Seite - 160 - in Biodiversity and Health in the Face of Climate Change

160 8.1 Key Concepts In this chapter we take a closer look at one of the central concepts of this book, biodiversity, and especially at the way it is defined. We do so because the definition of this concept has a bearing on what to measure, how best to measure it, and how to study its relationship to other concepts, such as mental health and well-being. The latter concepts are also discussed, but only briefly. 8.1.1 Biodiversity These days, the term ‘biodiversity’ is often interpreted and used by conservationists, policy-makers and the general public as an alternative for the broader term ‘nature’, more or less suggesting that they are interchangeable (Kaphengst et  al. 2014; for examples, see Wossink et  al. 1997; Wall et  al. 2016, Chap. 4). ‘Biodiversity’, how- ever, originates from the scientific fields of ecology and nature conservation, and there it has a much stricter meaning. Here we start from this original meaning in which biodiversity  – as defined by the Convention on Biological Diversity (CBD 1992)  – is the variability among living organisms and the ecological complexes of which they are part. Sources of this variability include intra-species diversity (e.g. genetic variability), interspecies diversity (species diversity) and diversity in eco- systems (from biomes to biotopes). Although biodiversity encompasses these three levels of variability, in relationship to human health the species diversity level seems to be the most studied level thus far (Lovell et  al. 2014; see also Marselle et  al. Chap. 9, this volume). To confine the discussion, in this chapter we therefore focus on this level. An initial question is whether species are required to be part of an ecological complex, and if so, what counts as such a complex. We equate the term ‘ecological complex’ with ‘ecosystem’, for which the CBD (1992) also has provided a defini- tion: a dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit. Some authors include humans as a possible species within an ecosystem. In this chapter, we do not. Given the requirement of interacting as a functional unit and the exclusion of humans, although a zoo contains many animal species, it can hardly be considered an ecosys- tem. The same holds true for a hortus botanicus or arboretum. With regard to spe- cies, Angermeier (1994) already made a distinction between biodiversity and artificial diversity. To a lesser extent, urban parks and private gardens may also contain combina- tions of plants and animals that do not occur in that composition in a (natural) eco- system, many of which may not be indigenous to the area. Non-indigenous plants include (wild) ornamental trees, shrubs, perennials and garden pond plants. Non- indigenous animals include (feral) cats, dogs, aviary birds and other pet species. The living nature that parks and gardens contain usually is not intended or allowed to S. de  Vries and R. Snep