Division of foraging behaviour: Assessments of pollinator traits when visiting a model plant species

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Diverse animals visit flowers but not all engage in pollination, and only behaviours involving stigmal contact result in successful pollination events. Ethological indices developed for sociobiological contexts (caste evolution) have unrealized potential to provide insights on pollination services but have not been applied in this context before. In the present study, we characterized foraging behaviours as functional traits, which allowed us to predict whether ecosystems services are robust to species-specific trait loss. We aimed to (1) document the variety, duration and frequency of on-flower behaviours, (2) determine which taxa engage in stigmal contact and (3) investigate vulnerabilities of pollination service to loss of pollinator taxa. We used video recordings to document on-flower behaviours of animals visiting a single apple cultivar (Malus domestica var. ‘Pink Lady’), which removed confounding factors to enable a robust assessment of functional pollination behaviour. We adapted division of labour statistics (designed to assess caste-specific behavioural task fidelity within social insect colonies) to investigate taxon-specific foraging behaviours within this assemblage of pollinators – a novel application. An ethogram of 11 behaviours was derived from 19,518 min of observations (2350 visits; 19 taxa). Most (53%) flower visits involved stigmal contact (termed ‘contact visits’), but the percentage of contact visits varied between taxa. We introduce division of foraging behaviour (DFB) indices – which imply the focal pollinator assemblage consists of a mix of behaviourally generalized and specialized taxa with a slight bias towards specialization: division of taxa into behaviours DFBY|X = 0.59; division of behaviours into taxa DFBX|Y = 0.76. Simulated extinction of taxa from this insect assemblage significantly shifted DFBY|X in four instances. These qualitative assessments of behavioural traits imply moderate functional redundancy in pollination services provided by 11 insect taxa to a model plant, even under simulated extinction events, suggesting pollination services may be somewhat resilient to animal–plant network disruptions in this Australian agroecological study system.