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  • Articles: DFG German National Licenses  (4)
  • 1990-1994  (1)
  • 1985-1989  (3)
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  • Articles: DFG German National Licenses  (4)
Material
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Factors regulating population dynamics of the marine bivalve Gemma gemma: intraspecific competition and salinity (1985)
    Springer
    Marine biology 86 (1985), S. 173-182 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A population of Gemma gemma (Totten) was investigated for 6 yr (1978–1983) in Connecticut, USA to determine the relationship between population fluctuations, life tables of successive cohorts and factors affecting life table parameters. Seasonal cycles occurred from 1978–1981. Although density was not abnormally low in summer of 1982, the population declined rapidly thereafter because individuals present during the reproductive season were smaller than the minimal size for reproduction. Forecasts of population size from a time series model based on past densities were compared to forecasts from the intrinsic rates of growth from four separate clam life tables. The latter approach was less precise but more consistent at successfully predicting temporal trends in population abundance. Two factors were identified that potentially controlled population density and structure during the study. Correlational evidence indicated that intraspecific competition between juveniles and adults was intense in 1978 but was reduced during subsequent years. This interaction reduced the size and subsequent fecundity of the young-of-the-year. Correlational evidence also indicated that low salinity in spring of 1978, 1979, 1982 and 1983 reduced juvenile survival, but not that of adults. Qualitative evidence indicated that a third factor, predation, might also have affected G. gemma's population size and structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00399024
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Divergence between populations of a monogamous polychaete with male parental care: Premating isolation and chromosome variation (1990)
    Springer
    Marine biology 107 (1990), S. 205-213 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Low dispersal and sexual selection are characteristic of the coastal polychaeteNereis acuminata Ehlers 1868 [also known asNereis arenaceodentata Moore 1903 andNereis (Neanthes) caudata Delle Chiaje 1841]. We assessed levels of premating isolation between populations of this polychaete. Four North American populations were used, two from the Atlantic and two from the Pacific. Worms from all sites (1) were collected in 1987 and 1988 from the same habitat type, (2) were morphologically similar and keyed out asN. acuminata, and (3) reproduced monogamously and exhibited male parental care, an extremely rare reproductive mode in marine invertebrates. There was no evidence from 10-min or 36-h trials of premating isolation between the two Pacific populations. Incomplete premating isolation was found between the two Atlantic populations. High aggression and non-pairing occurred in some 10-min trials between males and females. However, in 36-h trials males and females from the two Atlantic populations always paired to mate. Complete premating isolation was found between Atlantic and Pacific populations. During 10-min trials, males and females from different oceans often attacked and then avoided each other, and they never paired to mate. Nor did they pair to mate in longer, 36-h trials. One Pacific and one Atlantic population were compared for tolerance to cold temperature. Pacific individuals were less able to tolerate cold water than Atlantic individuals. Two Atlantic populations studied had karyotypes with 11 pairs of small acrocentric chromosomes (2n=22), while the two Pacific populations had nine pairs of large metacentric or submetacentric chromosomes (2n=18). Such extreme dissimilarity in karyotype was not expected considering the similarity in morphology, habitat, and reproductive mode. Results suggest strongly that the Atlantic and Pacific populations have been allopatric for a long time, and are different species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01319819
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Morphological divergence of Eastern Pacific and Caribbean isopods: effects of a land barrier and the Panama Canal (1989)
    Springer
    Marine biology 103 (1989), S. 143-152 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Isthmus of Panama rose approximately 3 million years before the present (mybp) and isolated biotas in the tropical eastern Pacific from those in the Caribbean Sea. Populations that were split by the Isthmus and have evolved in allopatry since that time are known as geminates. The surf zone/beach isopod Excirolana braziliensis Richardson was examined between 1984 and 1989 to test the hypothesis that divergence in geminate isopod morphology has occurred, and that geminate divergence is greater than divergence between local populations from the same coastline. Three morphs of Excirolana braziliensis, one in the Caribbean and two in the eastern Pacific, were discovered using numerical taxonomic methods that adjust for body size. The two Pacific morphs have overlapping large-scale distributions, but those morphs are segregated on a smaller scale by beach. We inferred that one Pacific morph and one Caribbean morph were geminates, based on their relative similarity in shape, their geographical ranges, and natural history information about the organism's dispersal capabilities. The origin of the third morph probably predates the Isthmus of Panama, given its relative dissimilarity from the geminate morphs. The presumed geminates differ primarily with respect to the rostrum, antennae and one male reproductive structure. Divergence between geminates is greater than divergence between local populations of any morph along a coastline. Because only one morph occurs in the Caribbean, that region contains less morphological variation than the eastern Pacific, which contains two morphs. There was weak evidence that some introductions may have taken place in the last century from the Caribbean to the Pacific; however, introductions have not masked the pattern of divergence that has developed over millions of years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00543341
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Demographic importance of ecological interactions: how much do statistics tell us? (1986)
    Springer
    Marine biology 93 (1986), S. 305-310 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Many investigators demonstrate the existence of intra- and interspecific interactions through rigorous statistical hypothesis testing. Statistical significance of an interaction, however, does not necessarily imply that it controls a species population size or distribution. Other analytical methods must be used to make these important determinations. This paper demonstrates one method, with an example, to quantify the demographic importance of statistically significant interactions. In our example, some of the statistically significant interactions with the polychaete Clymenella torquata (Leidy) have large impacts on the population growth rate of the bivalve Gemma gemma (Totten), while others do not. This demonstrates the necessity of distinguishing between statistical significance and demographic importance. In some cases, the demographic importance of the same interaction changes through time because of changes in the bivalve's life history. Interactions affecting juvenile bivalves often have a greater demographic importance than those affecting adults; but this is not always the case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00508268
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    Paper (German National Licenses)
    Fulltext
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