The interactions between most herbivores and their hosts are usually considered the result of a long coevolutionary process. Current theory states that most plants respond to herbivory by producing chemicals that adversely affect the growth or survivorship of the herbivores. Seastedt notes that certain consumers, however, may exhibit positive growth responses within these changes in plant chemistry occur. Increased growth is predicated whenever herbivory increases the quality of the food resource via plant stress or when it removes chemicals having a negative effect on the palatability or assimilation of the resource. A plant with ungrazed foliage may be an inferior food item for such organisms like nematodes, a resource that supports them at relatively low densities. The mechanism or mechanisms regulating the herbivore response may be a modification in the carbon-to-nitrogen ratios of living roots, a reduction in the root defensive substances, or an increase in root turnover resulting in a greater production of senescent roots. The author notes that regardless of the exact mechanisms, moderate levels of aboveground herbivory increase the quality of the belowground resource represented by living and dead roots. The belowground herbivore response, in turn, probably influences subsequent plant activity. Seastedt concludes that it might be better to consider the plant-consumer interaction as a consumer-plant-consumer interaction.
Citations and enhanced abstracts for journals articles and documents focused on rangeland ecology and management. RSIS is a collaboration between Montana State University, University of Idaho, and University of Wyoming.