Review
Functional biodiversity: An agroecosystem approach

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Abstract

Research and policies aimed at biodiversity conservation in agricultural ecosystems are often less successful than expected. One common assumption is that more research is needed to develop improved measures and indicators of biodiversity. The authors’ opinion is that this is only partly true and that most of the problems arise from the lack of a well-focussed approach to this subject. Based on the knowledge available in the scientific literature, a methodological framework was developed which can help researchers and policy makers to think in a better, more structured way about issues related to biodiversity conservation in a given agroecosystem. In order to frame the importance of biodiversity in agroecosystems, three main questions were addressed through literature search: (1) What does biodiversity mean in natural and agricultural ecosystems? (2) How is the concept of functionality used in relation to biodiversity? (3) Which biodiversity measures are currently used to express agriculture–biodiversity relationships?

Analysis of the literature resulted in a framework consisting of three steps. At first the objectives of biodiversity research and policies have to be defined. Three options can be foreseen here: (a) species, community, habitat or overall biodiversity conservation regardless of its functions, (b) biodiversity conservation to attain production and environmental protection services, and (c) use of bio-indicators for agroecosystem monitoring. In the second step the appropriate target elements for conservation have to be chosen based on an agroecosystem approach, and in the third step adequate biodiversity measures of composition, structure and function have to be selected for each target element.

Functional biodiversity is important in relation to the provision of specific agroecosystem services. The study of functional biodiversity should start with the definition of agroecosystem functional groups comprising all elements that interact with the desired service, and the consequent determination of the role of diversity within these functional groups for the fulfilment of the agroecosystem service. Therefore a more precise definition of ‘functional biodiversity’ would be “that part of the total biodiversity composed of clusters of elements (at the gene, species or habitat level) providing the same (agro)ecosystem service, that is driven by within-cluster diversity”.

Introduction

After the signing of the ‘Convention on Biological Diversity’ in Rio de Janeiro in 1992 the word ‘biodiversity’ has become a widely used term in science (number of publications with ‘biodiversity’ in title, abstract or key words in Scopus©: 3 for 1988, 133 for 1992, 1170 for 1998 and 4526 for 2005) and in policy making (Buchs, 2003). The success of ‘biodiversity conservation’ depends on the successful interactions between science and policy making. If research and policy making do not give the same meaning to the term ‘biodiversity’ and if they do not define precisely what objectives they pursue, there cannot be a good interaction between them and the results of research will not be used correctly. Ultimately, the policies chosen will not be as successful as they could have been.

The absence of detailed objectives for biodiversity conservation projects and policies does not only result in research projects which are hard to relate to policy making, and policies which are hard to evaluate (Kleijn and Sutherland, 2003), but it also increases the risk of unforeseen and negative side effects on other facets of biodiversity (Marshall and Moonen, 2002, Moonen et al., 2006).

Policy makers have responded to the alarm launched by researchers with regard to the need for ‘biodiversity conservation’. A reference to ‘the conservation of biodiversity’ is present in almost all conservation, land use management and environmental protection policies proposed at local, national and international scale. As can be seen from some reports and projects written at European Community (EC) level, policy makers use biodiversity for various goals and objectives without much specification. To start with, often there is no clear distinction between the use of biotic indicators and biodiversity indicators for the determination of the state of environmental aspects of ecosystems (Duelli and Obrist, 2003). ‘Biodiversity conservation’ has been defined as one of the aims of agri-environmental policies (AEP) (Parris, 2001; p. 7–8), and measures (AEM) (European Commission, 2005; p. 11–12), including the definition of High Nature Value Farmland (European Environment Agency, 2004), and it is at the same time used to measure impacts of AEP and AEM on ‘biodiversity’. Furthermore, it is used to measure impacts of agriculture on the environment and on agricultural sustainability (Parris, 2001; p. 7), and to measure the impacts of agriculture on ‘biodiversity’ (Parris, 2001; p. 13). All of these reports use ‘biodiversity’ without specification of the level or type that is desirable, and it is assumed that there is a cause–effect relationship between biodiversity (not specified) and environmental quality, agricultural sustainability, and between certain biodiversity indicators and the overall biodiversity level.

The lack of robust evaluation studies for the determination of the success of European AEM in conserving and promoting biodiversity as pointed out by Kleijn and Sutherland (2003), and for the same reason of other agro-environmental or conservation projects and policies at local, national or international scale, could be related to the absence of a well-defined quantitative measure for ‘biodiversity’, as proposed by Spangenberg (2007).

Instead, the impression of the authors of this paper is that the main problem is related to the wide variety of interpretations given to the terms ‘biodiversity’ and ‘functional biodiversity’, to the inefficient use of existing biodiversity measures, and also to the fact that, so far, mostly ecologists have been involved in the definition of research and policy making regarding biodiversity, which resulted in a biased perspective. This paper will underline the importance of an agroecosystem approach for questions involving agriculture–biodiversity relationships. Based on this approach, the aim is to create a methodological framework which provides guidelines for the determination of more effective biodiversity measures in agroecosystems. This framework differs from previously proposed frameworks for biodiversity or lists of bio-indicators in that it does not provide names of target elements to be studied, but gives guidelines for determination of the typology of biodiversity that should be addressed in relation to the various usages of biodiversity in agroecosystems. The exact names and measurers of target elements have to be defined based on agroecosystem characteristics, which will obviously vary depending on the context.

Section snippets

Methodology

In order to frame the importance of biodiversity in agroecosystems and to make it more tangible for research and policy making, three main questions had to be addressed through literature search:

  • (1)

    What is biodiversity?

    • (a)

      Disentangling ‘biodiversity’ in natural and agricultural ecosystems.

    • (b)

      Which objectives for biodiversity are pursued?

  • (2)

    What is functionality?

    • (a)

      The ‘functionality’ concept in relation to biodiversity in agroecosystems.

    • (b)

      Has research demonstrated the presumed mechanistic relations between

Functional groups for agroecosystem services

In the more classical ecology it is thought that functional groups are the principal determinants of the species communities composition. Therefore species are clustered into groups with similar ecophysiological and life-history traits such as dispersal strategy or the ruderal-competitor-stress tolerator characterisation (Grime et al., 1990). In this case, the ‘functional groups’ are not directly related to the services provided by natural ecosystems, but they are used to explain the state of

Diversity for ecosystem functioning

The question if ‘biodiversity’ (diversity in composition of alleles, species and habitat) really interferes with ecosystem functioning has been asked ever since Darwin, and ecologists have for long tried to gather scientific proof for it (Tilman and Lehman, 2002). However, the major reviews regarding this subject (Schwartz et al., 2000, Ekschmitt et al., 2001, Hector et al., 2001a, Schmid et al., 2002, Naeem and Wright, 2003, Hooper et al., 2005, Jackson et al., 2007) have shown that the

Fine-tuned definitions of functional biodiversity

From the above it becomes evident that the classical approach towards ‘functional biodiversity’ should be split up in a two-step approach to determine the functionality of biodiversity in agroecosystems. The first step consists of the definition of the ‘agroecosystem functional groups’, i.e. clusters of genes, species or ecosystems which contribute to the performance of determinate agroecosystem processes (services). This can be expressed as the determination of the ‘bio-functionality’.

Selection of bio-indicators

Biota or groups of biota (from genetic to community level) can be clustered based on their ecological and life-history traits, and therefore on their interaction with the agroecosystem. This results in two groups of bio-indicators: process-related bio-indicators and health-related bio-indicators, where ‘process’ and ‘health’ refer to the agroecosystem (Table 3). Not included in this classification are bio-indicators at landscape level, such as habitat or ecosystem measures. However, in general

Discussion

In our opinion, one of the most important aspects emerging from the reflections made in this paper is the importance of an interdisciplinary, agroecosystem approach involving ecological theories about population and community dynamics and structure, food web dynamics, biogeography, and landscape ecological principles related to spatial and temporal heterogeneity of patterns and processes. The integration of this knowledge helped to develop and distinguish valid approaches for biodiversity

Acknowledgements

The authors want to thank two anonymous reviewers and Claudine Thenail for their useful comments on the earlier version of this manuscript.

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