Natural selection on beak and body size in the song sparrow.

Abstract

Selection was observed in Melospiza melodia in association with both survival and reproduction. Selection on males was weak and stabilizing in association with overwinter survival. Selection on females was strong, was both stabilizing and directional, and was associated with both survival and reproduction. In females, traits that enhanced juvenile survival also reduced reproductive success; ie there was a trade-off between survival and reproduction. Selection occurred mainly on tarsus length and beak length. -from Authors