Plant damage from and defenses against ‘cryptic’ herbivory: A guild perspective

Abstract

Despite considerable interest in the factors affecting trophic cascades in terrestrial systems, there has been relatively little attention paid to the importance of the herbivore-plant link in explaining why some systems ''cascade'' (have strong topdown effects on plant survival and population growth) and others ''trickle'' (have top-down effects on plant damage, but little effect on plant fitness). This is despite the fact that herbivore guild identity has long been recognized as a major force affecting herbivore-plant interactions. We address the potential importance of herbivore guild identity in determining the strength of tritrophic interactions by reviewing literature concerning plant damage from and induced defenses against two ''cryptic'' herbivore guilds, predispersal seed predators and root/stem borers. Although both guilds are capable of strongly affecting plant fitness, the impact of root/stem borers on plants in natural systems seems far greater than that of predispersal seed predators. The large impact of root/stem borers occurs via their disruption of plant vascular systems, while a variety of factors (safe-site-limited plant populations, long-lived seed banks, temporal plant escape, etc.) each seem important in explaining the smaller effect of predispersal seed predators. While the lack of attention to herbivore guilds is understandable, given the (by necessity) single-species focus of much trophic cascade research, we suggest that predator suppression of root/ stem borers and predispersal seed predators will, respectively, yield strong versus weak top-down effects on plant fitness. The potential tritrophic consequences of herbivore feeding mode highlight the importance of research on varied predatorherbivore chains that share a common basal resource.

Effects of insect attack to stems on plant survival, growth, reproduction and photosynthesis

“…As Preisser and Bastow () suggested that stem herbivory could have more severe effects than herbivory to other plant parts, we sought other meta‐analyses that would allow us to compare our findings here with attack to other plant parts. Stem feeding and root herbivory appear to have comparable effects on plant growth and photosynthesis.…”

“…There is a growing appreciation that different types of insect herbivory may have very different effects on plant performance and population dynamics and thus impose different selection pressures (Crawley , Blossey and Hunt‐Joshi , Preisser and Bastow , Maron and Crone ). For example, Hoffman and Moran () report that the root‐crown boring weevil Neodiplogrammus quadrivittatus destroys large trees of Sesbania punicea that are replaced from seedlings produced by the seed‐bank.…”

“…The vast majority of research on the effects of insect herbivory on the host plant has focused on leaf‐feeding, particularly in the non‐applied ecological literature (Karban and Baldwin , Preisser and Bastow ). As leaves are one of the more replaceable tissues (Meldau et al ), we may not be getting a complete understanding of the ecological and evolutionary impacts of herbivory by focusing solely on leaves (Turcotte et al ).…”

“…As leaves are one of the more replaceable tissues (Meldau et al ), we may not be getting a complete understanding of the ecological and evolutionary impacts of herbivory by focusing solely on leaves (Turcotte et al ). Although there are likely to be more species of leaf‐feeding insects (Palmer and Pullen , Zhang et al ), attack to woody stems may be more severe than leaf attack (Preisser and Bastow ). Despite this we know remarkably little about the effects of insect attack to plant stems.…”

“…Drivers behind this dieback are usually insects that have attacked the stem (Butler et al ). A small number of individual insects can inflict severe plant damage (Preisser and Bastow ), since attack by insects along a stem often kills all tissue above the point of attack or stops its growth (Whitham and Mopper , DeClerck‐Floate and Price ). Insects in all major herbivorous orders attack all parts of woody stems.…”