extensively and effective treatments can anticipate the eventual discovery of the mechanism of action.
This approach does not, however, exclude the emergence of principles at the ecosystem level. A good example is the work of Simon Levin who builds a picture of diversity and complexity stemming from the interactions at the population level, with emphasis on the processes that occur at different scales (Levin, 1992). Although Levin does not explicitly reject self-organization at the level of the ecosystem, it is implicit that the population-level dynamics of interactions, dispersal, etc. are sufficient to generate the patterns at different scales of space, time and organization.
ECOSYSTEMS AS SELF-ORGANIZING ENTITIES
At the other extreme, there are several schools of thought that maintain that ecosystems are structured and organized by forces at the level of the ecosystem. Ecosystems are self-organizing entities and impose constraints on their components. At the extreme, the world is seen as having properties of a super-organism (Lovelock, 1988).
The major problem with viewing ecosystems (or communities) as evolving entities is that there is apparently no ‘blueprint’ for an ecosystem as there is the DNA blueprint for individual organisms. Thus the organization of the ecosystem cannot be stored at the ecosystem level and cannot be selected for in the way that organisms in a population can be selected and thus evolve. The holistic properties of an ecosystem must come from self-organizing principles of the system itself.
Much of the holistic approach derives from models based on thermodynamic considerations. Ecosystems are seen as energy-processing entities that maximize biological exergy and evolve the most ordered structure furthest from thermodynamic equilibrium (Jørgensen, 2002; Jørgensen et al., 2009).
Just how the organisms of an ecosystem interact and evolve to produce these phenomena is not immediately apparent – at least to many biologists like me. I find the ideas of self-organizing systems very interesting, but I remain sceptical until the mechanisms can be shown. Some work indicates that given certain thermodynamic and ecological relationships an aquatic ecosystem can adapt and move towards maximum resilience (Cropp and Gabric, 2002).
The practical application of the thermodynamic construct seems to have lagged behind its theoretical development. It does have explicit means for analysing real-world situations, and for instance has been applied to estuarine pollution stress (Marques et al., 1997), but thermodynamics has not become a common tool for environmental assessment and management, although models based on exergy have been taken up enthusiastically by certain engineers and applied to the environment. There is even a scientific journal called Exergy, but if we can judge by the number of ‘hits’ that we obtain for ‘exergy’ in the Ecological Society of America publications (three hits, and only one in a proper journal) this concept has not yet caught on in academic ecological circles.
Other aspects of ecosystem functioning have been incorporated into models and used for analysis of stress and sustainability in aquatic systems. The food-web modelling package ECOPATH incorporates analysis of the ‘maturity’ of the system as an indicator of exploitation of the fishery under study (Christensen and Walters, 2004).
ECOSYSTEMS WITH HEALTH AND INTEGRITY BUT NOT NECESSARILY WITH CONTROL
Many ecologists who would not defend ecosystem health as an emergent property will nevertheless use the concept as a goal for conservation and restoration. Likewise, ecosystem properties of resilience and elasticity can be measured along with productivity and nutrient cycling to evaluate the state of an ecosystem relative to the known parameters for similar, ‘reference’, ecosystems. The ecosystem provides a framework for accounting for the important interactions, setting the scale, etc., but evolution or selection at the level of ecosystem are not invoked.
VIGOUR, ORGANIZATION AND RESILIENCE
The holistic approach is often coupled with human components and a construct that can interface with economic and human-societal models. Robert Costanza and David Rapport and others have produced a great volume of publications and books in recent years which include such holistic concepts (Costanza, 1991; Costanza et al., 1992; Rapport et al., 1998a, 1998b; Jørgensen et al., 2009). At the basis of this work is the premise that ecosystems have intrinsic properties. Ecosystems are seen to suffer from stress and dysfunction and their health can be monitored and restored. The three measurable indicators of ecosystem health are vigour, organization and resilience (Rapport et al., 1998a, 1998b), and these are taken as goals for conservation and restoration. This scheme has widespread acceptance and application in aquatic conservation, for instance in the South East Queensland Healthy Waterways Programme (Bunn et al., 2010).
It is pertinent to recall in this year of Rio +20 that the Rio Declaration on Environment and Development (1992) contains Principle Seven, which states: ‘States shall cooperate in a spirit of global partnership to conserve, protect and restore the health and integrity of the Earth's ecosystems. In view of the different contributions to global environmental degradation, states have common but differentiated responsibilities.’ This is a clear statement of our common purpose and it specifically acknowledges health and integrity of ecosystems. I suggest that within this context we have plenty of good reasons for conserving and restoring environmental entities, and that we do not need to use the controversial and sometimes spurious arguments that imply organization at the level of ecosystem. I do not mean to say that this area of research into ecosystem properties should not be investigated – very much to the contrary, I think that it is imperative that we focus attention on it.
If at the end of this editorial the reader perceives that I am ‘fence-sitting’ on the position of ecosystem theory and its relevance to conservation, I can only reply that I seem to be in good company. My perception is that many ecologists wear two hats on this question – a reaction to the importance of comprehensive conservation in the face of the massive problems that we confront, which demands action and a multidisciplinary approach, and a reticence to go over to the ‘holistic’ position with its perceived lack of substantial theory.