Temporal variance of disturbance did not affect diversity and structure of a marine fouling community in north-eastern New Zealand
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Natural heterogeneity in ecological parameters, like population abundance, is more widely recognized and investigated than variability in the processes that control these parameters. Experimental ecologists have focused mainly on the mean intensity of predictor variables and have largely ignored the potential to manipulate variances in processes, which can be considered explicitly in experimental designs to explore variation in causal mechanisms. In the present study, the effect of the temporal variance of disturbance on the diversity of marine assemblages was tested in a field experiment replicated at two sites on the northeast coast of New Zealand. Fouling communities grown on artificial settlement substrata experienced disturbance regimes that differed in their inherent levels of temporal variability and timing of disturbance events, while disturbance intensity was identical across all levels. Additionally, undisturbed assemblages were used as controls. After 150 days of experimental duration, the assemblages were then compared with regard to their species richness, abundance and structure. The disturbance effectively reduced the average total cover of the assemblages, but no consistent effect of variability in the disturbance regime on the assemblages was detected. The results of this study were corroborated by the outcomes from simultaneous replicate experiments carried out in each of eight different biogeographical regions around the world.
We thank L. Benedetti-Cecchi (University of Pisa) for helping with the experimental design and data analysis; W. Nelson (National Institute of Water and Atmospheric Research), D. G. Fautin (University of Kansas), V. Pearse (American Microscopical Society) and J. Buchanan (Victoria University of Wellington) for helping with the taxonomic identification. Thanks to Chloe Rich (University of Wollongong), Carmen Kamlah (University of Rostock), Tiago Porto (Universidade Federal Fluminense) and Mauricio Cifuentes (Universidad Católica del Norte) for helpful discussions. This study was part of the international research project GAME (Global Approach by Modular Experiments), funded by Stiftung Mercator.
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