Scale‐dependent drivers of the phylogenetic structure and similarity of tree communities in northwestern Amazonia

Abstract

The extent to which historical dispersal, environmental features and geographical barriers shape the phylogenetic structure and turnover of tree communities in northwestern Amazonia at multiple spatial scales remains poorly understood. We used 85 floristically standardized 0.1‐ha plots (DBH ≥ 2.5 cm) distributed in three subregions of northwestern (NW) Amazonia across three main habitat types (floodplain, swamp and terra firme forests) to hypothesize that (a) historical dispersal overcome geographical barriers, which meant low local phylogenetic relatedness and low phylogenetic turnover. (b) Geographical barriers triggered dispersal limitation, causing high local and subregional phylogenetic clustering and high regional phylogenetic turnover. (c) Edaphic properties and flooding were negatively associated with stem size and determined the tree phylogenetic structure and turnover at local and regional scales in Amazon forests. We found that the extent to which environmental or evolutionary features shaped the phylogenetic structure and phylogenetic similarity of tree communities in NW Amazonia was scale dependent. Specifically, we show that the relative importance of environmental factors increases as spatial scale and species pool decreases. Furthermore, we find that these results are generally robust for both adult and juvenile trees. Synthesis. Our analysis at the regional (NW Amazon) scale lends support to the idea of Amazonian forests as a large meta‐community primarily structured by historical dispersal at large spatial scales with an increasing importance of environmental factors at finer spatial scales. The convergence of ancestral lineages across habitat types may have been due to the relatively recent formation of geographical barriers that promoted local isolation and allopatric speciation.

Amazon tree dominance across forest strata

“…These results are consistent with limited dispersal and diversification of understory hyperdominant species at a basin-wide scale over evolutionary timescales, as has been suggested by others 55 . Furthermore, the ability to become dominant in the understory of Amazonian forests is found across a diverse range of lineages, and therefore is relatively common.…”

Plant community assembly of alpine meadow at different altitudes in Northeast Qinghai‐Tibet Plateau

“…In our study, all of the traits were slightly different along altitude gradients, but the overall pattern was approximately the same, showing overdispersion (NFI < 0) patterns of traits at low altitudes (3000 and 3250 m) (Figure 4); this results mainly because low altitude has better hydrothermal conditions and the highest productivity (Liu et al, 2022), dominated by competition exclusion then leading to the functional traits, which were diverse (make traits more differentiated) (Xu et al, 2017). In contrast, the functional structure showed obvious clustering (NFI > 0) patterns at high altitudes (4000 and 4500 m); because forceful habitat filtering process influenced community assembly with limited hydrothermal resources (Zhu et al, 2019), species colonizing a site with a particular set of environmental conditions will tend to exhibit similarity for certain phenotypic traits leading to trait convergence and show clustering pattern (González‐Caro et al, 2020). At 3500‐ and 3750‐m altitudes, the distribution pattern of traits was close to clustering or random distribution; these results may be due to the clustered trait structure caused by the environmental stress in high‐altitude areas, or it may be due to the similar adaptive capacity among species; to obtain more environmental resources and adjust their own functional characters, interspecific competition is enhanced, and similarity restriction has become the main force of community character structure (Liu et al, 2022), which merely suggests that niche process (deterministic process) was more important in driving community assembly based on functional traits.…”

“…The phylogenetic structure of the 3750-m altitude is complex, which was close to 0 and overdispersion patterns at the same time (Figure 3). For this result, it may be because the habitat heterogeneity is more complex, which promotes the competition among species, the process of community assembly may be random, habitat filtration, and competition exclusion (Gonz alez-Caro et al, 2020;Mayfield & Levine, 2010). It may also be that environmental pressure will cause species that are not closely related to undergo convergent evolution, while other species left behind due to competitive exclusion are also irregular in relationship, so community assembly may be random or aggregated (Shi et al, 2019).…”

Habitat severity characteristics structure soil communities at regional and local spatial scales along the Antarctica Peninsula

“…Scale is an important consideration in understanding the drivers of terrestrial biogeography. The factors that influence community composition, whether they are biotic interactions with other species or abiotic drivers of the physical environment, may differ in relative importance at local vs regional scales (Usher & Booth 1984, Nemergut et al 2013, Danis et al 2020, González-Caro et al 2021). For example, climate (temperature and precipitation) tends to be an important driver of ecological processes at broad spatial scales, while other biotic and abiotic interactions become more important at fine spatial scales (e.g.…”

“…Lozupone & Knight 2007, Nemergut et al 2011) or 2) neutral, stochastic drift and dispersal-limited, historically contingent assembly that result in species replacements (turnover) across localities (e.g. Chase 2007, Dickie et al 2012, González-Caro et al 2021). Dissimilarity measures such as the Sørenson and Simpson indices can demonstrate whether community dissimilarity increases over spatial distances or environmental gradients and partition that dissimilarity into nestedness and turnover (Baselga 2010).…”