Meeting Abstract

1.8  Friday, Jan. 4  Thermal sensitivity of ectotherm growth: interactions of food quantity and food quality with climate change HUEY, R.B.*; KINGSOLVER, J.G.; Univ. of Washington, Seattle; Univ. of North Carolina hueyrb@uw.edu

How will the thermal sensitivity of growth rates of ectotherms be altered by climate warming? For predators fed ample food, growth rate increases with body temperature up to an optimum level and then drops rapidly at high temperature. But for predators fed restricted food, their growth at all temperatures is reduced; and the optimal temperature shifts lower, because energy gain at high temperature is insufficient to compensate for elevated metabolic rates. A simple energetics model (dating to J.R. Brett) predicts that if food levels decline, then ectothermal predators should preferentially select lower body temperatures. Note, however, that if food quantity declines as climate warms, then predators are caught in an energetic bind: climate warming may force them to be active at elevated body temperatures, even though energetics favors lower body temperatures: “metabolic meltdown” will result. But for herbivorous insects, the limiting resource is often nitrogen, not energy. When feeding on abundant but low-nitrogen plants, insects can grow fastest at relatively high body temperatures, because this facilitates compensatory consumption. Thus if food quality declines as climate warms and as atmospheric CO₂ increases (likely reducing leaf nitrogen and increasing secondary defensive compounds), then herbivores may achieve highest growth rates at elevated body temperatures. For herbivores then, climate change may increase consumption rates, growth rates and optimal temperatures. Thus, the effects of climate change on the thermal sensitivity and magnitude of ectotherm growth may reflect complex interactions with tropic level, food quantity, and food quality. Supported by NSF grants to RBH and to JGK.