Meeting Abstract
Tropical birds are typically longer lived than temperate counterparts. This slow “pace of life” is thought to be associated with reduced metabolic rates via mechanisms such as reduced oxidative stress and/or reduced cost of reproduction. Initial studies of avian metabolic rates failed to find significant differences among latitudes, but recent work has found lower metabolic rates in tropical species, fitting the pattern predicted by the pace of life hypothesis. However, latitude is merely a proxy for a variety of factors that may influence both adult survival probability and metabolic rate thus latitudinal patterns in metabolic rate do not explicitly link metabolism to variation in longevity. While tropical species are consistently longer-lived than temperate counterparts, extensive variation exists within latitudes. This unexplained variation provides the opportunity to determine the independent influence of metabolic rate on longevity independent of additional factors correlated with latitude such as temperature or seasonality. We measured resting metabolic rates (RMR) of Passerine birds via an open-flow respirometry system at tropical (Sabah, Malaysia, 6°N), and temperate (AZ, USA, 35°N) field sites. We estimated adult survival probability based on 21 (AZ), and 7 (MY) years of banding/resighting at the same sites where metabolic measurements were undertaken. Based on phylogenetic least-squares analyses, we found that metabolic rate explained variation in adult survival within but not among latitudes. Within sites, long-lived species had lower metabolic rates than would be predicted by mass and phylogenetic relationships alone. Additionally, tropical species were longer lived than temperate species, even after controlling for differences in metabolic rate. Our results support the pace of life hypothesis in that, within latitudes, species with high adult survival probability had low metabolic rates. However, our results also suggest that there is an additional effect of latitude on adult survival probability independent of variation in metabolic rate.
