Demographic responses of Heterocypris incongruens (Ostracoda) related to stress factors of competition, predation and food

Abstract

<em>Heterocypris incongruens</em> is a widely distributed ostracod which can maintain its populations under stressful conditions such as those in temporary ponds and under low-quality diets, for example, detritus. It often co-occurs with cladocerans and fish living in shallow water bodies. Nevertheless, little is known about its response to the presence of predators, its consumption capacity of cyanobacteria typically present in eutrophic systems, and its interaction with other species in similar habits. We studied here the demographic responses of <em>H. incongruens</em> fed the green alga <em>Scenedesmus</em> <em>acutus</em>, two strains of <em>Microcystis </em>cf. <em>aeruginosa</em> and <em>Limnothrix</em> sp. Experiments were conducted separately and together in the presence of the cladoceran <em>Simocephalus vetulus </em>and the cichlid fish, <em>Oreochromis</em> kairomones. The ostracod maintained growth in all treatments, the reproductive output decreased on dietary <em>Limnothrix </em>sp., and its life expectancy was significantly lower with the toxic strain of <em>Microcystis</em>. The coexistence of both crustacean species increased the rate of population growth (~ 0.33 day<sup>-1</sup>) of <em>S. vetulus</em> and life expectancy (36-44 days) of <em>H. incongruens</em> on the test diets compared with controls (23-33 days). Our study suggests facilitation affects the interaction between the two microcrustaceans, especially on poor quality cyanobacterial diets.