Statistical quantification of the effect of thermal stratification on patterns of dispersion in a freshwater zooplankton community |
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Authors: | Stephen J Thackeray D Glen George Roger I Jones Ian J Winfield |
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Institution: | 1. Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster, LA1 4AP, UK 2. Department of Biological and Environmental Science, University of Jyv?skyl?, PL 35, 40014, Jyv?skyl?n Yliopisto, Finland
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Abstract: | The vertical distribution of crustacean zooplankton species was examined during 2000 in Windermere, Cumbria. Patterns of dispersion
were evaluated quantitatively using two different approaches. Firstly, Morisita’s index was used to test whether patterns
of dispersion differed significantly from a state of randomness and, secondly, the relative distribution of zooplankton individuals
between the epilimnion and hypolimnion was investigated, for a series of standardised vertical profiles of organism density.
All six of the dominant species of planktonic crustaceans showed aggregated patterns of dispersion throughout the year. For
most species, patterns of dispersion were affected by the onset and breakdown of thermal stratification in the lake. The degree
of aggregation in the vertical plane, measured using Morisita’s index, increased when the lake became thermally stratified.
Furthermore, for most species, there was a positive association between the degree of vertical differentiation in abundance
across the thermocline, and the degree of temperature differentiation in the stratified water column. The results of the present
analysis provide quantitative evidence for the phenomenon known as ‘zooplankton stratification’ and for temporal variation
in patterns of zooplankton dispersion. |
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Keywords: | Morisita’ s index Plankton Spatial heterogeneity Zooplankton stratification |
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