DOI: 10.5061/dryad.8w9ghx3k9
title: Scale-dependent drivers of the phylogenetic structure and similarity of tree communities in northwestern Amazonia

description: 1. The extent to which historical dispersal, environmental features and
 geographic barriers shape the phylogenetic structure and turnover of tree
 communities in northwestern Amazonia at multiple spatial scales remains
 poorly understood.  2. We used 85 floristically standardized
 0.1-ha plots (DBH ³ 2.5 cm) distributed in three
 subregions of northwestern (NW) Amazonia across three main habitat types
 (floodplain, swamp, terra firme forests), to hypothesize that: i)
 historical dispersal overcome geographical barriers, which meant low local
 phylogenetic relatedness and low phylogenetic turnover. ii) Geographical
 barriers triggered dispersal limitation, causing high local and
 subregional phylogenetic clustering and high regional phylogenetic
 turnover. iii) Edaphic properties and flooding were negatively associated
 to stem size and determined the tree phylogenetic structure and turnover
 at local and regional scales in Amazon forests. 3. 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. Further, 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 metacommunity 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.
description: <i>Vegetation
 sampling and identification of botanical vouchers</i>
 A total of 85 0.1-ha plots
 were established: 35 in Metá-Chiribiquete (Duque et al., 2001; Duque,
 2004) and 25 in both Yasuní (Romero-Saltos, Valencia, & Macía,
 2001) and Ampiyacu (Grández et al., 2001) (Fig. 1). Plots were rectangular
 (20 x 50 m) and delimited by compass, tape and stakes from a random
 starting point respect to topographic conditions (i.e. elevation and
 slope), with the restriction that the long side of the plot was parallel
 to the contour line. The plots were located in areas with relatively
 homogeneous soils and physiognomically uniform forest stands. In each
 plot, all shrubs, treelets, and trees with DBH ≥ 2.5 cm were numbered and
 measured with tape. Plots were located in forest that lacked signs of
 human intervention, except in some swamp plots in the floodplain of the
 Ampiyacu River in Peru, where few palms had been cut recently to harvest
 fruits from <i>Mauritia flexuosa</i> L.f. Plots were
 established at a minimum between-plot distance of 500 m and were mapped
 with GPS. In each
 plot, at least one botanical collection of each morpho-species was
 collected. The nomenclature of families and genera followed Angiosperm
 Phylogeny Group version 4 (Chase et al., 2016). Within families or groups
 of closely allied families, specimens that could not be identified to
 species because of lack of sufficient diagnostic characteristics, were
 treated as morpho-species on the basis of simultaneous morphological
 comparisons with all other specimens in herbarium. Hereafter, we will
 mostly refer as to species for both morpho-species and species. Botanical
 identification took place at the herbaria COAH, QCA, QCNE, AMAZ, US MO,
 NY, and AAU. Vouchers of around 90% of the species and morpho-species
 described by each independent group were pooled together and compared in
 MO and AAU between 2000 and 2002.