Plant-herbivore theory

Our objective Is to examine some aspects of current plant herbivore theory using Douglas-flr (Pseudotsuga menzlesll) and western spruce budworm (Chorlstoneura occldentalls). Both plant and herbivore are widespread In western North America. Natural hosts of the budworm Include Douglas-flr, species of Abies, and, on occasion, other conifers (9). Variation In budworm density occurs on both a geographic and local scale. We have frequently observed differential defoliation In trees having overlapping crowns at sites In Montana, Idaho, and New Mexico. 

Secondary chemistry differs from primary chemistry principally in its distributional variability and it is this variability that has intrigued ecologists for the past 30 years. Theories [or provisional hypotheses (35)] to account for the structural differentiation and function of secondary metabolites, as well as the differential allocation of energy and materials to defensive chemistry, abound, but they are almost exclusively derived from studies of plant-herbivore interactions (Table 2). This emphasis may be because the function of secondary chemicals in plants is less immediately apparent to humans, who have historically consumed a broad array of plants without ill effects, so alternative explanations of their presence readily come to mind. The fact that animals upon disturbance often squirt, dribble, spray, or otherwise release noxious substances at humans and cause pain leads to readier acceptance of a defensive function [although there are skeptics who are unconvinced of a... 

Although plant-herbivore co-evolutionary theory provides a model for the evolution of the phytochemical diversity between species described above, the diversity of closely related compounds or analogs observed in any single species is not readily explained. Jones and Firn (1991), Berenbaum (1985) and Feng and Isman (1995) provided several hypotheses that have looked specifically at the evolution of diversity of phytochemical substances in a single species and the possibility of analog redundancy (a duplication of effort or production of compounds with... 

Robinson T (1974) Metabolism and function of alkaloids in plants. Science 184 430 135 Roff DA (1992) Evolution of life histories theory and analysis. Chapman Hall, New York Rohde S, Molis M, Wahl M (2004) Regulation of anti-herbivore defence by Fucus vesiculosus in response to various cues. J Ecol 92 1011-1018... 

Yates JL, Peckol P (1993) Effects of nutrient availability and herbivory on polyphenolics in the seaweed Fucus vesiculosus. Ecology 74 1757-1766 Zangerl AR, Bazzaz FA (1992) Theory and pattern in plant defense allocation. In Fritz RS, Simms EL (eds) Plant resistance to herbivores and pathogens. Chicago Press, Chicago, pp 363-391... 

Cornell HV, Hawkins BA (2003) Herbivore responses to plant secondary compounds a test of phytochemical coevolution theory. Am Nat 161 507-522 Cronin G (2001) Resource allocation in seaweeds and marine invertebrates chemical defense patterns in relation to defense theories. In McClintock JB, Baker BJ (eds) Mar Chem Ecol. CRC, Boca Raton, FL, pp 325-354... 

Rhoades F (1985) Offensive-defensive interactions between herbivores and plants their relevance in herbivore population dynamics and ecological theory. Am Nat 125 205-238... 

Hence tannin-tolerant insects with elevated gut pH s may be relatively resistant to these pathogens. According to theory (69,70), early successional plants should have low tannin contents and their herbivores should have lower gut pH values... 

Zangerl, A. R. and Bazzaz, F. A. (1992). Theory and pattern in plant defense allocation. In Plant Resistance to Herbivores and Pathogens Ecology, Evolution, and Genetics, eds. R. S. Fritz and E. L. Simms, pp. 363-391. Chicago University of Chicago Press. 

Martin, J.S., Martin, M.M., and Bemays, E.A., Failure of tannic acid to inhibit digestion or reduce digestibility of plant protein in gut fluids of insect herbivores implications for theories of plant defense, J. Chem. Ecol., 13, 605, 1987. 

Karowe, D.N., Differential effect of tannic acid on two tree-feeding lepidoptera implications for theories of plant anti-herbivore chemistry, Oecologia, 80, 507, 1989. 

The production of toxins is only one aspect of plant defense strategy. As a result of the persistent battle of plants and herbivores, many optimized phenotypes have evolved, such as the preferential accumulation of alkaloids in tissues with a pattern that is consistent with predictions of optimal defense theory,65 i.e., the defense metabolites are allocated preferentially to tissues with a high probability of attack.66 The inducibility of pathways leading to plant secondary compounds as a strategy to minimize the costs of plant defense is a result of permanent optimization. One of a few examples of inducible alkaloid biosynthesis is the different Nicotiana species that exhibit dramatic wound-induced increases of nicotine, nomicotine, or anabasine.67... 

Cornell HV, Hawkins BA (2003) Herbivore responses to plant secondary compoimds a test of phytochemical coevolution theory. Am Nat 161 507-522... 

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