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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.

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