Jordan's rule

Jordan's rule is an ecogeographical rule named after the father of American ichthyology David Starr Jordan describes the inverse relationship between water temperature and meristic characteristics. The most common found relationship is for fin ray, vertebrae, or scale numbers to increase with decreasing temperature.^[1]

References

Allen's rule Shorter appendages in colder climates
Bergmann's rule Larger bodies in colder climates
Cope's rule Bodies get larger over time
Foster's rule Small species get larger, large species smaller, after colonizing islands
Gloger's rule Lighter coloration in colder, drier climates
Haldane's rule Hybrid sexes that are absent, rare, or sterile, are heterozygous
Jordan's rule Inverse relationship between water temperature and no. of fin rays, vertebrae
Rapoport's rule Latitudinal range increases with latitude
Rensch's rule Sexual size dimorphism increases with size when males are larger, decreases with size when females are larger)
Thorson's rule No. of eggs of benthic marine invertebrates decreases with latitude

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