Buffering of Life Histories against Environmental Stochasticity: Accounting for a Spurious Correlation between the Variabilities of Vital Rates and Their Contributions to Fitness

• Published in: The American naturalist Vol. 163; no. 4; pp. 579 - 590
• Main Authors: Morris, William F., Doak, Daniel F.
• Format: Journal Article
• Language: English
• Published: United States The University of Chicago Press 01-04-2004; University of Chicago, acting through its Press
• Subjects: Biological Evolution; Biological variation; Coefficients; Correlation coefficients; Correlations; Demography; Ecosystem; Fertility rates; Flowers & plants; Fruit production; Models, Biological; Population Dynamics; Quantile regression; Selection, Genetic; Silene - genetics; Silene - growth & development; Silene acaulis; Statistical discrepancies; Statistical variance; Survival rates; Theory; Time Factors; sensitivity; environmental stochasticity; elasticity; Silene acaulis; demographic buffering
• ISSN: 0003-0147; 1537-5323
• DOI: 10.1086/382550

Life‐history theory predicts vital rates that on average make large contributions to the annual multiplication rate of a lineage should be highly buffered against environmental variability. This prediction has been tested by looking for a negative correlation between the sensitivities (or elasticities) of the elements in a projection matrix and their variances (or coefficients of variation). Here, we show by constructing random matrices that a spurious negative correlation exists between the sensitivities and variances, and between the elasticities and coefficients of variation, of matrix elements. This spurious correlation arises in part because size transition probabilities, which are bounded by 0 and 1, have a limit to their variability that often does not apply to matrix elements representing reproduction. We advocate an alternative analysis based on the underlying vital rates (not the matrix elements) that accounts for the inherent limit to the variability of zero‐to‐one vital rates, corrects for sampling variation, and tests for a declining upper limit to variability as a vital rate’s fitness contribution increases. Applying this analysis to demographic data from five populations of the alpine cushion plantSilene acaulis, we provide evidence of stronger buffering in the vital rates that most influence fitness.