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

first selections be designated A. This is a known factor, obtainable by experiments : When X is expressed from this, the final formula is : x = 1 — A, which is the unknown constant of the grade of efficacy of the method. In other words : the grade of efficacy of an extracting method, repeatable on identical materials (that is, biotop-portion) and in identical conditions, can be received if the number of specimens gained in the course of the second extraction is divided by the number of specimens gained in the course of the first extraction, and if the quotient is subtratcted from 1. This calculation may be applied to cases where the conditions between the two phases of extractions do not differ substantially, because then the grade of efficacy will not change either. This also means that the first extraction cannot be of a nature to exclude repetition. Its scope of application may, for instance, be the manual, one-by-one selection of materials received by sifting, or the calculation of the grade of efficacy of sweep-netting in the grass. It goes without saying that, in the case of such methods depending on individual abilities, the same person should do also the repetitions, since the efficacy-grade constant received on such occasions is but referable to the given person. For mechanical methods, the value of the constant is naturally independent of any person. Also, it is essential that the process be repeated in the same area, that is, on the same material, within a short time, and if possible, immediately. The above calculation cannot be applied in cases where the extraction of the material cannot be repeated in identical conditions. For example, in extracting by desiccation, the material will dry up in the course of the first extraction the majority of the animals still hiding in the mass will perish orbe temporarily incapable of movement. And, in the case of methods which yield their animal material by being based on differences in specific gravities, we shall fail to receive, on the first occasion, individuals which, due to some cause, are heavier than the others (injured, soiled specimens or ones which adhere to, or are filled with, particles of earth), while, on the second occasion, we are confronted by mainly these very same individuals, and the identical method for these specimens of a greater specific gravity is of a much poorer, or even 0, grade of efficacy. It was therefore necessary to work out, for such cases, a calculation in which two collecting, that is, selective methods, never influencing each other and of entirely different grades of efficacy, are combined. One should perform the extraction of the individuals by the two subsequent methods on one part of the material, the in a reverse order on any or the other part of the material. The identical size of the two materials or habitat areas is not important, it is more essential that the two parts of the material be of a similar nature or composition. In the field, therefore, a homogenous area of the biotope must be divided into two arbitrary portions, while, in the selecting of a collected material, it must first be homogenized before dividing it, or, as the case may be, two adjacent samples must be taken during collecting. (Even this method is unapplicable, however, if it is impossible to fix during investigation the area or size of the object, e. g. : when working with light-traps or traps placed in the soil level, or if the