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Some Properties of the Aggregations of Soil Arthropods: Collembola

M. B. Usher
Journal of Animal Ecology
Vol. 38, No. 3 (Oct., 1969), pp. 607-622
DOI: 10.2307/3038
Stable URL: http://www.jstor.org/stable/3038
Page Count: 16
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Some Properties of the Aggregations of Soil Arthropods: Collembola
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Abstract

Blocks of forty-eight small contiguous soil samples, each block being sited at random, were taken in a Scots pine (Pinus sylvestris) forest soil at Rannoch, Perthshire. An intensive study of the distribution of the Collembola within a block of samples shows three main distribution types: the uniform distribution (shown only by adults of Folsomia quadrioculata), the random distribution and the aggregated distribution, which occurred in 0.9%, 27.4% and 71.7% of blocks respectively. A co-ordinate technique for specifying the locations, number and distances between distinct aggregations is developed, and an analysis of variance technique for demonstrating gradients of numbers across a block is given. Three theories about the distinct aggregations are discussed. A Type I aggregation is characterized by having the correlation coefficient between the population density and the number of aggregates (rn) positive and significant, whilst the correlation between the population density and the mean number of insects per aggregate (rs) is either non-significant or negative and significant. Such an aggregation could result from some fixed attribute of the species such as the size of the egg cluster. It is shown by all the juveniles that have been included in the analyses (rs non-significant) and by Onychiurus absoloni, which has rs negative. A Type II aggregation is characterized by rn non-significant and rs positive and significant. It is argued that this would result from the aggregations being located either in particularly suitable ecological niches or in relation to food supply, and that the insects moved until they found such a niche. No species at Rannoch showed this aggregation type. Type III aggregations would be composite, with both rs and rn positive and significant, or neither significant. The discussion centres on the results of the six most abundant species, O. absoloni, Isotoma sensibilis, Friesea mirabilis, Folsomia quadrioculata, Tullbergia callipygos and Isotomiella minor. For each species the results from Rannoch are compared with other published results.

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