Insect‐plant interactions on a planet of weeds

Abstract

Two conflicting views confront ecologists and evolutionary biologists on the degree of symmetry in interactions between plants and phytophagous insects. The symmetrical view holds that insects and plants have strong effects on one another's evolutionary and ecological dynamics. Thus, herbivores are regarded as a major influence on plant distribution and abundance in contemporary ecosystems, and coevolution is commonly invoked to explain adaptive radiation in plants and insects, host specialization in insects, as well as much of the morphological and chemical variety observed in plants. The asymmetrical view acknowledges that plants have major effects on insects, but claims that insects seldom impose significant effects on plants. Proponents of the asymmetric view tend to ignore or discount insect-plant interactions in communities and ecosystems altered by human impacts. If we recognize the scope and scale of human impacts, and ways in which these impacts change insect-plant interactions, then our views about symmetry or asymmetry in insect-plant interactions will change. To understand, predict, and manage insect herbivory we need to study it in all its manifestations. In particular, the study of interactions involving alien species is both an urgent priority for environmental management and potentially a source of ecological insights on the role of herbivores in plant population and community dynamics. A complete theory of insect/host plant interactions must explain and predict interactions both within and beyond the native range. Such a theory might guide efforts to deal with environmental problems stemming from rapid rates of extinction and homogenization of the world's biota.

Herbivory alters resource allocation and compensation in the invasive tree Melaleuca quinquenervia

“…Consistent with these data, herbivory in unmanaged systems is typically low, ranging from 5 to 15% of leaf area (Crawley, 1989;Marquis, 1992). However, as demonstrated in this study, it can not be inferred that leaf feeders have little impact on plant performance (McEvoy, 2002).…”

“…As canopy held seedbanks continue to diminish over time, reproductive suppression is predicted to have direct, long-term effects on recruitment, invasion potential, and abundance. To test this prediction, future research will examine how herbivores affect stage-specific demographic transitions of M. quinquenervia and quantify the effects of herbivory in the context of the entire plant life cycle (Shea & Kelly, 1998;McEvoy, 2002).…”

Novel chemistry of invasive exotic plants

“…Although escape from herbivores as a mechanism of exotic plant invasion has received considerable attention in the literature (Keane & Crawley 2002) Secondary chemistry of exotic plants N. Cappuccino & J. T. Arnason 191 argument relies on the assumption that herbivores, when present, limit plant abundance and distribution-a question that has generated decades of debate (Keane & Crawley 2002;McEvoy 2002). The relationships we observed between unique chemistry, low herbivory and exotic plant invasiveness suggest an important role for enemy escape; however, other mechanisms that could drive invasiveness, such as allelopathy (Callaway & Aschehoug 2000;Callaway & Ridenour 2004) and the alteration of soil microbial communities (Kourtev et al 2002), are also likely to be important.…”

Predicting novel trophic interactions in a non‐native world

“…Despite the growing prevalence of nonnative plants, there are few effective tools for predicting the fate of non-native plants or their impacts on native communities (NAS 2002). One major determinant of a non-native plant's success and its effect on native communities is whether and to what degree that plant is colonised by native herbivores (Maron & Vil a 2001;McEvoy 2002). Generally, many non-native plants lose co-evolved herbivores when actively or passively introduced into a new area, and the loss of the co-evolved herbivores ('enemy release') is seen as one important reason for non-native plants' success and invasiveness (Keane & Crawley 2002).…”