Abstract
Results of studies on the population biologies of five species of brooding crustaceans, four amphipods and a myodocopid ostracod, from an unpredictable habitat at Kaikoura, New Zealand, provide a test of current theories of life-history tactics. Sediment depths inhabited provided a ranking of species habitat stabilities and mortality risks, both greatest at the sand surface. Population parameters confirm the ranking, but comparisons with species' combinations of life-history traits do not fit predictions of the various theories. The failure of these theories is principally due to phylogenetic constraints, the lack of viable genetic alternatives for a trait. A new theory is required, one that encompasses phylogenetic constraints and correlations of some traits with body size. Such a theory must recognize the possibility of several equally successful combinations of traits in a given situation and incorporate recent ideas on growth rates, body size and size-specific mortality.
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