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

a) Species having a general positive effect on diversity along the relevé series but not on its trend (i. e. removing data of a species of this kind from the data matrix will cause a small decrease uniformly in most of the relevés). There was only one species of this type (Fig. 11). b) Species having a local positive effect (i. e. omitting a species of this kind the diversity will decrease uniformly in a little sequence of relevés). Five species belonged to this group. c) Species having a positive effect mainly in the small salient diversity values deviating from the trend (Fig. 5 — relevés 7, 10 and 13), i. e. these species are responsible for such deviant diversity values. This group consisted of two species, one example is given in Fig. 12. Having analysed the diversity of the relevé series in question it can be stated (1) two species were responsible for the characteristic trend of diversity along the relevé series: the members of the abovementioned group A. Festuca pseudodalmatica caused the local minimum at the middle of the relevé series; the Brachypodium species was responsible for the minimum at the end ; the DIVDROP plots are well correlated with the quantity (coverage) of these species (Figs 9, 10); (2) some values deviating from the trend can be explained by the effect of the members of group B. c; (3) local minima in relevés 6, 14, 18—19 were due to the low species number (Fig. 8). (4) six from the 10 species selected had no systematic effect on the diversity of the relevé series, therefore they are of no interest in a study like this. Discussion — Diversity of communities (individuals) consists of two components : species number (number of attributes) and evenness. In certain cases species number (as it might be an index of diversity as well) can give an explanation as to the diversity trend itself. If it is not the case, we must analyse the second element, evenness. DIVDROP can be put to this purpose. This method proved to be satisfactory for explaining certain diversity patterns of individuals consecutive in any way. However, sometimes DIVDROP cannot prove the effect of some species occuring in the individuals. In these cases either species number may have an own trend with a more or less uniform evenness or the diversity trend may be influenced by not a few but many species. References HAJDÚ, L. (1977): Algal species diversity in two eutrophic fishponds I. Species-individual level. — Acta bot. hung., 23: 42-53. HAJDU, L. (1978): Algal species diversity in two eutrophic fishponds II. Other than species-individual levels. — Acta bot. hung., 23: 335-351. LYNCH, H. & SHAPIRO, J. (1981): Prédation, enrichment and phytoplankton community structure. — Limnol. Oceanogr., 26: 86-102. PADISÁK, J. (1980): Short-term studies on the phytoplankton of Lake Balaton in the summers of 1976, 1977 and 1978. — Acta bot. hung., 26: 397-416. PIELOU, E. C. (1975): Ecological diversity. — New York. Wiley and Sons Inc. SHANNON, C. E. (1948): A mathematical theory of communication. — Bell. Syst. tech. J.. 27: 379-423, 623-656. SOMMER, U. (1981): The role of r- and K-selection in the succession of phytoplankton in Lake Constance. — Acta oecol., 2: 327-342. SZUJKÓ-LACZA, J. & RAJCZY, M. (1983): Similarity investigations on a loess steppe fragment in a forest-steppe in Hungary. — Manuscript. WALL, D. & BRIAND, F. (1980): Spatial and temporal overlap in lake phytoplankton communities. — Arch. Hydrobiol., 88: 45-57. WHITING, H. C, BROTHERSON. J. D. & RUSHFORTH, S. R. (1978): Environmental interaction in summer algal communities of Utah Lake. — Great Basin Naturalist, 38: 31-41. Authors' address: DR. JUDIT PADISÁK and DR. MIKLÓS RAJCZY Botanical Department Hungarian Natural History Museum Budapest, pf. 222 H-1476