Abstract
Beta diversity represents how species in the regional pool segregate among local communities and hence forms a link between local and regional species diversities. Therefore, the magnitude of beta diversity and its variation across geographic gradients can provide insights into mechanisms of community assembly. Along with limits on local or regional level diversities, effects of local abundance that lead to under-sampling of the regional species pool are important determinants of estimated beta diversity. We explore the effects of regional species pools, abundance distributions, and local abundance to show that patterns in beta diversity as well as the mean of species abundance distribution have distinct outcomes, depending on limits on species pools and under-sampling. We highlight the effect of under-sampling in some established relationships between gamma diversity and beta diversity using graphical methods. We then use empirical data on ant communities across an elevational gradient in the Eastern Himalayas to demonstrate a shift from effect of reduction in species pool to under-sampling at mid-elevations. Our results show that multiple processes with contrasting effects simultaneously affect patterns in beta diversity across geographic gradients.
Highlights
Beta diversity represents how species in the regional pool segregate among local communities and forms a link between local and regional species diversities
Gradients in estimated beta diversity can be generated due to gradients in alpha diversity, gamma diversity, and its under-sampling through the influence of local abundance
We show that beta diversity is expected to have distinct patterns under the influence of gamma diversity and local abundance
Summary
Beta diversity represents how species in the regional pool segregate among local communities and forms a link between local and regional species diversities. The presence of a species within a local community is limited by niche related deterministic processes such as climate and habitat suitability, along with biotic processes such as competition, neutral processes such as chance dispersal and anthropogenic impacts such as d isturbance[3] Outcomes of such processes summed across many species give rise to species diversity of any given local community or ’alpha diversity (α)’. Sharp gradients and variability in environmental conditions across a landscape can limit the distribution of species near its optimal niche and result in segregated distributions among habitats Such deterministic variation in community composition is observed on mountains; for instance, most of the turnover among bird communities along elevational gradients in Costa Rica was due to habitat specialization[6]. We extend interpretations from known relationships between gamma diversity and beta diversity in order to separate the effects of under-sampling, and further test for the effects of limits on alpha diversity in generating patterns in beta diversity using null models
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