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RESEARCH INTERESTS
Plant ecology and evolutionary biology
Herbivory and plant defenses in tropical forests
Chemical ecology of tropical plants
Tritrophic-level interactions
Bioprospecting and sustainable development of tropical forests
PUBLICATIONS
Posters
Delayed greening in young tropical leaves
It's a jungle out there
Anti-herbivore Defenses of Tropical Trees Most of my work has focused on the role of defenses in protecting plants from damage by herbivores and pathogens. More recently I have been exploring how the third trophic level may regulate herbivore populations, and how plant traits may influence this interaction. I have chosen to address these questions in tropical rain forests because the high diversity allows multi-species comparisons, and because biotic interactions have played a particularly strong role in shaping tropical communities.
My early research quantified patterns of plant defense in tropical forests and tried to understand how selection may have favored different defense investments in species of different life histories and habitats (eg 'resource availability theory', Coley et al. 1985). Currently, in collaboration with Thomas Kursar, we are focusing on young leaves and their herbivores because 70% of a leaf's lifetime damage occurs during the short period of leaf expansion. Despite strong selection for defense, our studies in Africa, SE Asia and Panama show that any given species only invests in a subset of the possible defenses (Coley and Kursar 1996). One 'strategy' is to invest in effective chemical defenses during the period of expansion before the leaf can toughen up. Another 'strategy' is to expand rapidly, doubling in size every day, thereby shortening the window of vulnerability. However, rapid expansion requires high nitrogen and low toughness, and because of energetic constraints, the synthesis of secondary metabolites and photosynthetic machinery must be delayed until the leaf stops expanding. A major thrust of our present research is to characterize the secondary chemistry of fast- and slow-expanders, as we expect they will have very different chemical attributes.
We have also shown that the remarkable developmental trait of delayed greening, in which fast expanding young leaves appear white or pink, may be a defense (Kursar and Coley, 1992). The input of chlorophyll, light harvesting proteins and photosynthetic enzymes are delayed until the leaf is fully expanded and protected by toughness. The resulting low levels of nitrogen and energy mean that leaves with delayed greening loose fewer resources for a given amount of herbivory. This benefit outweighs the costs of forfeited photosynthesis under conditions of very low light (low cost) and very high herbivory (high benefit). However, these precise conditions are only met in the dark understory of tropical forests, and this is also the only place where one finds species with delayed greening.
I am also beginning to look at the defensive characteristics of herbivores and rates of attack by their natural enemies. Surprisingly high rates of parasitism (28%) and predation (13%/day for undefended caterpillars) suggest that pressure from the third trophic level is important. As a result, caterpillars demonstrate a battery of physical, chemical and behavioral traits that clearly evolved as defenses. Furthermore, I suggest that host plant traits determine the life history traits of their herbivores, which in turn affect their susceptibility to natural enemies. And finally, I am exploring the possibility that changes in climate will influence the dynamics between herbivores and the third trophic level (Coley, 1996).
In addition to these basic research goals, we are using our ecological knowledge of plant defenses to aid conservation of tropical forests by establishing a bioprospecting program in Panama (Capson et al., 1996).
Selected Publications
Coley, P.D., J.P. Bryant, F.S. Chapin, III. 1985. Resource availability and plant anti-herbivore defense. Science 230:895-899.
Coley, P.D. 1986. Costs and benefits of defense by tannins in a neo-tropical tree. Oecologia 70:238-241.
Coley, P.D. 1988. Effects of plant growth rate and leaf lifetime on the amount and type of anti-herbivore defense. Oecologia 74:531-536.
Coley, P.D. and T.M. Aide. 1991. Comparison of herbivory and plant defenses in temperate and tropical broad-leaved forests. Pages 25-49. In: Plant-Animal Interactions: Evolutionary Ecology in Tropical and Temperate Regions, edited by PW Price, TM Lewinsohn, GW Fernandes and WW Benson, Wiley & Sons, NY.
Kursar, T.A. and P.D. Coley. 1992. Delayed greening in tropical leaves: An anti-herbivore defense? Biotropica 24: 256-262.
Sagers, C.L. and P.D. Coley. 1995. Benefits and costs of plant defense in a neotropical shrub. Ecology 76:1835-1843.
Coley, PD and TA Kursar. 1996. Anti-herbivore defenses of young tropical leaves: Physiological constraints and ecological tradeoffs. Pages 305-336 In: Tropical Forest Plant Ecophysiology, edited by SS Mulkey, R. Chazdon and AP Smith. Chapman and Hall, NY.
Coley, P.D. and J.A. Barone. 1996. Herbivory and plant defenses in tropical forests. Annual Review of Ecology and Systematics 27:305-335.
Coley, P.D. 1998. The effects of climate change on plant-herbivore interactions in moist tropical rainforests. Climate Change 39:455-472.
Kursar, T.A, T.L. Capson, P.D. Coley, D.G. Corley, M.B. Gupta, L.A. Harrison, E. Ortega-Barría and D.M. Windsor. 1999. Ecologically guided bioprospecting in Panama. Journal of Pharmaceutical Biology 37 (supplement): 114-126.
Kursar, T.A. and P.D. Coley. 2003. Convergence in defense syndromes of young leaves in tropical rainforests. Biochemical Systematics and Ecology 21:929-949.
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