FRAZIER, M.; HUEY, R.B.; BERRIGAN, D.; Univ. of Washington, Seattle; Univ. of Washington, Seattle; National Cancer Institute, Bethesda, MD: Insect Population Growth: Hotter is Better
A long-standing debate concerns the ability of ectotherm physiology to evolutionarily compensate for shifts in body temperature. The �thermodynamic school� maintains that the thermodynamically governed increase in kinetic energy with temperature requires that maximum rates of population growth (rmax) increase with temperature, such that warm-adapted species must have higher rmax at their optimal temperature (To) than do cold-adapted species. The �biochemical-adaptation� school counters that biochemical adaptation is sufficiently malleable over evolutionary time to compensate for the rate depressing effects of low temperature, such that rmax should be independent of optimal temperature. Here we evaluate these conflicting views for insects by examining the relationship between rmax and To. Using a phylogenetic analysis (standardized independent contrasts), we find strong support of the thermodynamic hypothesis: warm-adapted insects do indeed have higher rmax than do cold-adapted insects. This pattern is robust and holds even when potentially conflating environmental factors are included in a path analysis. In terms of insect population growth rates, hotter is better.
