Juvenile survival of a planktonic insect: effects of food limitation and predation
1. An experiment was conducted to investigate potential impacts of food limitation and copepod predation on juvenile survival of Chaoborus purtctipennis. We tested the hypotheses that: (i) juvenile survival of Chaoborus is influenced more by copepod predation than by starvation in a productive environment, and (ii) food limitation and predation interact to affect survival. 2 Effects of food concentration (approximately 800, 1400 and 2300 microzooplankton 1–1) and predator density (0, 1 and 2 Mesocydops edax 1–1) on Chaoborus development and survival were evaluated using a 3 × 3 factorial design. Jars containing lake water, the appropriate food and predator treatments, and two Chaoborus (\textless12h old) were rotated on a plankton wheel at 25°C. Survival and developmental stage were monitored daily until all individuals had either died or moulted to instar II. 3 Predation by Mesocydops was the major source of mortality, causing 87.5\% of Chaoborus deaths over all treatments. Chaoborus mortality was significantly higher in treatments with Mesocydops (67–100\%) than in predator-free treatment (0–13\%). 4 Development time was significantly longer in the low-density food treatment than in the highest food treatment. 5 No significant interaction between food limitation and predation was detected. 6 These results suggest that predation by copepods may limit recruitment of juvenile Chaoborus in productive lakes.