Bottom-up effects of eutrophication on insect interaction networks

• Main Author: Villa Galaviz, Edith
• Other Authors: Memmott, Jane
• Published: University of Bristol 2019
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.767972

The need to increase productivity in grasslands has led to the addition of nutrients to the point where plant species have been lost. The cascading effect of this loss on the community of associated species is not well understood. The aim of my thesis is to study how variation in soil nutrients - both natural and by the addition of fertilisers - changes plant community composition and how these changes affect the structure of plant-flower visitor networks, plant-herbivore networks and herbivore-parasitoid networks. There are three parts to my study. First, I tested if high fertility decreases insect specialization using natural variation in soil fertility and a nutrient enrichment simulation. I observed that higher nutrients led to less specialist, but more robust ecological networks in both current and simulated scenarios. In the second study, I evaluated the effects of a 27-year experiment, which added both organic and inorganic fertiliser to replicate plots, on the three types of network. Eutrophication decreased the number of forb species, and this changed the structure of the ecological networks. These changes however, took place with no change in insect species richness. Finally, I compared the performance of organic and inorganic fertilisers on the production of livestock forage alongside its impact on biodiversity, asking if there is an optimum fertilizer strategy where both livestock and biodiversity can co-exist? While there was no fertiliser treatment that had the best performance for all the variables studied, the application of farmyard manure offered the closest to a win-win scenario. Looking forward, to evaluate the consequences of eutrophication and achieve sustainable production in grasslands, an interdisciplinary approach is needed where ecologists and livestock managers work closely together to identify management solutions acceptable to both.