Disentangling the effects of climate change in a mountain lake through community structure analysis

Pressures of climate change may trigger regime shifts in ecosystems. Identifying signs of these pressures before the critical transition remains challenging, and it could be useful to anticipate the regime shift. In this research, while exploiting the case of a lacustrine ecosystem, which passed from an unvegetated, phytoplankton-dominated state to a macrophyte-dominated regime, we analyzed the role of warming as a slow driver when far from the regime shift. To this end, we combined the analysis of the time series of the driver of pressure and of the response variables with the qualitative analysis of the lake community food web structure. Predictions obtained about the response of plankton populations to simulated press perturbations due to warming were consistent with observed variation in their levels of abundance, confirming that warming was a slow driver and unveiling the mechanistic basis of its effects. This case study suggests a novel approach to interpret early changes in ecosystems subjected to slow drivers of pressure, extending the toolkit beyond the analysis of statistical signature and manipulative experiments. Climatic variations gradually alter the external conditions that ecosystems face, and the approach presented here could help monitor their responses to climate change.