Estimating Fitness: Comparison of Body Condition Indices Revisited

Biometric Differences Among the DipperCinclus cinclusPopulations of Spain

“…A positive value indicated that the bird weight was higher than expected for its size, and vice versa. To find the body size with the best fit, two regressions were made for the weight versus the length of the wing and weight versus the length of the tarsus, as in other studies (e.g., Ormerod & Tyler 1990), with a logarithmic transformation recommended by Jacob et al (1996) and Kotiaho (1999). The regression analysis of log weight on log wing length (or log tarsus length), sex and age, excluded age from the analysis using the stepwise method (p = 0.38 and p = 0.33 for wing and tarsus, respectively).…”

Sexual selection mediated by the thermoregulatory effects of male colour pattern in the ambush bugPhymata americana

“…fat reserves) and, thus, a correlate of male quality or vigour (e.g. Jakob et al 1996; but see Kotiaho 1999). Since coloration in P. americana is condition dependent (Punzalan 2007), it is difficult to separate the effects of condition and male colour pattern without directly manipulating colour pattern.…”

Do sexual ornaments demonstrate heightened condition-dependent expression as predicted by the handicap hypothesis?

“…But this is problematic if scaling deviates from isometry, as the covariance with body size will persist (Packard & Boardman 1999) and condition dependence may arise as an artefact. Residuals derived from the regression of trait size on body size have also been used, but this procedure has been the subject of recent criticism (Kotiaho 1999;Green 2000;Darlington & Smulders 2001;García-Bertou 2001). A preferable approach is to express trait size as a function of body size and statistically account for it as a covariate in general linear models, which avoids the drawbacks associated with relative and residual measures (Darlington & Smulders 2001;García-Bertou 2001).…”

“…Typical indexes attempt to control for body size by taking simple ratios (mass divided by the cube of body size), slope-adjusted ratios (slope of log(body mass) on log(body size)) or residuals (Jakob et al 1996). All of these indexes have been criticized, largely because the true relationship between the two variables is unknown a priori, and each method introduces assumptions that may not be biologically or statistically justified (see Jakob et al 1996;Kotiaho 1999;Packard & Boardman 1999;Green 2000;Darlington & Smulders 2001;García-Bertou 2001). To confound matters, there is no assurance that fresh weight is always a good indicator of fat reserves, or that fat reserves are a good indicator of fitness.…”