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Measures of central tendency of aquatic habitat parameters: application to river macrophyte communities\ud

By Krzysztof Szoszkiewicz, Dariusz Kayzer, Ryszard Staniszewski and Hugh F. Dawson

Abstract

The aim of this paper is to assess\ud usefulness of different measures when determining\ud central tendencies which characterise the\ud environmental requirements of living organisms.\ud Mathematical analyses were made of the environmental\ud parameters of river macrophyte communities\ud which were taken as a representative\ud pattern of different levels of biological structures.\ud To deliver a representative dataset, botanical surveys\ud were carried out on a range of British rivers\ud together with environmental assessment and the\ud plant communities groups were identified based\ud on characteristic species according to eslished\ud phytosociological criteria. The mean values and\ud standard univariate medians of the revealed associations\ud were compared with means calculated\ud on the basis of advanced transformation and also\ud with the rarely calculated multivariate L median.\ud Due to high variance and asymmetrical distribution,\ud the analyses based on the mean-value appeared\ud to be limited in application. To avoid this\ud disadvantage transformation to obtain normality\ud of the dataset standardisation was proposed\ud although even this did not fully reach a satisfactory\ud symmetry. It was concluded that each environmental\ud variable for each single biota must be\ud individually treated by a suile transformation to\ud obtain approximately normal distributions. The\ud univariate median was very resistant to the effects\ud of outliers but gave a flattened output of the\ud environmental dataset making the partitioning of\ud biological units very difficult. The multivariate L\ud median appeared to be unaffected by outliers. It\ud enabled to obtain considerable ordering of communities\ud against individual environmental parameters\ud without data transformation

Year: 2010
OAI identifier: oai:nora.nerc.ac.uk:12256
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