Diet analysis using generalized linear models derived from foraging processes using R package mvtweedie. Issue 5 (16th March 2022)

• Record Type: Journal Article
• Authors: Thorson, James T.; Arimitsu, Mayumi L.; Levi, Taal; Roffler, Gretchen H.
• Is Part Of: Ecology. Volume 103:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-16
• Subjects: diet -- foraging theory -- generalized additive model -- generalized linear model -- metabarcoding -- point process -- Poisson process -- predation -- Tweedie distribution; Ecology -- Periodicals; Ecology -- Periodicals; Écologie -- Périodiques; Ecologie; Écologie; Écologie animale; Écologie végétale; Ecology; Periodicals; 577.05
• DOI: 10.1002/ecy.3637
• Languages: English
• ISSNs: 0012-9658

Abstract

Abstract: Diet analysis integrates a wide variety of visual, chemical, and biological identification of prey. Samples are often treated as compositional data, where each prey is analyzed as a continuous percentage of the total. However, analyzing compositional data results in analytical challenges, for example, highly parameterized models or prior transformation of data. Here, we present a novel approximation involving a Tweedie generalized linear model (GLM). We first review how this approximation emerges from considering predator foraging as a thinned and marked point process (with marks representing prey species and individual prey size). This derivation can motivate future theoretical and applied developments. We then provide a practical tutorial for the Tweedie GLM using new package mvtweedie that extends capabilities of widely used packages in R ( mgcv and ggplot2 ) by transforming output to calculate prey compositions. We demonstrate this approach and software using two examples. Tufted Puffins ( Fratercula cirrhata ) provisioning their chicks on a colony in the northern Gulf of Alaska show decadal prey switching among sand lance and prowfish (1980–2000) and then Pacific herring and capelin (2000–2020), while wolves ( Canis lupus ligoni ) in southeast Alaska forage on mountain goats and marmots in northern uplands and marine mammals in seaward island coastlines.