Systematic loss in biotic heterogeneity but not biodiversity across multiple trophic levels in Erhai lake, China.

Anthropogenic disturbances and climate change have significantly altered the biotic composition across many ecosystems, leading to changes in biodiversity and even ecological collapse. An ecosystem comprises multiple trophic levels, and the issue how these disturbances affect their assembly processes remains unclear. Ecological stability of assemblages was maintained by their structure, and thus, revealing structure changes across trophic levels could improve our understanding of how ecosystems response to disturbances as a whole. In this study, we combined methods from palaeolimnology, ecology and network analysis, and observed the changes of biodiversity and network structure of two trophic levels (algae - diatoms and zoobenthos - chironomids) in Erhai lake, Southwest China over the last century. Results showed nutrient enrichment induced shifts in diatom and chironomid assemblages at ∼2001 CE, suggesting that the shift in Erhai lake may have occurred at multiple trophic levels. We found biodiversity exhibit different trends across trophic levels as it decreased in diatoms but increased in chironomids. However, network skewness declined in both trophic levels, indicating the common loss of biotic heterogeneity. The consistent decline of skewness among trophic levels long before the compositional shift is a potential parameter to warn of the shifts in lake ecosystems.