Introduction

With the adoption of the Convention on Biological Diversity (United Nations1992), the sustainable management and protection of biodiversity shifted from being an option to an acknowledged necessity: sustainability is now the high-level goal of environmental management policy. Sustainability implies the ability for processes and activities to be able to continue indefinitely. Within the specific context of environmental management this has been taken to mean meeting the needs of the present without compromising the ability of future generations to meet their own needs (derived from the definition of sustainable development developed by the Brundtland Commission (World Commission on Environment and Development 1987)). More recently the concept has been expanded to explicitly include three elements, sometimes referred to as the three pillars of sustainability: environmental, social and economic (Table 7.1). For many policy makers, sustaining social structures and hence economic systems is the imperative, while many scientists would argue that you cannot have a sustainable economy without sustainable use of natural systems.

Introduction

The sustainable use, management and conservation of ecosystems, as promoted by the Convention on Biological Diversity's Ecosystem Approach (United Nations 1992), and recent initiatives such as the Millennium Ecosystem Assessment (United Nations 2005), emphasise the inter-dependence between ecological systems and human well-being. Healthy social systems demand healthy ecosystems and vice versa. This emergent world view is compelling and persuasive to conservationists, policy makers and managers alike, because it implies win-win solutions for nature conservation and for human development which relies on the continued provision of ecosystem goods and services. Ecosystem management within this context requires a holistic approach that acknowledges the need to work with and across a broad range of natural, physical, social and economic sciences. Whilst there are many successful programmes which have achieved this, mainstream ecologists who have so much to bring to the table have been slow to embrace such approaches. Jones and Paramor (this volume) consider many of the important cultural challenges. The view that humans are part of, not apart from, the biophysical system in which they are embedded has not always sat comfortably with academic researchers, who have traditionally seen their prime focus on, and responsibility to, either the natural system or to broader societal goals, but rarely both. In addition, there are misunderstandings and fears about what holistic ecosystem approaches really are, in turn due to the divergent pathways along which different sections of the ecological community have developed.

What can ecological science contribute to the sustainable management and conservation of the natural systems that underpin human well-being? This is a question that is taxing many professional ecologists, learned societies and science funders. The question has been driven by both the increased awareness of the present ecological crisis and the publication of several documents influential at the highest political level, such as the Intergovernmental Panel on Climate Change (IPCC) reports, the Stern Review, GEO4 and, most relevant to the present volume, the Millennium Ecosystem Assessment. The impetus and stimulation for this volume came in part from workshops hosted by UK Pop Net and the British Ecological Society (BES) in 2003 and 2007, respectively, which aimed to seek an answer to the question: how can mainstream ecology, and by definition the ecologists within learned societies like the BES, contribute to national and international initiatives aimed at implementing a holistic ecosystem approach for environmental management? That workshop revealed a huge potential within the community but also frustrations about, and ignorance of, the different perspectives on ecosystem ecology held by the different sectors within mainstream ecology: reductionist versus holistic approaches, inter-disciplinary versus mono-disciplinary approaches, those which recognise humans as part of versus apart from the ecosystem.

Ecosystem Ecology implies both a different perspective and a different approach to the science. The more holistic view tends to regard the ecosystem as rich in ecological linkages, some of which may be strong but many of which will be individually weak.

Introduction: origins and development of the ecosystem health concept

The need to understand and quantify ecosystem behaviour and condition has come to the forefront of environmental policy due to a greater emphasis on environmental sustainability and an accompanying recognition of the scarcity of natural resources, such as water, soil and biological diversity. Increasing concern regarding human impacts on the environment and the possibility that some human-induced changes in ecological systems may be irreversible has also focused attention on ways in which such changes can be assessed and, if possible, avoided. From the policy maker's perspective, the concern is not only in terms of the possible extent of these problems, but also the likelihood of their occurrence and the timeframe over which they may operate. In the context of global climate change, understanding the functioning of ecosystems, and how their health and performance can be measured and monitored over time are of critical importance, since these are linked inextricably with human health and well-being.

A considerable body of literature over the past decade has sought to define ecosystem health in practical terms. The majority of the definitions of ecosystem health concentrates exclusively on ecological aspects. For example, Costanza (1992) defines the term as follows: ‘An ecological system is healthy and free from “distress syndrome” if it is stable and sustainable – that is, if it is active and maintains its organisation and autonomy over time and is resilient to stress.’

Introduction

Ecologists have long been aware of regularities and patterns in the body size of organisms in populations and communities, observations that go back at least to Alfred Wallace and continue through the works of Elton, Thienemann, Hutchinson, MacArthur and many others. The classical contribution of R. H. Peters (1983) codified such patterns through the concept of body-size allometry, of metabolic rate and other features, and led on to many of the phenomena now included under macroecology (Blackburn & Gaston, 2003). Brown and colleagues (Brown et al., 2004; Brown, Allen & Gillooly, this volume), in particular, added new advances in scaling theory and, incorporating the exponential effect of temperature on metabolic rate, sought to explain a wide variety of patterns and processes in ecology at levels of organization from individuals to ecosystems.

The focus on aquatic systems at the Hatfield symposium, and in this resultant volume, is justified because body-size patterns may be more important, or at least more obvious, in aquatic ecosystems. Woodward and Warren (this volume) offer three possible reasons. First, the most important primary producers in water are small and, along with small heterotrophic micro-organisms and small detritus particles, are gathered from suspension by larger consumers. Second, they point out that conventional predators, larger in turn than their prey, seem particularly prominent in aquatic systems where there may be fewer parasite food chains (see Cohen, this volume).

More than ten years ago, two of us (AGH and DGR) were lucky enough to edit a previous symposium of the British Ecological Society (BES) – Aquatic Ecology: Scale, Pattern and Process (Giller, Hildrew & Raffaelli, 1994). In the Introduction to that volume, we pointed out that the BES had not devoted a single previous symposium to aquatic ecosystems. Evidently we did not change the culture, since the Body Size symposium held at the University of Hertfordshire in September 2005 was only the second! Aquatic Ecology: Scale, Pattern and Process had two objectives: (i) to explore how the scale of approach affected the patterns that were detected and the processes that appeared to be important, and (ii) to compare freshwater and marine ecosystems. In Body Size: The Structure and Function of Aquatic Ecosystems, both those questions of scale and comparison among systems are very much still alive as continuing themes. Body size determines overwhelmingly the scale at which organisms perceive and navigate through their physical world, and the contrasts between freshwater and marine ecosystems remain evident. Body size is a species trait with implications beyond scale, however, and we believe that the present volume shows that more similarities than differences are evident among the diverse aquatic systems considered. Indeed, several authors argue here that fundamental ecological processes are revealed by comparing marine, freshwater and terrestrial systems.