Results/Conclusions
I examined these questions in an artificial aquatic community composed of waterlily aphids (Rhopalosiphum nymphaeae) and one or two strains of duckweed, Lemna minor and Spirodela polyrrhiza. These experimental populations of duckweed vary in their response to temperature. At 20°C the two species do not differ in growth rate, but at 29°C S. polyrrhiza produces more fronds per unit time than L. minor. Our first experiment showed a significant positive indirect effect on both prey species after a single generation in temperatures averaging 20°C, but no indirect effect on either species at average temperatures of 29°C. That is, prey grew faster under predation at lower temperatures when another prey species is present than alone under predation at the same temperature. A second experiment of the same design was run to contrast single generation dynamics with multi-generational dynamics. Our prediction was that short term positive indirect effects would become negative over time, as aphids respond numerically to greater amounts of duckweed. Results indicate reciprocal negative indirect effects between duckweed populations at the lower temperature. However, at the higher temperature, S. polyrrhiza had a greater negative indirect effect on L. minor than L. minor had on S. polyrrhiza.