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The Influence of Seasonality and Stability on the Species Equilibrium
Author(s) -
Osman Richard W.
Publication year - 1978
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1936381
Subject(s) - ecology , seasonality , extinction (optical mineralogy) , habitat , colonization , environmental science , invertebrate , abundance (ecology) , climate change , biology , paleontology
The species equilibrium theory has proven to be a useful framework in which to analyze the distribution and abundance of species, especially for islands and habitats distributed as islands. In this study, the distribution of marine epifaunal invertebrates on rocks has been interpreted using this model. The relationship between area and the number of species present is sustained within this community. However, the increase in the number of species with increasing area appears to result from increasing immigration rather than decreasing extinction, as predicted by the model. Two factors have a major effect on the species equilibrium: seasonality and substrate stability. The seasonality of the climate causes the immigration rate to change seasonally. Colonization curves are dependent on the time of initial immersion of the substrate and vary in shape. However, with time, all converge. A simple model which allows immigration to fluctuate seasonally is developed. It predicts both the initial difference in the slope of the colonization curves and their eventual convergence. This same model also predicts that the colonization curve will cycle between a summer high and a winter low. The duration of the study was only long enough to test weakly this last prediction. The physical and temporal stability of a rock "island" is also a function of its size. Smaller rocks are disturbed more frequently than larger ones. This leads to an undersaturation in species on small rocks, causing an increase in the rate of change in the number of species with increasing area. Other changes in the slope of the area—species curve were found to be caused by changes in other environmental parameters. The species equilibrium theory is a fairly robust model in that changes in many parameters have a predictable effect on immigration and extinction which, in turn, determine species diversity. Although the utility of such an all—encompassing model may be questioned, its predictive framework makes it a very attractive tool for examining the diversity of communities.