Oldal 43 [43]
OCR
§ The structural elements of the animal assemblage | 41 events in one population will reverberate throughout the whole network, sometimes, also, in distant and seemingly independent elements. Therefore, one cannot deny that the herbivorous semaphoronts have the potential to transform an association; this capacity of semaphoronts is the reason that we consider them zoocoenologically distinct from other elements of the coenosis. One should not see a homocentrism in the term “corrumpent” - it is not identical with “pest”; we only want to emphasize the key position that herbivores occupy between plants and the other components of animal associations. From this point of view, one cannot consider the death of a plant solely in terms of the activity of corrumpents, because this will result in life conditions for a series of intercalary populations. On the other hand, the previously existing animal assemblage and, what is more, the biocoenosis itself, must fall apart. This is why they are called corrumpents! It is another matter that, because of agricultural cultivation, all corrumpent populations living on cultivated plants are classified as pests. This term relates to an economic category, restricted to the interest of one species and a pest is neither unnatural nor extraordinary. This standpoint continues when considering the biocoenosis. There is no doubt that, from the point of view of the codling moth, the Anthonomus, by destroying the buds, is harmful just as the colding moth is a pest from the human point of view. A biocoenosis, however, serves the interest of no species; it exists precisely because of the often-contradictory interests of the component species and a complicated network of living organisms develops that enables the sustained existence of the coenosis. Zoophagous populations form the obstant (counterweight) elements of the zoocoenosis, because, at least, some of them directly hunt the herbivores, or parasitise them, therefore influencing their population densities, preventing their gradation, and, thus, blocking their threat to the existence of the association. Obstant elements are also predators, preying on hyperparaites or episites that, despite relying on consuming insectivores that prey on herbivores (thus limiting their effect), means their role culminates in limiting the impact of primary parasites or predators, thus preventing the herbivores from becoming extinct in the area. Ultimately, this would result in the elimination of the first consumer level in the trophic chain, the herbivores, that would cause the collapse of the whole community. A characteristic example of the importance of obstant elements is the role of the parasitoid Trichgramma evanescens, in keeping the herbivore Mamestra (Barathra) brassicae in check on poppies. This lepidopteran, annually, lays many eggs on the underside of poppy leaves. Judging from the number of eggs laid, the entire emerging caterpillar population would be fatal to the poppies but, with the same regularity, they fall victim to this parasitic wasp to the degree that only a fraction of eggs produce a caterpillar. In our experience, there was only one occasion, at the end of the 1930s in Biharnagybajom,
