title: A hierarchical Bayesian model to estimate the unobservable predation rate on sawfly cocoons by small mammals.
abstract: Predation by small mammals has been reported as an important mortality factor for the cocoons of sawfly species. However, it is difficult to provide an accurate estimate of newly spun cocoons and subsequent predation rates by small mammals for several reasons. First, all larvae do not spin cocoons at the same time. Second, cocoons are exposed to small mammal predation immediately after being spun. Third, the cocoons of the current generation are indistinguishable from those of the previous generation. We developed a hierarchical Bayesian model to estimate these values from annual one-time soil sampling datasets. To apply this model to an actual data set, field surveys were conducted in eight stands of larch plantations in central Hokkaido (Japan) from 2009 to 2012. Ten 0.04-m(2) soil samples were annually collected from each site in mid-October. The abundance of unopened cocoons (I), cocoons emptied by small-mammal predation (M), and empty cocoons caused by something other than small-mammal predation (H) were determined. The abundance of newly spun cocoons, the predation rate by small mammals before and after cocoon sampling, and the annual rate of empty cocoons that remained were estimated. A posterior predictive check yielded Bayesian P-values of 0.54, 0.48, and 0.07 for I, M, and H, respectively. Estimated predation rates showed a significant positive correlation with the number of trap captures of small mammals. Estimates of the number of newly spun cocoons had a significant positive correlation with defoliation intensity. These results indicate that our model showed an acceptable fit, with reasonable estimates. Our model is expected to be widely applicable to all hymenopteran and lepidopteran insects that spin cocoons in soil.
authors.affiliation: The University of Tokyo Forests, Graduate School of Agricultural and Life Sciences, The University of Tokyo Tokyo, Japan.
authors.forename: Panisara
authors.initials: P
authors.lastname: Pinkantayong
authors.affiliation: The University of Tokyo Chichibu Forest, Graduate School of Agricultural and Life Sciences, The University of Tokyo Chichibu, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Department of Electrical and Computer Engineering, Graduate School of Natural Science and Technology, Kanazawa University Kanazawa, Japan.
authors.forename: Mamoru
authors.initials: M
authors.lastname: Kubo
authors.affiliation: Ishikawa National College of Technology Tsubata, Ishikawa, Japan.
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Muramoto
authors.affiliation: The University of Tokyo Chichibu Forest, Graduate School of Agricultural and Life Sciences, The University of Tokyo Chichibu, Japan.
authors.forename: Naoto
authors.initials: N
authors.lastname: Kamata
keywords: Apodemus argenteus; Apodemus speciosus; Myodes rufocanus bedfordiae; cocoon dynamic models; predation rate estimation