Distinct diurnal and nocturnal flower visitor communities provide pollination services in urban gardens

Abstract

Urban gardens are considered a key tool for mitigating biodiversity and plant‐pollinator interaction loss due to their ubiquity in urban landscapes and the variety of resources they provide. To date, most urban garden pollination research has focused on diurnal pollination, omitting a potentially important group—nocturnal pollinators. To assess the diversity and pollination activity of both diurnal and nocturnal flower visitors in urban gardens, I monitored arthropods on focal inflorescences of Eupatorium perfoliatum, a common Michigan‐native species, for 24‐h cycles and recorded the number and duration of visits. I also measured diurnal and nocturnal communities' pollination services using a temporal floral visitation exclusion experiment. Flowers averaged nearly twice as many visits during the day as compared with night within 24‐h cycles, but nocturnal visit durations were 2.5‐fold longer on average. Day and night floral visitor communities were distinct, with day visits being dominated by Diptera, ants and other Hymenoptera, and night visits being carried out most frequently by ants, Dermaptera and Hemiptera. In the floral visitor exclusion experiment, plants open to only nocturnal visits produced larger seeds, whereas plants open to only diurnal visits trended towards producing more seeds, signalling a potential trade‐off between seed quantity and size among visitor communities. Overall, diurnal and nocturnal floral visitor communities were distinct, and nocturnally pollinated plants had reproductive output comparable to diurnally pollinated treatments. Given the emphasis on diurnal pollinators in most pollination studies, it is possible that relevant plant‐pollinator interaction information may be missed in cases where anthesis spans both day and night.