No abstract

No abstract

The authors studied the life table demography and population growth of Daphnia laevis using the green alga Chlorella vulgaris and the cyanobacterium Microcystis aeruginosa (offered in colonial form) under two food concentrations (1´10 6 and 3´10 6 cells ml 1 ). The experimental design consisted of two types of food, and of two concentrations of algae, each with three replicates. The design was the same for both the life table study and the study of population growth. The variables derived were: age speci c survivorship, age-speci c reproduction, average lifespan, age-speci c life expectancy, gross reproductive rate, net reproductive rate, generation time, reproductive effort, stable age distribution, and rate of population growth derived iteratively. While survivorship variables were not affected signi cantly either by the type of food or by the concentration offered, reproductive variables of D. laevis were signi cantly in uenced by the type of alga rather by than its density. Cladocerans fed Chlorella reached maximal population abundance earlier than those fed Microcystis. Throughout the population growth study, peak population abundance values of D. laevis varied from 0.34 to 0.49 ind. ml 1 . There was no signi cant difference in the peak population density reached with respect to food type or food concentration. The rate of population growth per day varied from 0.1 to 0.15. Our study indicates that D. laevis can successfully utilize a basically toxic strain of M. aeruginosa, with which it co-exists in a man-made reservoir in Mexico. RESUMENEstudiamos la tabla de vida demográ ca y crecimiento poblacional de Daphnia laevis utilizando el alga verde Chlorella vulgaris y la cianobacteria Microcystis aeruginosa (ofrecida en forma colonial) en dos concentraciones de alimento, a 1´10 6 y 3´10 6 células ml 1 . El diseño experimental consistió en dos tipos de alimento, dos concentraciones de algas, cada una con tres réplicas. El diseño 3 )

Population growth patterns of the ostracod, Heterocypris incongruens have been studied using the green alga, Scenedesmus acutus or organic waste from a water treatment plant as food, and using dry weight equivalents of 5.8, 11.6, and 23.2 μg ml −1 for 50 days. H. incongruens, in our study, reproduced only parthenogenetically. The colour of the eggs and the carapace valves differed depending on the type of food. Populations cultured on the algae appeared bright orangecoloured, while those on organic waste were pale yellow. Regardless type and concentration of food, H. incongruens had a long lag phase of about 3 weeks, after which the exponential phase began that continued for the next 20 to 30 days. In treatments containing an algal diet, the density of H. incongruens increased with the increase of food level from 5.8 to 11.6 μg ml −1 . However, a further increase in food density did not result in a higher peak of abundance. In the treatments containing organic waste, population density was higher (about 1.6 ind. ml −1 ) at 5.8 and 11.6 μg ml −1 , but it decreased to half this density with a further increase in the amount of food (23.2 μg ml −1 ). The rate of population increase (r) of H. incongruens ranged from 0.03 to 0.07 per day, depending on food type and concentration. RESUMENSe estudiaron los patrones de crecimiento poblacional del ostrácodo Heterocypris incongruens utilizando el alga verde Scenedesmus acutus o desechos orgánicos de una planta de tratamiento de aguas residuales como alimento bajo diferentes densidades (como los equivalentes de peso seco de 5,8, 11,6 y 23,2 μg ml −1 ) durante 50 días. H. incongruens en nuestro estudio sólo se reproduce partenogenéticamente. El color de los huevos y las valvas de los ostrácodos difiere dependiendo del tipo de alimentos. Los cultivados en alga presentaron un color naranja brillante, mientras que los cultivados con residuos orgánicos mostraron un color amarillo pálido. Independientemente del tipo de alimento y la concentración, H. incongruens presentó una larga fase de adaptación de aproximadamente 3 semanas. Una vez que la fase exponencial se inició, esta tuvo una duración de 20 a 30 días. En los tratamientos de la dieta que contienen algas, la densidad de H. incongruens aumentó cuando se elevó la concentración de alimento de 5,8 a 11,6 μg ml −1 . Sin embargo, al incrementar la densidad en los alimentos no se reflejó en las abundancias máximas de la población de H. incongruens. Dentro de los tratamientos que contienen residuos orgánicos, la densidad de población fue mayor (alrededor de 1,6 ind. ml −1 ) a 5,8 y 11,6 μg ml −1 , pero se redujo a la mitad con mayor aumento de la densidad de los alimentos (23,2 μg ml −1 ). La tasa de aumento de la población (r) variaron entre 0,03 a 0,07 por día, dependiendo del tipo de alimentos y la concentración.