Abstract
Ecosystem managers frequently need a simple indicator of the well-being of ecological systems in order to assess human impacts. Hitherto measures of structural diversity are often used for such purpose. Structural diversity indices are generally based on species richness as well as on the relative abundance of species. Yet, no information is used on the type of species, and two areas with totally different species compositions may have the same structural diversity. In the last decade the field of macroecology has been put in the forefront of ecology. This approach emphasizes the study of empirical patterns in the relationship between structural characteristics at the level of the population (e.g. abundance) and functional characteristics at the level of the individual organism (e.g. maximum body size). In a similar way, empirical patterns might be sought between structural characteristics of the community, e.g. diversity, and functional characteristics of the constituent populations. The characteristics of the various populations can best be described in terms of the functional variability within the community. So, one might, for example, ask the question whether species-rich (a structural measure) communities show more variability in body size (a functional measure) than species-poor communities? We propose here to study the possible link between the structural diversity of a community and a description of the functional variability of the constituent populations. In order to arrive at such link, we first have to develop a so-called functional diversity index. Such index should describe the diversity of the functional roles species play. The index we propose to develop can be regarded as an extension of Simpson's species diversity index. Simpson's index gives, when two individuals are selected at random from the community, the chance that they belong to the same species. The new index should give the expected difference in functional role between two randomly selected individuals. The definition of functional role will be described in terms of aspects of the energy budget (or, more general, in terms of physiology), and will partly be empirically derived. Practically, this means that we will use empirical data from marine coastal areas that have been under various levels of human intervention, and choose that specific functional role, whose diversity provides the greatest discriminatory ability between such areas. Dynamic energy budget models will be used and literature studies will be performed in order to get reliable estimates of the energy budget parameters for the individual species. Hence the main objective of the proposed study is to develop and empirically validate (using data on macrobenthos occurrence in the North Sea and Wadden Sea) a functional biodiversity index and link this index with a classical structural index.
Netherlands