The Community of Invertebrates in Decaying Oak Wood

This paper is concerned with the community of invertebrates living in small decaying oak logs on the forest floor. The reactions of species' populations to various factors inside and outside the logs were determined by the use of `synthetic logs', models of the habitat whose initial characteristics were known. Comparison of the results from these models with those from natural logs indicates that the former were good substitutes. Forty-five of the 108 species considered showed significant differences in abundances associated with one or more features of the environment. Some of these were expected on the basis of prior knowledge of the species' ecology, others suggest reactions that merit further study. The presence or absence of a reaction was not predictable from knowledge of a species' frequency, median abundance or taxonomic group. The recurrent grouping procedure indicated a major group that may be considered the basic fauna of small decaying oak logs. Smaller groups are added to this, depending on the specific environmental and log characteristics. Although there was a great diversity of dominant species, all the log populations had similar structure. The average synthetic log contained 900 individuals distributed among forty-one species as follows: two species contributed 50% of the individuals (A), three species contributed an additional 25% (C), twenty-four species had two to seventy-four individuals and the remaining twelve species were represented by single individuals (S). Forty-six of the 108 species were at least once in classes (A) or (C) but none was always in this class and only four of these were never in (S). The structure was successfully simulated by a computer model that assumed that frequency is a measure of the probability that a species will invade a log, that rates of increase can be derived from maximum numbers observed per log and that invasion and establishment are random processes.