OCR Output

§ 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,