How many is enough? Determining optimal count totals for ecological and palaeoecological studies of testate amoebae |
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Authors: | Richard J Payne Edward A D Mitchell |
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Institution: | 1.Geography, School of Environment and Development,The University of Manchester,Manchester,UK;2.WSL Swiss Federal Research Institute, Ecosystem Boundaries Research Unit,Wetlands Research Group,Lausanne,Switzerland;3.Ecole Polytechnique Fédérale de Lausanne, Laboratory of Ecological Systems,Lausanne,Switzerland |
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Abstract: | Testate amoebae are increasingly used in ecological and palaeoecological studies of wetlands. To characterise the amoeba community
a certain number of individuals need to be counted under the microscope. To date, most studies have aimed for 150 individuals,
but that sample size is not based on adequate evidence. When testate amoeba concentrations are low, it can be difficult or
impossible to reach this total. The impacts of lower count totals have never been seriously scrutinised. We investigated the
impact of count size on number of taxa identified, quantitative inferences of environmental variables and the strength of
the links between amoebae and environmental data in the context of predicting depth to water table. Low counts were simulated
by random selection of individuals from four existing datasets. Results show progressively diminishing returns by all criteria
as count size increases from low numbers to counts of 150. A higher count is required to identify all taxa than to adequately
characterise the community for transfer function inference. We suggest that in most cases, it will be a more efficient use
of time to count a greater number of samples to a lower count. While a count of 50 individuals may be sufficient for some
samples from some sites we recommend that counts of 100 individuals should be sufficient for most samples. Counts need only
be increased to 150 or more where the aim is to identify relatively minor, but still potentially ecologically relevant community
changes. This approach will help reduce lack of replication and low resolution, which are common limitations in testate amoeba-based
palaeoecological and ecological studies. |
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