How many is enough? Determining optimal count totals for ecological and palaeoecological studies of testate amoebae

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

Storminess as an explanation for the decline of pine woodland ca. 7,400 years ago at Loch Tulla, western Scotland

Pinus wood remains some 7,400 years old are abundantly preserved near the base of eroding peat at Clashgour, west of Loch Tulla on Rannoch Moor in western Scotland. Measurements are presented of the orientations of root systems in 42 in situ stumps, the direction of fall in 27 fallen trunks and the orientation (where direction of fall cannot be defined) in 40 fallen trunks. There are statistically significant orientations in the root systems, which suggests that the root structure of the trees had responded to stress from westerly winds. However, despite this the orientations and directions of fall in tree trunks, also statistically significant, show that many trees were probably blown over by strong westerly winds. The data suggest that increased precipitation and accelerated paludification are less likely explanations for tree loss at this site than a sudden demise through wind-throw