TY - JOUR
T1 - Common condition indices are no more effective than body mass for estimating fat stores in insectivorous bats
AU - McGuire, Liam P.
AU - Kelly, Lewis A.
AU - Baloun, Dylan E.
AU - Boyle, W. Alice
AU - Cheng, Tina L.
AU - Clerc, Jeff
AU - Fuller, Nathan W.
AU - Gerson, Alexander R.
AU - Jonasson, Kristin A.
AU - Rogers, Elizabeth J.
AU - Sommers, Amie S.
AU - Guglielmo, Christopher G.
N1 - Funding Information:
Thanks to J. Boyles, C. Seewagen, and S. Olson for helpful comments when preparing the manuscript, and to the many field assistants that aided in collection of the original data sets. Long Point Bird Observatory and the University of Central Oklahoma provided housing and logistical support in the field. This is contribution no. 18-133-J from the Kansas Agricultural Experiment Station. Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, Ontario Ministry of Natural Resources, Pennsylvania Department of Environmental Protection, United States Fish and Wildlife Service, Texas Tech University, Kansas State University, and University of Massachusetts at Amherst. This project has been funded in whole or in part with Federal funds from the Department of Defense, Strategic Environmental Research and Development Program, under contract number W912HQ-16-C-0015.
Publisher Copyright:
© 2018 American Society of Mammalogists, www.mammalogy.org.
PY - 2018/10/10
Y1 - 2018/10/10
N2 - Researchers often use simple body condition indices (BCI) to estimate the relative size of fat stores in bats. Animals determined to be in better condition are assumed to be more successful and have higher fitness. The most common BCI used in bat research are the ratio index (body mass divided by forearm length) or residual index (residuals of body mass-forearm length regression) of size-corrected body mass. We used data from previous and ongoing studies where body composition (fat mass and wet lean mass) was measured by quantitative magnetic resonance to test basic assumptions of BCI, determine whether BCI is an effective proxy of fat mass, and whether other approaches could be more effective. Using data from 1,471 individual measurements on 5 species, we found no support for the underlying assumption that, within species, bats with longer forearms weigh more than bats with shorter forearms. Intraspecific relationships between body mass and forearm length were very weak (R 2 < 0.08 in all but one case). BCI was an effective predictor of fat mass, driven entirely by the relationship between fat mass and body mass. With little variation in forearm length, calculation of BCI is essentially equivalent to dividing body mass by a constant. We evaluated alternative approaches including a scaled mass index, using tibia length, or predicting lean mass, but these alternatives were not more effective at predicting fat mass. The best predictor of fat mass in our data set was body mass. We recommend researchers stop using BCI unless it can be demonstrated the approach is effective in the context of their research.
AB - Researchers often use simple body condition indices (BCI) to estimate the relative size of fat stores in bats. Animals determined to be in better condition are assumed to be more successful and have higher fitness. The most common BCI used in bat research are the ratio index (body mass divided by forearm length) or residual index (residuals of body mass-forearm length regression) of size-corrected body mass. We used data from previous and ongoing studies where body composition (fat mass and wet lean mass) was measured by quantitative magnetic resonance to test basic assumptions of BCI, determine whether BCI is an effective proxy of fat mass, and whether other approaches could be more effective. Using data from 1,471 individual measurements on 5 species, we found no support for the underlying assumption that, within species, bats with longer forearms weigh more than bats with shorter forearms. Intraspecific relationships between body mass and forearm length were very weak (R 2 < 0.08 in all but one case). BCI was an effective predictor of fat mass, driven entirely by the relationship between fat mass and body mass. With little variation in forearm length, calculation of BCI is essentially equivalent to dividing body mass by a constant. We evaluated alternative approaches including a scaled mass index, using tibia length, or predicting lean mass, but these alternatives were not more effective at predicting fat mass. The best predictor of fat mass in our data set was body mass. We recommend researchers stop using BCI unless it can be demonstrated the approach is effective in the context of their research.
KW - body condition index
KW - body mass index
KW - fat stores
KW - quantitative magnetic resonance
KW - size-corrected body mass
UR - http://www.scopus.com/inward/record.url?scp=85055043991&partnerID=8YFLogxK
U2 - 10.1093/jmammal/gyy103
DO - 10.1093/jmammal/gyy103
M3 - Article
AN - SCOPUS:85055043991
VL - 99
SP - 1065
EP - 1071
JO - Journal of Mammalogy
JF - Journal of Mammalogy
SN - 0022-2372
IS - 5
ER -