Abstract
The relationship between β-diversity and latitude still remains to be a core question in ecology because of the lack of consensus between studies. One hypothesis for the lack of consensus between studies is that spatial scale changes the relationship between latitude and β-diversity. Here, we test this hypothesis using tree data from 15 large-scale forest plots (greater than or equal to 15 ha, diameter at breast height ≥ 1 cm) across a latitudinal gradient (3–30o) in the Asia-Pacific region. We found that the observed β-diversity decreased with increasing latitude when sampling local tree communities at small spatial scale (grain size ≤0.1 ha), but the observed β-diversity did not change with latitude when sampling at large spatial scales (greater than or equal to 0.25 ha). Differences in latitudinal β-diversity gradients across spatial scales were caused by pooled species richness (γ-diversity), which influenced observed β-diversity values at small spatial scales, but not at large spatial scales. Therefore, spatial scale changes the relationship between β-diversity, γ-diversity and latitude, and improving sample representativeness avoids the γ-dependence of β-diversity.
Highlights
Decreasing species richness from the equator to the poles is one of the best-recognized patterns in ecology [1,2]
Grain size had a very strong relationship with both the number of individuals sampled and g-diversity (R2 . 0.95). For both Lambir and Barro Colorado Island (BCI) sites, b-deviation did not differ from stochastic expectation at small grain sizes (b-deviationj, 1.96), but increased with grain size (Lambir: R2 1⁄4 0.28, p, 0.001; BCI: R2 1⁄4 0.63, p, 0.001; figure 2)
Our results demonstrate that spatial scale changes the relationship between b-diversity and latitude
Summary
Decreasing species richness from the equator to the poles is one of the best-recognized patterns in ecology [1,2]. This latitudinal pattern in species richness is consistent across different spatial scales, habitats and taxonomic groups [3]. Difficulties in disentangling the variation caused by pooled species richness (g-diversity) and site-to-site variation in species composition (b-diversity), as well as in the estimation of b-diversity itself, pose challenges to understanding the latitudinal b-diversity patterns. A b-deviation of zero indicates that the observed b-diversity is similar to random sampling, while positive b-deviation values reflect species aggregation [6,8]. As the degree of species aggregation is known to increase with grain size [13], we should expect spatial scale effects on b-deviation as well [10,11]
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