Showing papers by "Steven M. Stanley published in 1980"
TL;DR: The balanoids have an advanced feeding mechanism, but the most important adaptive breakthrough leading to their competitive success was probably the origin of a tubiferous wall structure, which affords rapid skeletal growth for the efficient monopolization of free space and for the destruction of chthamaloids.
Abstract: Barnacles living along rocky shores provide the classic example of competitive dominance in the marine ecosystem: by means of firm attachment and rapid growth, balanoid barnacles commonly undercut and overgrow the genus Chthamalus, which is thereby restricted to the upper fringe of the intertidal zone, where balanoids are physiologically incapable of living. Today, after perhaps less than 50 Myr of evolution, balanoid barnacles are in the midst of rampant adaptive radiation, being represented by about 273 species, of which about half are free-living species of intertidal or shallow subtidal habitats. Chthamaloid barnacles, in contrast, are on the decline, having originated at least 70 Myr ago but today comprising only about 53 living species, approximately 40 of which occupy the uppermost intertidal. The remainder persist as localized, relict, and often disjunct populations. Through competitive exclusion, balanoid barnacles have apparently caused the ecological restriction and decline of the chthamaloids. The balanoids have an advanced feeding mechanism, but the most important adaptive breakthrough leading to their competitive success was probably the origin of a tubiferous wall structure, which affords rapid skeletal growth for the efficient monopolization of free space and for the destruction of chthamaloids.
76 citations
TL;DR: In this article, the authors have calculated Lyellian percentages for gastropod and bivalve faunas of Japan and western North America and compared them against geologic age, showing that gastropods have higher rates of extinction than bivalves.
Abstract: Since the birth of modern geology, Cenozoic deposits have commonly been dated according to Lyellian percentages (proportions of living species within fossil faunas), but this approach has never been tested. To remedy this situation, we have calculated Lyellian percentages for gastropod and bivalve faunas of Japan and western North America. When plotted against geologic age (determined by independent methods), the percentages for each class form a narrow band that reveals similar patterns of extinction for the two regions and an absence of major pulses of extinction. The plots thus seem to represent useful “standard” curves but display enough spread of data to cast doubt on the value of Lyellian percentages to chronostratigraphy.
Our plots do have many other useful applications: (1) They reveal differences in regional patterns of extinction; in particular, they document a Pleistocene mass extinction of Mollusca in the confined seas of the tropical Americas and an unusually low rate of extinction in the enormous tropical Indo-Pacific region. (2) They indicate that gastropods are characterized by higher rates of extinction than bivalves. (3) They provide a mechanism for evaluating differences in rates of extinction between discrete subgroups of taxa, such as tropical species and temperate species, or species with planktic larvae and species with nonplanktic larvae.
27 citations