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Contrasting effects of producer and consumer resource use efficiency on trophic asynchrony and stability of food web under multiple stressors
Summary
A six-month mesocosm experiment exposed freshwater food webs to multiple simultaneous stressors — including microplastics, nutrient pollution, dissolved organic carbon, and invasive fish — and found that microplastics and other stressors reduced phytoplankton diversity and food web stability through complex pathways involving how efficiently organisms use resources. Notably, greater producer diversity did not always stabilize consumer communities, challenging the assumption that biodiversity uniformly buffers ecosystems. This highlights that microplastic pollution, combined with other human pressures, can destabilize aquatic food webs in ways that simple single-stressor studies would miss.
The ongoing global biodiversity loss caused by multi-stressors has raised concerns about the potential consequences of species extinctions on the functionality and stability of ecosystems. It has been widely recognized that biodiversity could stabilize the ecosystem by enhancing the asynchronous dynamics among species within a single trophic level. However, in natural multi-trophic ecosystems, asynchronous changes between trophic levels (trophic asynchrony) are expected to increase trophic mismatch and alter trophic interactions, which may consequently alter ecosystem stability. Under changeable environments, it is currently unclear how biodiversity in different trophic levels affects the stability of food web by changing the trophic interactions (represented by resource use efficiency, RUE) and trophic asynchrony, which is key to providing further insights into the biodiversity effects on ecosystem stability. Using a 6-month mesocosm experiment, we tested how multi-stressors—microplastics, eutrophication, dissolved organic carbon, and invasive fish—affected species richness and RUE of phytoplankton (producer) and zooplankton (consumer), subsequently influencing temporal stability of food web via altering the trophic asynchrony. Our results demonstrated that multi-stressors could shape ecosystem temporal stability through species richness-RUE-trophic asynchrony pathways, emphasizing the cascading impacts of multi-stressors on ecosystem functions and stability. Increasing species diversity of phytoplankton and zooplankton enhanced the RUE within that trophic level. However, greater producer diversity decreased RUE of consumers, probably due to an increase in inedible producer species. This suggests that benefits of biodiversity of producer could diminish functions at higher trophic levels. In addition, zooplankton RUE increased trophic asynchrony, whereas phytoplankton RUE decreased it. Crucially, trophic asynchrony stabilized phytoplankton and food web but destabilized zooplankton community, highlighting contrasting impacts of trophic asynchrony on stability across trophic levels. Our study showed that producer diversity may indirectly decrease the functions and stability of consumers under multiple stressors, which challenged the simplistic expectation that more diversity universally stabilized ecosystems. This study provided a new insight into the biodiversity-ecosystem stability relationships by highlighting the mediating roles of RUE and trophic asynchrony under realistic environmental change scenarios.
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