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

Lee Dyer, Tulane University

 

Field and laboratory experiments designed to examine the effects of climate change on tritrophic interactions Parasitic insects are disrupted by extreme weather events (figure in upper left hand corner), which can lead to herbivore outbreaks and lower productivity in natural ecosytems. Field experiments funded by NICCR are providing experimental tests of these relationships in salt marsh habitat (lower left corner and background pictures depict flooding experiments). Increased CO2 and temperatures can also disrupt tritrophic interactions, causing insect outbreaks and lower productivity. The picture on the right depicts a microcosm experiment where small alfalfa ecosystems with caterpillars and parasites are exposed to increased CO2 and increased temperatures.

 

Abstract

1. 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 and the trophic interactions that control them. 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 main objective of the work is to determine specific effects of climate change on plant chemistry, plant biomass, insect pest populations, natural enemy populations, and the interactions between these factors in alfalfa fields, grasslands, and forests in the southwestern United States.
2. Laboratory experiments, chemical analyses, and insect curation will be conducted at Tulane University in New Orleans, LA. Field collections will occur at alfalfa fields, grasslands in forests in Louisiana, Texas, New Mexico, Arizona, and Colorado.
3. The proposed research will test 5 specific hypotheses. Hypothesis 1 - Plant investment in carbon-based anti-herbivore defenses will be positively correlated with temperature and atmospheric CO₂, with greater defenses in warmer, carbon-enriched environments. Hypothesis 2 - Differences in leaf quality caused by elevated CO₂ and temperature will directly affect herbivore communities by decreasing overall diversity and increasing populations of adapted specialist herbivores. Hypothesis 3 - Diversity of herbivores will be low while herbivory by specialists will be high in warmer, CO₂ enriched climates. Hypothesis 4 - Parasitism and predation will be increased on generalists and decreased on specialists in warmer, CO₂ enriched climates. Hypothesis 5 - Extreme weather events cause decreases in levels of parasitism on herbivorous insects.
4. The approach combines field and laboratory experiments with correlational data and path analysis. 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, insect abundance, and parasitism data from alfalfa fields, grasslands, and forests along climatically variable transects.
5. The project will provide important insight into how insect outbreaks will be controlled in a changing climate and how potential increases in insect outbreaks will affect productivity of ecosystems in the Southcentral Region of NICCR.

Publications

Dyer, L.A., M.S. Singer, J.T. Lill, J.O. Stireman III, G.L. Gentry, R.J. Marquis, R.E. Ricklefs, H.F. Greeney, D.L. Wagner, H.C. Morais, I.R. Diniz, T.A. Kursar, and P.D. Coley. 2007. Host specificity of Lepidoptera in tropical and temperate forests. Nature 448:696-699.

Pearson, C.V. and L.A. Dyer. 2006. Trophic diversity in two grassland ecosystems. Journal of Insect Science 6:23.

Stireman III, J.O., L.A. Dyer, D.H. Janzen, M.S. Singer, J.T. Lill, R.J. Marquis, R.E. Ricklefs, G.L. Gentry, W. Hallwachs, P.D. Coley, J.A. Barone, H.F. Greeney, H. Connahs, P. Barbosa, H.C. Morais, and I.R. Diniz. 2005. Climatic unpredictability and caterpillar parasitism: implications of global warming. Proceedings of the National Academy of Sciences 102:17384-17387.

Stireman, J.O. III, Dyer, L.A., and R.M. Matlock. 2005. Top-down forces in managed versus unmanaged habitats. Pages 303-323 in: Barbosa, P. and I. Castellanos (eds.). Ecology of Predator-Prey Interactions. Oxford University Press, Oxford.