Seite 109 [109]
OCR
§ The question of permanent species representation | 107 The gradation of the corrumpent elements can have serious influence on the composition of catenaria and presocia, and can substantially change them. These, however, are only hypotheses, in need of a proof. The precise censusing of zoocoenoses depends not only on today’s imperfect methods, but also on the distribution of the constituent populations that is, overwhelmingly, discontinuous (Thalenhorst, 1951): we face populations with island-like distributions. The unevenness of dispersion is not changed by increasing the survey area until the originally “unsuitable” dispersion will become more even (Balogh, 1953: 56). The resulting means do not reflect reality, because the dispersion of the populations remains clumped, irrespective of our calculations. The degree of dispersion depends on the needs of the developmental stage of the species. The bigger the area necessary, the more dispersed the population will be. The highest degree of dispersion in insects is that of the adults, because this is the stage that best expresses the spatial needs of the species. A high degree of dispersion can result in a population getting below the detection threshold, thus a low abundance does not necessarily mean a minor role in the coenosis. A gradation of Aporia crataegi larval population can reach unheard of densities, denuding all fruit trees over considerable areas. The resulting adult population will, inevitably, be smaller; not only because the adult population must be smaller than the original larval population, but also because the adults disperse, and they do this more readily if the trees have been denuded by the larval population. Birds and larger mammals are also rare within a biotope due to their large area needs; this must be independent of anthropogenic effects, because their hunting areas cannot support more individuals. Species with high spatial needs always tend towards their detection threshold during regressive phases of the population dynamics, while during gradations, they grossly exceed it (Dociostaurus maroccanus, Loxostege sticticalis). Consequently, the constant presence of a species, given that this needs to be proven by our imperfect detection methods, stands on shaky logical grounds and, if our studies nonetheless indicate that certain plant stands always contain certain species combinations, even if this mirrors the fauna, this points to the suitability of our primitive methods to allow a view into the composition of animal communities. This view will only be complete if the constituent catenae, and the resulting catenaria, are uncovered; otherwise, the current practice of coenological surveys and analytical methods leads to the emphasis on the populations of common species, those that have wide ecological tolerance limits (valence). The “stable” species detected will project only a mirage of stability. We have to assume that the characteristic species combinations will be subject to smaller or bigger changes by the gradocoen; some species may go missing or sink below the detection threshold, but the zoocoenosis can also be enriched by a sudden gradation of otherwise rare species. Such species with narrow tolerance limits may,
