Abstract
The cross-pollination of most alpine plants depends on insects, whose altitudinal distribution is limited by temperature. However, although global warming is causing shifts in temporal and spatial species distribution, we are still largely unaware of how plant-pollinator interactions change with elevation and time along altitudinal gradients. This makes the detection of endangered interactions and species challenging. In this study, we aimed at providing such a reference, and tested if and how the major flower-visiting insect orders and families segregated by altitude, phenology and foraging preferences along an elevational gradient from 970 m to 2700 m in the Alps. Flies were the main potential pollinators from 1500 m, as bees and beetles decreased rapidly above that limit. Diptera, Coleoptera and Hymenoptera differed significantly in the angiosperm assemblages visited. Within Diptera, the predominant group, major families segregated by both phenology and foraging preferences along the gradient. Empidids, muscids and anthomyiids, whose role in pollination has never been investigated, dominated the upper part of the gradient. Our results thus suggest that flies and the peculiar plants they visit might be particularly at risk under global warming, and highlight the blatant lack of studies about critical components of these rich, yet fragile mountain ecosystems.
Highlights
Mountains are biodiversity hotspots with high endemism that harbour one-quarter of terrestrial life, including a remarkably high plant richness in alpine life zones[1]
We examined how the abundance and species richness of flower visitors varied along an altitudinal gradient, in order to understand how they segregate according to space, time and trophic resource
More than 99.8% of them belonged to the four major orders of anthophilous insects: Diptera accounted for 49.2% (N = 2706, 253 species) of the interactions, Hymenoptera 27.5% (N = 1511, 134 species), Coleoptera 18% (N = 989, 102 species) and Lepidoptera 5.2% (N = 289, 29 species)
Summary
Mountains are biodiversity hotspots with high endemism that harbour one-quarter of terrestrial life, including a remarkably high plant richness in alpine life zones[1]. Because climate change is expected to strongly affect mountain ecosystems[1], it becomes urgent to develop a better knowledge of the insects involved in the pollination of alpine plants, as well as to investigate the factors structuring plant-pollinator networks along altitudinal gradients. From a plant species viewpoint, it means that the assemblages of potential pollinators may vary in both time and space over the gradient and favorable season To our knowledge, this issue has never been investigated in temperate mountains, phenology was found to be the main driver of species’ interactions in a bird–flowering plant network in the high Andes of Peru[40] and is known to shape pollination networks in lowland areas[41]. To what extent the sets of flowers visited by the different orders or families of anthophilous insects overlap across elevation gradients is still not widely known
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