Evolution of life histories along elevational gradients: Trade-off betweenparental care and fecundity

Life history responses to environmental conditions include a combination of fecundity-survival schedules and behavioral strategies that yield tile hig hest fitness in a given environment. In this study, we examined the pattern of covariation in avian life history strategies along an elevational gradi ent by comparing variation in life history traits, including most component s of parental care, between phylogenetically paired taxa from low- and high -elevation sites. We found that high-elevation species had significantly lo wer annual fecundity but provided greater parental care to their offspring. However, a strong negative relationship between offspring number and durat ion of parental care along the elevational gradient suggested that high-ele vation species were shifting investment from offspring number toward offspr ing quality. Although adult survival did not differ between high- and low-e levation species, higher juvenile survival may have compensated for lower a nnual fecundity in high-elevation species. The elevation at which breeding occurred strongly influenced the partitioning of parental behavior between sexes. Male participation in nestling provisioning was significantly greate r in high-elevation species. In turn, altitudinal variation in the frequenc y of biparental care closely covaries with the intensity of sexual selectio n, ultimately resulting in the strong elevational pattern of sexual dimorph ism. Moreover, elevational variation in costs of development and maintenanc e of secondary sexual traits constitutes an additional effect on fecundity- survival schedules along elevational gradients. Thus, a trade-off between f ecundity and parental care, and associated interactions among morphological , life history, and behavioral traits play important roles in the evolution of life history strategies in birds.