Abstract
Traditional productivity‐diversity theory predicts that eutrophication will result in greater species richness due to increased resources at the bottom of the food web. However, few studies on the effects of increasing ecosystem productivity on biological communities have included responses at multiple trophic levels. We hypothesized that the effect of eutrophication on species richness would vary between different trophic levels due to shifts in community composition and trophic interactions. To investigate the mechanisms driving productivity‐richness relationships, we constructed food webs for 18 streams across a eutrophication gradient on South Island, New Zealand, and measured productivity, water quality, and habitat characteristics in each stream. A principal components analysis yielded two orthogonal axes of eutrophication: one associated with macrophytes, benthic substrate, and gross primary productivity (GPP) and the other with catchment area, temperature, and algal standing stock (chlorophyll a). Surprisingly, the majority of community response variables, especially defended primary consumer abundance and biomass, were more strongly associated with the macrophyte/habitat axis. The lack of change in abundance and declines in biomass and average mass of predatory invertebrates and fish with increasing eutrophication, despite increases in prey abundance, suggest that energy was not being passed up the food chain to higher trophic levels. The predominance of defended producers (macrophytes) and consumers (snails and microcrustacea) in eutrophic streams likely served as trophic bottlenecks; both are largely inedible by higher trophic levels. Consequently, our results suggest that managers need to focus on preserving food web linkages and energy flow, as well as biodiversity, in eutrophic systems.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.