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gamete production at low population density, and (b) smaller size with lower gamete
production at higher population density. The results obtained by Levitan (1991)
suggest that influence of population density on fertilization success should be
recognized and incorporated into an assessment of the reproductive potential of an
organism. These essentially indicate that the influence of body size on fertilization
success and reproductive output in shallow-water invertebrates is not important. If a
gain in fertilization success balances the cost of reduced gamete production, then
small-sized organisms living at high population density may be just as fecund as large
organisms living a low population density. However, the converse is true to species
living in the deep sea where the low population densities would increase the
importance of body size.
The most recent models of life-history theory explain the evolution of patterns
of covariation in reproductive traits based on demographic parameters and in relation
to variable environmental conditions (Ramirez-Llodra, 2002). The Winemiller-Rose
Model is based on a modification and extension of the two-dimensional r-K model
(McArthur and Wilson, 1967; Pianka, 1970) by incorporating three major
demographic components of fitness (fecundity, survivorship of juveniles and age at
maturity). The model implies that trade-offs among life-history traits are based on
physiological and ecological constraints that ultimately select for genetic correlations.
In the Winemiller-Rose Model, the r strategy is divided into periodic and
opportunistic strategists. The periodic strategists similar to the classical r strategists
have high fecundity and low juvenile survivorship. They differ, however, in that they
are large, long-lived and have late maturation (Ramirez-Llodra, 2002). The periodic
strategy maximizes age-specific fecundity at the expense of turnover time and
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