Scale sensitivity of the relationship between alpha and gamma diversity along an alpine elevation gradient in central Nepal

Abstract

AbstractAimComponents of scale, such as grain, focus and extent, influence the spatial patterns of alpha and gamma diversity and the relationships between them. We explored these scale relations by testing whether the gamma diversity and alpha diversity along an elevation gradient were related independent of scale and whether the elevational patterns of herbaceous and woody species richness were dependent on scale.LocationLangtang National Park, Nepal.MethodsWe estimated alpha diversity (plot richness) for woody and herbaceous plant species along an alpine elevation gradient (3,900–5,000 m a.s.l.) in nested plots of 1 m2, 16 m2 and 100 m2 and gamma diversity (regional richness) from published sources. Generalized linear modelling was used to analyse alpha and gamma diversity and their correspondence at different grain sizes.ResultsElevational trends of gamma and alpha diversity were significantly correlated for both woody and herbaceous species at all grain sizes. The concordance increased with increasing grain size and area for gamma diversity estimation, particularly for the monotonously decreasing elevational gamma and alpha diversity patterns of woody species. The hump‐shaped patterns of elevational gamma and alpha diversity for herbaceous species were also significantly correlated, but the concordance between the alpha diversity of herbaceous species and local gamma diversity was stronger. Elevational patterns of alpha diversity were coarsely consistent across grain sizes, although the patterns became more pronounced at larger grain sizes.Main conclusionsThe correspondence of elevational gamma and alpha diversity was largely scale invariant, implying that elevational and possibly other geographical diversity patterns can reliably be studied at different spatial scales. Nonetheless, the alpha diversity pattern was the least pronounced at fine grain size, particularly for woody life‐forms. This finding suggests that for large‐scale patterns such as elevational gradients at regional or continental scales, coarse grain sizes and large areas for gamma estimation are more appropriate.