Network parameters quantify loss of assemblage structure in human-impacted lake ecosystems

Abstract

Lake biodiversity is an incomplete indicator of exogenous forcing insofar as it ignores underlying deformations of community structure. Here we seek a proxy for deformation in a network of diatom assemblages comprising 452 species in 273 lakes across China. We test predictions from network theory that nodes of similar type will tend to self-organise in an unstressed system to a positively skewed frequency distribution of nodal degree. The empirical data reveal shifts in the frequency distributions of species associations across regions, from positive skew in lakes in west China with a history of low human impacts, to predominantly negative skew amongst lakes in highly disturbed regions in east China. Skew values relate strongly to nutrient loading from agricultural activity and urbanisation, as measured by total phosphorus in lake water. Reconstructions through time show that positive skew reduces with temporal intensification of human impacts in the lake and surrounding catchments, and rises as lakes recover from disturbance. Our study illustrates how network parameters can track the loss of aquatic assemblage structure in lakes associated with human pressures.

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Identifiers

ORCID for John Dearing: orcid.org/0000-0002-1466-9640

ORCID for Charles Doncaster: orcid.org/0000-0001-9406-0693

ORCID for Peter Langdon: orcid.org/0000-0003-2724-2643

ORCID for Yanjie Zhao: orcid.org/0000-0001-9307-8138

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