Ton, R., and T. E. Martin. 2019. Nest Predation and Adult Mortality Relationships with Post-natal Metabolic Rates and Growth among Temperate and Tropical Songbirds. Journal of Experimental Biology 223: doi: 10.1242/jeb.226563.
Variation in life history expression is thought to arise from selection acting through physiological mechanisms, but selection pressures may differ or even conflict between life stages. High offspring predation risk can favor fast growth rates among species that may be achieved by faster post-natal metabolic rates. Faster metabolism, on the other hand, may create costs for adults, such that species with low adult mortality rates may be expected to minimize such adult costs through slower metabolism. Thus, mortality at the two different life stages may differentially influence offspring metabolism. We tested these possibilities among 43 songbird species studied on three continents. We found that nest predation risk and adult mortality probability were indeed interactive in their association with offspring metabolic rates across species. Our results provide a rare example of ecological sources of mortality during different life stages being correlated with post-natal metabolic rate as a mechanism underlying offspring growth.