Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 53. (Budapest 1961)

Pócs, T.: The calculation of the quantitative grade of efficacy of collecting and extracting methods of materials used in zoocoenology

ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Tomus 53. PARS ZOOLOGICA 1961. The Calculation of the Quantitative Grade of Efficacy of Collecting and Extracting Methods of Materials Used in Zoocoenology By T. Pócs, Budapest It is one of the requirements of zoocoenological investigations that, if possible, every individual of a given animal group be registered within the debmited sample area. Unfortunately, the ideal target can be reabzed but partly, because the several collecting and extracting (selective) methods never furnish us with quantitatively absolute results, and thus there is always a certain percent of error. However, if the grade of efficacy of the various extracting methods (selective processes during collecting or on collected samples) could be calculated, we might advance substantially. By its aid namely, we may on the one hand select a method affording the best grade of efficacy, — therefore the most exact one to furnish us with the greatest quantitative results (not unimportant from also the point of view of collection augmentation) — and on the other, if we calculate the grade of efficacy of the several extracting methods appbed for the various groups of animals, the grade will yield a constant value for the given group and method, debvering thereby a medium to receive more exact results. All these problems arose anew when I began to experiment with the very effective floating method worked out byj. Vágvölgyi for mollusks (Vágvölgyi 1952). Instead of „nemit" (aryl-alkyl-sulphonate) used in floating, I serached for a cheaper and more easily obtainable surface tension reducing material. The use of the well-known fatty-alcohol-sulphonate was obvious, since, due to its very tension-reducing property, it is the main basic material of modern washing substances. It had to be established therefore whether, similarly to nemit, it were to yield satisfactory results in the sorting out of the materials by the floating method.* The calculation of the grade of efficacy did not seem to be an easy task, since, whatever control method be used to find out the grade of efficacy of a certain method, the control method itself is of an unknown efficaciousness, so that a simple control will almost always render imperfect results. For the solution of the problem, I started from the assumption that if the living beings be selected or sifted from a biotop or a sample by the application of a selecting method of an unkown degree of efficacy, and then if the process be repeated on the biotop or on the residue of the mass, a certain number of individuals will be received on both occasions. The ratio of the two values will depend on the grade of efficacy of the given method. Let the total amount of individuals in the sample be designated S. The unknown efficacy grade-constant of the method is x. Accordingly, the first extraction will result in an Sx number of individuals. There remained in the sample an amount of S — Sx individuals. If this sample residue be selected again by a method of an x grade of efficacy, the second occasion will result in an (S — Sx) x amount of individuals. Let the quotient of the numbers of individuals gained by the second and the * Hereby I offer my expression of thanks to Miss Gizella Gelencsér and to Mr. doc. Imre Loksa for their advices.