Plant-Pollinator Interactions along the Altitudinal Gradient in Berberis lycium Royle: An Endangered Medicinal Plant Species of the Himalayan Region

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Abstract Mountain ecosystems influence species distribution by offering climatic variables intertwined with rising altitude. These climatic factors determine species phenology and niche width. Although the distributional patterns of some prominent insect groups in relation to altitude have been determined, the environmental preferences along the altitudinal range that differentially influence the pollination of specific plant species are unknown. Here we assess how the composition and abundance of pollinator fauna of the important medicinal plant Berberis lycium Royle (Berberidaceae) differ across five distinct altitudinal gradients (800-2200 m) in the Pir-Panjal mountain range in the northwestern part of the Indian Himalayas. We monitored insect pollinators of major groups (bees, butterflies, wasps, flies) over two consecutive flowering seasons during 2022-2023. In total, 39 insect species belonging to five orders and 17 families were observed visiting the plant species during the flowering period across the altitudinal gradient. The results of the linear regression model depict that all four pollination indices show a negative correlation with increasing altitude in foraging activities when all the data are pooled together. However, only foraging speed (FS) and index of visiting rate (IVR) were statistically significant. In the case of individual orders, only Lepidoptera exhibited a notable relation to altitude. However, asynchrony in foraging activities among other pollinator groups has been reported along altitudinal gradients. The reproductive output (fruit and seed production) shows a significant negative correlation with increasing altitude. We concluded that while altitude influences species distribution, it also differentially shapes plant-pollinator interactions, pollinator activities, and reproductive output. This work is of great significance in order to monitor plant-pollinator interactions, which are essential component of biodiversity rich but fragile mountain ecosystem.

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