John J. Welch

“ Accordingly, the standardized-major-axis slope (solid line) was very close to one, and the permutation test showed no significant deviation from the pattern expected if deep-sea colonization had no effect on body size evolution (n = 254; b = 1.020; permutation p = 0.476) .
Body sizes of deep-sea gastropods and their shallow-water congeners.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”. ”

“ These data are clearly noisy, and the slope is strongly influenced by a single outlier (the largest value on both axes) . This point represents the genus Fasciolaria, which contains just a single deep-sea species, the recently discovered Fasciolaria tephrina [25] . To restrict the influence of such isolated observations, McClain et al. [4] excluded from their analyses all genera with fewer than two shallow and two deep species. ”

“ With this definition, 254 genera contained both deep and shallow species, and their generic mean body sizes are plotted in Figure 1A. Applying the standard test [6] , [4] , the ordinary-least-squares regression slope (dashed line) is found to be highly significantly less than one (n = 254; b = 0.902; t-test p = 0.0015) , which offers strong apparent support for the island rule. ”

“ But there is little evidence that reduced predation characterises the deep-sea [4] , [8] , and indeed there is direct evidence of substantial predation acting on deep-sea gastropods [4] , [33] – [34] . ”