Introduction
Ninety percent of flowering plants are pollinated by animals (Ollertonet al . 2011; Tong et al . 2023). Without pollinators, many plants could not set seed and reproduce; and without plants to provide pollen, nectar, and other floral rewards, many animal populations would decline (Kearns et al . 1998). Pollinators tend to move both within and among neighboring plants, and the pollen transfer efficiency of pollinators varies markedly, so that most plants end up with a mixed mating strategy at the point of being pollinated (Harder and Barrett 1996; Goodwillie et al . 2005). Vogler and Kalisz (2001) reviewed available data to show that most plants achieve a mixture of selfing and outcrossing. Plants can control their mating opportunities by the way they manipulate their visitors. Attracting a larger number of pollinators is mainly determined by the advertising traits and floral rewards of plants. Therefore, understanding the pollination efficiency of various pollinators can help predict how different floral visitors could influence plant reproduction.
In animal-pollinated plants, the contribution of different pollinator species to plant’s reproductive fitness differs significantly because their pollination efficiency varies greatly due to differences in body size, foraging behavior, and visitation rate (Chang et al . 2023). Fewer pollinator visits or less pollen delivered per visit may reduce the reproductive success of plants (Olsen 1996; Ashman et al . 2004; Sahl and Conner 2007). Body size is an important functional characteristic that underlies pollination-related ecological processes (Kendall et al . 2019). The body size of pollinators such as body length and intertegular distance can influence the amount of deposited pollen (Goulson et al . 2002; Földesiet al . 2020). The intertegular distance is a useful body size index established by Cane (Cane, 1987). Goulson et al . (2002) found that the amount of pollen transferred by bees was influenced by the intertegular distance. Larger bees tended to deposit more pollen on stigmas at each visit than smaller bees, and the interspecific body length and intertegular distance of bees had a positive effect on pollen deposition (Földesi et al . 2020; Chang et al . 2023). There was no correlation between intertegular distance and pollen deposition among individuals of the same species (Chang et al . 2023). However, whether pollen removal and pollination efficiency (pollination efficiency = pollen deposition/pollen removal, see Li et al . 2022) are affected by body size of pollinators is still unknown.
In this study, we used a generalist plantHibiscus mutabilis as an example to investigate the impact of pollinators’ body size on pollination efficiency. We measured the floral traits of plants and the body length and intertegular distance of various pollinator species. We identified the breeding system of H. mutabilis by imposing four pollination treatments. We compared the visitation rates of various pollinator species. To assess pollination efficiency, we examined pollen deposition and pollen removal of each pollinator species. Based on field investigations, we aimed to address the following three questions: (1) Are there differences in visitation rate and pollination efficiency among various pollinator species in H. mutabilis ? (2) Does the species H. mutabilis have a mixed mating system? (3) Is the body size of pollinators related to pollination efficiency?