![]() Among the best illustrations of this complexity is a series of studies in northern Arizona, including long-term manipulation of a stem-boring moth, Dioryctria albovittella, and piñon needle scale, Matsucoccus acalyptus, on insect-resistant and susceptible pinyon pines, Pinus edulis, in a semiarid woodland ( J. The complexity of herbivore effects on ecosystem structure and functionĪlthough herbivore effects on primary production are obvious and well-known, herbivores have complex direct and indirect effects on community structure, biogeochemical processes, and climate that may affect long-term ecosystem productivity and other functions. ![]() This study showed that herbivores are capable of influencing local climate, potentially modifying the ability of vegetation to control climate and ecosystem processes. The larger size of moth-susceptible trees and moth concentration on shoots and cones may minimize moth effects on microclimate, despite changes in crown architecture. The magnitude of scale insect-driven change in soil temperature and moisture was similar to global change scenarios and sufficient to drive changes in ecosystem processes. However, both insects reduced canopy interception, by 51% (scale insect) and 29% (moth). Scale insects reduced leaf area index of susceptible trees (by 39%) and increased soil temperature (by 26%) and moisture (by 35%), whereas moths had no effect on these variables. Herbivore effects on local climate were demonstrated by Classen et al. (2005) found that herbivory on Populus decelerated decomposition rate, but this effect depended on plant genotype. These effects were strongly mediated by seasonal rainfall. The direction of nutrient release changed with time, that is, net nitrogen immobilization one year and net mineralization a second year, perhaps reflecting alternating periods of nitrogen mineralization and leaching. Herbivory increased nitrogen concentration in pinyon pine litterfall but reduced microbial biomass. Herbivory by both the moth and scale insects was shown to affect litter quality, mineralization rate, and soil microbial abundance and activity. (2006) developed a model of “extended phenotype” that showed how heritable traits that control interactions among organisms and their effects on community and ecosystem dynamics could lead to evolution at community and ecosystem levels.Įffects on biogeochemical processes were demonstrated by Chapman et al. Concurrently, Gehring and Whitham (1991, 1995) showed that folivory significantly reduced mycorrhizal colonization and growth on stressed trees, but not on unstressed trees, demonstrating the importance of plant stress to folivore effects on belowground processes. These data indicated that herbivores could influence the relative contributions of susceptible and resistant trees to seed production, perhaps reducing the susceptibility of the future community. Birds avoided entire stands of trees with reduced cone production, even though individual insect-resistant trees produced substantial numbers of cones. ![]() albovitella reduced cone production and seed dispersal by birds. Christensen and Whitham (1991) found that D. Subsequent studies addressed herbivore effects on community dynamics. However, when water or nutrients were insufficient for compensation, herbivory reduced plant production. ![]() Under conditions of adequate water or nutrient supply, naturally growing plants were capable of substantially overcompensating for herbivory, that is, increasing primary production in excess of amounts necessary to replace lost plant tissues. In two of the earliest studies to demonstrate a range of plant responses to herbivory, Paige and Whitham (1987) and Maschinski and Whitham (1989) found that effects of herbivory depended on the interaction of timing and intensity of grazing and availability of water or nutrients. ![]() Among the best illustrations of this complexity is a series of studies in northern Arizona, including long-term manipulation of a cone- and stem-boring moth, Dioryctria albovitella, and piñon needle scale, Matsucoccus acalyptus, on insect-resistant and susceptible pinyon pines, Pinus edulis, in a semiarid woodland ( Brown et al., 2001). Box: The complexity of herbivore effects on ecosystem structure and functionĪlthough some herbivore effects on primary production are obvious and well known, herbivores have complex direct effects on community structure, biogeochemical processes, and climate that may affect long-term ecosystem productivity and other functions in less obvious ways. ![]()
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