Dissertation Abstract

Individual variation in plant traits drives species interactions, ecosystem functioning, and responses to global change

Read, Quentin D  2016  quentinread.com

Ecology & Evolutionary Biology, University of Tennessee at Knoxville (United States), 163 pp.

Ecologists have long sought to understand the processes that lead to the riotous diversity in
communities of organisms that inhabit disparate climates and landscapes. Such a diversity of
traits leads to a diversity of interactions among species in natural communities, which in turn
generates a diversity of potential responses to ongoing global change. In this dissertation, I do
three things: I explore the forces that structure plant communities and the ecosystem functions
that they mediate, I describe patterns of variation among communities, species, and individual
organisms across environmental contexts, and I disentangle the direct effects of global change
from the indirect, cascading effects that result from disruptions of species interactions. I
accomplish these goals through the synthesis of global data, the development of statistical and
mathematical models, and the manipulation of global change drivers in field experiments. In the
first chapter, I present a globe-spanning meta-analysis of plant functional trait patterns along
elevational gradients. This meta-analysis shows that the plant traits that drive ecosystem function
follow predictable trends with elevation due to climate filtering, and that much of this variation is
at the level of the individual organism. In the second chapter, I present simulated data sets and
illustrative experimental case studies that quantify how important individual-level variation is for
explaining patterns in nature. In the third chapter, I present results from intensive plant sampling
across a wide range of mountain environments; even in these harsh environments where only the
hardiest species can survive, individual-level variation is so high that it makes predictions based
on species identity nearly impossible. The fourth and fifth chapters consist of experimental
evidence that ongoing human-caused global change is affecting montane plant communities, that
species interactions mediate many of these effects, and that variation in the abiotic environment
causes variation in both species interactions and in global change response. I demonstrate this
through an experiment that combines nitrogen fertilization with removal of a dominant plant
species in a montane meadow, and an experiment replicated at low and high elevations crossing
dominant species removal with simulation of global warming.