Our reseach covers a lot of ground in basic and applied entomology and ecology. Generally, we use insects and plants to explore the dynamic interplay of biodiversity, food web interactions, and ecosystem function in the context of rapid environmental change.
Some of the broad questions we explore in the lab:
- How do species interactions constrain community diversity, function, and invasion?
- What are the relative roles of history, evolution, genetic structure, and biotic interactions in assembling diverse, functional communities?
- How do food web patterns vary across patches, landscapes, ecosystems, and over time, and how resilient are these structures to perturbation?
- How can we use our knowledge of ecology to predict and ameliorate the manifold impacts of humanity?
Here are some of the project themes in the lab:
1. Causes, Constraints, and Consequences of Diversification in the Hawaiian Islands
The Hawaiian Islands are a crucible of spectacular evolutionary radiations and a model system for understanding ecosystem development, species diversification, the assembly of ecological communities, and their disassembly via invasions of introduced species. Beginning with my dissertation research, the archipelago has been a fertile playground for my research merging large scales of time and space with localized biotic interactions. (to right: Anomalochrysa machlachlani)
|link to the kīpuka project for a virtual tour!||
In a current collaboration with Tad Fukami (Stanford), Christian Giardina (USDA Forest Service), and David Flaspohler (Michigan Tech), we are using the natural landscape of volcanic forest fragmentation (called 'kipuka') on the youngest island (Hawaii) to test the importance of fragment size (0.1 to 10 ha) and productivity for food web complexity. Via experimental elimination of invasive rats on the kīpuka-scale, we can measure their impacts as omnivores on bird nestlings and eggs, arthropods, and plants. Together we expect the impacts of rats to be far more pervasive in small forest kipuka. (to left: a forested kīpuka on Hawai`i island)
In a new collaborative project, we are quantifying the feedbacks between microbial and invertebrate mutualists, parasites, and competitors in the transitional phases of population differentiation, diversification, and assembly into complex arthropod communities. Such a study, glimpsed but never grasped in my dissertation research, is only possible via integration of genomics and bioinformatics, systematics and phylogenetics, theoretical and empirical community ecology, and lots of hard work on the ground in a model ecosystem.
2. Synthesis of Trophic Interactions and Cascades across Ecosystems
|Beginning with a working group I co-led (with Jon Shurin and Helmut Hillebrand), through the National Center for Ecological Analysis and Synthesis, quantitative syntheses have played a central role in testing general theory and producing new hypotheses to advance community ecology.
At NCEAS, we synthesized data from global ecosystems to evaluate ecological mechanisms that control primary productivity, herbivory, and trophic cascades (indirect impact of predators on plants and ecosystems). Our synthesis of the interactive effects of grazers and nutrients (top-down and bottom-up controls) on primary production confronted mechanistic predictions from consumer-resource dynamical theory, and we proposed a new conceptual model for these effects on species diversity. Another report overturned long-standing textbook dogma that single nutrients – nitrogen on land and phosphorus in lakes – limit primary production. We also demonstrated comparable effect sizes of both nitrogen and phosphorus across marine, freshwater and terrestrial ecosystems worldwide. A complementary contribution challenged “Liebig’s law of the minimum” and demonstrated the prevalence of co-limitation by both nitrogen and phosphorus in these globally distributed ecosystems. This work is increasing our mechanistic understanding of how trophic interactions ramify in natural webs as a result of human impacts like eutrophication or extirpation of top consumers. (to left: fig. from Shurin et al. 2006)
Meta-analyses should not be endpoints, but should stimulate novel or more powerful investigations. A welcome outgrowth of this working group is an exciting global research cooperative project called the Nutrient Network. The NutNet project, which involves more than 60 research sites on 6 continents worldwide, investigates the effects of nutrient resources and consumption on herbaceous plant communities and ecosystem processes. The combined power of this site replication and a single, shared experimental protocol allows for an unparalleled, piercing analysis of fundamental unresolved questions in community and ecosystem ecology.
(to right: experimental setup inlaid on scene from Sagehen Creek Station in the California Sierra Nevada, photo by collaborator Louie Yang)
3. Responses of Coastal Ecosystems to Rapid Environmental Change
Coastal ecosystems provide many services, such as erosion control, detoxification of runoff, and nursery habitat for fisheries, yet they are also exposed to extraordinary pressure from human development and climate change. In a collaboration with Drs. Candy Feller, John Parker, and Rick Osman with the Smithsonian Environmental Research Center and Jim Kellner in UMCP Geography, we are analyzing an historical time series of satellite and airborne imagery to document the rate and extent of change on a global level. Climate change is the most likely explanation for broad patterns, however we are evaluating specific hypotheses that include abiotic (warmer air or water temperatures, less frequent or less severe cold snaps, changes in precipitation, sea level rise), biotic (altered relationships with competitors, pollinators, herbivores or decomposers), and anthropogenic mechanisms (nutrient or chemical eutrophication, land use change, fisheries exploitation) which may interact to create complex outcomes.
to right: mangrove and marsh ecosystems from the Indian River Lagoon, east coast of Florida; photos from Dan Gruner, John Parker, Heather Eversole
link to the Mangrove Tracking blog hosted by SERC!
4. Nematodes, Microbes, and the Little Things That Run the World Beneath our Feet
With postdoctoral advisor Dr. Donald Strong at the Bodega Marine Lab, I went underground to study the dynamics of a powerful trophic cascade in coastal California prairies. Entomopathogenic nematodes (EPN) in the soil, by infecting and killing caterpillars in roots, confer a blanket of protection to lupine shrubs. These EPN have a fascinating intrinsic biology, with two independent evolutionary lineages converging to the same solution: symbioses with a bacterial partner packing a lethal punch to soil insect hosts. They also offer tremendous (but elusive) potential for biological control of insects with life history stages in the soil. At local sites across Maryland, we find an impressive diversity of these nematodes which is reduced under intensive cultivation. We seek to better understand the soil properties and management practices that will improve EPN persistence and reduce the likelihood and intensity of economically costly pest outbreaks. Microbial partners and antagonists are also fundamental to the biology of invasive Sirex woodwasps and may be the key to predicting their economic impacts in North America.
To right: the nematode-ghost moth-lupine trophic cascade at Bodega Marine Reserve. a) Bush lupine (Lupinus arboreus) in flower in June 2001; b) the same stand in July 2003 after ghost moth outbreak; c) ghost moth caterpillars (Hepialus californicus) in a lupine stem; d) healthy Galleria waxworm used as sentinel bait insect; e) Galleria waxworm infected by nematode Heterorhabditis marelatus, indicated by the red-gold color of symbiotic luminescent bacterium Photorhabdus; f) release of thousands of EPN infective juveniles (all photos: Don Strong)