I am an ecologist, broadly interested in the processes determining species distributions and abundances. These processes include climatic variability, biotic interactions, local environmental heterogeneity, dispersal and disturbance. My interest in these things is twofold: (1) I have a basic curiosity about how underlying processes shape patterns that we see in nature; and (2) I'm interested in forecasting how species, and ecological systems more generally, are likely to respond to ongoing, interconnected global changes, including climate and land use changes, and biological invasions. Understanding how underlying processes combine to yield patterns of species distributions is challenging because these processes interact in complex ways over multiple spatial and temporal scales. Fine scale biotic interactions commonly interact with local abiotic heterogeneity within the context of broader scale abiotic gradients and patterns of disturbance. This tends to be the case across ecological systems, creating the perennial problems of scale- and context-dependence in ecological studies. My research addresses these challenges by drawing on and testing ideas from niche theory, and using biological invasions as 'natural experiments'. I use experimental designs and statistical modeling that can test hypotheses and quantify processes at different spatial and temporal scales. Depending on the question, I use field monitoring, field experiments, targeted greenhouse experiments, and broad scale database analyses to get different perspectives on these processes. And tying these approaches together, I use modern quantitative tools such as hierarchical Bayesian modeling to: (1) quantify how processes interact at different scales, (2) address common challenges in ecological data (limited, unbalanced, and often missing data), and (3) build toward realistic, flexible forecasts based on a basic understanding of underlying processes. Specific projects: Species distributions, niche theory and climate change  Niche theory generally describes the relationship between habitat suitability and species distributions. There is not a direct correspondence between suitability and distributions for a number of reasons, including biotic interactions and a variety of processes with high stochasticity, such as dispersal or disturbance. My research in the southern Appalachian Mountains (including Coweeta LTER) focused on several aspects of this relationship between suitability and distribution, and showed that:
Ecology of Biological Invasions  I am interested in biological invasions both as 'natural experiments' with which we may test basic ecological and evolutionary ideas, and as a pressing environmental problem that can threaten biological diversity and cause significant economic costs. Here in New Zealand I am exploring several key questions about species invasions: (1) Why do some species successfully naturalize and become invasive while others do not? I
am using large scale databases to ask why some introduced species
successfully establish and spread while others fail. Much of my focus
has been on whether taxonomy, as an integrative measure of ecological
similarity, is important for community assembly. Our work has suggested
that the answer depends on both spatial scale and the stage of
invasion (Diez et al 2008, Ecology Letters; Diez et al in prep). (2) What controls finer scale processes of species' establishment and spread? I
have been working with data from field monitoring and experiments to
test hypotheses about finer-scale controls over species establishment
and spread. I am collaborating to help explain how individual invasive
species respond to the combination of abiotic heterogeneity at
different scales, management actions, and propagule pressure. (Duncan et al. in press Ecology; Diez et al. in press) (3) How do biotic interactions influence the establishment and spread of introduced species? I
have conducted greenhouse experiments to test the importance of soil
biota in particular for shaping the success of introduced species. The
enemy-release hypothesis suggests that one reason introduced species
are successful is by escaping the pathogens, herbivores, or predators
that control their numbers in the native range. We are testing a
dynamic version of this hypothesis that suggests the advantage for
introduced species conferred by escaping natural enemies may diminish
over time as pathogens and herbivores 'catch up' evolutionarily or
through dispersal. |
