Bias Introduced by the Simplified Method for the Estimation of the Intrinsic Rate of Increase of Aphid Populations: a Meta-Analysis

Abstract

The intrinsic rate of increase, denoted as r or r(m), describes the rate of population growth. Simplified formulas for estimating r have been developed to reduce labour and avoid complicated computations. The aim of this paper was to demonstrate and quantify the systematic bias in estimates of the intrinsic rate of increase provided by the simplified method (Wyatt & White 1977) compared to the age-stage, two-sex life table theory using a set of independently collected aphid life tables and meta-analytical approaches. The factors behind the variation in the bias across the studies were also explored. We analysed 112 aphid life tables from 24 independent experiments. The simplified method provided significantly greater estimates of the intrinsic rate of increase than the age-stage, two-sex life table theory in 98 out of 112 life table studies, and the difference was, on average, 27.6 % (95% CI: 24.0-31.3 %). The magnitude of the log-ratio of the two approaches was positively influenced by the pre-reproduction mortality and by variations in the duration of the total pre-reproduction period within a cohort. We concluded that although using simplified methods may be appealing because it saves time during the data collection phase and analysis, researchers, reviewers and journal editors should critically evaluate whether using the simplified method(s) is worthwhile, taking into account that such data are inaccurate and potentially lead to false conclusions. Current advances in the life-table theory and computer capacity have eliminated the need for simplified methods in population ecology.