Freezing and water availability structure the evolutionary diversity of trees across the Americas

Abstract

<jats:title>Abstract</jats:title><jats:p>The historical course of evolutionary diversification shapes the current distribution of biodiversity, but the main forces constraining diversification are unclear. We unveil the evolutionary structure of tree species diversity across the Americas to assess whether an inability to move (dispersal limitation) or to evolve (niche conservatism) is the predominant constraint in plant diversification and biogeography. We find a fundamental divide in tree lineage composition between tropical and extratropical environments, defined by the absence versus presence of freezing temperatures. Within the Neotropics, we uncover a further evolutionary split between moist and dry forests. Our results demonstrate that American tree lineages, though broadly distributed geographically, tend to retain their ancestral environmental relationships and that phylogenetic niche conservatism is the primary force structuring the distribution of tree biodiversity.</jats:p>

Biomes as evolutionary arenas: Convergence and conservatism in the trans‐continental succulent biome

“…Succulent biome phylogenetic conservatism, far from being restricted to legumes where it was first documented (Donoghue, 2019; Gagnon et al, 2019; Lavin et al, 2004), is prevalent across a range of plant families, and certain animal lineages (Supporting Information Table S5). These findings are comparable to some of the most striking examples of global phylogenetic biome conservatism (Crisp et al, 2009; Donoghue & Smith, 2004; Wiens & Donoghue, 2004), suggesting that phylogenetic conservatism may be most apparent at this broad biome level (Segovia et al, 2019). Furthermore, our results benefit from the additional rigour that comes from a quantitative biome model and use of detailed species occurrence data to objectively and quantitatively assign species to biomes.…”

“…We highlight the utility of the convergence of key plant functional traits for defining and mapping the little‐known succulent biome. We show that this biome forms a tightly delineated geographically disjunct, trans‐continental evolutionary arena for drought‐adapted plant lineages, providing some of the strongest evidence to date that ecology has played a key role in dictating the geographical turnover of clades across the lowland tropics (Segovia et al, 2019). We suggest that the dichotomy between succulent‐rich, grass‐poor, fire‐free and succulent‐lacking, grass‐dominated, fire‐prone vegetation reflects a fundamental functional distinction underpinning recognition of two distinct non‐forest tropical lowland biomes, both of which are ‘open’ vegetation formations with seasonally dry climates, and both of which are ancient and merit attention (Bond, 2005; Cowling et al, 2005; White, 1983).…”

“…The Chaco has characteristics of SDTFs (seasonally dry, fire‐free, grass‐poor), is clearly not a savanna, as indicated in the latest global map of grassy biomes (Lehmann et al, 2019), appears to comprise a mosaic of elements from several biomes (Segovia et al, 2019), and has been considered a distinct biome based on differences in soils, occurrence of frost, and floristic composition (DRYFLOR, 2017; Pennington et al, 2000; Silva de Miranda et al, 2018). The affinities of the Chaco remain debatable (Kuemmerle et al, 2017; Segovia et al, 2019). Twenty‐three species of stem succulents occur in the Chaco, some of them endemic there, and the Chaco is clearly included in our succulent biome model (Figure 1).…”

“…While striking examples of large‐scale phylogenetic biome conservatism have been demonstrated (e.g. Crisp et al, 2009; Donoghue, 2008; Lavin et al, 2004; Segovia et al, 2019), the overall extent and prevalence of phylogenetic biome conservatism versus biome shifting remain debatable (Donoghue & Edwards, 2014; Edwards & Donoghue, 2013). Here we investigate these two important attributes of biomes, evolutionary convergence and phylogenetic conservatism, to test to what extent biomes can be considered as distinct evolutionary arenas.…”

Adaptation and coordinated evolution of plant hydraulic traits

“…Some models, however, were also fitted using the species‐level phylogeny from Smith and Brown (2018), to assess the robustness of our results to the taxonomic resolution of our phylogenetic data. To construct the genus‐level phylogeny, sequences of the rbc L and mat K plastid gene for 707 angiosperm tree genera were obtained from Genbank (http://www.ncbi.nlm.nih.gov/genbank/) building on previous efforts (Dexter and Chave, 2016; Neves et al ., 2020; Segovia et al ., 2020). Sequences were aligned using the MAFFT software (Katoh and Standley, 2013).…”