PS 8-104 - Biodiversity ecosystem function relationships across space in the context of degradative function in North American pitcher plants

Abstract: Biodiversity-ecosystem function (BEF) theory traditionally posits that increased biodiversity correlates with increased ecosystem functioning, explained by mechanisms such as positive selection and complementarity. However, there are other possible outcomes such as, functional redundancy and negative selection; which has been hypothesized to be common in metabolic nutrient breakdown. Importantly, studies have traditionally considered these biodiversity-ecosystem function relationships to be fixed across spatial scales, and considering a dynamic BEF in space may broaden our understanding of functional consequences of community diversity and composition. The aim of this study is to determine differences in the BEF relationship in two carnivorous pitcher plants species growing in separate coasts in North America. Pitcher plants are well suited as a system to explore BEF relationships because their pitcher-shaped fluid-filled leaves represent a replicable microbial community with a specified function: prey degradation. Across this spatial scale, several mechanisms can result in different BEF relationships, namely differences in species richness, functional redundancy, habitat filtering, diet breadth, and environmental conditions. We collected fluid from Darlingtonia californica in Gasquet, CA and Sarracenia purpurea in Petersham, MA and conducted a dilution to extinction experiment testing prey degradation. Results displayed differences in BEF relationships with S. purpurea microcosms showing functional redundancy and D. californica showing a negative BEF relationship. We compared site specific environmental and plant associated parameters and discussed relevant mechanisms driving these differences, such as colonist pool, site specific water flow, and diet breadth. Additionally, we determined which taxa are more likely involved in degradation by analyzing bacterial relative abundance data. Different taxa provide essential functions for each pitcher plant species. Although we cannot fully distinguish between BEF that covary across our sites, we demonstrate that neutral to negative BEF relationships may be more common across ecological space than previously assumed.