Spatial distribution of amoebae
Very interesting data may be obtained if we will analise the
overall (I mean in all collected samples, repetitive and single)
frequency of species occurrence. First of all, there is no species,
which were always found. Frequency of species occurrence gradualy decrease,
showing that there is no sufficient break between "rare" and "usual"
species. Small-size amoebae are, of course, among the most frequently
occurred, but there are also medium-sized species among them, as well.
Of course, large species are below in this chart - the pattern of
distribution generally corresponds to the usual for protists.
Most intersting data were obtained from the cores of sediments.
From each core several (7-12) samples were taken from different depth
- from the sediment surface and up to the bottom of the core.
Differential counting of species allowed to recognize ther so-to-say
"ecological groups" of amoebae, different in the patterns of vertical
distribution in the sediments.
Some species were found actually at every depth in the sediments.
This group called here "cosmopolites" - provision, and not the best name.
It includes small and medium-sized amoebae.
Species of the second group were found only as a "pathches" inside the
sediments. They were occured in sufficient number in one and the only
sample from the core, at different depths. These are exclusively medium-sized
Third, and most numerous ecological group, is the population of the
sediments surface. This group includes species of all size range. All
large species belong exclusively to this group.
Following three curves illustrate number of species, the accumulation
of fauna starting from the first sample in the core and the abundnace
of amoebae in every sample. These are data on one typical core, results
from other cores are similar in general patters. From the right side is
the respective vertical profile of sediments in the core.
We may see, that both species diversity and abundance decrease
with the increment of the depth. Really, only the layers consisting of
detrit with gradually increasing content of ooze are inhabited with
amoebae. However species diversity was exhausted only at the depth of
20 cm into the sediments. This, together with the data on three
ecological groups of amoebae, shows us, that the usual samples of
the "upper 3-4 mm layer" of the bottom sediemnts are far not enough
to make any representative conclusion even on the biodiversity of
amoebae in the sedeiments. Definitely, amoebae are most abundant in
surface layers. However, usualy the maximum of abundace is situated not
on the sediemnt surface, but below - at the depth 5 - 10 cm. I am not
trying to explain this, but perhaps this point also should be noted
when we are truing to calculate number of amoebae in the sediemnts from the
data on surface samples.
Analising the data on species composition, distribution
and abundabce of amoebae we may note that the distribution is
very heterogenous. For example, in stereotype samples taken
from the same place all the year round, show that no one species
was found in all of the samples (i.e. with 100% frequency).
Moreover, most of species were noted only one-two times
during all the period of observations and should be considered
to be rare. This is examplified in the Figs. 1-2.
Fig.1 Occurrence of amoebae species in 5 monitoring sites
in 1992-1993. +:was found; H: sample was not collected (this was
connected with the overal water level in the lake).
Fig.2 % of occurrence of amoebae species in 5 monitoring sites
in 1992-1993. Calculated from the total number of cases of species
occurrence in all samples as listed in the Fig.1.