Subtropical Communities Research Articles

Sponsorship of sport by tobacco companies

<h3>ABSTRACT</h3> Classic niche theory assumes that species-level functional traits affect species relative fitness and thus community structuring, but empirical tests of this assumption are scarce. Moreover, recent evidence shows increasing functional over-redundancy towards the tropics, suggesting that the extent to which functional traits confer species’ fitness and thus impact community structuring differs across latitudes. Here, we develop a new method: comparing the frequencies of trait categories in the species-rank abundance distributions of local communities versus their frequencies in the regional average species pool. We contrasted subarctic versus subtropical copepod communities for six important traits. In subarctic communities, medium-sized and cold-water species are selected to dominate, thus traits affect relative fitness as predicted by classic niche theory. In subtropical communities, most species are small and warm-water, but these categories are not selected to dominate, suggesting that greater diversity towards the tropics results from lesser trait-based fitness differences allowing more species to coexist.

Karyotype Evolution and Speciation in Lizards (Genus Sceloporus) During Evolution of the North American Desert

Karyotype evolution apparently involving Robertsonian centric fusion of chromosomes in iguanid reptilian species (Sceloporus clarki and Sceloporus magister) is consistent with the recent evidence pertaining to the evolution of North American Desert species of animals and plants derived from tropical and subtropical communities of the Madro-Tertiary Geoflora during the evolution of the North American Desert. Two iguanid species in the spinosus species group of Sceloporus, long suspected of close relationship, are distributed in the American Southwest in a highly suggestive complementary geographic and ecologic fashion. In this species-pair, one of them (Sceloporus magister Hallowell, 1854) is distributed almost wholly within the newly evolved North American Desert environment, while the other (Sceloporus clarki Baird and Girard, 1852) lies almost wholly outside of and adjacent to it, being widely distributed within the bordering arid subtropical scrub (tropical deciduous forest) from which North American Desert plant species recently have evolved (Axelrod, 1950, 1958, and elsewhere). Earlier examination of the chromosomes of these two morphologically similar species of lizards revealed markedly different karyotypes (Lowe, Wright, and Cole, 1966). We report here on an analysis of these karyotypes and their implications bearing on chromosome evolution and speciation in the genus Sceloporus. Chromosomes of bone marrow cells were examined on slides prepared by means of Patton's (1967) modification of the colchicine-hypotonic citrate method of Ford and Hamerton (1956). The specimens from which chromosomes were examined (N = 215 cells analyzed from 24 individuals) are catalogued and preserved in the herpetological collection, Department of Biological Sciences (Zoology), The University of Arizona (see list of specimens examined, be-

Myasthenia gravis in a southern community.

Epidemiologically oriented studies of myasthenia gravis in well-defined populations can provide useful data on racial susceptibility, sex preponderance, and geographic distribution. Also, the influence of environmental and genetic factors in etiology may be clarified. Information based on analysis of the experience of special clinics or interested physicians is not necessarily representative of the population as a whole and has little comparative value. A study was conducted in Charleston County, S.C., during 1957 and 1958, in which information about myasthenia gravis was collected from hospitals, clinics, practitioners, and records of vital statistics. These data are felt to provide a reasonably accurate approximation of the occurrence of myasthenia gravis in this southern community. Description of the Community Charleston County is a subtropical seaboard community with a population in January, 1956, estimated at 188,000, half of which is Negro. The medical school and hospital facilities in the city of Charleston have made this