Species richness and food-web structure jointly drive total biomass and its temporal stability in fish communities

Alain Danet, Centre d'Écologie et des Sciences de la Conservation, Museum National d'Histoire Naturelle, Paris, France, Maud A. Mouchet, Centre d'Écologie et des Sciences de la Conservation, Muséum National d'Histoire Naturelle, Paris, France, Willem Bonnaffé, Ecological and Evolutionary dynamics lab, Oxford Université, Paris, France, Élisa Thébault, Institute of Ecology and Environmental Sciences of Paris, Sorbonne Université, CNRS, IRD, INRAE, Université Paris Est, Créteil, Paris, France and Colin Fontaine, Centre d’Ecologie et des Sciences de la Conservation, Muséum national d’Histoire naturelle, Paris, France

Background/Question/Methods
Biodiversity-ecosystem functioning (BEF) and food-web complexity-stability
relationships are central to ecology. However, they remain largely untested in
natural context. Here we study the links among environmental conditions,
richness, food-web structure, annual biomass and its temporal stability using a
standardized monitoring dataset of 99 stream fish communities spanning from 1995
to 2018.
Results/Conclusions
We first reveal that both richness and average trophic level are
positively related to annual biomass, with effects of similar strength. Second,
we show that food-web structure affects community stability, with a positive
effect of mean trophic level, and contrary to expectation, a destabilizing
effect of species richness. Finally, we find that environmental conditions
affect both biomass and its stability via effects on richness and network
structure. Strikingly, effects on stability are mediated by changes in
population stability rather than synchrony, which contrasts with results from
single-trophic communities and might be characteristic of multi-trophic
communities.