title: Toxin constraint explains diet choice, survival and population dynamics in a molluscivore shorebird.
abstract: Recent insights suggest that predators should include (mildly) toxic prey when non-toxic food is scarce. However, the assumption that toxic prey is energetically as profitable as non-toxic prey misses the possibility that non-toxic prey have other ways to avoid being eaten, such as the formation of an indigestible armature. In that case, predators face a trade-off between avoiding toxins and minimizing indigestible ballast intake. Here, we report on the trophic interactions between a shorebird (red knot, Calidris canutus canutus) and its two main bivalve prey, one being mildly toxic but easily digestible, and the other being non-toxic but harder to digest. A novel toxin-based optimal diet model is developed and tested against an existing one that ignores toxin constraints on the basis of data on prey abundance, diet choice, local survival and numbers of red knots at Banc d'Arguin (Mauritania) over 8 years. Observed diet and annual survival rates closely fit the predictions of the toxin-based model, with survival and population size being highest in years when the non-toxic prey is abundant. In the 6 of 8 years when the non-toxic prey is not abundant enough to satisfy the energy requirements, red knots must rely on the toxic alternative.
authors.affiliation: Department of Marine Ecology, Royal Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg (Texel), The Netherlands. jan.van.gils@nioz.nl
authors.forename: Jan A
authors.initials: JA
authors.lastname: van Gils
authors.forename: Matthijs
authors.initials: M
authors.lastname: van der Geest
authors.forename: Jutta
authors.initials: J
authors.lastname: Leyrer
authors.forename: Thomas
authors.initials: T
authors.lastname: Oudman
authors.forename: Tamar
authors.initials: T
authors.lastname: Lok
authors.forename: Jeroen
authors.initials: J
authors.lastname: Onrust
authors.forename: Jimmy
authors.initials: J
authors.lastname: de Fouw
authors.forename: Tjisse
authors.initials: T
authors.lastname: van der Heide
authors.forename: Piet J
authors.initials: PJ
authors.lastname: van den Hout
authors.forename: Bernard
authors.initials: B
authors.lastname: Spaans
authors.forename: Anne
authors.initials: A
authors.lastname: Dekinga
authors.forename: Maarten
authors.initials: M
authors.lastname: Brugge
authors.forename: Theunis
authors.initials: T
authors.lastname: Piersma
mesh_terms: D000818:Animals; D049872:Bivalvia / Q000145:classification / Q000502:physiology*; D046091:Charadriiformes / Q000502:physiology*; D002755:Choice Behavior / Q000187:drug effects*; D005247:Feeding Behavior / Q000187:drug effects*; D008435:Mauritania; D008954:Models, Biological; D011156:Population Density; D011157:Population Dynamics; D011235:Predatory Behavior / Q000187:drug effects*; D015996:Survival Rate; D014118:Toxins, Biological / Q000494:pharmacology
chemical_list: D014118:Toxins, Biological
keywords: diet choice; hydrogen sulphide; optimal foraging theory; predator–prey interactions; survival rate; toxins