Abstract
Insects are keystone species as they provide vital pollination services. Among the most cited drivers of insect decline worldwide are landscape homogenization, spread of introduced pathogens, use of pesticides, ongoing climate change and, most importantly, the loss of floral resources. Therefore, current environmental strategies to mitigate insect loss mainly advocate enhancing the floral resource abundance. However, whereas the primary focus now lays on increasing the quantity of food provisioning, maintaining sufficient food quality may be equally, or perhaps even more important for conservation. The quality of floral resources is primarily contingent upon the composition and relative abundance of nutrients such as nitrogen, phosphorus and base cations, sugars (mainly sucrose, fructose and glucose) and proteins and amino acids in both plant tissue and nectar and pollen. One of the primary environmental factors that can affect the nutritional quality of floral resources is plant nutrient availability, as it strongly affects plant physiological processes. However, nutrient pollution of natural and semi-natural ecosystems currently constitutes one of the most important components of global change worldwide, which is reflected by an approximate respective 100% and 400% increase of reactive nitrogen and phosphorus fluxes in global nutrient cycles.
In an era of ever increasing nutrient pollution, this research proposal will focus on the specific contribution of different types of nitrogen pollution on the current biodiversity crisis. This research proposal is original in its focus on the link between nitrogen pollution and host plant quality, studying the underexplored hypothesis that degradation of plant resource quality may contribute to the widely observed insect decline. Further unique novelties include experimentally disentangling direct and indirect effects of nitrogen pollution and its common mitigation strategies in nature restoration and disentangling effects of pollution with reduced (mainly originating from agriculture) versus oxidized (mainly originating from combustion processes) nitrogen compounds via experiments and large-scale observational evidence across Europe (>25 000 standardized observations in >10 countries). We also aim to identify, for the first time, species-specific critical thresholds of pollution with oxidized and reduced nitrogen across taxonomic groups. This novel evidence may have far reaching ramifications for environmental policy regarding nitrogen that currently does not discriminate among reduced versus oxidized compounds for biodiversity conservation. To obtain these goals, we will use host plants and butterflies as model species as they have been proven to be very sensitive to environmental changes and relatively easy to use in experimental designs.
The general objectives of this research proposal are to quantify the effects of nitrogen pollution on plant resource quality on the one hand, and to evaluate the subsequent effects on the behavior and fitness of phytophagous butterflies, on the other. Furthermore this proposal aims to disentangle the primary effects of nitrogen pollution from secondary, potentially confounding effects of nature restoration methods to mitigate nitrogen pollution. The general expectation is that the nutritional quality of plant resources is affected by nitrogen pollution and, in turn, negatively affects butterfly fitness and behavior. We also expect that current nitrogen pollution mitigation strategies also negatively affect butterflies, potentially compounding the general decline of insects. Finally, we expect that the experimentally determined relative contribution of both drivers will be reflected in large-scale observations of species decline and that these insights will lead to novel environmental policies and nature restoration strategies to mitigate biodiversity loss.
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