Micah Scholer, Peter Arcese, Gustavo Londono, Martin Puterman, Jill Jankowski
Scientists have long sought to understand the ecological and physiological trade-offs associated with long- versus short-lived animals. One potential explanation may lie in a species’ rate of metabolism ― their fire of life. According to this view, a lower metabolic rate decreases accumulation of cellular damage, extending lifespan overall. Yet, few studies have explored how metabolic rate varies with survival in the same population of animals living in the wild.
We investigated the relationship between survival and one of the most common measures of energy metabolism, basal metabolic rate (BMR), in 37 species of tropical birds in the Peruvian Andes. We captured and marked birds with aluminum leg bands and tracked their survival over a six-year period for species living at low (<400 m) versus high elevation sites (up to 2900 m), the latter of which were colder and more seasonal compared to lowland habitats. We then paired this data with measurements of BMR previously collected at these same study sites. This provided us with an ideal context to ask how both environmental conditions and an organism’s physiology interact to influence survival rates.
We found a negative relationship between survival and BMR supporting the view that low metabolic rate may be associated with longer lifespan. Additionally, we found that bird species living at higher elevations had lower survival than lowland birds. This suggests that either harsher climatic conditions act to decrease species survival at high elevations or, from an evolutionary perspective, that high elevation species are still adapting to local climatic conditions. Because our models of survival were unable to distinguish between birds that died, versus those that emigrated, our estimates of low survival could also indicate that the high elevation species we studied are more likely to make wide-ranging movements compared to sedentary lowland birds.