Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 75. (Budapest 1983)
Rajczy, M. ; Padisák, J.: DIVDROP analysis - a new method for the interpretation of species importance in diversity changes
ANNALES HISTORICO-NATURALES MUSEI NATION ALIS HUNGARICI Tomus 75. Budapest, 1983 p. 97-105. DIVDROP analysis - a new method for the interpretation of species importance in diversity changes by M. RAJCZY & J. PADISÁK, Budapest Abstract — With the aid of a new method named DIVDROP, the process of changes in diversity can be analysed as a trend. The importance of the species can be estimated in shaping the great changes in the value of the diversity. The method is demonstrated on two vegetational examples : 1. on algological samples taken in 30 consecutive days from Lake Balaton and 2. on 20 consecutive relevés of Salvio-Festucetum along a forest road. In both cases a large proportion of diversity changes proved to be satisfactory explained by using the DIVDROP method. A computer programme written in FORTRAN-IV language is part of the BP programme package of the Hungarian Natural History Museum. With 12 figures. Introduction — Any student working on diversity studies of communities often speculates on the problem why the value of diversity is so high or low and what species are more or less important in forming it. The question arises mainly in cases where the individuals (relevés, samples, etc.) are part of some kind of series (time series ; a row of sampling plots or quadrates ; sampling plots or quadrates along any kind of gradients, etc.). In studies like these diversity often has a characteristic trend along the series, with the existence of local maxima and minima. One would like to answer the question whether there are a few (mainly one or two) species responsible to various extent for this trend or not. To solve these problems we propose a new method, the DIVDROP analysis. The DIVDROP method The method itself can be adapted to any weighted measure of diversity (cf. PIELOU 1975), though we have used the Shannon index with a logarithm based to 2. This index has a lot of advantages and is widely used (cf. HAJDU 1977, 1978). The essence of the method is that we remove the data of the species to be analysed from the whole matrix of data and calculate the diversity values again. If we compare these values with the original values of diversity we will get useful information about the importance of the given species. In symbols: (SHANNON 1948) where O; is the quantity (cover, number, biomass, etc.) of the i-th species ; s is the number of species in the individual; and This way the resulting "reduced" diversity will be: where H"red k is the "reduced" diversity omitting the k-th species. A computer programme was written in FORTRAN-IV language to implement this analysis. The programme, named DIVDROP, has been incorporated into the BP programme package of the Hungarian Natural History Museum which runs on the CDC-3300 machine of the Hungarian Academy of Sciences under Master 4.1. Annls hist.-nat. Mus. natn. hing., 75, 1983
