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§ Succession in animal communities | 109 will allow an expansion of the zoocoenosis. Such a change is, naturally, very slow, and we can assume that, above a certain degree, it will trigger an opposite effect: a pine or beech forest of closed canopy, with its subdued undergrowth, is less favourable to support animal life than a thinner forest or a grasslandforest mosaic. Succession due to the activity of animal communities can happen when the constituent populations exhaust their energy sources, destroying their own living conditions (Tischler, 1950: 184). Thus, in an agrilignosa, an Aspidiotitena perniciosi can be followed by an Eccoptogastritena rugulosi, not forgetting that the latter is not linked to a previous zoocoenosis, as it can also appear in an oecus of frost-damaged trees. Catenae on the excreta of herbivorous animals also follow each other in a succession-like manner (Madle, 1934; Kuehle, 1950 cit. Schmidt, 1935; Mohr, 1943 cit. Park see Allee et al., 1949), directed not only by the atmospheric effects on the excreta, but also by the activity of the intercalary elements that serially follow each other, causing transformations of the resource base. The succession often only impacts a part of the zoocoenosis, as we can see in the succession of intercalary elements feeding on debris (Pukowski, 1933; Fourman, 1938 cit. Kuehnelt, 1950) that, in the different phases of disorganisation, are represented by different populations. The decisive role of plant-based energy sources is indicated by the fact that, on excreta of the obstants, no catenae develop composed of intercalary elements (Kuehnelt, 1950:229). We do not know if a similar difference exists between cadavers of corrumpent vs. obstant mammals. The changes mentioned undoubtedly belong to the phenomenon of succession, even if restricted to a small area and a single energy source (microsere, Mohr, 1943 cit. Park see Allee 1949). On the other hand, changes that accompany the gradual extension of zoocoenoses do not constitute succession (Kuehnelt, 1950:281). In cases where an uninhabited area is colonised, such as a rock (Falger, 1914, 1922-23, cit. Franz, 1950; Bachmann, 1910; Heinis, 1910; Rahm, 1910, cit. Kiihnelt, 1950: 281; Oosting and Anderson, 1939, cit. Park, see Allee et al. 1949: 464.), species that once colonised remain to be detected, and the community will gradually become richer by the arrival of new populations. Here, we do not talk about succession but the “filling out” of a zoocoenosis. The first signs of succession appear when changes in the plant cover cause the disappearance of the first pioneer species, assuming that these are accompanied by similar disappearance of animal associations. What we observe on cultivated areas mirrors these phenomena. The main difference between the arvideserta and agrilignosa and the less disturbed biotopes is that, in the former, human interference prevents succession; the soil is cultivated, and the producents are regularly changed in a rotation as if ona chessboard. Here, we cannot talk about succession, as succession cannot happen;the catenaria are facing a new situation every year, and they have to move to another area, while the presocium and supersocium can be sustained
