Life-history variation & evolution across geographic gradients
Tropical birds lay fewer eggs at high elevations
Life-history strategies generally vary along a slow-fast gradient, with “fast” species characterized by high fecundity, fast growth and short life and “slow” species, the opposite. In birds, this gradient is manifested and well documented across latitudes, with adult mortality probability implicated as a likely driver (e.g. Martin et al. 2015, Boyce & Martin 2016). The slow-fast continuum of life-histories appears to be expressed across elevations as well, with high-elevation species showing lower clutch-sizes than close relatives at lower elevations (Boyce et al. 2015), yet whether a gradient in adult mortality is also driving this pattern remains unknown.