I. Types and Patterns of Herbivory

A. Herbivore Functional Groups

B. Measurement of Herbivory

C. Spatial and Temporal Patterns of Herbivory

II. Effects of Herbivory

A. Plant Productivity, Survival and Growth Form

B. Community Dynamics

C. Water and Nutrient Fluxes

D. Effects on Climate and Disturbance Regime

III. Summary

HERBIVORY IS THE RATE OF CONSUMPTION BY ANIMALS OF ANY PLANT parts, including foliage, stems, roots, flowers, fruits, or seeds. Direct effects of insects on plant reproductive parts are addressed in Chapter 13. Herbivory is a key ecosystem process that reduces density of plants or plant materials, transfers mass and nutrients to the soil or water column, and affects habitat and resource conditions for other organisms. Insects are the primary herbivores in many ecosystems, and their effect on primary production can equal or exceed that of more conspicuous vertebrate grazers in grasslands (e.g., A. Andersen and Lonsdale 1990, Gandar 1982, Sinclair 1975, Weisser and Siemann 2004, Wiegert and Evans 1967).

Loss of plant material through herbivory generally is negligible, or at least inconspicuous, but periodic outbreaks of herbivores have a well-known capacity to reduce growth and survival of host species by as much as 100% and to alter vegetation structure over large areas. A key aspect of herbivory is its variation in intensity among plant species, reflecting biochemical interactions between the herbivore and the various host and nonhost species that comprise the vegetation (see Chapter 3).

Effects of herbivory on ecosystem processes depend on the type of herbivore and pattern of consumption, as well as its intensity. Measurement and comparison of herbivory and its effects among ecosystems and environmental conditions remain problematic as a result of lack of standardized techniques for measuring or manipulating intensity. Few studies have assessed the effects of herbivory on ecosystem processes other than primary production. Nevertheless, accumulating evidence indicates that effects of herbivory on ecosystem processes, including primary production, are complex. Ecosystem management practices that exacerbate or suppress herbivory may be counterproductive.

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