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142 IVIL Zoocoenological characteristics
must, instead, consider biomass relations, degree of corrumpency and degree
of obstancy. The relationship between presocium and insectivorous vertebrates,
for example, is so complicated that this can be best expressed by the mass of
food consumed, rather than by abundance values. The degree of obstancy,
on the other hand, can be established - at least in individual cases - by the
decrease in abundance of the target populations. The corrumpents will be
related neither to individual plants nor oeci, but to whole plant stands, even
if they only consume certain parts of it (e.g. granivores). Ihe degree of
corrumpency manifests itself in the direction of presocia, and the food
consumed can be measured by mass.
9. Dispersion
Examining the spatial distribution of any zoocoenosis based on abundance,
we find very uneven numbers, indicating that the spatial distribution of
populations is extremely patchy.
Dispersion expresses the spatial distribution of a population. This is the
only characteristic that exclusively expresses spatial distribution, and can
only be studied in space, without considering the inter-population relationships.
Our perception of dispersion is formed through censuses of abundance.
The abundance values obtained by the censuses will indicate that populations
may be of heterogeneous distribution, even under similar conditions, although
we can find the opposite, too. In larval populations of Operophthera, there
may be no obstants in some parts of the canopy, causing different abundances
of Operophthera at certain canopy levels, as the obstants are more abundant
in the upper or lower canopy. It is also possible that the cynipid Eulophus
abdominalis is more active on the sunny southern side of the canopy than in
the shady northern one. Dispersion is, therefore, a strictly space-dependent
feature, because the spatial distribution of species can be influenced by factors
over and above the energy source, hinting at microclimatic influence. Hence,
parts of an oecus can be suitable for the development of a different zoocoenosis.
Therefore, dispersion points to the “clumped” nature of the zoocoenosis,
also indicating its varied nature, and hints at additional factors influencing
their association. Even where the energy source is otherwise available,
dispersion constitutes an important characteristic, allowing insight of the
inner life and development of the zoocoenosis.
Dispersion is not a phenomenon that ceases to exist through increasing
the number of samples (Balogh, 1953), but something that requires our close
attention. An uneven dispersion does not become even if we perform various
calculations, and this warns us about the reliability of quantitative calculations.
Of course, this does not mean that such calculations are impossible in
principle, only that sample size might not be great enough, and the quantitative
data obtained are of uncertain precision.