Technical Comments

Comment on “Bateman in Nature: Predation on Offspring Reduces the Potential for Sexual Selection”

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Science  03 May 2013:
Vol. 340, Issue 6132, pp. 549
DOI: 10.1126/science.1233413

Figures

  • Fig. 1 The negative relationship between the metric termed “Bateman slope” and fawn mortality in pronghorn.

    Data are from figure 3 in (9). Neither the slope (t8 = 0.18, P = 0.86) nor the intercept (t8 = 0.61, P = 0.56) of the observed relationship (dashed regression line) differ from that predicted (solid line) under the relationship Y = 1 – X (i.e., survival equals one minus mortality). Overall, the observations across years have slightly positive “residuals” when compared with the predicted values (t9 = 3.21, P = 0.011), which could be due to a minor but systematic inferential bias when estimating the “Bateman slope” (i.e., survival rate). This could be because the estimates of “Bateman slopes” of Byers and Dunn were likely based on data showing heteroskedasticity and containing observations with high leverage, both of which can bias slope estimates in ordinary least squares regression. Additional important statistical problems include severe collinearity, overparameterization in their main inferential model [table 2 in (9)], and a lack of independence of data points because an unknown number of individuals were present during multiple years.

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