Abstract
AbstractModern and historical climate are known to codetermine broad‐scale species richness and composition patterns in temperate regions. Nonetheless, is poorly understood the extent to which these effects individually or in combination determine functional diversity, many studies have simply assumed equilibrium between current climate and functional diversity. We estimated functional richness (FRich) and dispersion (FDisp) of North American broad‐leaved trees by combining distribution and trait information. Then, we determined if contemporary water‐energy availability, current topographic variability, historical climatic stability, and lagged immigration from glacial refugia co‐determined the functional diversity of North American broad‐leaved trees. We did this by assessing the directionality, magnitude, and relative importance of various contemporary and historical environmental factors know to affect species diversity. Contrasts were performed across all North America (Mexico, United States, and Canada), and areas within this region that were glaciated or ice‐free during the Last Glacial Maximum (~21 000 yr ago). FRich and FDisp showed distinct geographic patterns that are strongly associated with both contemporary environmental conditions and glacial–interglacial climate change. Model averaged regression coefficients and AIC‐based variable relative importance estimates show that contemporary productivity (FRich‐wAIC: 1.0; FDisp‐wAIC: 1.0), annual precipitation (FRich‐wAIC: 0.81; FDisp‐wAIC: 1.0), and accessibility to glacial refugia (FRich‐wAIC: 0.92; FDisp‐wAIC: 1.0) have the strongest associations to FRich and FDisp. Furthermore, the association of functional diversity with topographic heterogeneity showed steeper slopes in ice‐free regions. These findings suggest that, contrary to the expectation climate‐diversity equilibrium, functional diversity of North America broad‐leaved trees is codetermined by current climate and lagged immigration from glacial refugia.
Highlights
There is increasing evidence that the marked geographic gradients in species diversity across the globe can be considered the result of the interacting effects of contemporary and historical environmental conditions (Ricklefs 2004, Wiens and Donoghue 2004, Fritz et al 2013)
High functional richness (FRich) were primarily concentrated in the Appalachians, southeastern Coastal Plains, and Northeast mixed wood temperate forests (Fig. 1b), a pattern closely matching that of species richness (Fig. 1a)
Wider trait ranges and larger trait variances resulted in a higher FRich and Functional dispersion (FDisp), respectively
Summary
There is increasing evidence that the marked geographic gradients in species diversity across the globe can be considered the result of the interacting effects of contemporary and historical environmental conditions (Ricklefs 2004, Wiens and Donoghue 2004, Fritz et al 2013). diversity as the range and dispersion of multiple functional traits within a species assemblage. Phylogenetic diversity or beta-diversity, contemporary environment and historical conditions could mutually and independently determine current functional diversity patterns. The extent to which historical environmental conditions could shape functional diversity is poorly known (but see Mathieu and Davies 2014, Ordonez and Svenning 2015, Svenning et al 2015). Such lack of knowledge is the result of the prevailing idea of equilibrium between climate and functional diversity at large geographic scales
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