Competition, coexistence, and survival: a computer simulation study of ostracods living in a temporary puddle

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Abstract
A modelling study of the population biologies of two species of ostracod (Herpetocypris reptans Baird, 1835 and Cyprinotus carolinensis Fergusson, 1958) in a temporary puddle shows that competition is mediated via density-dependent mortality and maturation rates. Herpetocypris is the superior competitor, despite its longer maturation time, because it is better able to withstand crowding and the stress of food shortage. In addition, the structure of the habitat and periodic freezing are shown to play important roles in maintaining spatial separation of the species. The simulation model shows that Herpetocypris is dominant over Cyprinotus by a factor of 7:1 and this reduces the possibility of environmental instability favouring coexistence. Competitive exclusion of Cyprinotus by Herpetocypris is prevented by periodic freezing of part of the puddle which destroys all the ostracods, but harms population growth of Herpetocypris more than that of Cyprinotus.