Morphological trait‐matching in plant–Hymenoptera and plant–Diptera mutualisms across an elevational gradient

Abstract

1. Morphological trait-matching and species abundance are thought to be the main factors affecting the frequency and strength of mutualistic interactions. However, the relative importance of trait-matching and species abundance in shaping species interactions across environmental gradients remains poorly understood, especially for plant-insect mutualisms involving generalist species.2. Here, we characterised variation in species and trait composition and the relative importance of trait-matching and species abundance in shaping plant-Hymenoptera and plant-Diptera mutualisms in four meadows across an elevational gradient (2,725-3,910 m) in Yulong Snow Mountain, Southwest China. We also evaluated the effects of morphological traits of flower visitors and plant composition on their foraging specialisation (d' and normalised degree).3. There was a high degree of dissimilarity in the composition of Hymenoptera and Diptera visitors and their visited plants between communities. This variation was mainly driven by the spatial replacement of species. Both for plant-Hymenoptera and plant-Diptera networks, trait-matching between nectar tube depth and proboscis length was a stronger predictor of the interactions between temporally co-occurring plants and flower visitors than species abundance. Fourth-corner analyses revealed statistically significant trait-matching between nectar tube depth and proboscis length in plant-Hymenoptera networks at all sites, suggesting that Hymenoptera consistently foraged on plant species with nectar tube depths matching their proboscis lengths. By contrast, significant trait-matching in plant-Diptera networks was only observed at the two lower elevation sites.The species-level specialisation d' of flower visitors increased significantly as the proboscis length and the difference in nectar tube depth between the plant community and the plants visited by flower visitors increased.

Floral resource partitioning of coexisting bumble bees: Distinguishing species‐, colony‐, and individual‐level effects

“…Flower morphology is also often considered an important influence on bumblebee floral resource use, due to its match with tongue length (Sponsler et al, 2021). Bumblebees and various flies are dominant pollinators in our study system, but flies are generally restricted to open flowers while bumblebees prefer deep and closed flowers, suggesting potential floral use partitioning with Diptera (Zhao et al, 2021). Previous studies also suggested a key role of rewards (nectar and pollen) in structuring bumblebee foraging (Cnaani et al, 2006; Konzmann & Lunau, 2014; Vaudo et al, 2016).…”

Community-wide patterns in pollen and ovule production, their ratio (P/O), and other floral traits along an elevation gradient in southwestern China

“…Further, our findings that increased pollen production, and hence P/O, but no concomitant changes in ovule number with the increasing elevation may indicate that pollinator dependence and pollination efficiency have a greater effect on the evolution of pollen production compared to ovule production [ 61 ]. The pollinator guild of the Himalayan-Hengduan Mountains region is dominated by hymenopteran visitors at higher elevations [ 55 , 62 ], whereas in other regions, bee abundance and richness decrease with increasing elevation and are replaced by flies as the dominant visitors [ 63 ]. Many of the herbaceous flowering plant species in our study sites are insect-pollinated [ 55 , 62 ], and as such, pollinator dependence and pollination efficiency may play a large role in the trends for pollen production and P/O found in our study, although this source of variation remains to be empirically tested in the field.…”

“…The pollinator guild of the Himalayan-Hengduan Mountains region is dominated by hymenopteran visitors at higher elevations [ 55 , 62 ], whereas in other regions, bee abundance and richness decrease with increasing elevation and are replaced by flies as the dominant visitors [ 63 ]. Many of the herbaceous flowering plant species in our study sites are insect-pollinated [ 55 , 62 ], and as such, pollinator dependence and pollination efficiency may play a large role in the trends for pollen production and P/O found in our study, although this source of variation remains to be empirically tested in the field.…”

Patterns of flower-visiting insects depend on flowering phenological shifts along an altitudinal gradient in subalpine moorland ecosystems

“…In particular, given that Hymenopteran species have a greater preference for owering plants than Dipteran species (Branquart and Hemptinne 2000; Mizunaga and Kudo 2017), our results suggest a greater preference for G. pentapetalum, N. crista-galli, and S. soldanelloides by Hymenopteran species over other species in these moorland ecosystems. In contrast, many Dipteran species are generalists (Classen et al 2020;Zhao et al 2021), with phenological shifts across time (i.e., between early July and mid-August) and space (i.e., with altitude) having less of an effect on their ower-visiting frequency.…”