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Effects of Defoliation on Competitive Interactions between Invasive Crofton Weed (Eupatorium adenophorum) and its Native Neighbors: Implication for Biocontrol

  • Li Zhu (a1) and Weiguo Sang (a1)


Defoliation can affect plant competition in at least two ways: negative effects on the performance of defoliated plants and positive effects on nondefoliated plants due to neighbor defoliation. It has been suggested that these effects can alter competitive relations between plants, and this study was designed to test this in an experiment using Crofton weed as the invasive category, and its two neighbors Japanese brome and Dichrocephala as the native category. The plants were grown from seed and potted either singly or in pairs. The pairs consisted either of two conspecific plants (same pairs) or of one plant of each category (mixed pairs). Randomly preselected plants were defoliated twice in the growing season, at 9 wk and again at 5 wk before final biomass sampling. Competition reduced growth by 51 to 78%, with the plants of the native category consistently more affected than the invasive category. When grown singly, Crofton weed grew larger (average 67%) than the native species. As compared with plants grown singly, Crofton weed plants grown in mixed pairs were 40% smaller. The corresponding data for the native species were 78% smaller for Japanese brome and 73% smaller for Dichrocephala. The effects of neighbor defoliation differed among categories and competition. All the nondefoliated plants grown singly were larger than plants grown with a defoliated conspecific neighbor. For the corresponding relationship in mixed pairs, the native plants grown singly were significantly larger than the same native species grown together with a defoliated, invasive neighbor. Defoliation of Crofton weed reduced the growth of native neighbors and increased negative competitive effects on native plants. For the invasive species, however, Crofton weed plants grown in mixed pairs with neighbor defoliation compensated fully for the competitive effects, i.e., they were not significantly different from nondefoliated plants grown singly. Consequently, the effects of defoliation on competition between invasive Crofton weed and its native neighbors may depend on the ability to undertake compensatory growth, and probably on the allelopathic exudation of Crofton weed to herbivory. Our data suggest that herbivory by biocontrols can make an already superior competitor even stronger, especially if the biocontrol agent does not effectively damage or kill the target plant. Owing to complex interactions between competition and defoliation, the indirect effects of herbivory may be more complicated than currently conceived, and understanding the indirect effects of biocontrol agents before their release is crucial.


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Baldwin, I. T. 1990. Herbivory simulations in ecological research. Trends Ecol. Evol. 5:9193.
Baldwin, I. T. and Schultz, J. C. 1983. Rapid changes in tree leaf chemistry induced by damage: evidence for communication between plants. Science. 221:277279.
Bentley, S. and Whittaker, J. B. 1979. Effects of grazing by a chrysomelid beetle, Gastrophysa viridula, on competition between Rumex obtusifolia and Rumex crispus . J. Ecol. 67:7990.
Blossey, B. and Notzold, R. 1995. Evolution of increased competitive ability in invasive nonindigenous plants: a hypothesis. J. Ecol. 83:887889.
Broughton, S. 2003. Effect of artificial defoliation on growth and biomass of Lantana camara L. (Verbenaceae). Plant Protect. Q. 18:110115.
Bryant, J. P., Tuomi, J., and Niemelä, P. 1988. Environmental constraint of constitutive and long-term inducible defenses in woody plants. in Spencer, K.C., ed. Chemical Mediation of Coevolution. New York Academic. 367389.
Callaway, R. M., DeLuca, T., and Belliveau, W. M. 1999. Herbivores used for biological control may increase the competitive ability of the noxious weed Centaurea maculosa . Ecology. 80:11961201.
Capinera, J. L. and Roltsch, W. J. 1980. Response of wheat seedlings to actual and simulated migratory grasshopper defoliation. J. Econ. Entomol. 73:258261.
Colpetzer, K., Hough-Goldstein, J., Harkins, K. R., and Smith, M. T. 2004. Feeding and oviposition behaviour of Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) and its predicted effectiveness as a biological control agent for Polygonum perfoliatum L. (Polygonales: Polygonaceae). Environ. Entomol. 33:990996.
Crawley, M. J. 1986. Plant Ecology. Oxford, UK Blackwell.
DeWalt, S. J., Denslow, J. S., and Ickes, K. 2004. Natural-enemy release facilitates habitat expansion of the invasive tropical shrub Clidemia hirta. Ecology. 85:471483.
Farmer, E. E. 2001. Surface-to-air signals. Nature. 411:854856.
Fowler, N. L. and Rausher, M. D. 1985. Joint effects of competitors and herbivores on growth and reproduction in Aristolochia reticulata. Ecology. 66:15801587.
Gelbard, J. L. and Belnap, J. 2003. Roads as conduits for exotic plant invasions in a semiarid landscape. Conserv. Biol. 17:420432.
Grace, J. B. and Tilman, D. 1990. Perspectives on plant competition. San Diego, CA Academic.
Harper, J. L. 1977. Population biology of plants. London, England Academic Press.
Hjältén, J. 2004. Simulating herbivory: problems and possibilities. in Weisser, W.W. and Siemann, E., eds. Ecological Studies, Vol. 173: Insects and Ecosystem Function. Berlin Springer-Verlag. 243255.
Keane, R. and Crawley, M. J. 2002. Exotic plant invasions and the enemy release hypothesis. Trends Ecol. Evol. 17:164170.
Lee, T. D. and Bazzaz, F. A. 1980. Effects of defoliation and competition on growth and reproduction in the annual plant Abutilon theophrasti . J. Ecol. 68:813821.
Lehtil, K. and Boalt, E. 2004. The use and usefulness of artificial herbivory in plant-herbivore studies. in: Weisser, W.W. and Siemann, E., eds. Ecological Studies, Insects and Ecosystem Function. Volume 173. Berlin Springer-Verlag. 257275.
Maron, J. L. and Vila, M. 2001. When do herbivores affect plant invasion? Evidence for the natural enemies and biotic resistance hypotheses. Oikos. 95:361373.
Massey, F. P., Massey, K., Press, M. C., and Hartley, S. E. 2006. Neighbourhood composition determines growth, architecture and herbivory in tropical rain forest tree seedlings. J. Ecol. 94:646655.
McEvoy, P. B. 2002. Insect–plant interactions on a planet of weeds. Entomol. Exp. Appl. 104:165179.
McEvoy, P. B., Cox, C. S., and Coombs, E. M. 1991. Successful biological control of ragwort Senecio jacobaea, by introduced insects in Oregon. Ecol. Appl. 1:430442.
McNaughton, S. J. 1983. Compensatory plant growth as a response to herbivory. Oikos. 40:329336.
Montgomery, S. C. 1984. Design and analysis of experiments. 2nd ed. New York John Wiley and Sons. 117118.
Paige, K. N. 1992. Overcompensation in response to mammalian herbivory: from mutualistic to antagonistic interactions. Ecology. 73:20762085.
Pimentel, D. E. 2002. Biological Invasions: Economic and Environmental Costs of Alien Plant, Animal, and Microbe Species. Boca Raton, FL CRC Press.
Rai, J. P. N. and Tripathi, R. S. 1985. Effects of herbivory by the slug, Mariaella dussumieri, and certain insects on growth and competitive success of two sympatric annual weeds. Agr. Ecosyst. Environ. 13:125137.
Rogers, W. E. and Siemann, E. 2002. Effects of simulated herbivory and resource availability on native and invasive exotic tree seedlings. Basic Appl. Ecol. 3:297307.
Shea, K. and Chesson, P. 2002. Community ecology theory as a framework for biological invasions. Trends Ecol. Evol. 17:170176.
Siemens, D., Garner, S., Mitchell-Olds, T., and Callaway, R. M. 2002. The cost of defense in the context of competition. Brassica rapa may grow and defend. Ecology. 83:505517.
SPSS 1999. SPSS for Windows. Release 10.0.1. Chicago, IL SPSS.
Strauss, S. Y. 1991. Indirect effects in community ecology: their definition, study, and importance. Trends Ecol. Evol. 6:206210.
Strauss, S. Y. and Agrawal, A. A. 1999. The ecology and evolution of plant tolerance to herbivory. Trends Ecol. Evol. 14:179185.
Thelen, G. C., Vivanco, J. M., Newingham, B., Good, W., Bais, H. P., Landres, P., Caesar, A., and Callaway, R. M. 2005. Insect herbivory stimulates allelopathic exudation by an invasive plant and the suppression of natives. Ecol. Lett. 8:209217.
Tremmel, D. C. and Bazzaz, F. A. 1993. How neighbor canopy architecture affects target plant performance. Ecology. 74:21142124.
Trumble, J. T., Kolodny-Hirsch, D. M., and Ting, I. P. 1993. Plant compensation for herbivory. Annu. Rev. Entomol. 38:93119.
Welter, S. C. 1991. Responses of tomato to simulated and real herbivory by tobacco hornworm (Lepidoptera: Sphingidae). Environ. Entomol. 20:15371541.
Wilcove, D. S., Rothstein, D., Dobow, J., Phillips, A., and Losos, E. 1998. Quantifying threats to imperiled species in the United States. Bioscience. 48:607615.
Wilkinson, L. 1990. SYSTAT: The system for statistics. Evanston, IL SYSTAT. 313.
Windle, P. N. and Franz, E. H. 1979. The effects of insect parasitism on plant competition: greenbugs and barley. Ecology. 60:521529.
Wirf, L. A. 2006. The effect of manual defoliation and Macaria pallidata (Geometridae) herbivory on Mimosa pigra: implications for biological control. Biol. Control. 37:346353.
Wooton, J. T. 1994. The nature and consequences of indirect effects in ecological communities. Annu. Rev. Ecol. Evol. S. 25:443466.



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