Colleagues, I am pleased to announce a publication that presents a new clustering method to detect hidden structure in fatty acid signature data and potentially improve estimates of consumer diet composition using quantitative fatty acid signature analysis, a method commonly used in studies of marine mammals. Citation: Bromaghin, J. F., S. M. Budge, and G. W. Thiemann. 2017. Detect and exploit hidden structure in fatty acid signature data. *Ecosphere* 8(7): e01896. Available open access at http://onlinelibrary.wiley.com/doi/10.1002/ecs2.1896/full Abstract: Estimates of predator diet composition are essential to our understanding of their ecology. Although several methods of estimating diet are practiced, methods based on biomarkers have become increasingly common. Quantitative fatty acid signature analysis (QFASA) is a popular method that continues to be refined and extended. QFASA is based on differences in the signatures of prey types, often species, which are recognized and designated by investigators. Similarly, predator signatures may be structured by known factors such as sex or age class, and the season or region of sample collection. The recognized structure in signature data inherently influences QFASA results in important and typically beneficial ways. However, predator and prey signatures may contain additional, hidden structure that investigators either choose not to incorporate into an analysis or of which they are unaware, being caused by unknown ecological mechanisms. Hidden structure also influences QFASA results, most often negatively. We developed a new method to explore signature data for hidden structure, called divisive magnetic clustering (DIMAC). Our DIMAC approach is based on the same distance measure used in diet estimation, closely linking methods of data exploration and parameter estimation, and it does not require data transformation or distributional assumptions, as do many multivariate ordination methods in common use. We investigated the potential benefits of the DIMAC method to detect and subsequently exploit hidden structure in signature data using two prey signature libraries with quite different characteristics. We found that the existence of hidden structure in prey signatures can increase the confusion between prey types and thereby reduce the accuracy and precision of QFASA diet estimates. Conversely, the detection and exploitation of hidden structure represents a potential opportunity to improve predator diet estimates and may lead to new insights into the ecology of either predator or prey. The DIMAC algorithm is implemented in the R diet estimation package qfasar. Regards, Jeff ----------------------------------------------- Jeffrey F. Bromaghin, PhD Research Statistician USGS Alaska Science Center Marine Ecosystems Office 4210 University Drive Anchorage, AK 99508 907-786-7086 jbromaghin@usgs.gov *http://alaska.usgs.gov/science/biology/quantitative_ecology/index.php <http://alaska.usgs.gov/science/biology/quantitative_ecology/index.php>*