Figure 1.

Seasonal temperature dynamics of water bodies from three summer-active northern populations (a–c) and three winter-active southern populations (d–f). The black line marks temperature recorded in 30 min intervals. Time periods with water conditions suitable for planktonic Daphnia have a green background; time periods with unsuitable conditions have a blue (less than 5°C, northern populations) or a red background (dry, southern populations). During dry periods, daily temperature fluctuations are much stronger. In northern water bodies, suitable periods are at the hottest period of the year, while in the south, suitable periods fall in the rainy winter season. Data logger failure (low battery and vandalism) is shown in white. The temperature peaks in late autumn (October/November) in the Aegelsee pond of Switzerland are caused by hot water inflow (condensation water) from a sugar factory (the pond is used as a sewage pond from October to December). The lower summer temperatures of the desert population (f) are caused by vegetation shading the data logger. (Online version in colour.)