English: Part A shows how different tests of the ‘island rule’ can give qualitatively different results. “Deep-sea” species were defined as those with a depth range midpoint >200m, and all other species defined as “shallow-water”. The ordinary-least-squares regression (dashed line) differs significantly from the 1∶1 line of the null (dotted line), but the standardized-major-axis regression (solid line) shows no significant departure. Part B shows a less ambiguous case: “deep-sea” species are those never observed above 400m, and “shallow-water” species those never observed below 200m; body sizes are within-genus means, taking equal numbers of deep- and shallow-water species in each genus.