Studies on soil animals in a remote region of Amazonia : particularly in relation to population assessment using field extractors.

Sortwell, Andrew (1984). Studies on soil animals in a remote region of Amazonia : particularly in relation to population assessment using field extractors. BPhil thesis The Open University.



This study was undertaken whilst leading expeditions to the Amazon in 1978 and I981.
Laboratory and field methods of extracting invertebrates in soil are reviewed so as to highlight the problems inherent in collecting soil animals in remote regions. The main problem is to find an efficient, portable extraction unit that will provide reliable population estimates suitable to the environment under study.
Following a detailed analysis of available literature it was decided to test a chemical extraction unit using turpentine as a repellent. This was a modification of Lewis’s extraction unit (1970) which was successfully used to repel thrips from flower heads. A trial comparison of the chemical extractor with a dry Tullgren technique using soil samples from temperate oak woodland showed that there was insufficient difference between the results to demonstrate the unsuitability of either technique.
However, when the two techniques were compared with soil samples from tropical rain forest in Amazonia, the dry Tullgren funnel collected more species than the chemical unit. Further, the dry Tullgren funnel results suggested a much higher and more realistic soil animal population estimate than the chemical extractor which in turn was more efficient than a hand-sorting technique.
The literature on tropical soil animal studies is reviewed. A comparative study of the soil animals living in a cultivated field and tropical rain forest soil was undertaken using a chemical extractor. The inefficiency of this type of extractor renders the results inconclusive. The evidence does however suggest that the efficiency of the chemical extractor improved when repelling animals from the drier soil collected at the cultivated field.
Though the Tullgren funnel was more efficient in isolating organisms and the number of species was greater, the chemical extraction unit was a simpler method and still produced a number of different species so could be a useful and more easily managed tool for taxonomic investigations in remote areas.
A limited number of soil cores collected two days after burning a cleared rain forest site demonstrated that the site still contained soil animals albeit in greatly reduced numbers.
A modification of a type of corer used by Fletcher (1976) is described. This proved to be easily portable yet robust.

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