Behavioral Ecology of Pollinator Species

Abstract

Pollinators are declining globally, with cascading consequences for wild plant reproduction and agricultural food production, yet the behavioural ecology mechanisms underlying pollinator foraging decisions, inter-specific competition, and habitat use remain incompletely characterised across landscape gradients relevant to European agricultural systems. This study investigated the behavioural ecology of six wild bee species (Bombus terrestris, Bombus lapidarius, Apis mellifera, Andrena fulva, Osmia bicornis, and Halictus rubicundus) and three hoverfly species (Episyrphus balteatus, Eristalis tenax, Syrphus ribesii) across 42 sites spanning a flower-resource gradient from flower-rich semi-natural grasslands to resource-poor intensive arable landscapes in central Italy and southern France. Focal animal behavioural observations (12,840 individual foraging bouts, 2020-2023), RFID-tagged forager tracking (284 B. terrestris colonies; 8,420,000 foraging events), and floral resource mapping (18 plant families quantified at 50 m grid) were combined to quantify: (i) inter-specific foraging niche partitioning; (ii) floral constancy and flower-handling efficiency; (iii) foraging distance and habitat use in relation to landscape context; and (iv) inter-specific competition intensity. Resource partitioning was significant across all species pairs tested (Pianka's niche overlap O < 0.40 in 18 of 28 pairs), with partitioning primarily by flower species identity rather than plant family or foraging height. Bumble bee foraging distances were 2.84-fold greater in resource-poor (mean 1,284 +/- 284 m) than resource-rich landscapes (mean 448 +/- 84 m). Flower-handling time was 1.84-fold longer at low flower density sites, consistent with information search costs increasing with decreasing resource density. These findings identify flower species diversity -- rather than flower abundance alone - as the primary determinant of pollinator behavioural ecology and foraging efficiency.