Seed loss before seed predation: experimental evidence of the negative effects of leaf feeding insects on acorn production

Abstract

Insect herbivory decreases plant fitness by constraining plant growth, survival and reproductive output. Most studies on the effects of herbivory in trees rely on correlational inter-individual comparisons and could, thus, be affected by confounding factors linked to both herbivory and plant performance. Using the Mediterranean Holm oak (Quercus ilex) as a study model, we followed an experimental approach in which leaf-feeding insects (mainly Lepidoptera caterpillars) were excluded from some shoots in all study trees. Shoots subjected to herbivore exclusion exhibited lower defoliation rates and produced more acorns than control shoots. Defoliation constrained shoot growth throughout the study period, but had no effect on the number of female flowers produced per shoot. Acorn production was, however, lower in control shoots due to their higher abortion rates, and also to their greater mortality risk during summer drought, as shoots with fewer leaves were less likely to survive. Plant reaction to herbivory inhibits certain physiological pathways involved in plant growth, which, together with the effects of physical damage, reduces the amount and efficiency of the photosynthetic tissue. This increases their vulnerability to environmental stresses, such as water deficit, which limit resource assimilation. Defoliation is likely a key factor affecting oak regeneration, as it may be a significant source of seed loss prior to pre-dispersal acorn predation. Further experimental studies could help to elucidate its effects in contrasting environments. In Mediterranean regions, the harsher droughts predicted by climate change models could worsen the effects of insect herbivory on oak reproductive output.

Flowering synchrony drives reproductive success in a wind‐pollinated tree

“…In support of this hypothesis, in one past study, Quercus lobata individuals with earlier budburst suffered more leaf damage, which reduced their seed production (Pearse et al, 2015a). Past experiments in our study system indicated that insect herbivory can decrease Q. ilex seed set by half (Canelo et al, 2018). Early trees gain the advantage of reduced pollen limitation, but may suffer reduced seed set due to other factors, such as herbivory.…”

“…Past experiments in our study system indicated that insect herbivory can decrease Q . ilex seed set by half (Canelo et al ., 2018). Early trees gain the advantage of reduced pollen limitation, but may suffer reduced seed set due to other factors, such as herbivory.…”

Plant‐animal interactions: patterns and mechanisms in terrestrial ecosystems

“…They found that the strength of this scatterhoarder-tree mutualism is strongest for red oaks (Q. rubra), weakest for white oaks (Q. alba) and intermediate for chestnut oak (Castanea dentata) and hybrid chestnut (C. dentata x Castanea mollissima). Canelo et al (2018) employ a careful experimental approach to quantify the effects of herbivory by a leaf-feeding insect on the Mediterranean Holm oak's (Q. ilex) physiological responses in individual shoots that ultimately results in a drop in acorn production. Unlike other correlational studies, this study demonstrated the causal physiological links between herbivory and reproductive loss.…”

Resource manipulation through experimental defoliation has legacy effects on allocation to reproductive and vegetative organs inQuercus ilex

“…Most defoliation and herbivore exclusion experiments on temperate forest trees and fruit trees have shown a negative effect of defoliation on fruit set (Mehouachi et al 1995;Obeso 1998;Iglesias et al 2003;Frioni et al 2018) and on fruit size (Obeso 1998;Hoch 2005;Matsumoto et al 2017). In oaks, most studies concerned natural herbivory and showed also negative impact on fruit set and total fruit production (Crawley 1985;May and Killingbeck 1995;Hochwender et al 2003;Pearse et al 2015;Nakajima 2015;Canelo et al 2018). However, other studies have found no effect of herbivory on fruit set, fruit size or yield in other species (Obeso and Grubb 1993;Mehouachi et al 1995;Tamura and Hiura 1998;Ezzahouani and Williams 2003;Bañuelos and Obeso 2005;Frioni et al 2018;Pasqualotto et al 2019).…”