The population biology of Cyprinotus carolinensis and Herpetocypris reptans (Crustacea, Ostracoda)

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Abstract
The population mechanics of two species of ostracod in a temporary freshwater puddle are considered in relation to their competitive interaction in a variable environment. Both species survive dry periods as eggs. When the puddle refills eggs hatch over a long period of time but in two main groups. Cyprinotus spreads hatching more evenly between the two groups, recruits more slowly, but requires less time to mature than Herpetocypris. Unhatched eggs decay at lower rates for Cyprinotus, which inhabits the shortest lived part of the puddle.Cyprinotus mortality is more affected by density than is Herpetocypris. In mixed culture, Cyprinotus mortality increases disproportionately with density while Herpetocypris mortality is simply related to joint density. This difference may be attributed to a lower resistance to food shortage by Cyprinotus which also becomes more crowded at high density. Increased density increases time required to mature. Both species lay eggs at similar rates which decline with increasing density and decreasing temperature.Natural selection has favoured competitive prowess and rapid recruitment in Herpetocypris, which is suited to a permanent environment. In Cyprinotus, which is suited to a temporary, variable environment, selection has favoured the production of durable eggs and conservative recruitment.

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