title: Mass-based condition measures and their relationship with fitness: in what condition is condition?
abstract: Mass or body-size measures of 'condition' are of central importance to the study of ecology and evolution, and it is often assumed that differences in condition measures are positively and linearly related to fitness. Using examples drawn from ecological studies, we show that indices of condition frequently are unlikely to be related to fitness in a linear fashion. Researchers need to be more explicit in acknowledging the limitations of mass-based condition measures and accept that, under some circumstances, they may not relate to fitness as traditionally assumed. Any relationship between a particular condition measure and fitness should first be empirically validated before condition is used as a proxy for fitness. In the absence of such evidence, researchers should explicitly acknowledge that assuming such a relationship may be unrealistic.
authors.affiliation: Department of Life Science, Rikkyo University, Tokyo, Japan.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Barnett
authors.affiliation: Department of Life Science, Rikkyo University, Tokyo, Japan ; Department of Evolutionary Studies of Biosystems, The Graduate University for Advanced Studies, Kanagawa, Japan.
authors.forename: Toshitaka N
authors.initials: TN
authors.lastname: Suzuki
authors.affiliation: Behavior, Ecology, Evolution, and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA.
authors.forename: Scott K
authors.initials: SK
authors.lastname: Sakaluk
authors.affiliation: Behavior, Ecology, Evolution, and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA.
authors.forename: Charles F
authors.initials: CF
authors.lastname: Thompson
keywords: birds; condition; fat reserves; fitness; individual phenotypic quality; insects; mammals; mass reserves