Environmental diversity: on the best-possible use of surrogate data for assessing the relative biodiversity of sets of areas

Abstract

The conservation goal of representation of biodiversity (in the broad sense of all species) in protected areas requires best-possible use of available surrogate information. One standard approach is based on 'indicator' groups of taxa. A minimum set of areas having at least one representation of each indicator species is taken to be representative of other organisms. This same minimum-set approach is adapted to other 'attributes' of biodiversity, for example, derived environmental clusters. A weakness of these approaches is that useful information is lost; for example, for environmental clusters, there is no distinction made either among or within clusters. A more powerful surrogate approach can use some expression of environmental and/or biotic pattern so that variation among areas is seen as part of a continuum rather than partitioned into arbitrary clusters/attributes. The challenge in using pattern effectively is to adopt a robust model for the relationship between pattern and the underlying units of biodiversity, i.e. species. An environmental space (a continuum or ordination pattern), combined with the standard ecological continuum model relating species to environmental space, has advantages over other patterns based on hierarchy or distance matrices. Because an environmental space can be estimated either directly (observed environmental data) or indirectly (data on indicator groups), the corresponding surrogate-measure of biodiversity, 'environmental diversity' (ED) makes best-possible use of either kind of data. We conclude that the arbitrariness of the 'attribute' approach can be replaced by a robust surrogate ~pattern' approach that is flexible and avoids unwarranted assumptions.

Using Phylogenetic Dissimilarities Among Sites for Biodiversity Assessments and Conservation

“…The dissimilarities, the ordination methods and GDM all are relatively robust approaches under a general model of unimodal responses to environmental gradients ( Fig. 1b; Faith et al 1987;Faith and Walker 1996a;Ferrier et al 2009).…”

“…Walker (1994, 1996a) demonstrated that, under a simple unimodal response model, species representation will be maximised by a selected set of sites if and only if it satisfies this continuous p-median criterion. Note that the ED score, because it counts un-represented species based on a sum of distances, is numerically small when the number of represented species is large (see example calculations below and in Faith and Walker 1996a). The ED surrogates approach therefore provides a rationale for interpreting high environmental diversity for a set of localities as implying high biodiversity for the set (see Beier and Albuquerque 2015).…”

“…In the simple case, unimodal response implies that features are effectively counted up when we apply calculations linked to the p-median; in other cases, the model implies calculations that are modifications of the simple p-median. Simple ED variants include weighting of demand points when species richness varies over the space (Faith and Walker 1996a;Faith et al 2004), and creating an extended environmental space ('extended polytope'; Walker 1994, 1996a, b;Faith et al 2004; see also Hortal et al 2009). These options modify the parameters used in calculating the p-median.…”

“…Demand points occur continuously along the gradient and define the centers of distribution for features or branches. These features are assumed to have a uniform distribution of range-extents along the gradient (Faith and Walker 1996a). Graphically, the height to the top of the gray area above any demand point (Fig.…”

“…The power term, z, is interpreted as analogous to that in species-area curves ). Ferrier et al (2004) drew on "principles of the "environmental diversity" (ED) approach proposed originally by Faith and Walker (1996a) as a means of assessing the representativeness of protected areas within a continuous environmental or biological space." Both p and ED intend to convert dissimilarities into a measure of representativeness (e.g., of a subset of sites), but the similarities and differences between the two methods have not been investigated.…”