Camera-trap monitoring reveals flower visitor diversity and diel activity patterns in the forest understory: bramble patches (Rubus fruticosus agg.) as a model system

Pollinator communities in deciduous temperate forest understories remain poorly understood, particularly regarding the relative roles of temporal activity patterns and microclimatic conditions in structuring flower visitor assemblages. We developed a non-invasive video monitoring system to investigate flower visitor communities on brambles (Rubus fruticosus agg.) across four forest patches in the Fontainebleau forest (Île-de-France, France), recording 3,636 visits from 17 morphotype groups during 369 hours. Ants dominated visits (45%), followed by non-syrphid flies (10%), whereas bees, hoverflies, and Lepidoptera together accounted for 32%. Visitor assemblages exhibited substantial spatial and temporal variation, with evidence of temporal niche partitioning. Generalized additive mixed models (GAMMs) revealed taxon-specific diurnal activity patterns, with most taxa peaking during late morning to afternoon (10:00–18:00), though ants showed crepuscular activity and some groups including non-syrphid flies and hoverflies displayed bimodal distributions in certain patches. Nocturnal activity was observed for several taxa. Microclimatic effects on visitor occurrence were taxon-specific and limited: non-syrphid flies and ants responded negatively to light intensity. In addition, non-syrphid flies and hoverflies showed shorter visit durations under higher light intensity, and non-syrphid flies additionally showed temperature-dependent foraging behavior, reducing visit duration by 57% per 10°C increase. Visit duration varied markedly among taxa, ranging from a few seconds in bumblebees and hoverflies to over an hour in some Coleoptera and Orthoptera. These findings reveal that forest flower visitors partition temporal niches more strongly than microclimatic niches. This non-lethal monitoring approach successfully captured complex ecological patterns, demonstrating brambles' potential as a model system for forest pollination ecology while preserving natural environmental contexts and enabling continuous day-night observations.