Connectivity mediates the spatial ecological impacts of a glyphosate-based herbicide in experimental metaecosystems

Abstract

Connectivity is important for the structure and functioning of metaecosystems. We experimentally replicated metaecosystems in the laboratory using gradostats - a modified chemostat with flasks linked by a controlled flow of medium - as a model system. Metaecosystems were represented in our experiment as chain of flasks connected by spatial flows of medium containing glyphosate based herbicide (RoundUp). With this experimental set-up, we tested the effects of structural and functional connectivity and herbicide on phytoplankton productivity, diversity and population stability. Gradostats were composed of interconnected equally-spaced habitat nodes where resources and producers flow directionally along a gradient of increasing distance from the source of the herbicide. We predicted that connectivity would mediate the effects of the herbicide spreading through the chain of connected ecosystems. We found that RoundUp impacted overall phytoplankton productivity and diversity by reducing algal biomass and species-level abundances of phytoplankton in the treated flasks compared to controls. This effect was mediated by structural connectivity, which in interaction with flow, had reduced phytoplankton community stability by the end of the experiment at the local level, especially in the first flask receiving herbicide. The effects did do not scale up to the entire metaecosystem. Together, these results point to the importance of structural connectivity as a mediator of the ecological effects of herbicide transferred by flows across a linear chain of ecosystems.