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Density Dependence in the Life-Cycles of Animals and its Importance in K- and R-Strategies

Mary Stubbs
Journal of Animal Ecology
Vol. 46, No. 2 (Jun., 1977), pp. 677-688
DOI: 10.2307/3837
Stable URL: http://www.jstor.org/stable/3837
Page Count: 12
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Density Dependence in the Life-Cycles of Animals and its Importance in K- and R-Strategies
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Abstract

(1) A survey of density dependent mortalities has been made using `b', the slope of the k-value log density plot of Varley and Gradwell. (2) The animals are divided up according to whether they live in more-temporary or more-permanent habitats and this can be related to the magnitude and distribution of the b values for their density dependent mortalities. Whereas 86% of the density dependent mortality in the life cycle acts on the young stages for temporary habitat animals (r-stategists) the comparable figure for permanent habitat animals (K-strategists) is only 15%. Instead, parasitism and predation (30%) and reduced fecundity (35%) seem to occur more frequently in these animals. (3) The relationship between the type of mortality and the size of b is also discussed. It was found that whereas parasitism, predation and reduced fecundity gave b values that were not on the whole over-compensating, intraspecific effects for temporary habitat animals were mainly over-compensating. They are tending towards scramble competition. Where permanent habitat animals are showing intraspecific effects b is 1.2 or less. The overall pattern is for permanent habitat animals to have exactly- or under-compensating mortalities administered in the least wasteful manner possible whereas temporary habitat animals tend to have very small, under-compensating mortalities at low population densities changing fairly sharply to over-compensating mortalities as population density rises. This allows them to make maximum use of resources for the limited time that they are available. (4) This difference in strategy can also be seen in the differences in reproductive rate between the two groups.

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