Zs. P. Komáromy szerk.: Studia Botanica Hungarica 12. 1977 (Budapest, 1977)

Szujkóné Lacza, Júlia; Sen, Subir: Distribution, diversity and equitability of the Hungarian species of Gentiana and Gentianella ciliata L. (Gentianaceae)

of distribution, diversity and equitability of three species of Gentiana and one species of Gentianella (G. ciliata) reported from Hungary. All our observations are based on the dried specimens of the Herbarium of the Hungarian Natural History Museum, Budapest which embodies a huge collection of Gentiana species from various parts of Hungary since the middle of the 19th century. The herbarium sheets frequently contain a good deal of information regarding the type of community in which the plants occur, the exact locality, altitude, etc. From the available information we have summarized the frequency of each species in different communities and factor gradients (altitude, annual precipitation) and calculated the diversity and equitability of each species. The communities have, however, not been designated here according to BRAUN-BLANQUET's system, as most of the sheets, particularly the old ones, are not labelled accordingly. We have, therefore, used the term habitat as difined and differentiated from niche and ecotype by WHITTAKER, LEVIN and ROOT (1973) to describe the range of environments and communities over which a species occurs. This term comes nearer to the old European term formation. MAC ARTHUR (1961) pointed out that the territories of most species are scattered rather sparsely over the area, and the territories of very few species form a mosaic. We, therefore, believe that within the area of a species the discontinuity of its distribution is more characteristic than continuity, because, as we suppose, every species is regulated by more than one environmental factors in different degree. In other words, most of the species can and have to adapt to different habitat and environmental factors within a tolerance range. Therefore, we have made an attempt to find out the factor which produces the minimum diversity and nearly maximum equitability in four species within the Carpathians and Great Hungarian Plain. Similarly, we have calculated the diversity in the flowering frequency of the species. Lastly, the mutual information between one examined factor and species has been determined. Diversity which is a measure of community structure was first quantified by MARGALEF (1956) by methods derived from SHANON's information theory and SHANON and WEAVER'S index. (1963) Later, MAC ARTHUR and MAC ARTHUR (1961) used it to measure the community structure of birds. PIELOU (1966) who used the diversity index to investigate the structure and stability of communities, suggested that diversity means the number of bits per individual (i.e. number of individuals/species). We have regarded here the bits to mean number of individuals per species along its distributional range. ODUM (1969) states "Diversity is a mathematical expression which expresses the ratio between the species and individuals in a biotic community", Equitability is an important measure of relative diversity (SHELDON 1969). It represents the ratio of observed diversity to maximum diversity (MARGALEF 1969, PATTEN 1962). LLOYD and GHELARDI (1964) have recognized two distinct components of species diversity: the number of species and the equitability with which the individuals are apportioned among the species.