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Endemism and Environment: Some Shore Molluscs of the Tropical Atlantic

Geerat J. Vermeij
The American Naturalist
Vol. 106, No. 947 (Jan. - Feb., 1972), pp. 89-101
Stable URL: http://www.jstor.org/stable/2459839
Page Count: 13
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Endemism and Environment: Some Shore Molluscs of the Tropical Atlantic
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Abstract

1. An analysis of geographic distribution as a function of habitat parameters is presented for rocky-shore molluscs at Ilha Fernando de Noronha, Brazil (3⚬56' S, 32⚬26' W), and Takoradi, Ghana (4⚬53' N, 1⚬45' W). 2. At both localities, species ranging into or restricted to high shore levels are significantly more limited in latitudinal range than those restricted to low shore levels. At Takoradi there is no significant difference in extent of longitudinal distribution between high-level and low-level species, or between species on open rock surfaces and those restricted to cryptic habitats. Transoceanic species at Takoradi are either restricted to cryptic habitats and/or eurytopic with respect to shore level. At Fernando de Noronha, species on open surfaces were significantly more restricted in geographic range than cryptic species, but this effect cannot be well separated from that of shore level. There is no significant difference in extent of latitudinal distribution between cryptic and open-surface species at Takoradi. 3. It is proposed that steep environmental gradients with latitude and physical uniqueness on a large geographic scale in a physically rigorous environment such as the high intertidal are associated with precise physiological and morphological adaptations to the particular physical regime at hand and with relatively narrow latitudinal ranges of resident species. Less marked gradients and physical uniformity on a large geographical scale in a less physically rigorous environment are associated with wider geographic distribution of the resident species.

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