Effects of climate change on multi-trophic interactions in agriculture and grasslands in the Southwestern United States

P.I./institution: Lee A. Dyer, Tulane University

Summarize in two to four sentences what activities will be (are being) carried out in the project: In order to examine how tri-trophic interactions vary in model agricultural and natural systems across a natural temperature gradient, we will perform field surveys of arthropod (herbivore, predator and parasitoid) diversity and abundance and laboratory analyses of plant nitrogen, carbon, water and defensive chemical content in nine alfalfa fields and natural grasslands located in Texas, New Mexico and Colorado. In order to identify which processes or mechanisms are responsible for generating these patterns and how these patterns may be affected by changes in
temperature or atmospheric C02 content, we will perform a series of laboratory experiments. Six rearing chambers will be used to manipulate C02 and temperature conditions (elevated temperature vs. control, elevated C02 vs. control, or elevated temperature and C02 vs. control) for the growth of alfalfa and native grass plants. These experiments will be performed in the presence and absence of specialist and generalist herbivores along with their parasitoids.

Project Abstract: The potential for increases in economically devastating pest outbreaks in response to climate change is high and warrants intensive investigation into the effects of climate on insect pests. Furthermore, useful predictions of how insect pests in natural and managed systems will respond to climate change must take into account the fact that these insects are part of complex multi-trophic interactions. We propose to examine the effects of climate change on plant chemistry, insect pests and their associated food webs in alfalfa fields and grasslands throughout the southwestern United States. The general questions that will be addressed by this research are: 1) How do tri-trophic interactions vary in model agricultural and natural systems across a temperature gradient? 2) What underlying processes or mechanisms are responsible for generating these patterns? 3) How do the effects of temperature on tritrophic interactions compare to the effects of CO2? We will combine field and laboratory experiments with correlational data and path analysis to address this question. The experiments will be full factorial laboratory and field experiments examining the effects of increased CO2 and increased warming on alfalfa saponins, herbivores, and parasitoids. The correlational approach will involve collecting plant chemistry and insect abundance data from alfalfa fields and grasslands on a transect from southern Texas to northern Colorado.

Summary of Proposed Work: This proposal directly addresses Goal 2 of the Southcentral Regional Center: experiments focusing on the effects of multiple environmental changes associated with energy production on key terrestrial ecosystems in the region. The methods are relevant to questions on the role of climatic variability in grassland and agricultural composition and productivity.