Environmental constraints on growth of painted turtles (Chrysemys picta) in northern climates

Growth rates of free-living juvenile painted turtles (Chrysemys picta) in A lgonquin Park, Ontario, were positively correlated with air temperature dur ing growing seasons between 1990 and 1996. To test whether this positive co rrelation was directly due to temperature or indirectly due to increased fo od availability in warmer years, we experimentally separated the effects of temperature and food on growth of 90 hatchlings from Algonquin Park. Hatch lings were provided with varied opportunities to thermoregulate through bas king for 0-5 out of five days and were fed either to satiety or to about 60 % of the amount required for satiety. Growth in the laboratory was positive ly correlated with basking frequency but not with quantity of food provided . Presumably, in this experiment, we did not restrict food sufficiently in the lower food group to reduce growth. Turtles that never had basking oppor tunities ate significantly less (37.5%) than the amount eaten by turtles al lowed to bask daily and 46.7% of the amount eaten by turtles allowed to bas k four out of five days. Passage rate of food was faster in turtles that we re allowed to bask. Passage rate may be one of the factors that contributed to the relationship between temperature and growth observed both in the la boratory and in the field.