Seite 74 [74]
OCR
72 | III. Biotope and animal associations trophic relations, but the divergent ecological factors following from the oecus-structure of the biotopes. Similar differences are reported by Kuehnelt (1950:251) who demonstrated microclimatic variances between neighbouring tree stumps, and whose zoocoenoses, consequently, reflected these differences. The oecus, above all, must be seen as an energy source of special quality, even though a manifestation of defined environmental conditions; the first characteristic may be of decisive importance for colonising populations. The same oecus can therefore harbour different zoocoenoses. To complete our understanding, we have to examine one further circumstance. When several plant species form a characteristic plant association, this also results in groups of oecuses, showing structure-related features that influence the microclimate. Such a sub-biotope (see Varga, in Fehér et al., 1954) is the ecotone; in the arvideserta, the crop plus its weeds and in an agrilinosa, the fruit trees and the weeds growing among them. The structure of the biotope follows from the grouping of the oecus, and changes in the microclimatic relations that are influenced by this structure, while the essence of the energy source remains unchanged. The same oak species will represent the same energy source everywhere, but will be available under various microclimatic conditions in a gallery forest vs. a forest of closed canopy. The animals do not only need food, but a certain combination of macro- and microclimatic conditions and, only when these are available, can they utilise the food source. The influence of soil moisture can be illustrated well by the behaviour of Nicrophorus (Necrophorus) populations: on moist, clay forest soils, N. humator; on dry, sandy soils N. vespilloides and; on meadows, N. vespillo populations will live on the same food source (Pukowski, 1953). A few more words on the concept of the statio, that is also needed in zoocoenology, because we separate the various animal populations by their species identity. To survive in a zoocoenosis, a population needs to find the conditions that it can tolerate as an inherited feature of its species. As a population of a species is a member of an animal association, so do all populations belong to a species. The statio is a spatial expression of the species-specific need concerning the living and non-living elements of its environment. This need can be modified by evolutionary adaptations, but such needs are always present. The realised zoocoenosis of a given biotope, or oecus, also depends on the statio needs of the populations of the species present. At this point, the syn- and idiobiological viewpoints must meet even though they must not be mixed, because the latter helps to better understand the formation of the association under study. With better description of animal associations and zoocoenoses, more light will be shed onto the ecological needs of the participating species, thus increasing our idiobiological knowledge about them. This illustrates why, in zoocoenology, we need to pay attention to the idiobiological concept of statio that mirrors the speciesspecific needs. The law of changing stadia (Bej-Bienko, see Tschegolev, 1951; Bej-Bienko and Mishtschenko, 1951; see also Elton, 1927; Kühnelt, 1943;
