Geoscience Reference
In-Depth Information
other factors. In the 1940s the American ecologist
Hutchinson introduced a distinction between the
funda-
mental niche
and the
realized niche
. The fundamental
niche is the maximum 'theoretically inhabited hyper-
volume' where a species, free from any sort of interference
from another species, can occupy its full range to the outer
limits of its tolerances. The realized niche is a smaller
hypervolume which is occupied by the species under
interference from the competition of other species. A
niche is thus defined by
n
variables, and can be defined as
'the limits, for all important environmental features,
within which individuals of a species can survive, grow
and reproduce'.
maximum occurring at the times of the equinoxes.
Vegetation is classed as the
Tropical evergreen rain forest
zone
(1). The
Tropical zone
(II) is located between 10
and
30
N and S approximately. Some seasonal variation in
mean daily temperature is noticeable. Rainfall is at a
maximum during the summer rainy season, and in the
cool season there is a dry season that increases in duration
with increasing distance from the equator
. Tropical moist
forests
(2) and
Dry deciduous forests and savannas
(2a)
occur here. The
Subtropical dry zone
(III) is the hot desert
zone and is located poleward of 30
S. Rainfall
is very low, daytime temperatures are very high, and at
night in the winter months the temperatures may drop to
zero. The main tracts of these
Subtropical deserts and
semi-deserts
(3) occur in the Sahara and Libyan deserts
of northern Africa, the Arabian desert in Asia and the
Middle East, interior Australia, south-western parts of
North America, south-western Africa, northern Chile and
Pakistan.
The
Transitional zone with winter rain
(IV) is located
at latitudes approximately 40
N and 40
S. In this
Mediterranean climate there is rain in winter, a long
summer drought and no cold season, although frosts do
occasionally occur. The
sclerophyllous forests of the winter
rain regions
(4) occur along the Mediterranean coasts, in
central and southern California, central Chile, the Cape
of Good Hope in South Africa, and south-western and
southern Australia. The
Warm temperate zone
(V) has
scarcely any or no winter. It is extremely wet, especially in
summer.
Temperate wet evergreen forests
(5) are most
extensive in eastern Asia. They are also located on the
south-eastern coast of Australia, the North Island of New
Zealand, the east coast of South Africa, south-eastern
N and 30
In describing the terrestrial vegetation of the entire Earth,
the large units of vegetation formations or biomes are
used. In 1936 the American ecologists Clements and
Shelford used the term 'biome' to describe the dominant
vegetation formation associated with specific climatic
conditions in a particular locality. The German biogeo-
grapher Walter in 1976 recognized nine climatic zones and
corresponding vegetation zones (
Table 20.3
and
Figure
given a double label e.g. I (III). Mountainous regions
were designated as X, with a second label, e.g. X (V)
indicating the climatic zone from which the mountains
rise (
Figure 20.4
).
The
Equatorial zone
(I) lies between
about 10
S. The daily variation in temperature
is greater than the annual variation, which is in the range
25-27
N and 10
C. Generally annual rainfall is high, with the
Climatic zone
Vegetation zone
I
Equatorial
1
Tropical evergreen rain forest
II
Tropical
2
Tropical moist forest
2a
Dry deciduous forest and savanna
III
Subtropical dry
3
Subtropical desert and semi-desert
IV
Transitional and winter rain
4
Sclerophyllous forests of winter rain regions
V
Warm temperate
5
Temperate wet - evergreen forest
VI
Typical temperate
6
Deciduous forest
VII
Arid temperate
7
Steppe
7a
Semi-desert and deserts with cold winters
VIII
Boreal cold temperate
8
Boreal coniferous
IX
Arctic
9
Tundra
X
Montane
10
Mountain
Source: After Walter (1976).
