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Lack's Clutch Size Hypothesis: An Examination of the Evidence Using Meta-Analysis
Eric Vander Werf
Vol. 73, No. 5 (Oct., 1992), pp. 1699-1705
Published by: Wiley
Stable URL: http://www.jstor.org/stable/1940021
Page Count: 7
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Meta-analysis is a method ecologists may find useful for quantitatively reviewing and systematically examining results from a large number of studies on a subject for which there is conflicting evidence. I used meta-analysis to integrate results from 42 independent brood-enlargement studies and tested Lack's hypothesis that clutch size in birds has evolved toward that which produces the most surviving offspring. Cumulative evidence did not support Lack's hypothesis. Significantly (two-tailed P = .016) more fledglings were produced in enlarged broods than in a normal-sized broods, indicating parents could raise more young than they had eggs. The standardized treatment effect of brood enlargement across all studies was a mean (@+ 1 se) increase of 0.55 (@+0.22) standard deviations in the number of young produced. This result does not appear to be affected by a publishing bias and is unlikely to be reversed by inclusion of additional studies. I also examined differences in methodology and species studied as possible confounding factors and explanations for conflicting results. Longer studies and species with altricial young were more likely to show food limitation. Latitude and date of study, degree of brood enlargement, validity of a study, and annual adult survival did not affect results.
Ecology © 1992 Wiley