Abstract
Understanding how environmental drivers induce changes in plant composition and diversity across evolutionary time can provide important insights into community assembly mechanisms. We evaluated how taxonomic and phylogenetic diversity and structure of plant communities change along a local-scale edaphic and elevational gradient in the Tepequém table mountain, Brazilian Amazon. We selected three phytophysiognomies along the altitudinal gradient: Open Rupestrian Grassland, Shrubby Rupestrian Grassland, and Forest. We compared community composition and taxonomic and phylogenetic diversity between phytophysiognomies, and analysed effects of altitude and soil properties on species richness and phylogenetic metrics using linear mixed-effects models. The highest species richness and phylogenetic diversity were found at a lower elevation for Forest. All standardised phylogenetic metrics were significantly lower in Shrubby Rupestrian Grassland. This phytophysiognomy showed phylogenetic clustering. Forest showed a cluster pattern when only terminal nodes are considered and random dispersion to deep phylogenetic nodes. Open Rupestrian Grassland also showed a random phylogenetic structure. The linear mixed-effects models showed that species richness and different phylogenetic structure metrics were explained by altitude and soil properties. Our study revealed that key plant diversity dimensions (i.e. taxonomic and phylogenetic) are shaped by a local-scale edaphic and elevational gradient on an isolated tepui of Brazilian Amazonian.
Highlights
Mountain ecosystems have been recognised as a remarkable ecological scenario to evaluate the effect of environmental drivers on plant community diversity and structure (Qian et al 2014; Liu et al 2019a)
The nonmetric multidimensional scaling (NMDS) showed that species composition varied considerably among phytophysiognomies along the altitudinal gradient, mainly among FOR with SRG and ORG (Fig. 2a)
In the evolutionary composition ordination a contrasting phylogenetic composition pattern was observed between phytophysiognomies (Fig. 2b)
Summary
Mountain ecosystems have been recognised as a remarkable ecological scenario to evaluate the effect of environmental drivers on plant community diversity and structure (Qian et al 2014; Liu et al 2019a). The plant communities’ assembly is associated with stochastic processes based on neutral theory to explain different ecological processes, such as dispersal limitation, speciation, and extinction (Hubbell 2001; Liu et al 2019a) and niche-related deterministic processes, such as environmental filtering and limiting similarity (Webb et al 2002; Cadotte et al 2011) In this context, an approach based on phylogenetic diversity of plant communities can provide insights to explain ecological processes that shape the assemblages along environmental gradients at local and regional scales (Webb 2000; Liu et al 2019a,b). The local ecological community can show a random phylogenetic pattern when various niche-based processes operating simultaneously in species selection or neutral factors are more important (Webb 2000; Sobral and Cianciaruso 2012)
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