Effects of arthropods as physical ecosystem engineers on plant-based trophic interaction webs

Abstract

Introduction Insect herbivores and other arthropods create a variety of constructs on their host plants: silk webs, leaf shelters, galls, and stem cavities. This state change, often modifying resource availability for species other than the construct-builder (constructor, hereafter), is an example of allogenic physical ecosystem engineering. Physical ecosystem engineers are “organisms that directly or indirectly control the availability of resources to other organisms by causing physical state changes in biotic or abiotic materials” (Jones et al. 1994, 1997). In the case of allogenic engineering (in contrast to autogenic engineering), the physical state change is caused by the engineer, but the engineer is not part of the new physical state. The presence of constructs can impact the species richness, food web structure, and trophic interactions of the community of arthropods associated with engineered plants. The impact of engineering will depend on the responses of individual species to the presence of the constructs and the resulting interactions with all other species. One approach to understanding the nature of these responses is to view the engineered plant as a mosaic of engineered and nonengineered habitats. The response of a particular animal species to a plant that has been colonized by a constructor will depend on the relative value of the engineered versus nonengineered habitat to that animal. This value will be a function of differences between the two habitat types in the intensity of abiotic stress, the relative quality of food resources, competitive and mutualistic interactions (with other species in nonengineered habitats and with other secondary inhabitants in engineered habitats), and responses of natural enemies to engineering.