Oldal 134 [134]
OCR
132 IVII. Zoocoenological characteristics 64 Formica rufa were found, and 147 larvae also contained larvae (a total of 1598) of Eulophus abdominalis. The abundance values obtained as a result look totally different to those that were realised using the same spatial reference that we used for one population (for a corrumpent, let us say). From these numbers, that shed light on the relative abundance relations of a zoocoenosis (or a catena), we can draw important conclusions. If, for example, at a subseguent census, we find that the number of larvae on 100 leaves decreased from 600 to 546, while the number of ants increased from 4.6 to 29.8, solely based on these numbers, we can assume that the ants forage in the canopy not just for the looper caterpillars because, if that were the case, their numbers should have decreased. There can be two possibilities: that the ants are related to other populations as well, or their presence in the canopy is aimless meandering (see Elton 1927, 56: “All cold-blooded animals and a large number of warm-blooded ones spend an unexpectedly large proportion of their time doing nothing at all, or at any rate, nothing in particular”). In the former case, ant numbers should also be related to these populations (that is, the combined populations of Operophthera + Archips + Pandemis spp.), meaning that F rufa cannot be constrained in one catena, but associates at the level of a catenarium and, in considering this, we should not overestimate the obstant role of ants in the regulations of the Operophthera population (see p. 111 - degree of obstancy). Thus, the numbers representing abundance are full of detail, providing additional information about the borders of the zoocoenosis its internal trophic relationships, and are not merely “dead” columns of numbers, that we are unable to explore and analyse. The value of abundance should express the number of individuals in the zoocoenosis. However, we have to register the number of individuals in a unit of space and, perhaps, even combined with a unit of time; the result obtained can only tell us that, in the examined part of space, the size of certain populations had certain values. Anything further relies on assumptions, and the more studies we do, the closer we get to the truth, without being able to reach it with our current methods. Abundance can have two meanings, depending on whether it refers to the number of individuals in a population or the number of populations (see Tischlers (1950) “Individuenabundanz vs. Artenabundanz”). Both are informative because the population density can refer to the role ofthe given population group in the zoocoenosis, whilst the species density can refer to the completeness of the zoocoenosis. The high abundance of some population can be a cause of low species abundance in others, because those other populations are squeezed out. We can see this in the case of Diaspidiotus perniciosus, whose high abundance can cause the absence of Sphaerolecanium prunastri, D. ostreaeformis, and Epidiaspis leperii.
