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My fundamental interest is with the origin and maintenance of biodiversity in ecological communities. I seek to understand the geographic patterns of relative abundance and species richness, and the factors that promote local population persistence and species coexistence in ecosystems, especially among the hyperdiverse insects and invertebrates. Field research at Bodega: Plant-insect-nematode interactions
The bush lupine (Lupinus arboreus) is a dominant woody shrub in the grasslands of Bodega Head and along the California coast (Fig1a). Outbreaks of the root-feeding larvae of ghost moths (Hepialus californicus , Fig1c) can devastate lupine stands, especially in dry years (Fig1b). However, entomopathogenic nematodes infect ghost moth caterpillars in soils and root systems, kill and mummify them with toxins from symbiotic bacteria, and indirectly protect lupines from fatal root herbivory. A single nematode can infect a host and produce hundreds of thousands of infective juveniles (Fig1d-e). Thus, the population dynamics of these worms are highly volatile and, because of their potential to rapidly overexploit hosts or go extinct in dry summer soils, probably unstable. Building on piles of previous work by Don Strong , Evan Preisser, Chris Dugaw, John Maron, Mike Eng, and many others, I hope to understand the spatial dynamics of this ‘top-down trophic cascade.' In particular, I am working with Don, Karthik Ram , and Justin Bastow to investigate the roles of alternative hosts, nematode movement and dispersal, spatial refugia, and invertebrate-mediated phoresy in the long-term persistence of this apparently unstable system. Arthropod community ecology
Tropical canopy arthropod communities are renowned worldwide for their astonishing species diversity—some global estimates from canopy fogging run in the tens of millions of species. My dissertation research used large-scale canopy arthropod surveys across the Hawaiian archipelago, combined with manipulative field experiments at a single site, to the understanding of both pattern and process in these model communities. I surveyed arthropods from the Hawaiian tree ‘ohi‘a lehua (Myrtaceae: Metrosideros polymorpha) on a well-characterized gradient of volcanic substrate age from Hawai‘i to Kaua‘i (300 years--4.1 million years old) established by Peter Vitousek and others. Although historical and evolutionary processes determined site-specific species composition of these communities, their functional structure was similar across sites, and patterns of abundance and diversity were driven primarily by local ecological factors. In a collaboration with researchers at the Smithsonian Institution, I hope to determine the role of insects and other resources in the explosive evolutionary radiation of Hawaiian forest birds.
Trophic dynamics and food webs Such a coarse approach allows inferences about large-scale processes, but even well-constrained surveys cannot test alternative causal hypotheses about local mechanisms. Thus, I examined in detail the food web dynamics of insect-eating birds, arthropods, and their host plant, ‘ohi‘a lehua (Fig.4). For almost 3 years, I maintained bird exclusion cages and regularly punished field assistants and former friends with 80# backpacks of granular fertilizer, hauled over ‘a‘a and pahoehoe lava. From these manipulations I created a detailed mechanistic picture of how resources and predators influence the relative abundance, biomass and species diversity of insect and spider communities. Spiders proved to be the crucial link in the food web—they absorbed the effects of bird predators and fertilization, but did not propagate these effects further down the food chain, thus short-circuiting the possibility of trophic cascades.
Biological invasions on islands I have spent considerable time exploring islands of the Pacific Basin , most notably the Hawaiian Islands , but also Fiji , Samoa , and Palmyra Atoll. Although invasion of non-native species is a prominent global concern, the ecological impacts of introduced species appear to be more severe on oceanic islands, for numerous reasons. However, it is far from clear that oceanic islands are more invasible than continental ecosystems. My experiments excluding birds showed that these generalist feeders can actually halt or decelerate, or resist the population expansion of introduced spiders.
In separate applied projects, I have investigated the distribution, impacts and control of introduced social insects, such as vespid wasps and ants. Because the Hawaiian Islands lack any native social insects (e.g. ants, wasps, termites), we predict (and observe!) large impacts of these invaders on the native flora and fauna. In collaboration with K-12 students and teachers, we documented the spatial distribution of exotic ants on several islands and experimented with management solutions. Please visit www.hawaii.edu/ant/ for more information. |
