Lagged effects of early-season herbivores on valley oak fecundity

Abstract

The seasonal match between folivore and leaf phenology affects the annual success of arboreal folivore populations because many folivores exploit developing leaves, which are an ephemeral resource. One strategy for folivores to exploit early-season leaves is to anticipate their emergence. The consequence of this behavior for trees is that individuals that set leaves earlier may experience greater rates of folivore damage, with potential negative fitness consequences. To test this hypothesis, we surveyed the early-season phenology, insect folivore damage, and acorn crop of a population of valley oaks (Quercus lobata) over a 3-year period. We found that trees that set leaves earlier experienced greater rates of folivore damage than trees that set leaves later in the season. In addition, we observed a lagged effect of folivore damage on acorn production, whereby trees with greater leaf damage produced fewer acorns in the subsequent year. These results indicate potential negative fitness consequences of earlier leaf phenology. Our study suggests that folivore pressure may be one factor that affects the optimal timing of leaf set in oaks.

Phenological sensitivity to temperature mediates herbivory

“…Our findings align with other studies showing that phenological timing can affect herbivory rates within species or genera (Mopper & Simberloff, 1995; Pearse, Baty, et al, 2015; Pearse, Funk, et al, 2015; Pearse & Karban, 2013), and may have fitness consequences (Pearse, Funk, et al, 2015). For example, valley oak ( Quercus lobata ) genotypes that leafed out early in a given year also experienced higher herbivory rates in that year and reduced acorn production in the following year (Pearse, Funk, et al, 2015). Our herbarium dataset provides the rare opportunity to extend this framework to entire plant communities.…”

“…This could be because phenologically sensitive plants and their insect herbivores are shifting timing of leaf‐out and emergence, respectively, in synchrony. In warm years, more sensitive plants may also be more synchronized with each other and with early season herbivores (Hansen et al, 2020; Pearse, Funk, et al, 2015). However, it is also possible that either generalist herbivores or a diversity of opportunistic herbivores dominate the insect herbivore community—which might be relatively common in temperate latitudes (Forister et al, 2015)—such that temporal escape from one herbivore increases exposure to another.…”

Future vulnerability mapping based on response to extreme climate events: Dieback thresholds in an endemic California oak

“…We found that NDVI was lower in observed dieback than in non-dieback areas (Appendix S1). Non-climatic factors, absent from our analysis, that may have contributed to dieback include biotic interactions (Buse, Dury, Woodburn, Perrins, & Good, 1999;Pearse, Funk, Kraft, & Koenig, 2015), potential local genetic variation (Sork et al, 2010), soil characteristics that impact plant water availability, and the varied topography and geology of the region (Norris & Webb, 1990).…”

Flowering synchrony drives reproductive success in a wind‐pollinated tree

“…One hypothesis is that early trees suffered more folivore damage, which could decrease their photosynthetic capacity and limit seed set. 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 .…”