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or biological traits
Functional diversity is a biodiversity measure based on functional traits of the species present in a community. Functional traits are those that define species in terms of their ecological roles - how they interact with the environment and with other species (Diaz and Cabido, 2001). In phytoplankton, for example, these traits usually include body size, tolerance and sensitivity to environmental conditions, motility, shape, N-fixation ability and Si requirements (Reynolds et al., 2002; Weithoff, 2003). In terrestrial plant communities, researchers have included more complex traits like rates of growth, nutrient requirements and water uptake (Walker and Langridge, 2002; Barnett et al, 2007.)
Trait- based approaches to community ecology, linking ecological strategies, community assembly theory and functional diversity (Grime, 2006), have the potential to unify the demographic and functional differences among co-occuring species in relation to mechanisms of coexistence (Tilman 1994). Studies have linked characteristics (or else traits) such as feeding mechanisms, longevity, body size and mobility to changes in species distribution in communities exposed too stressors such as sewage pollution (Poore and Kudenov 1978, Grizzle 1984), anoxia (Beukema et al. 1999) and fishing (Brown and Wilson 1997, Ramsay et al. 1998, Spencer et al. 1998, Hall-Spencer et al. 1999).
The selection of biological traits for Biological Traits Analysis (BTA) is important. A wide variety of traits are potentially available for describing ecological functioning, but they may not all be equally useful. Trait selection is constrained by the amount of information available (Gayraud et al., 2003) and the costs of processing it. Different traits can describe different aspects of ecological functioning and some are intimately linked to particular functions, whereas others serve only as indirect indicators (Lavorel and Garnier, 2002). The type of trait included in analyses has the potential to affect the way benthic assemblages are viewed, so the number and type of traits chosen for BTA should not be an arbitrary decision. Development of BTA must therefore also include an assessment of which traits provide the most useful description of ecological functioning so that selection is optimised (Bremner et al., 2006).
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