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Trophic pyramids reorganize when food web architecture fails to adjust to ocean change

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Science  14 Aug 2020:
Vol. 369, Issue 6505, pp. 829-832
DOI: 10.1126/science.aax0621

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Inflexible webs

It is clear that human activities are negatively affecting current ecosystems. Predicting how our activities will affect future systems is more challenging because it involves estimating the unknown. Nagelkerken et al. overcame some of these unknowns by constructing small versions, or mesocosms, of a marine ecosystem that included species representing all trophic levels (see the Perspective by Chown). They then exposed these systems to predicted future levels of carbon dioxide and acidification. The trophic structure was relatively resistant to acidification but not to warming. Warmed systems experienced a reorganization of trophic structure that was not rescued by functional redundancy or other stabilizing responses. Such inflexibility may be a precursor of ecosystem collapse.

Science, this issue p. 829; see also p. 770

Abstract

As human activities intensify, the structures of ecosystems and their food webs often reorganize. Through the study of mesocosms harboring a diverse benthic coastal community, we reveal that food web architecture can be inflexible under ocean warming and acidification and unable to compensate for the decline or proliferation of taxa. Key stabilizing processes, including functional redundancy, trophic compensation, and species substitution, were largely absent under future climate conditions. A trophic pyramid emerged in which biomass expanded at the base and top but contracted in the center. This structure may characterize a transitionary state before collapse into shortened, bottom-heavy food webs that characterize ecosystems subject to persistent abiotic stress. We show that where food web architecture lacks adjustability, the adaptive capacity of ecosystems to global change is weak and ecosystem degradation likely.

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