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Body Sizes of Poikilotherm Vertebrates at Different Latitudes

C. C. Lindsey
Evolution
Vol. 20, No. 4 (Dec., 1966), pp. 456-465
DOI: 10.2307/2406584
Stable URL: http://www.jstor.org/stable/2406584
Page Count: 10
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Body Sizes of Poikilotherm Vertebrates at Different Latitudes
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Abstract

The maximum sizes of 12,503 species of poikilotherm vertebrates have been analyzed for latitudinal trends, using published data from 75 faunal studies. A general trend appears, which may be summarized by the rule: "among fish and amphibian faunas the proportion of species with large adult size tends to increase from the equator towards the poles." The rule holds for freshwater fish, deepsea fish, anurans, urodeles, and marine neritic fish (arranged roughly in order of decreasing clarity of the trend). In general the rule applies not only within these groups of families but also within single families. In reptile groups, the rule holds weakly among snakes and not at all among lizards or non-marine turtles. Possible explanations include an association between small size and greater specialization in the tropics; the possibility in poikilotherms of heat conservation or of some other physiological process related to surface/volume ratio; selection for larger size in regions subject to winter food shortages; and an association between large adult size and high reproductive potential in cold regions. Other suggestions can be advanced, but all are conjectural and few are subject to test. Global size-latitude trends should be looked for in other living groups.

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