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Plant phenologyflowersspider

The Phenology of Plant Invasions: How changing seasons and temporal niches assemble plant communities

NSF Postdoctoral Fellowship in Bioinformatics

Understanding why certain exotic species become invasive in particular habitats but not others is complex but important for conservation. Several common theories suggest invasive species benefit from exploiting unused resources in an ecosystem (vacant niche), establishing before native species each season (priority effects) or responding more rapidly to variability in climate (increased plasticity). Most studies to date have attempted to examine these theories using empirical data on a single location or species. This research employs extensive phenological datasets that include a large number of species, including those newly available through U.S. National Phenology Network (NPN), to test all three theories at once over tremendous spatial and temporal scales.

Read more in my paper in Frontiers here.


Forecasting Phenology: Integrating ecology, climatology, and phylogeny to understand plant responses to climate change

NCEAS working group with Ben Cook

Understanding species responses to climate change has been a major focus of ecology in recent years. A suite of responses has been documented related to timings of life history events (phenology), with some species altering their phenology earlier or later, while other species change little. Robust explanations for this diversity of phenological responses are largely absent from the literature, but are crucial for predicting how communities and the ecosystem services they provide will change in the future. To fill this gap, we propose to synthesize observational and experimental phenology studies across North America and Europe. Because understanding phenology is inherently an inter- disciplinary problem, our working group brings together ecologists, climatologists, and phylogeneticists to address phenological responses to climate change at the species and community levels. We organize our efforts into two parts. First (1), we will conduct a meta-analysis that will compare short-term (most <5 years) experimental studies to longer-term (generally >20 years) observational studies. This will test how responses to shorter-term climate forcing scale up to longer term responses. Second (2), we will use some of the longest plant phenology datasets from North America and Europe, spanning over 150 years, to test how well the evolutionary history of plant traits can predict species responses to climate change. While previous efforts have provided a useful survey of general trends in phenological responses, our goal is to use ecological and evolutionary theory to suggest mechanisms which underlie the variability of responses. Our results will provide new baselines for forecasting community changes in response to global warming, develop new approaches for integrating climate data in ecology, and inform the design of future climate change research.

You can read more about the project here.

If you're a working group member, access the collaborative website here.

Detritus in food webssage_experiment

sage_frameworkField experiment: Grass invasion in coastal scrub - San Diego, California

Invasion by exotic plant species threatens biodiversity and ecosystem functioning worldwide. My PhD research combined field experiments with mathematical modeling to characterize complex interactions among abiotic and biotic factors in plant communities, thereby elucidating both impacts and mechanisms of plant invasions. Grass invasion increased both productivity and soil moisture, which enabled native and exotic plant species to co-exist, and indirectly supported larger and richer arthropod communities. Experimentally added exotic grass litter also increased soil carbon and nitrogen pools by 20% in only two years, showing that ecosystem responses to invasion can be more dynamic than previously believed. Together my findings demonstrated that field experimentation can reveal community and ecosystem impacts of invasion that differ substantially from observational studies.

Papers in Ecology, Global Change Biology, Journal of Vegetation Science and Oecologia give detail on my findings.

Models & Synthesis: Brown-green omnivory across food webs

Understanding the prevalence and role of omnivory in food webs is a long-standing area of research in community ecology. Recent work suggests that multi-channel omnivory---feeding on distinctly different food sources---may structure food webs and promote trophic cascades. Collaborating with Claire de Mazancourt, Stefano Allesina and Kathy Cottingham, John Moore, Stuart Sandin, we used empirical data and modeling to test the prevalence and effect of a common type of multi-channel omnivory, feeding on both living-autotroph (green) and detritus-based (brown) webs. Considering 23 food webs spanning terrestrial, freshwater and marine systems, we found that brown-green omnivory is common across all ecosystem types, occurring most often among primary consumers. Therefore, we developed a simple four-compartment nutrient cycling model for consumers eating autotrophs and detritus. Our model results show that across terrestrial and aquatic systems, omnivorous consumption of detritus is destabilizing at high attack rates on the autotroph, and stabilizing at low attack rates on the autotroph; however, the set of conditions for stable webs with omnivory is much narrower for aquatic systems. Comparing our model predictions with empirical food web data suggests that most food webs have brown-green omnivores that would produce stable webs. Together our results demonstrate that brown-green omnivory is extremely common across ecosystems and may be a stabilizing force in real webs. (Manuscript currently in revision.)



Additional projects

Nutrient Network
Hanover, New Hampshire

In 2007, Kathy Cottingham and I started the Hanover, New Hampshire Nutrient Network site as part of a global collaborative experiment. Our site consists of 30 plots and the complete manipulative design (NPK fertilization experiment with large vertebrate exclosures, my undergrad student Britt Ousterhout is pictured here working on fence set up in year 1) in an old field setting several miles from the main campus of Dartmouth.

We collected all vegetation (and most arthropod) data with the help of students from the Biology department's Methods in Ecology course. In this course students design their own questions and experiments on lakes, in streams and forests throughout the summer but for several weeks were able to work on and analyze data from a global carefully-designed study. Many thanks to the 2007-2010 students for all their help, and to Ernesto Ruelas and Erik Stange who taught the course in 2009 and 2010. Special thanks to Craig Layne who has helpedLanguedocVignoble extensively with the experiment and its educational opportunities.

Cross-continental coherency in climate forcing of wine grapes

Understanding how climate change will affect agriculture is a critical goal of modern global change research, yet progress towards this goal is stymied by disparate crops and varying agricultural practices as well as little spatially and temporally extensive data. Wine grape records represent some of the most long-term recorded data on earth (harvest records in Europe stretch back over 1,000 years) and information on differing practices is often available. Working with Kim Nicholas (Lund University for Sustainability Studies) and Leanne Webb (Melbourne University and CSIRO) we are compiling data to compare climate forcing of grape harvests from Australia, Europe and North America.

We're still in the early stages of getting this project off the ground, however, Kim just presented early results in her talk 'Trends in Climate and Phenological Changes in California and Australia' at the American Society of Enology and Viticulture meeting (June 2011).



Beetle communities in forest fragments
Tana River, Kenya

I am collaborating on David Mbora's project to understand how forest fragmentation affects dung beetle species composition and abundances in tropical forests. Read more about his project here.

Advances in global change research require open science at the individual-level

Progress in global change research over the last 20 years has come alongside a distinct shift towards synthetic work. Previously, excellent ecological research was underpinned by observations, experiments, and models often conducted by the same researcher or research group. Today, however, the best work includes syntheses of these three pillars of research through time and space, combining data, methods, and insights from disparate experiments, multiple long-term datasets, and theories.

Data sharing, often mandated in other fields, is generally low in ecology, and code for models and analyses is rarely included with publications. Such a lack of transparency forces ecologists to work without key data and analytical resources, retards collaboration, and impairs research with strong conservation relevance by making most findings difficult to study in depth, build upon, or reproduce. Although ‘open ecology’ appears to have potentially large benefits for the discipline, the vast majority of ecologists have never shared their data for a variety of perceived and real issues. Thus, working with Mary O'Connor and Jim Regetz we are working on an article to outline and address the major concerns and advantages of data and code-sharing, and address the skill sets and logistical needs at the individual and lab-based level.


Just to review: Your options are to visit Home or Data, Publications, you're at Research which includes my work on Phenology, Detritus and other projects, you can also visit Teaching, including an overview of my experience and my current undergrad’s blog on our bioinformatics work, my Resources page with my links to favorite LaTex, Sweave and R help sites, a Grants list, Writing, and the almighty leftover stuff at Other. You can download my CV here.