A half a century of measuring ungulate body condition using indices: is it time for a change?

Abstract

From a literature review of five wildlife ecology journals since 1937, we document how using indices to monitor ungulate body condition is common practice, with the kidney fat index (KFI = weight of fat around the kidneys/weight of kidneys without fat × 100) as the favoured tool (82% of studies). In this context, we highlight the problems of using indices when underlying statistical assumptions are not met (isometry, parallel slopes between treatments). We show, with real and simulated data for two cervids with contrasting fat storage strategies, how results from analysis of variance of KFI values differ from analysis of covariance (ANCOVA) of raw data. We conclude that the KFI is affected by the restrictions typically associated with derived index values, and as a consequence, statistical analysis of the KFI could generate spurious results leading to erroneous interpretations concerning variation in body condition of ungulate populations. Thus, we recommend analysing fat weight as an untransformed variable in ANCOVA (kidney weight as covariate) to describe body condition variation in ungulates. References (24) About this Article Title A half a century of measuring ungulate body condition using indices: is it time for a change?

Diet quality and immunocompetence influence parasite load of roe deer in a fragmented landscape

“…However, it remains difficult to quantify the simple effect of spleen mass on macroparasite load without taking into account the confounding effects of body reserves and condition and their relationship with host nutrition (Coop and Kyriazakis 2001;Vicente et al 2007b;Serrano et al 2008). By correcting spleen mass for body mass (a reliable index of condition in roe deer, see Toïgo et al 2006), we observed significantly lower parasite loads in deer with relatively large spleens (for a given body size), suggesting that spleen size is indeed a reliable indicator of immunocompetence.…”

Opposite responses of body condition and fertility in adjacent moose populations

“…We included the harvest date as a covariate for all analyses involving body mass. We added kidney mass as a covariate to models of kidney fat mass to correct for the effect of organ size on fat mass (Serrano et al ) and the hind foot length to models of peroneus mass to correct for the effect of body size.…”

The effects of winter severity and population density on body stores in the Iberian wild goat (Capra pyrenaica) in a highly seasonal mountain environment

“…Both KM and KF are positively correlated to nutritional status in Iberian wild goats (Serrano et al 2008b) and to body condition in a great range of mammals of different body sizes (from roe deer to moose, Serrano et al 2008a). As predicted, heavier goats (skeletally bigger and fatter) had more KM (R 2 =0.73, F 1,461 =1,281; p<0.01, linear relationship between body weight and KM) and KF (R 2 = 0.26, F 1,461 = 159.5; p < 0.01 following the same procedure) than lighter ones.…”

“…Changes in body condition-this term includes tissues necessary for a functionally normal life (defined as 'body reserves', according to Lindström and Piersma 1993) and those accumulated in anticipation of periods of shortage (defined as 'body stores', according to King and Murphy 1985)-have been related to several life-history traits in several ungulate species (Serrano et al 2008a). Commonly, this group of mammals allocates large amounts of energy to each breeding attempt (Pélabon et al 1995) and exhibits a wide range of resource-use tactics within the income-capital breeder continuum (Jönsson 1997).…”

“…Finally, taking into account the fact that most methods for measuring fat stores require necropsy (Serrano et al 2008a), we evaluated whether or not the residuals from the linear regression between body size and body mass (named 'mass-size residuals', according to Green 2001) are useful for predicting fat reserves in wild goats.…”