Research Results
Over the past few years, the PIs and Earthwatch volunteers have documented an increase in herbivore damage on the invasive Chinese tallow (Triadica sebifera) primarily due to herbivory by a leaf-mining caterpillar species. Other ecologists studying tallow in its invasive range throughout the south-eastern U.S. have concurrently observed the same trend, leading to the hypothesis that this herbivore has been introduced from China.
Research for the 2009 field season was primarily focused on developing a new concept for ecology, conservation biology and climate change biology: interaction diversity across environmental gradients. The new interactions documented at our Earthwatch sites, between plants, caterpillars, and parasitoids (organisms that exist on or within a host), play key roles in the origin and maintenance of species diversity. The study of these interactions has contributed to important theoretical advances in ecology and evolutionary biology.
A simple measure of interaction diversity was developed using plant-herbivore-enemy feeding relationships that were uncovered by Earthwatch data at all of our sites. Scientists have demonstrated that this and other measures of interaction diversity can provide novel insight into climate change predictions and correlations between diversity, stability, productivity, and ecosystem services. For example, models predict that climate change will cause declines in interaction diversity that are more extreme than declines in standard measures of biodiversity. As a consequence, ecosystem services will decline rapidly, such as biological control in banana plantations provided by rainforest parasitoids.
In Costa Rica and Ecuador, Earthwatch teams examined how climatic changes across elevation gradients affect the interactions between common shrubs in the genus Piper (Piperaceae), the ants hosted by this plant (from the species Pheidole), the associated community of caterpillars (from the species Eois), and their enemies. Plant survival and growth rates were found to be affected by the climatic changes associated with elevation, with ants and plants experiencing low survival above 1600m. Ant colonies were also important and had significant effects on caterpillar densities and growth of Piper immutatum shrubs. This approach of studying the contributions of ant mutualists on the habitat range of a myrmecophyte (a plant living mutualistically with an ant colony), yields insight into the role of mutualisms - and diversity of mutualistic interactions - in determining community structure.
Diego Salazar Amoretti. In press. Herbivores on a dominant understory shrub increase local plant diversity in rain forest communities. Ecology
Dyer, L.A., T.R. Walla, H.F. Greeney, J.O. Stireman III, and R.F. Hazen (2010) Diversity of interactions: A metric for studies of biodiversity. Biotropica, 42 (3): 281-289
Smilanich, A.M., L.A. Dyer, M.D. Bowers, and J.Q. Chambers (2009) Immunological costs to specialization and the evolution of insect diet breadth. Ecology Letters 12:612-621.
Smilanich, A.M., L.A. Dyer, and G. L. Gentry (2009) The insect immune response and other putative defenses as effective predictors of parasitism. Ecology 90:1434-1440.