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Reconciling theories of biodiversity patterns

Final Activity Report Summary - RTBP (Reconciling Theories of Biodiversity Patterns)

The current biodiversity crisis is leading to a pressing need to understand the basic rules governing the diversity of life on Earth and the processes that generate and maintain it. A number of such rules have been offered and several attempts have been made over the last decade in order to build a universal, concise theory of these biodiversity and, particularly, macroecological, patterns. Empirical tests of such theory necessitate the comparison of available data with outputs of exact models. Simple tests on the fit of modelled patterns to various data sets, for example the calculation of correlation coefficients and information criteria, failed however to differentiate between potential underlying ecological mechanisms.

During the two years of this Marie Curie fellowships project, referred to as 039576-RTBP-EIF, a new framework for testing macroecological patterns was developed and demonstrated using three mutually interconnected patterns:

1. the species-abundance distribution (SAD)
2. the spatial species’ richness pattern and
3. the latitudinal gradient in the north-south extent of species spatial ranges.

Each test focussed on crucial aspects of a focal pattern rather than on simple model fitting. These aspects were:

1. the robustness of a tested pattern against changes in spatial and taxonomic resolution
2. the deviations between data and the diversity pattern which were mathematically determined by the frequency distribution of species’ richness among sites and by changes in the diversity pattern when changing symmetry of the species’ richness distribution
3. the simultaneous changes in latitudinal diversity gradients and the extent of species’ ranges.

In order to build the tests a new concept of area and taxon invariance was developed. This concept helped to identify a statistical mechanism responsible for right skewed, unimodal SADs. This mechanism was likely to act in other fields of science, such as social science and physics. Most importantly, however, a set of variables with potential to reveal ecological underlying mechanisms was identified. These were the Jaccard index of species spatial turnover, the nestedness of species spatial ranges and the asymmetry in the north-south extent of species’ ranges along a meridian. These had the potential to properly capture changes in biodiversity and, subsequently, to act towards its protection.