Search

The N-mixture model proposed by Royle in 2004 may be used to approximate the abundance and detection probability of animal species in a given region. In 2006, Royle and Dorazio discussed the advantages of using a Bayesian approach in modelling animal abundance and occurrence using a hierarchical N-mixture model. N-mixture models assume replication on sampling sites, an assumption that may be violated when the site is not closed to changes in abundance during the survey period or when nominal replicates are defined spatially. In this paper, we studied the robustness of a Bayesian approach to fitting the N-mixture model for pseudo-replicated count data. Our simulation results showed that the Bayesian estimates for abundance and detection probability are slightly biased when the actual detection probability is small and are sensitive to the presence of extra variability within local sites.

Partitioning the variance of a response by design levels is challenging for binomial and other discrete outcomes. Goldstein (2003) proposed four definitions for variance partitioning coefficients (VPC) under a two-level logistic regression model. In this study, we explicitly derived formulae for multi-level logistic regression model and subsequently studied the distributional properties of the calculated VPCs. Using simulations and a vegetation dataset, we demonstrated associations between different VPC definitions, the importance of methods for estimating VPCs (by comparing VPC obtained using Laplace and penalized quasilikehood methods), and bivariate dependence between VPCs calculated at different levels. Such an empirical study lends an immediate support to wider applications of VPC in scientific data analysis.

Impounding large rivers has often led to reductions in aquatic habitat diversity over time. One approach used to restore habitat on the Upper Mississippi River is island construction. A specific purpose of island construction is to increase the growth and diversity of aquatic macrophytes. We addressed whether this purpose was met for islands constructed in a reach of the Upper Mississippi River. Aquatic macrophyte levels and richness around 2 constructed island complexes were compared with those in open water reference areas in 1998 and 2000. These data suggest that macrophyte levels increased in the construction area relative to the reference area for the second but not the first island complex. Findings were similar for both percent frequency of occurrence and richness index models. These differences in response are attributed to the differing maturities of the 2 island complexes. The first complex was completed 6 years prior to the initiation of aquatic macrophyte sampling, whereas sampling be...