Tree seedling richness, but not neighborhood composition, influences insect herbivory in a temperate deciduous forest community

Abstract

Insect herbivores can serve as important regulators of plant dynamics, but their impacts in temperate forest understories have received minimal attention at local scales. Here, we test several related hypotheses about the influence of plant neighborhood composition on insect leaf damage in southwestern Pennsylvania, USA. Using data on seedlings and adult trees sampled at 36 sites over an approximately 900 ha area, we tested for the effects of total plant density, rarefied species richness (i.e., resource concentration and dietary‐mixing hypotheses), conspecific density (i.e., Janzen–Connell hypothesis), and heterospecific density (i.e., herd‐immunity hypothesis), on the proportion of leaf tissue removed from 290 seedlings of 20 species. We also tested for the effects of generic‐ and familial‐level neighborhoods. Our results showed that the proportion of leaf tissue removed ranged from zero to just under 50% across individuals, but was generally quite low (<2%). Using linear mixed models, we found a significant negative relationship between insect damage and rarefied species richness, but no relationship with neighborhood density or composition. In addition, leaf damage had no significant effect on subsequent seedling growth or survival, likely due to the low levels of damage experienced by most individuals. Our results provide some support for the resource concentration hypothesis, but suggest a limited role for insect herbivores in driving local‐scale seedling dynamics in temperate forest understories.

Local adaptation to herbivory within tropical tree species along a rainfall gradient

“…Values of the raw percentage of leaf area lost were highly right‐skewed and zero‐inflated. We therefore scaled our data with the following equation:where x is percent leaf area missing per plant and N is the total number of plants sampled (Smithson and Verkuilen 2006, Murphy et al 2016). Scaled values were then log‐transformed to approximate a normal distribution (Appendix , Fig.…”

“…We calculated total plant leaf area and standing herbivory using the software ImageJ version 1.48k (Abràmoff et al 2004), following the methodology of Murphy et al (2016). Briefly, missing leaf area at the margins was hand‐estimated with the draw tool, as was overlapping leaf area.…”

Global woodland structure from local interactions: new nearest-neighbour functions for understanding the ontogenesis of global forest structure

“…Thus the spatial spread of an infection can be slowed down or even stopped by mixtures of susceptible and resistant species (Begon et al 2006). Therefore individual plant fitness should be enhanced in stands involving many species but reduced in stands with low species diversity (Wills et al 1997;Murphy et al 2016).…”

Do experimental drought stress and species' drought sensitivity influence herbivory in tropical tree seedlings?

“…where x is percent leaf area missing per plant and N is the total number of plants sampled across species (Murphy et al, 2016;Smithson & Verkuilen, 2006). Due to significant right skew, we then logtransformed these data.…”