4. HUMANS AND THE ENVIRONMENT
55
Ecosystems at different levels of hierarchy are not isolated from
one another; rather, they are interconnected in innumerable ways.
For this reason, processes taking place in a system at a lower level
affect both the neighbouring systems at the same level and all the
ecosystems at higher levels in the ecosystem hierarchy. Thus, the
number of migratory
birds of a particular species, for example,
the Black Stork, in some regions of Latvia depends on the survival
success of this species in Africa.
The Amazonian rain forest deforestation causes not just local
climate changes; it also affects climate in the entire region of the
Amazon Basin, South America and the Pacific Ocean, because the
rain forest ecosystems, by means of intensive evaporation of water
and release of specific substances into the atmo sphere, determine
the height of rain cloud formation above the region. Ultimately,
these changes affect the global climate as well. Admittedly, today’s
knowledge on causal relationships in ecosystems is still incomplete.
Theoretically it is possible that minor changes in one element of
the system might cause significant changes in the whole system.
This principle is metaphorically denoted as ‘the butterfly effect’,
and it also applies to
causal relations in ecosystems, as expressed
by the saying that the flap of a butterfly’s wings in the rain forest
of South America can set off a storm in Europe. A small increase
in the concentration of phosphorus-nitrogen compounds in a lake
under favourable water temperature may cause an avalanche-like
multiplication of algae and cyanobacteria (blue-green algae) that has
a substantial effect on the whole ecosystem of the lake.
The hierarchic structure of ecosystems spatially manifests
itself as the diversity of biotopes within a single ecosystem. A large
diversity of biotopes is characteristic of natural landscape eco systems,
where all kinds of ecosystems alternate: different forest types, dry
and
wet meadows, peat bogs and marshlands, dunes, lakes. Landscape
ecosystems with a low diversity of biotopes, in turn, in many cases
are human-made: large tracts of human-planted forest,
agricultural
fields and pastures.
Species communities or biological communities represent the
living components of the ecosystem. Biological communities consist
of bacteria, fungi, plants and animals. These organisms depend on
environ mental conditions (temperature, moisture, soil fertility),
at the same time transforming these conditions themselves. For
example, plants with roots and litter as well as animals with digging
and excrements transform non-living rocks into soil. Earthworms
play an outstanding role in this process. The famous British natural
scientist Charles Darwin once compared them with a farmer’s
plough because there are hundreds of
earthworms per square meter
of a field, and they continually feed on the soil, so that almost all
56
ENVIRONMENT, POLLUTION, DEVELOPMENT: THE CASE OF UZBEKISTAN
of the field’s topsoil passes through their digestive tracts within the
period of one year. Earthworm castings are called coprolites, and
they are chemically stable structural elements of the soil. In fact,
they make the soil fertile by becoming the activity centres of the
microbiological processes taking place in the soil.
A characteristic feature of a biological commu nity is species
diversity measured by the number of species within the community.
The highest species diversity is found in the ecosystems of tropical
rain forests and coral reefs. For example, the entomologist Terry
Erwin has discovered that an average of 1200 species of beetles
inhabit the foliage of one species of
tree in the Panamanian rain-
forest. Of course, the species diversity is much lower in the forest
ecosystems of the northern and temperate zones, where the environ-
mental conditions are more severe. For example, in coniferous
forests, the number of species can be easily counted on the fingers
of one’s hand. Nevertheless, tens of different species of small arthro-
pods and worms live in the forest soil.
Ecosystems constantly change and develop. Biological commu-
nities transform into different ones, with a different composition of
species. This development process of ecosystems is called ecological
succession. A telling example of ecological succession is a field
overgrown with weeds and grass, transforming into a meadow; then,
the meadow is overgrown with shrubs; and, finally, the shrubbery
transforms into a forest (Figure 4.12).
Time
period
Field
Meadow Shrubbery Low deciduous forest
Spruce forest
Ecological successions can be of different durations: from
relatively short-term to very long. There can be short micro-
successions that run for about a few weeks. In contrast, a gradual
overgrowing of a lake and its transformation into a swamp may
take thousands of years (Figure 4.13). The remains of aquatic plants
and animals gradually settle on the lake’s bottom; consequently, it
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