ECQLOQY, SYSTEMATICS AND EVOLUTION OF AUSTRALIAN FROGS 43
Frogs occur in the desert despite the low rainfall; they survive because they can make use of water when it is present and 80 breed and
feed. When water is not present they avoid the aridity usually by
burrowing. The nature of the weather pattern which typically brings
rain to the desert or the better watered south-west corner of Western
Australia can best be illustrated by synoptic charts. The synoptic
situation and the resultant rainfall for a typical summer tropical
cycloce is shown in Fig. 3a and B and the winter southern cyclone in
Fig. 3~ to I.
The first of these weather patterns is characteristic of summer conditione, warm, moist, tropical air associated with cyclonic conditions
arising in the Timor Sea moves south-westward across northern Western
Australia as a tropical hurricane. Along the north-west coast it changes
course and moves south-eastward across the continent as shown by
rainfall in Fig. 3 ~ .
Rainfall associated with cyclones of tropical origin
is always widespread and heavy.
On other occasions tropical air is associated with a trough of low
pressure unaccompanied by cyclonic conditions. Such conditions produce scattered rains usually associated with thunderatorm activity. The
synoptic situation producing such rain is not illustrated. Frogs which
breed during the summer or at high air temperature are dependent on
rain resulting from either of the foregoing synoptic situations which
only 03cur a few times in a normal semon and fail altogether during
drought.
During winter (May-September) rains are usually associated with
frontal systems or cyclonic disturbances of southern oceanic origin. Air
temperatures associated with rains derived from such systems are much
cooler than for rain-bearing depressions of tropical origin. Air temperatures of 18°C can be regarded aa warm for winter depressions and air
tempersturea of 6-10"C regarded as cold. Most frogs which breed in
winter or spring do so within the range 6-18°C. The typical winter
weather pattern is for a sequence of cyclonic depressions to pass across
the scuthwest corner or a little to the south of Western Australia
(Fig. ~ D - H ) bringing rain every 6-8 days. They are thus more frequent
in occwence and less likely to fail to occur than the summer time rainbearing air masses. Figure 3 (D-H) shows the typical synoptic situation
bringing opening winter rains. The examples given are for the 1964
winter. Figure 3c shows the rainfall resulting from a surge of cold
southern air when cold front activity mused widespread tropical rain.
However, with this rainfall the only tropical desert fiog to breed was
Peeudophryne douglmi becauee the associated air temperatures were
below that at which other tropical or desert speciee breed. Figure 3 ~ - H
shows the more typical opening winter raina of southern Western
Frogs occur in the desert despite the low rainfall; they survive because they can make use of water when it is present and 80 breed and
feed. When water is not present they avoid the aridity usually by
burrowing. The nature of the weather pattern which typically brings
rain to the desert or the better watered south-west corner of Western
Australia can best be illustrated by synoptic charts. The synoptic
situation and the resultant rainfall for a typical summer tropical
cycloce is shown in Fig. 3a and B and the winter southern cyclone in
Fig. 3~ to I.
The first of these weather patterns is characteristic of summer conditione, warm, moist, tropical air associated with cyclonic conditions
arising in the Timor Sea moves south-westward across northern Western
Australia as a tropical hurricane. Along the north-west coast it changes
course and moves south-eastward across the continent as shown by
rainfall in Fig. 3 ~ .
Rainfall associated with cyclones of tropical origin
is always widespread and heavy.
On other occasions tropical air is associated with a trough of low
pressure unaccompanied by cyclonic conditions. Such conditions produce scattered rains usually associated with thunderatorm activity. The
synoptic situation producing such rain is not illustrated. Frogs which
breed during the summer or at high air temperature are dependent on
rain resulting from either of the foregoing synoptic situations which
only 03cur a few times in a normal semon and fail altogether during
drought.
During winter (May-September) rains are usually associated with
frontal systems or cyclonic disturbances of southern oceanic origin. Air
temperatures associated with rains derived from such systems are much
cooler than for rain-bearing depressions of tropical origin. Air temperatures of 18°C can be regarded aa warm for winter depressions and air
tempersturea of 6-10"C regarded as cold. Most frogs which breed in
winter or spring do so within the range 6-18°C. The typical winter
weather pattern is for a sequence of cyclonic depressions to pass across
the scuthwest corner or a little to the south of Western Australia
(Fig. ~ D - H ) bringing rain every 6-8 days. They are thus more frequent
in occwence and less likely to fail to occur than the summer time rainbearing air masses. Figure 3 (D-H) shows the typical synoptic situation
bringing opening winter rains. The examples given are for the 1964
winter. Figure 3c shows the rainfall resulting from a surge of cold
southern air when cold front activity mused widespread tropical rain.
However, with this rainfall the only tropical desert fiog to breed was
Peeudophryne douglmi becauee the associated air temperatures were
below that at which other tropical or desert speciee breed. Figure 3 ~ - H
shows the more typical opening winter raina of southern Western