5 years ago

Phylogenetic structure of regional angiosperm assemblages across latitudinal and climatic gradients in North America

Brody Sandel, Hong Qian
Aim Phylogenetic structure of regional species assemblages is determined by environmental conditions and biogeographical history. Typically, assemblages are thought to become increasingly clustered at higher latitudes, because relatively few clades can tolerate low temperatures. However, numerous other patterns can produce phylogenetic structure. Here, we derive and test four hypotheses for phylogenetic structure of all angiosperms and five major angiosperm clades in North America. These are as follows: (a) angiosperms assemblages at higher latitudes are more phylogenetically clustered; (b) stronger phylogenetic clustering occurs in the drier climates of the west; (c) species are more closely related in the warm, dry southwest than in the cooler, wetter northwest; and (d) latitudinal patterns of phylogenetic structure in central North America are intermediate between those of the east and west. Location North America. Major Taxa Studied Angiosperms. Methods We divided North America into 65 regions across three longitudinal zones. We constructed a phylogeny based on the largest time-calibrated species-level mega-tree of plants available. Two phylogenetic metrics were used to quantify phylogenetic structure of angiosperms as a whole and each major clade in each region and were related to four major climate variables using correlation and regression analyses. Results For all angiosperms, results were consistent with our four predictions, with increasing clustering in drier and colder conditions. In many cases, clustering was more strongly related to precipitation than to temperature. Patterns of phylogenetic structure were inconsistent among major angiosperm clades, although the sister clades malvids and fabids did show remarkably similar patterns of net relatedness index. Main conclusions The latitudinal temperature gradient has played an important role in assembling species of the continental pool into regional floras. However, other geographical and biogeographical processes are also influential. Extreme dry climate in the southwest has caused more phylogenetic clustering than extreme cold climate. The observed phylogenetic structure patterns are generally consistent with the tropical niche conservatism, acting along distinct gradients of environmental filtering.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/geb.12634

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