Scale Dependence of the Beta Diversity-Scale Relationship
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COMMUNITY ECOLOGY 16(1): 39-47, 2015 1585-8553/$ © AKADÉMIAI KIADÓ, BUDAPEST DOI: 10.1556/168.2015.16.1.5 Scale dependence of the beta diversity-scale relationship 1 1,4P 2 3 1 Y. ZhangP , K. MaP , M. AnandP , W. Ye and B. FuP 1 State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China 2 Global Ecological Change Laboratory, School of Environmental Sciences, University of Guelph, Guelph, Ontario, N1G 2W1, Canada 3 Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China 4 Corresponding author. Tel/Fax: 86-10-62849104, Email: [email protected] Keywords: Alpha diversity, Diversity partitioning, Gamma diversity, Power law, Scaling. Abstract: Alpha, beta, and gamma diversity are three fundamental biodiversity components in ecology, but most studies focus only on the scale issues of the alpha or gamma diversity component. The beta diversity component, which incorporates both alpha and gamma diversity components, is ideal for studying scale issues of diversity. We explore the scale dependency of beta diversity and scale relationship, both theoretically as well as by application to actual data sets. Our results showed that a power law exists for beta diversity-area (spatial grain or spatial extent) relationships, and that the parameters of the power law are dependent on the grain and extent for which the data are defined. Coarse grain size generates a steeper slope (scaling exponent z) with lower values of intercept (c), while a larger extent results in a reverse trend in both parameters. We also found that, for a given grain (with varying extent) or a given extent (with varying grain) the two parameters are themselves related by power laws. These findings are important because they are the first to simultaneously relate the various components of scale and di- versity in a unified manner. Abbreviations: DBH–Diameter at Breast Height, SAR–Species-area relationship. Introduction for nature reserves (He and Legendre 1996, Dengler 2009). Actually, the power law scaling relationship of SAR is also Ecologists have long distinguished three fundamental dependent on scale, as it has been shown that its parameters components of species diversity: alpha diversity (α), which (especially the scaling exponent z) vary with spatial scale measures the species diversity at the local scale, beta diver- (Crawley and Harral 2001, Drakare et al. 2006). sity (β), which measures the extent of local diversity change Spatial scale can be separated into several components, in a region, and gamma diversity (γ), which measures the total including grain, extent, and lag (Wiens 1989), but grain and diversity of a region (Whittaker 1972). All of these diversity extent are used primarily for SAR scale dependence studies. components are scale dependent: alpha diversity depends on Grain is the size of the individual units of observation—the the size of the local scale, gamma diversity depends on the quadrats of a field ecologist or the sampling units of a statisti- size of the regional scale, and beta diversity, which links al- cian—which correspond to the minimum scale sampled (of- pha and gamma diversity, depends on both local and regional ten the size of individual quadrats) in a study, and extent is the scales (Loreau 2000). However, considerable attention has overall area encompassed by a study (Wiens 1989). Palmer been given primarily to the scale dependency issues of alpha and White (1994) observed that spatial grain and extent in- (or gamma) diversity. fluence the shape of the SAR curve in a plant community. The species-area relationship (SAR) is well-known for Crawley and Harral (2001) considered the spatial extent ef- describing the scale dependency behavior of alpha or gamma fects on slope of the power SAR of plant communities, and diversity components when measured by species richness found that scaling exponent z has a unimodal pattern which (the species richness and diversity are use synonymously in shows the peak at intermediate spatial extent sizes with low this paper). The most common form of SAR is the power law values at small and large spatial extent size. Drakare et al. scaling relationship (S=cAz, where S is number of species or (2006) considered the effects of both spatial grain and spa- species richness; A is area measured; parameter z is the scal- tial extent on SARs and provided evidence of the fact that ing exponent with value less than 1, and parameter c is a con- coarse spatial grain follows a steeper slope (z), while spatial stant, Arrhenius 1921). This can help determine the minimal extent does not show clear pattern on scaling exponent z. The sampling area for biodiversity surveys, extrapolate species inconsistency between these two works on the spatial extent richness in response to habitat loss, and plan optimal sizes effect on the SAR is due partially to the fact that the results 40 Zhang et al. of Drakare et al. (2006) were based on 794 SARs from differ- while varying extent, 2) fixing extent while varying grain, and ent geographical location and taxonomic groups which also 3) co-varying extent and grain. The main purpose of our work impact on the slope of SAR. Drakare et al. (2006) found that is to explore whether scale dependence properties exist for steeper slope of SAR are generated at lower latitudes and by scaling relationship between beta diversity and scale (spatial larger organisms also. The scale dependency of SAR is still extent and spatial grain). Specifically, we want to analyze the an open issue, especially for the extent effects. To our knowl- spatial grain effects on the scaling relationship between beta edge, there have been surprisingly few attempts to quantify diversity and spatial extent and the spatial extent effects on both spatial extent and grain dependence of the power law the scaling relationship between beta diversity and spatial SAR in one dataset analytically and systematically. Spatial grain. Therefore, the first two ways suggested by Barton et grain and extent exist simultaneously for any dataset. In the al. (2013) for spatial scaling of beta diversity were used in SAR, the minimum area (A ) sampled for analysis corre- min our work. The scaling relationship between beta diversity and sponds to the spatial grain, and the maximum area (A ) sam- max scale is assumed in power law form. This assumption is based pled for analysis corresponds to the spatial extent which made on the fact that alpha diversity and gamma diversity could the spatial grain and spatial extent have been included in an be scaling up by power law. As previously stated that beta implicit way. Therefore, it is hard to explore the scale (spatial diversity is a function of alpha diversity and gamma diversity, grain and spatial extent) dependency of SAR analytically and when exploring beta diversity and extent scaling relationship, systematically in an explicit way. namely fixing alpha diversity but changing gamma diversity, Beta diversity, which is considered as important as alpha and given the power law scaling of gamma diversity, it is diversity in understanding ecosystem functions and man- reasonable to assume beta and extent may have power law agement and biodiversity conservation (Wilson and Shmida scaling relationship. Similarly, when exploring beta diversity 1984; Legendre et al. 2005), has the potential to include the and grain scaling relationship, namely fixing gamma diver- spatial grain and extent explicitly when dealing with scale de- sity but changing alpha diversity, and given the power law pendency issues. Although diverse definitions and measures for beta diversity have been reviewed, discussed, and recom- scaling of alpha diversity, it is reasonable to assume beta and mended extensively (see papers of Wilson and Schmida 1984, extent may have power law scaling relationship also. Based Vellend 2001, Koleff et al. 2003, Tuomisto 2010a, 2010b, on this power law scaling relationship assumption between Anderson et al. 2011), the beta diversity in our work refers beta diversity and scale, we explored the scale dependency to that which is related directly to alpha and gamma diversity of this relationship by the mathematical inference. The power components. It is well known that two different perspectives law beta diversity scaling assumption and mathematical pre- exist for relating beta diversity components directly with al- dictions on the scale dependency of this scaling relationship pha and gamma diversity components: the multiplicative per- were also verified through the analysis of forest community spective (betamul=gamma/alpha-1; Whittaker 1972) and the data from an elevational transect of warm, temperate de- additive perspective (betaadd=gamma-alpha; MacArthur et al. ciduous broadleaf oak (Quercus liaotungensis Koidz) forest 1966). There have been extensive discussions with respect in Beijing, North China and a 20-ha subtropical, evergreen to which perspective is better in partitioning an “independ- broadleaf forest plot in Guangdong province, South China. ent” beta diversity (Jost 2007, Ricotta and Marignani 2007, Ricotta 2008, de Bello et al. 2010, Chao et al. 2012, c.f. a Methods recent Forum in Ecology [2010] edited by Ellison, and papers in it). However, there is no perfect metric for measuring beta Mathematical inference diversity (Ricotta 2010) and both additive and multiplicative partitioning can be extremely useful