184 PAUL J. MARKWICK
Fig. 4. Environmental parameters plotted against absolute latitude for (a) MAT. (b) CMM, (c) WMM, (d)
cumulative T 5°C, (e) radiation, (f) annual precipitation, (g) months with T 10°C and P 40 mm (see
Lottes & Ziegler 1994), (h) PET, (i) mean annual NDVI, (j) NDVI, 1SD. See Table 1 for an explanation of
each parameter.
spread of data away from this trend is far greater
than that observed for reptiles. Spatially this
shows strong longitudinal gradients superim-
posed on the overall latitudinal trend (Fig. 7),
and a general pattern that is similar to the
modern distribution of precipitation around the
globe (i.e. with highs in the wettest regions of
North America (NW and SE USA) and NE
Australia). The low-diversity, low-latitude data
points in Figure 3d all reflect areas of reduced
water availability (the deserts of southern
Africa and Australia; Table 5). Like reptiles,
amphibians are also precluded from the coldest
parts of the world (Fig. 7). This distribution
