Does the munch affect the bunch? Using community science to explore insect herbivory and fruit production in an understory plant

Digital, community-sourced natural history records are valuable for
understanding species attributes such as phenology and geographic
distribution. When these records include photographs, they can also be
analysed for individual phenotypes and species interactions to develop or
test ecological hypotheses. Here, we use observational and experimental
approaches to assess how insect herbivory affects reproductive success in
a widespread forest plant, bunchberry (Cornus canadensis). We
queried the Global Biodiversity Information Facility (GBIF) and assembled
a dataset of 2,578 photographic records of fruiting plants. Of these, 891
showed evidence of insect herbivory, but herbivory was not significantly
associated with fruit production. In a field study we monitored 200 plants
over five weeks. Herbivory was widespread (78% of plants showed insect
feeding), but damage was generally low—only 5% of plants experienced
herbivory ≥40% of total leaf area. No relationship was found between
natural herbivory and fruit production. In a second study, we simulated
high herbivory by mechanically removing 40% of leaf area in early and
mid-season. Early-season herbivory reduced fruit production by 100%, while
mid-season herbivory reduced fruit production by 87.3%. These
results suggest that although high herbivory early in the season can
substantially reduce fruiting, natural levels of herbivory exert limited
top-down control on reproduction in bunchberry. By combining
large-scale community-sourced records with controlled field experiments,
this study demonstrates the value of mixed-methods approaches for testing
ecological hypotheses and gaining insight into the processes that shape
plant–insect interactions.