Abstract
BackgroundSo far, macroecological studies in the Himalaya have mostly concentrated on spatial variation of overall species richness along the elevational gradient. Very few studies have attempted to document the difference in elevational richness patterns of native and exotic species. In this study, this knowledge gap is addressed by integrating data on phylogeny and elevational distribution of species to identify the variation in species richness, phylogenetic diversity and phylogenetic structure of exotic and native plant species along an elevational gradient in the Himalaya.ResultsSpecies distribution patterns for exotic and native species differed; exotics tended to show maximum species richness at low elevations while natives tended to predominate at mid-elevations. Native species assemblages showed higher phylogenetic diversity than the exotic species assemblages over the entire elevational gradient in the Himalaya. In terms of phylogenetic structure, exotic species assemblages showed majorly phylogenetic clustering while native species assemblages were characterized by phylogenetic overdispersion over the entire gradient.ConclusionsThe findings of this study indicate that areas with high native species richness and phylogenetic diversity are less receptive to exotic species and vice versa in the Himalaya. Species assemblages with high native phylogenetic overdispersion are less receptive to exotic species than the phylogenetically clustered assemblages. Different ecological processes (ecological filtering in case of exotics and resource and niche competition in case of natives) may govern the distribution of exotic and native species along the elevational gradient in the Himalaya.
Highlights
Exotic species cause both ecological and economic harms by lowering biological diversity, resource availability, human health and altering ecosystem functions (Sala et al 2000; Pimentel et al 2005; Vilà and Hulme 2017)
The positive values of Net relatedness index (NRI) and nearest taxon index (NTI) (> 0) in the current study indicated presence of phylogenetic clustering, while negative values of NRI and NTI (< 0) indicated phylogenetic overdispersion
A total of 307 exotic angiosperm species belonging to 55 families and 1274 native angiosperm species belonging to 100 families were recorded in the Sikkim Himalayan region
Summary
Exotic species (non-native species introduced by human activity to the areas outside their natural distribution) cause both ecological and economic harms by lowering biological diversity, resource availability, human health and altering ecosystem functions (Sala et al 2000; Pimentel et al 2005; Vilà and Hulme 2017). Their management and control becomes highly important. The mountain ecosystems that were earlier thought to be immune to the ecological invasion process (Averett et al 2016) are being increasingly invaded by exotic species due to climate and land-use changes, human population growth, road development, agricultural intensification and other anthropogenic activities (Dietz et al 2006; Pauchard et al 2009). This knowledge gap is addressed by integrating data on phylogeny and elevational distribution of species to identify the variation in species richness, phylogenetic diversity and phylogenetic structure of exotic and native plant species along an elevational gradient in the Himalaya
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