Oldal 55 [55]
OCR
§ The question of balance in the biocoenosis | 53 The equilibrium of the structural elements can only be conceived if the biocoenosis becomes permanent, and the producent level, once formed, does not change, either qualitatively, or quantitatively. Such a permanency is made impossible by the succession. Therefore, the concept of equilibrium can only be accepted if we consider it a fixed process, with a start and an end. Reaching the sea is not the aim of the river it must run due to the forces of physics, and the farther it flows, the more likely is that it will unite with other rivers, and increase in size. The end status of the plant cover is the climax; in this state, it will reach the stage at which, permitted by conditions of climate and soil, its production of biomass will reach a maximum. If this state becomes permanent, the consequence would be that the production of plant biomass would be largely unchanged. However, the composition and production of the climax plant cover certainly undergo considerable between-year changes (Tansley, 1935; Ramaley, 1939; Talbot et al., 1939; Costello and Turner, 1944; Scharff, 1954). On one side of the balance, there are the climatic and soil conditions and, on the other, the vegetation determined by them. Can this be called an equilibrium? Seemingly, yes, but it is much more appropriate if we talk about the adaptedness of the plant cover to the conditions. This becomes even more appropriate when we consider that this is not merely the impact of abiotic conditions on the plant cover, but also due to allelopathy; the individual plants (species) also influence each other, and must adapt to conditions created by each other. The cornerstone of the system of interactions in a biocoenosis, however, rests on the producents. Any external impact that disrupts this group will, unavoidably, disturb the interactions and, if this destroys the producents, the biocoenosis will disappear, because it cannot survive in the same form with the loss of those producents. Undisturbed interactions can, undeniably produce a balance-like state, illustrated by natural examples. For example, on the Kaibab Plateau of Arizona, there were 4000 deer. After humans exterminated the cougars and wolves that hunted them, forcefully breaking the existing interactive links, deer numbers increased so greatly that they consumed the food base necessary for overwintering, and the population, from its peak of 100 000, fell to 40,000 by 1925, and to 20,000 by 1931 (Leopold, 1943). Looking at the bare figures, instead of the original 4,000, today, the number of deer are around 20,000, whilst the numbers that primary production in the area can support is around 30,000. Is this a matter of balance? Even if one unwillingly believes this with some scepticism, we can only talk about the nature of the interaction, because a certain amount of primary production is suitable to support a limited number of transforming animals. If, however, primary production can support 20,000 deer, why was the deer population at a lower level when exposed to the undisturbed predatory activity of obstant elements? There is only one answer: the number of predators was so high that the deer population could not grow beyond 4,000, despite of the existence of surplus food base. An
