Soil eutrophication shaped the composition of pollinator assemblages during the past century

Abstract

Atmospheric nitrogen deposition and other sources of environmental eutrophication have increased substantially over the past century worldwide, notwithstanding the recent declining trends in Europe. Despite the recognized susceptibility of plants to eutrophication, few studies evaluated how impacts propagate to consumers, such as pollinators. Here we aim to test if soil eutrophication contributes to the temporal dynamics of pollinators and their larval resources.We used a temporally and spatially explicit historical dataset with information on species occurrences to test if soil eutrophication, and more specifically nitrogen deposition, contributes to the patterns of change of plant and pollinator richness in the Netherlands over an 80 yr period. We focus on bees and butterflies, two groups for which we have good knowledge of larval resources that allowed us to define groups of species with different nitrogen related diet preferences. For each group we estimated richness changes between different 20-yr periods at local, regional and national scale, using analytical methods developed for analyzing richness changes based on collection data.Our findings suggest that the impacts of soil eutrophication on plant communities propagate to higher trophic levels, but with a time-lag. Pollinators with nitrogenrelated diet preferences were particularly affected, in turn potentially impairing the performance of pollinator-dependent plants. Pollinator declines continued even after their focal plants started to recover. In addition, our results suggest that current levels Research 210 of nitrogen deposition still have a negative impact on most groups here analyzed, constraining richness recoveries and accentuating declines.Our results indicate that the global increase in nitrogen availability plays an important role in the ongoing pollinator decline. Consequently, species tolerances to soil nitrogen levels should be considered across all trophic levels in management plans that aim to halt biodiversity loss and enhance ecosystems services worldwide.

Wildlife conservation strategies should incorporate both taxon identity and geographical context ‐ further evidence with bumblebees

“…We first performed a principal component analysis to visually investigate potential clustering of some species based on the relative importance of environmental variables in each species distribution model. Because population trends, both at the local and global scales, could be impacted by the environmental requirements of species (Carvalheiro et al., 2020), we investigated the relation between the cumulative importance of the four climatic variables in the species distribution models (hereafter referred to as the “total contribution of climatic variables”) and three species‐specific characteristics: (a) the species population trend status, (b) the species conservation status and (c) the species range size (which was approximated by computing the area of the minimum convex hull polygon built around all occurrence records for the considered species). Population trend and conservation statuses were obtained from the International Union for Conservation of Nature (IUCN) database of Red List of Threatened Species database (https://www.iucnredlist.org; Nieto et al., 2014).…”

The role of soils on pollination and seed dispersal

“…Even in regions where plant richness is recovering (e.g. northwest Europe), increases of species are dominated by nitrophilous plants, benefitting only those pollinators that are able to make use of such species [21]. Other important macronutrients (phosphorus, potassium, calcium) may also affect flower availability, but are still poorly studied.…”

“…Similarly, some vertebrate dispersers benefit from soil nutrient enrichment, while ant dispersers seem more frequent on infertile soils [16,19]. Diet preferences may partly explain such variability in species responses [20,21], which effects scale up to shape communities (e.g. increased dominance [18], reduced density and richness [21][22][23] and changes in overall interaction network patterns [24]).…”

“…Diet preferences may partly explain such variability in species responses [20,21], which effects scale up to shape communities (e.g. increased dominance [18], reduced density and richness [21][22][23] and changes in overall interaction network patterns [24]). Understanding the mechanisms that mediate the propagation of soil changes to pollinators and seed dispersers is essential to improve our ability to predict impacts of ongoing environmental changes and define adequate conservation plans.…”

Temperature drives variation in flying insect biomass across a German malaise trap network

“…Changing land cover due to human activities is also a major threat to insects (Wagner 2020), with wide-ranging impacts from loss of resources and nesting locations at local scales, to fragmented habitats at larger scales (Newbold et al 2020). Heavily human modified landscapes come with associated pressures, such as eutrophication and pesticide use with agricultural intensification (Goulson et al 2018, Carvalheiro et al 2020, and light pollution from urban environments (Owens et al 2020). Urban land cover can result in declines of both insect diversity (Fenoglio et al 2020, Piano et al 2020, and biomass (Macgregor et al 2019, Svenningsen et al 2020.…”