192 PAUL J. MARKWICK
Fig. 11. Mean annual temperature (MAT) as a function of the percentage of each fauna represented by
ectotherm (amphibian and reptile) species. The least squares regression through these data is used to retrodict
MATs for specified fossil faunal compositions.
species diversity during the Neogene may
reflect a corresponding decrease in primary
productivity.
These physiologically based differences in the
pattern of taxonomic diversity suggest that the
species-energy hypothesis should be modified to
account for how organisms procure energy,
rather than describing diversity as simply a
function of the amount of available energy. But
diversity must also be considered in the context
of history. Organisms rarely occupy the full
geographic area that physiologically they could
survive in. Alligatorids are not found in Austral-
asia or Africa (Markwick 1998a,b); salamanders
are absent from sub-Saharan Africa, SE Asia
and Australasia, which partly contributes to the
lower amphibian diversities observed for these
regions in Figure 3d. These absences reflect the
Fig. 12. The residuals for MAT from Figure 11, as a function of percentage ectotherm species. No trends are
observed.