Incidental pollination by passing animals: An overlooked mechanism?

Societal Impact Statement The conservation of pollinators is essential for sustaining the ecosystem services of pollen transfer, which support crop production, biodiversity conservation and ecosystem health. While primary pollinators have been the focus of most conservation efforts, subordinate or incidental pollinators have been largely overlooked. Animals that pass through vegetation may compensate for pollination deficits in the context of ongoing pollinator declines. Such incidental pollinators could potentially enhance gene flow among plants over greater distances and in more varied directions compared to primary pollinators alone. To fully benefit from these supplementary pollination services, it is essential to preserve diverse habitats across broader landscapes and spatial scales. Summary Terrestrial angiosperms primarily employ two pollination strategies: anemophily and zoophily. Anemophilous flowers produce large quantities of small pollen grains for wind‐mediated transport, which is often inefficient. In contrast, zoophilous flowers attract flower‐visiting insects, other invertebrates and vertebrate pollinators using visual, olfactory and other cues, often in exchange for other rewards. However, non‐target animals, including mammals, birds and arthropods, frequently visit flowering plants without consuming floral rewards. These incidental visitors may inadvertently transfer pollen between plants, potentially contributing to fruit set. This phenomenon, termed “background pollination”, may be particularly relevant in mass‐flowering species, generalist flowers, riverine plants and zoochorous plants, where the passage of animals, combined with static electricity, facilitates pollen deposition. Detecting such pollination mechanisms poses challenges for traditional methods, such as in situ observation or bagging experiments in the field. Emerging approaches, including camera trapping and the examination of wild‐caught animals' body surfaces, may offer useful insights into these interactions. Background pollination likely complements anemophilous and zoophilous pollination strategies, introducing additional complexity to gene flow dynamics within plant populations.