Intraspecific trait variation across elevation predicts a widespread tree species' climate niche and range limits.

Michael E Van Nuland,Ian M Ware,Shannon L J Bayliss,Liam O Mueller,Jennifer A Schweitzer,Joseph K Bailey,John B Vincent,Kendall K Beals

doi:10.1002/ece3.5969

Abstract

Global change is widely altering environmental conditions which makes accurately predicting species range limits across natural landscapes critical for conservation and management decisions. If climate pressures along elevation gradients influence the distribution of phenotypic and genetic variation of plant functional traits, then such trait variation may be informative of the selective mechanisms and adaptations that help define climatic niche limits. Using extensive field surveys along 16 elevation transects and a large common garden experiment, we tested whether functional trait variation could predict the climatic niche of a widespread tree species (Populus angustifolia) with a double quantile regression approach. We show that intraspecific variation in plant size, growth, and leaf morphology corresponds with the species' total climate range and certain climatic limits related to temperature and moisture extremes. Moreover, we find evidence of genetic clines and phenotypic plasticity at environmental boundaries, which we use to create geographic predictions of trait variation and maximum values due to climatic constraints across the western US. Overall, our findings show the utility of double quantile regressions for connecting species distributions and climate gradients through trait‐based mechanisms. We highlight how new approaches like ours that incorporate genetic variation in functional traits and their response to climate gradients will lead to a better understanding of plant distributions as well as identifying populations anticipated to be maladapted to future environments.

Highlights

In a rapidly changing world, a variety of tools and approaches are required to predict species distributions for conservation planning and to achieve management goals
We found many cases that are more consistent with plastic trait responses to climate
We modeled how genetic clines in P. angustifolia growth traits are constrained by applying quantile regressions that were significant for DBH and annual growth diameter to gridded climate data

Summary

| INTRODUCTION

In a rapidly changing world, a variety of tools and approaches are required to predict species distributions for conservation planning and to achieve management goals. Double quantile regression was recently used to examine the mechanistic relationship between plant functional traits and climate range limits (Stahl et al, 2014) This approach incorporates functional trait variation across a species' distribution to predict their upper, median, and lower climate extremes, and the resulting response patterns shed light on potential filtering mechanisms and adaptations to climatic range limits. Hypothesis 2 Common garden trait-climate relationships will show similar response patterns as field traits, indicating the presence of genetic clines that constrain trait variation at range limits

| METHODS

Findings

| CONCLUSIONS