A population of the isopod Tylos punctatus on a California beach was sampled by simultaneous coring and pitfall trapping. The traps showed a statistically significant bias against females, particularly gravid ones, and against juvenile isopods when compared to the cores. It is concluded that, for studying the population structure of this species, and perhaps others as well, pitfall traps produce samples that are too inaccurate to be useful.
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Willis B. Hayes (1970) studied this question.
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