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Chun-Wei Chang and Chih-hao Hsieh

Prof. Chih-hao Hsieh from the Institute of Oceanography, NTU and postdoc Dr. Chun-Wei Chang from the National Center for Theoretical Science lead an international team to reveal how warming influenced ecosystem dynamics via weakening the system-level causal networks associated with biodiversity. This study, published in Global Change Biology (Oct 20), provides empirical evidence for long-lasting debates about whether climate warming stabilizes or destabilizes ecosystems. Their findings provide novel mechanisms explaining how biodiversity-mediated ecosystem network stabilizes ecosystem dynamics; these findings bear important implications for ecosystem managements.

To understanding how ecosystems respond to climate changes, a network view considering interactions and feedbacks between biodiversity, productivity, and physicochemical factors is needed. This view is critical different from the traditional view that investigates individual ecosystem properties (e.g. biodiversity or environmental factors) or individual correlations (e.g. how productivity is related to nutrients).

To bridge the knowledge gap, the research team analyzed long-term time series (16-39 years) data from ten aquatic ecosystems located worldwide. They applied a novel approach, convergent cross-mapping (CCM), to reconstruct the causal networks quantifying the interactions between system-level properties, including phytoplankton diversity, biomass, and physicochemical factors. The results indicated that any single indicator (e.g., species richness or nutrient concentration) cannot predict the ecosystem stability (here, temporal variability of total phytoplankton biomass as a proxy). Rather, a causal pathway that integrates the interactions between diversity, nutrient cycling and biomass (Fig. 1) was the best indicator predicting ecosystem stability.

Interestingly, this causal pathway was weakened when ecosystems underwent more intensive warming. Moreover, this impact was found not only in the datasets from the ten monitoring systems, but also in a compiled global-scale ocean dataset, revealing a significant negative relationship between warming rate and ecosystem stability in global ocean. The results call for a more holistic network view, instead of thinking in terms of separate factors, to understand and predict climate impacts on temporal stability of ecosystems.

Figure 1. A cross-system study analyzing long-term time series data collected from 10 aquatic ecosystems revealed novel mechanisms explaining how warming destabilized the dynamics of ecosystem functioning (e.g., phytoplankton biomass). The core analysis centred on empirically quantifying causal relationships between the big-picture ecosystem variables: diversity, nutrient cycling, phytoplankton biomass and others. Systems experiencing stronger long-term warming had weakened diversity-mediated regulatory pathways, and the weakened regulatory pathways made ecosystems less stable. The findings of this study for the first time emphasize the importance of a holistic network view of ecosystems, indicating that integrated regulatory pathways, instead of individual variables or interactions, best predict ecosystem stability.

Reference:

Chang, C. W., H. Ye, T. Miki, E. R. Deyle, S. Souissi, O. Anneville, R. Adrian, Y. R. Chiang, S. Ichise, M. Kumagai, S. S. Matsuzaki, F. K. Shiah, J. T. Wu, C. h. Hsieh, G. Sugihara. (2020) Long-term warming destabilizes aquatic ecosystems through weakening biodiversity-mediated causal networks. Global Change Biology 26: 6413-6423.