Spatial modelling of biodiversity at the community level

Summary Statistical modelling is often used to relate sparse biological survey data to remotely derived environmental predictors, thereby providing a basis for predictively mapping biodiversity across an entire region of interest. The most popular strategy for such modelling has been to model distributions of individual species one at a time. Spatial modelling of biodiversity at the community level may, however, confer significant benefits for applications involving very large numbers of species, particularly if many of these species are recorded infrequently. Community‐level modelling combines data from multiple species and produces information on spatial pattern in the distribution of biodiversity at a collective community level instead of, or in addition to, the level of individual species. Spatial outputs from community‐level modelling include predictive mapping of community types (groups of locations with similar species composition), species groups (groups of species with similar distributions), axes or gradients of compositional variation, levels of compositional dissimilarity between pairs of locations, and various macro‐ecological properties (e.g. species richness). Three broad modelling strategies can be used to generate these outputs: (i) ‘assemble first, predict later’, in which biological survey data are first classified, ordinated or aggregated to produce community‐level entities or attributes that are then modelled in relation to environmental predictors; (ii) ‘predict first, assemble later’, in which individual species are modelled one at a time as a function of environmental variables, to produce a stack of species distribution maps that is then subjected to classification, ordination or aggregation; and (iii) ‘assemble and predict together’, in which all species are modelled simultaneously, within a single integrated modelling process. These strategies each have particular strengths and weaknesses, depending on the intended purpose of modelling and the type, quality and quantity of data involved. Synthesis and applications . The potential benefits of modelling large multispecies data sets using community‐level, as opposed to species‐level, approaches include faster processing, increased power to detect shared patterns of environmental response across rarely recorded species, and enhanced capacity to synthesize complex data into a form more readily interpretable by scientists and decision‐makers. Community‐level modelling therefore deserves to be considered more often, and more widely, as a potential alternative or supplement to modelling individual species.