Fragmentation of nest and foraging habitat affects time budgets of solitary bees, their fitness and pollination services, depending on traits: Results from an individual-based model

Abstract

Solitary bees are important but declining wild pollinators. During daily foraging in agricultural landscapes, they encounter a mosaic of patches with nest and foraging habitat and unsuitable matrix. It is insufficiently clear how spatial allocation of nesting and foraging resources and foraging traits of bees affect their daily foraging performance. We investigated potential brood cell construction (as proxy of fitness), number of visited flowers, foraging habitat visitation and foraging distance (pollination proxies) with the model SOLBEE (simulating pollen transport by solitary bees, tested and validated in an earlier study), for landscapes varying in landscape fragmentation and spatial allocation of nesting and foraging resources. Simulated bees varied in body size and nesting preference. We aimed to understand effects of landscape fragmentation and bee traits on bee fitness and the pollination services bees provide, as well as interactions between them, and the general consequences it has to our understanding of the system. This broad scope gives multiple key results. 1) Body size determines fitness more than landscape fragmentation, with large bees building fewer brood cells. High pollen requirements for large bees and the related high time budgets for visiting many flowers may not compensate for faster flight speeds and short handling times on flowers, giving them overall a disadvantage compared to small bees. 2) Nest preference does affect distribution of bees over the landscape, with cavity-nesting bees being restricted to nesting along field edges, which inevitably leads to performance reductions. Fragmentation mitigates this for cavity-nesting bees through increased edge habitat. 3) Landscape fragmentation alone had a relatively small effect on all responses. Instead, the local ratio of nest to foraging habitat affected bee fitness positively through reduced local competition. The spatial coverage of pollination increases steeply in response to this ratio for all bee sizes. The nest to foraging habitat ratio, a strong habitat proxy incorporating fragmentation could be a promising and practical measure for comparing landscape suitability for pollinators. 4) The number of flower visits was hardly affected by resource allocation, but predominantly by bee size. 5) In landscapes with the highest visitation coverage, bees flew least far, suggesting that these pollination proxies are subject to a trade-off between either longer pollen transport distances or a better pollination coverage, linked to how nests are distributed over the landscape rather than being affected by bee size.

Are honeybees suitable surrogates for use in pesticide risk assessment for non‐Apisbees?

“…in‐hive bees, foragers or brood, on colony survival to be modelled. Such an A. mellifera ‐centred approach should be complemented by similar in silico approaches for non‐ Apis bee populations (e g. BumbleBEEHAVE and SOLBEE) using ecologically relevant effect endpoints from A. mellifera laboratory data.…”

Wild bees of Grand Staircase-Escalante National Monument: richness, abundance, and spatio-temporal beta-diversity

“…Setting aside large interconnected areas may be especially important for maintaining bee communities, both because of the localized nature of all but a few species, and also because the floral resources on which they rely must be considered within a connected landscape matrix, rather than individually. This is further complicated by the varying life-history traits even among the dominant bees, suggesting that a multitude of resources might be needed to maintain bee communities ( Everaars, Settele & Dormann, 2018 ; Winfree et al, 2018 ; Harrison, Gibbs & Winfree, 2017 ; Nicholson et al, 2017 ; Heard et al, 2007 ; Cane et al, 2006 ).…”

Local landscapes and microhabitat characteristics are important determinants of urban–suburban forest bee communities

“…Bee species richness generally increases with habitat area (Steffan-Dewenter 2003) and is inversely related to habitat size and habitat interior-to-edge ratio (Brosi et al 2008). Spatiotemporal variation in community structure is dependent upon differences in natural history requirements across taxa as well as environmental covariates that may differentially affect species and populations (Everaars et al 2018). Smaller, cavity-nesting bees may preferentially use smaller, disturbed forests, whereas larger, ground-nesting bees may be more commonly observed in larger and lessdisturbed habitats (Wray et al 2014).…”