Behaviourally Defined Ecological Resources and Speciation in Tisbe (Copepoda: Harpacticoida)

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Abstract
The swimming behaviors of 2 sibling species of Tisbe (Copepoda; Harpacticoida) were analyzed. Interference competition for copepod- (encounter-) free space, a behaviorally defined resource, led to vertical habitat displacement of one of the competitors. This swimming adaptation may facilitate the coexistence of 2 or more (sibling) species of Tisbe observed in contemporary stiuations. On an evolutionary time scale, such competitive displacement could lead to sexual isolation. Such interactions provide a paradigm for the origin of planktonic copepods from benthic ancestors. The resource utilization curves of these species inferred from the frequency distributions of their swimming behaviors were highly leptokurtic. Differing degrees of leptokurtosis in resource utilization curves accounted for patterns of speciation in the genus Tisbe.