Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

Evaluating Dependence among Mule Deer Siblings in Fetal and Neonatal Survival Analyses

Chad J. Bishop, Gary C. White and Paul M. Lukacs
The Journal of Wildlife Management
Vol. 72, No. 5 (Jul., 2008), pp. 1085-1093
Published by: Wiley on behalf of the Wildlife Society
Stable URL: http://www.jstor.org/stable/25097659
Page Count: 9
  • Download ($42.00)
  • Subscribe ($19.50)
  • Cite this Item
Evaluating Dependence among Mule Deer Siblings in Fetal and Neonatal Survival Analyses
Preview not available

Abstract

The assumption of independent sample units is potentially violated in survival analyses where siblings comprise a high proportion of the sample. Violation of the independence assumption causes sample data to be overdispersed relative to a binomial model, which leads to underestimates of sampling variances. A variance inflation factor, c, is therefore required to obtain appropriate estimates of variances. We evaluated overdispersion in fetal and neonatal mule deer (Odocoileus hemionus) datasets where more than half of the sample units were comprised of siblings. We developed a likelihood function for estimating fetal survival when the fates of some fetuses are unknown, and we used several variations of the binomial model to estimate neonatal survival. We compared theoretical variance estimates obtained from these analyses with empirical variance estimates obtained from data-bootstrap analyses to estimate the overdispersion parameter, c. Our estimates of c for fetal survival ranged from 0.678 to 1.118, which indicate little to no evidence of overdispersion. For neonatal survival, 3 different models indicated that ĉ ranged from 1.1 to 1.4 and averaged 1.24-1.26, providing evidence of limited overdispersion (i.e., limited sibling dependence). Our results indicate that fates of sibling mule deer fetuses and neonates may often be independent even though they have the same dam. Predation tends to act independently on sibling neonates because of dam-neonate behavioral adaptations. The effect of maternal characteristics on sibling fate dependence is less straightforward and may vary by circumstance. We recommend that future neonatal survival studies incorporate additional sampling intensity to accommodate modest overdispersion (i.e., ĉ = 1.25), which would facilitate a corresponding ĉ adjustment in a model selection analysis using quasi-likelihood without a reduction in power. Our computational approach could be used to evaluate sample unit dependence in other studies where fates of individually marked siblings are monitored.

Page Thumbnails

  • Thumbnail: Page 
1085
    1085
  • Thumbnail: Page 
1086
    1086
  • Thumbnail: Page 
1087
    1087
  • Thumbnail: Page 
1088
    1088
  • Thumbnail: Page 
1089
    1089
  • Thumbnail: Page 
1090
    1090
  • Thumbnail: Page 
1091
    1091
  • Thumbnail: Page 
1092
    1092
  • Thumbnail: Page 
1093
    1093