![]() ![]() The effect of area per se in maintaining diversity is through redundancy that provides protection from stochastic extinctions, and the value of redundancy decreases as area increases. The usual species-area curve is steeper among small areas than larger ones, which indicates greater sensitivity at the small end of the scale (except among very small islands Triantis et al., 2006). Belmaker & Jetz, 2011 Daru et al., 2020 Rahbek, 2005 Willis & Whittaker, 2002) thus, we expect the relationship of diversity to area and environmental heterogeneity to be scale dependent. Scale dependence for patterns related to diversity have been proposed and observed (e.g. They concluded that heterogeneity was most important at intermediate extents-perhaps because they did not include climate, which is a factor acting at greater extents (McGill, 2010). They highlighted the collinearity of area and heterogeneity and the entanglement of area and resolution, showing that the effects of resolution varied with area and vice versa. Wang et al., 2012), The effects of extent and spatial resolution on AvE were discussed in depth by Stein et al. ( 2014). The amount of debt, and the number of eventual extinctions, will depend on AvE: that is, whether heterogeneity is sufficient across enough area to support minimum viable populations.Īlthough the drivers of diversity are known to vary with extent, the role of area per se at different extents is seldom differentiated (e.g. During this process, increases in local diversity may occur (Steinbauer et al., 2018), but an extinction debt will be incurred (Dullinger et al., 2012). The total area will be reduced, especially where the highest elevations are already occupied or consist of bare rock or ice. Engler et al., 2011 Körner & Hiltbrunner, 2021 Malanson et al., 2019). Warming will shift alpine habitats upwards while spatially reorganizing them among microsites of current zones (e.g. As an example, the potential for species in alpine habitats-and other island-like environments-to survive climate change depends on the current area, heterogeneity of climate, and their effect on diversity relative to climate changes. The importance of the area versus environmental heterogeneity (AvE) question goes beyond theoretical matters. These explanations are the central elements of the neutral and niche theories of diversity (Chisolm & Pacala, 2010), and like many other ecological theories may depend on the scale of observations (McGill, 2010 Willis & Whittaker, 2002). Heterogeneity per se maintains diversity because more environments can support more specializations and species, each with a minimum population (e.g. The significant importance of area per se in small territories indicates that microrefugia, even with an unlikely full range of heterogeneity, will suffer local extinctions in the face of climate change.Īrea per se is important because more individuals can be divided into more species, each with a minimum population, given the basis of a fixed number of individuals per unit area (MacArthur & Wilson, 1967). The potential heterogeneity–effective area trade-off may be limited to locations where the environmental heterogeneity is quite discrete or if the added environment is beyond the niches of any species in the potential pool. ![]() Scale dependence may account for discrepancies among past empirical studies wherein environmental heterogeneity has usually outweighed area in the explanation of species richness and it is not affected by nestedness. The heterogeneity–effective area trade-off occurred in a few simulations of more discrete habitats. This qualitative pattern was maintained regardless of whether and how nestedness was represented. The simulation revealed that heterogeneity was consistently more important, but less so among smaller areas. The explanation of the observed regional richness was shared by area and heterogeneity. A simulation was developed to separate the relative importance of area and heterogeneity at different extents and representations of spatial nestedness, and the heterogeneity-effective area trade-off was evaluated by altering spatial discreteness. We applied commonality analysis to partition the unique and shared explanation of the observed vascular plant species richness among selected metrics. We developed metrics of climatic and edaphic heterogeneity, using principal components analyses and the shoelace algorithm, and added elevation range. LocationĪlpine grasslands of 23 mountain ranges of southern and central Europe. ![]() Here, we empirically examined this relationship and parsed their relative importance, and that of the heterogeneity-effective area trade-off, at different spatial scales and in different spatial representations in simulations. Area and environmental heterogeneity together explain most patterns of species diversity but disentangling their relative importance has been difficult. ![]()
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