Page 44 [44]
OCR
42 | II. Biocoenosis and zoocoenosis when, obviously due to the absence of Trichogramma, the caterpillars completely destroyed a small field of poppies. This damage peaked after flowering, thus destroying the whole insect community of the poppies as well. The limiting role of Trissolcus (Microphanurus) semistriatus and many predatory insects (Treml and Batkina, 1951) on population densities of Eurygaster maura and Eurygaster austriaca is also well known. Obstant elements are, therefore, all the semaphoronts that live on other populations, and their role is to reduce densities of other populations, irrespective of the role of those populations. Thus, a semaphoront living on another obstant population is also, itself, an obstant. The deeper importance of obstancy for the community is shown in the phenomenon that, in their absence, the otherwise corrumpent population itself gives rise to such elements, as a part of them starts to behave as obstant populations. Cannibalism is no doubt an obstant activity, and the result is the decline of the abundance of the corrumpent population. An excellent example is the case of Tribolium confusum (Chapman, 1931) where, at high densities, more and more of the semaphoronts start to consume eggs and pupae, with the consequence of a reduction in densities, whereupon cannibalism declines, and the “balance” between food and densities is restored. The sustinents merit their category because of their important role in sustaining the association by mediating plant reproduction. By this, they assure not only the survival of certain plants in the association, but contribute to yield, through which the formation of further trophic chains (seed feeders) occurs. Membership is not gained by lifestyle (feeding on nectar, pollen, honeydew) but by playing a role in fertilisation without causing damage to the plant itself (e.g. as Meligethes aeneus does, see Friederichs, 1921). The intercalary elements (decomposers) live on dead material, and are important members of the biocoenosis because they decompose material. Their importance is especially notable subterraneously, and can be divided into three groups: a) some of them live directly on dead and decomposing plants; b) the food of the next group is excreta of herbivores, and thus are indirectly linked to plants as a resource. Plant material is important in this case, clearly indicated by the rich insect assemblages on such excreta, while that of carnivores is less frequented (Kuehnelt, 1950). The third group lives on carcasses or other resources that are shed by animals (recuperants, sensu Woynarovich, 1954). Their characteristic position does not represent the last step of the trophic chain, as they can be linked to any contributor. From the point of energy transfer, the first two groups are unequivocal, as belonging to the plant-feeding, biophagous group the populations in the third group, however, are intermediate members of a trophic chain starting with herbivores. The feeding biology of intercalary element, in many respects, is still to be established. We know little of their food specialisation. They constitute elements that provide horizontal links between populations, and their numbers increase
