Growth, survivorship and reproduction of Daphnia middendorffiana in several Arctic lakes and ponds

The growth, survivorship and reproduction of Arctic region Daphnia middendorffiana was investigated in several lakes and ponds on the tundra in northern Alaska and additionally in a laboratory study. Growth rate equations, reproduction rates and survivorship under natural conditions were determined. The natural environments differed in the available resources; investigations were made in undisturbed oligotrophic lakes, lakes undergoing nutrient manipulations, takes recovering from nutrient manipulation, and a small human-created pond. The lakes also differed in the presence or absence of fish. The results indicated that resource availability affected the growth, survivorship and reproduction of D. middendorffiana. The take with the highest resources produced the greatest reproduction and growth. The environments with the lowest resources had the least reproduction. Secondly, resource level was observed to influence life history choices. Under low resource conditions D. middendorffiana produced ephippia at first reproduction rather than neonates. Third, the results also indicated that refuge from predation significantly affects the distribution of D. middendorffiana. Lakes that contain fish do not support significant populations of D. middendorffiana, although the growth and survivorship studies indicate they could do well in those environments.