A Debreceni Déri Múzeum Évkönyve 1986 (Debrecen, 1987)
Természettudomány - Juhász, Lajos–Bozsko, Szvetlana: The Ornithofauna of Debrecen II. Synecological Analysis
evenness (Table 10), thus, at this time the particular areas can be characterized by the most differentiated, but at the same time, most uniform fauna. The ornis of the outskirts only slightly selecting the species is the most even (0.9220), and species rearrangement is less promoted by the unfavourable conditions of the modern housing estates (0.7172). The species stabilization of the nesting aspect and the specializing effect of the particular areas is manifested in the decreasing values of evenness. The internal areas of the town (town centre, old city centre, housing estates) the outstanding dominance values of some species is due to the high individual count, other species are only colouring elements in the bird community. On the other hand, the orderedness of species is extremely low in the housing estates (0.6607), and so is it in the town centre (0.7714). On the other hand, the ornithologically bleak industrial zone makes us guess a proportionally distributed fauna. This is, however, only due to the extremely low species- and individual counts, which is also indicated by the lack of species with very high D values. Thus, the small number of birds distribute among one another the available space of the habitat (J =0.9077). The poor selective effect of the large green areas and the outskirts is also manifested in the orderedness of the fauna (See Table 10). The autumn migration is weaker in the town as compared to the spring one, thus, the fluctuation of birds leads to less even proportions. It is only the old city centre that shows a high degree of orderedness (0.9268), however, this is due to the lack of some migratory species and the fairly identically high D proportion of the remaining mass species. The northern species immigrating into the city in the winter period, together with the wanderers, give rise to an ecofaunistically heterogeneous species composition, but a more even numerical distribution. Extremely low J values occur only in the old city centre. Here the feed is a decisive factor (the fruit of the hackberry tree) which has the consequence of a basic preponderance of one or two species (Turdus pilaris, Bombycilla garrulus). This circumstance is manifested in a negative way in the evenness values (0.5893%). d) Dominance identity conditions of the ornithofauna in the urban biotopes The bird communities of the urban areas with different ecological conditions, on account of the different adaptational capacities of the particular species and the interspecific effects between the species, give different dominance values. There may be marked divergences within the town in the species too. In the course of our work comparison was made for the similarity of species with identical D value within the particular biotopes in the ornithological ly most important two periods: the nesting and the hard winter (Fig. 1). In the nesting period the highest dominance identity can be pointed out between the bird communities of the outskirts and the small urban parks (70.2%). The species occurring in common (Streptopelia decaocto, Turdus merula, Passer domesticus and montanus, Hirundo rustica), making use of the slight selective effect of the areas, show identical dominance in a high per cent. The bird community of the outskirts zone continue to show high D identity with the dominant species of the large green areas. The similar species- and individual counts account for the high dominance identity values of the ornises in the Great Forest and the Public cemetery (70.2%). On the other hand, the permanence of dominance and similarity in the avifauna of the wholly urbanized parts of the town can only be expressed in the case of some species (Streptopelia decaocto, Passer domesticus). The qualitative effect of the different environmental conditions comes to light in this value too (see Fig. 1). The regularity is similar in the relationship between the urbanized bird communities of the housing estates and the less selected, high diversity stock of the Cemetery (25.17%), the identity of their D values is hardly evaluable. In the nesting period the bird fauna of other parts of the town show partial D identity. 51