title: Merging resource availability with isotope mixing models: the role of neutral interaction assumptions.
abstract: BACKGROUND
  Bayesian mixing models have allowed for the inclusion of uncertainty and prior information in the analysis of trophic interactions using stable isotopes. Formulating prior distributions is relatively straightforward when incorporating dietary data. However, the use of data that are related, but not directly proportional, to diet (such as prey availability data) is often problematic because such information is not necessarily predictive of diet, and the information required to build a reliable prior distribution for all prey species is often unavailable. Omitting prey availability data impacts the estimation of a predator's diet and introduces the strong assumption of consumer ultrageneralism (where all prey are consumed in equal proportions), particularly when multiple prey have similar isotope values.
  
  
  METHODS
  We develop a procedure to incorporate prey availability data into bayesian mixing models conditional on the similarity of isotope values between two prey. If a pair of prey have similar isotope values (resulting in highly uncertain mixing model results), our model increases the weight of availability data in estimating the contribution of prey to a predator's diet. We test the utility of this method in an intertidal community against independently measured feeding rates.
  
  
  CONCLUSIONS
  Our results indicate that our weighting procedure increases the accuracy by which consumer diets can be inferred in situations where multiple prey have similar isotope values. This suggests that the exchange of formalism for predictive power is merited, particularly when the relationship between prey availability and a predator's diet cannot be assumed for all species in a system.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, California, United States of America. jdyeakel@gmail.com
authors.forename: Justin D
authors.initials: JD
authors.lastname: Yeakel
authors.forename: Mark
authors.initials: M
authors.lastname: Novak
authors.forename: Paulo R
authors.initials: PR
authors.lastname: Guimarães
authors.forename: Nathaniel J
authors.initials: NJ
authors.lastname: Dominy
authors.forename: Paul L
authors.initials: PL
authors.lastname: Koch
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Ward
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Moore
authors.forename: Brice X
authors.initials: BX
authors.lastname: Semmens
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D058448:Biota; D019992:Databases as Topic; D020387:Food Chain; D049851:Gastropoda / Q000502:physiology; D007553:Isotope Labeling; D008954:Models, Biological; D009520:New Zealand; D011235:Predatory Behavior; D015203:Reproducibility of Results; D013045:Species Specificity