Associational Resistance and Associational Susceptibility: Having Right or Wrong Neighbors

Abstract

Specific plant associations may decrease (associational resistance, AR) or increase (associational susceptibility, AS) the likelihood of detection by, and/or vulnerability to, herbivores. We discuss presumed mechanisms leading to AR and AS, suggest others, and conduct meta-analyses on plant and herbivore traits affecting AR and AS, and the effects of habitat. Specific plant associations determine the likelihood of detection and/or vulnerability of focal plants to herbivores. AS is more likely with insects and AR more likely with mammals. Unpalatable neighbors increase the likelihood of AR. An herbivore's feeding guild, diet breadth, and habitat type do not influence the likelihood of AR or AS. The effectiveness of AR in reducing herbivore abundance is independent of whether neighboring plants are within a plot of focal crops or along the edge of a plot. AR and AS may be applicable to associations among herbivores, and may be appropriately studied from a landscape perspective.

Young conifer stands form a deer browsing refuge for an oak admixture: silvicultural implications for forest regeneration under herbivore pressure

“…The authors concluded that ''balsam fir patches are typically quite dense, hard to manoeuvre through, and difficult to visually inspect, thus creating a physical barrier for whitetailed deer''. In the literature, other types of biotic (browsing) refuges were also found to reduce herbivore pressure on target trees, including shrubs with spines (Barbosa et al 2009), forest understorey (Heuze et al 2005;Jensen et al 2012), woody debris (Smit et al 2012) and slash on clear-cuts (Bergquist and Ö rlander 1998). Our study provides evidence that also in artificially regenerated stands, browsing on attractive admixed tree species can be reduced by a browsing refuge created by a less attractive main tree species.…”

Early recruitment responses to interactions between frequent fires, nutrients, and herbivory in the southern Amazon

“…The length and severity of the dry season at our study site distinguishes it from these other forests, indicating competition may become important for tropical seedlings when moisture is scarce. Plot diversity was related to increased seedling survival, which suggests having heterospecific neighbors is beneficial, fitting with the resource concentration hypothesis (Tahvanainen and Root 1972;Barbosa et al 2009). Another useful result was the consistent finding that early herbivory had the strongest effects on survival, richness, and diversity.…”

Interactions between repeated fire, nutrients, and insect herbivores affect the recovery of diversity in the southern Amazon

“…We found herbivory did increase the probability of seedling mortality, and our hypothesis was supported in that herbivores were related to higher diversity in burned plots with nitrogen (higher H 0 , lower D) or phosphorus additions (lower D). This suggests Janzen-Connell effects may be strongest in disturbed sites, perhaps due to greater herbivore activity or lower initial plant species evenness and diversity in these areas (conditions that could favor specialist herbivores; Barbosa et al 2009). Abundant nutrients also seem necessary for Janzen-Connell effects to become apparent.…”