The manner in which individual life history traits respond to the environment and to each other, and how these traits combine to form overall patterns of life history variation, remains poorly characterized in wild populations. We monitored breeding Dark-eyed Juncos (Junco hyemalis) across a 700-m elevational range. We compared breeding season length, temporal patterns of breeding activity, adult body size, clutch size, brood size, nestling quality, and nest mortality among elevations. We also compared environmental measures across the studied elevations to determine whether abiotic factors explained life history trait variation. We used 12 microsatellite loci to test for genetic differentiation in populations at different elevations. Finally, we constructed a computer simulation to evaluate the combined effects of observed variation in life history traits. We found differences among elevations in breeding season length and in patterns of reproductive timing, which did not match each other and which were not explained solely by abiotic factors. We found no differences among elevations in adult body size, clutch size, brood size, or nestling quality. Nest mortality increased significantly with elevation. Genetic differentiation was too low to define distinct subpopulations. The simulation suggested that differences in mortality, in combination with differences in breeding season length, contributed to substantial differences in reproductive success among elevations. Thus, although individual life history traits showed little evidence of variation in response to the environment or to each other and little genetic differentiation, variation in breeding season length and in nest mortality were potential drivers of substantial elevational variation in overall life history in this system. These results demonstrate that individual life history traits may vary substantially in their patterns of variation, and that some life history traits may have disproportionate effects on overall life history.
Bibliographical noteFunding Information:
J. Scullen at the San Francisco Bay Bird Observatory provided training. S. Beissinger, L. Smith, and T. Hammond provided advice. The following research assistants contributed to data collection: J. Bates, J. Carlisle, A. Gilbert, L. Hall, K. R. Hayes, V. Kimzey, K. Langhans, K. Lyberger, A. M. Lee, K. Marsh, S. Maclean, A. Misraraj, H. Park, J. Spool, J. Tseng, and J. Van Bourg. Funding statement: Funding for K.L. was provided by a National Science Foundation (NSF) Graduate Research Fellowship, a Berkeley Fellowship from UC Berkeley, Museum of Vertebrate Zoology funds, and grants from the American Ornithologists’ Union, the Animal Behavior Society, and Sigma Xi. No funders had input into the content of the manuscript, and no funders required their approval of the manuscript before submission or publication. Ethics statement: All methods were approved by UC Berkeley’s Animal Care and Use Committee (protocol #R317-0815). Author contributions: Both authors conceived the idea, design, and experiment (supervised research, formulated question and/or hypothesis), and wrote the paper; K.L.
K.L. was provided by a National Science Foundation (NSF) Graduate Research Fellowship, a Berkeley Fellowship from UC Berkeley, Museum of Vertebrate Zoology funds, and grants from the American Ornithologists Union, the Animal Behavior Society, and Sigma Xi. No funders had input into the content of the manuscript, and no funders required their approval of the manuscript before submission or publication.
© 2018 American Ornithological Society.
- Breeding phenology
- Junco hyemalis
- life history variation
- nest mortality