Breaking the sticks: a hierarchical change-point model for estimating ontogenetic shifts with stable isotope data

Matthieu Authier*, Celine Martin, Aurore Ponchon, Stephanie Steelandt, Ilham Bentaleb, Christophe Guinet

*Corresponding author for this work

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

1. Stable isotopes are increasingly used in ecology to investigate ontogenetic shifts in foraging habitat (via d13C) and in trophic level (via d15N). These shifts are in essence an individual-level phenomenon, requiring repeated measures throughout the life of individuals, i.e. longitudinal data. Longitudinal data require in turn specifying an appropriate covariance structure. Here we present a hierarchical model to jointly investigate individual ontogenetic shifts in d13C and d15N values. 2. In a Bayesian framework, we used a Cholesky decomposition for estimating a moderately-sized covariance matrix, thereby directly estimating correlations between parameters describing time-series of isotopic measurements. We offer guidelines on how to select the covariance structure. 3. The approach is illustrated with a hierarchical change-point (or broken stick) model applied to a data set collected on Southern Elephant Seals, Mirounga leonina. Ontogenetic shifts in foraging habitat, following a juvenile and variable stage, were detected and interpreted as fidelity to a foraging strategy; while ontogenetic shifts in trophic level were more likely the result of complete independence frommaternal resources followed by a gradual increase in trophic level as seals aged. 4. Specifying both an appropriate covariance and mean structure enabled us to draw strong inferences on the ecology of an elusive marine predator, and has wide applicability for isotopic ecology provided repeated isotopic measurements are available.

Original languageEnglish
Pages (from-to)281-290
Number of pages10
JournalMethods in Ecology and Evolution
Volume3
Issue number2
DOIs
Publication statusPublished - Apr 2012

Keywords

  • Bayesian methods
  • linear models
  • modelling
  • population ecology
  • statistics
  • SOUTHERN ELEPHANT SEALS
  • LONGITUDINAL DATA
  • TROPHIC ECOLOGY
  • CARBON
  • DELTA-C-13
  • NICHE
  • NITROGEN
  • VARIANCE
  • OCEAN
  • PLANKTON

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