Functional biogeography of Neotropical moist forests: trait-climate relationships and assembly patterns of tree communities

Aim: Here we examine the functional profile of regional tree species pools
across the latitudinal distribution of Neotropical moist forests, and test
trait-climate relationships among local communities. We expected
opportunistic strategies (acquisitive traits, small seeds) to be
overrepresented in species pools further from the equator due to long-term
instability, but also in terms of abundance in local communities in
currently wetter, warmer and more seasonal climates. Location: Neotropics.
Time period: Recent. Major taxa studied: Trees. Methods: We obtained
abundance data from 471 plots across nine Neotropical regions, including
~100,000 trees of 3,417 species, in addition to six functional traits. We
compared occurrence-based trait distributions among regional species
pools, and evaluated single trait-climate relationships across local
communities using community abundance-weighted means (CWM). Multivariate
trait-climate relationships were assessed by a double-constrained
correspondence analysis that tests both how CWMs relate to climate and how
species distributions, parameterized by niche centroids in climate space,
relate to their traits. Results: Regional species pools were
undistinguished in functional terms, but opportunistic strategies
dominated local communities further from the equator, particularly in the
northern hemisphere. Climate explained up to 57% of the variation in CWM
traits, with increasing prevalence of lower-statured, light-wooded and
softer-leaved species bearing smaller seeds in more seasonal, wetter and
warmer climates. Species distribution were significantly but weakly
related to functional traits. Main conclusions: Neotropical moist forest
regions share similar sets of functional strategies, from which local
assembly processes, driven by current climatic conditions, select for
species with different functional strategies. We can thus expect
functional responses to climate change driven by changes in relative
abundances of species already present regionally. Particularly, equatorial
forests holding the most conservative traits and large seeds are likely to
experience the most severe changes if climate change triggers the
proliferation of opportunistic tree species.