title: Predictive modelling of habitat selection by marine predators with respect to the abundance and depth distribution of pelagic prey.
abstract: Understanding the ecological processes that underpin species distribution patterns is a fundamental goal in spatial ecology. However, developing predictive models of habitat use is challenging for species that forage in marine environments, as both predators and prey are often highly mobile and difficult to monitor. Consequently, few studies have developed resource selection functions for marine predators based directly on the abundance and distribution of their prey. We analysed contemporaneous data on the diving locations of two seabird species, the shallow-diving Peruvian Booby (Sula variegata) and deeper diving Guanay Cormorant (Phalacrocorax bougainvilliorum), and the abundance and depth distribution of their main prey, Peruvian anchoveta (Engraulis ringens). Based on this unique data set, we developed resource selection functions to test the hypothesis that the probability of seabird diving behaviour at a given location is a function of the relative abundance of prey in the upper water column. For both species, we show that the probability of diving behaviour is mostly explained by the distribution of prey at shallow depths. While the probability of diving behaviour increases sharply with prey abundance at relatively low levels of abundance, support for including abundance in addition to the depth distribution of prey is weak, suggesting that prey abundance was not a major factor determining the location of diving behaviour during the study period. The study thus highlights the importance of the depth distribution of prey for two species of seabird with different diving capabilities. The results complement previous research that points towards the importance of oceanographic processes that enhance the accessibility of prey to seabirds. The implications are that locations where prey is predictably found at accessible depths may be more important for surface foragers, such as seabirds, than locations where prey is predictably abundant. Analysis of the relative importance of abundance and accessibility is essential for the design and evaluation of effective management responses to reduced prey availability for seabirds and other top predators in marine systems.
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USA.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Boyd
authors.affiliation: Instituto del Mar del Perú, Callao, Lima, Peru.
authors.forename: Ramiro
authors.initials: R
authors.lastname: Castillo
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USA.
authors.forename: George L
authors.initials: GL
authors.lastname: Hunt
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USA.
authors.forename: André E
authors.initials: AE
authors.lastname: Punt
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USA.|Washington Cooperative Fish & Wildlife Research Unit, US Geological Survey, Seattle, WA, USA.
authors.forename: Glenn R
authors.initials: GR
authors.lastname: VanBlaricom
authors.affiliation: Centre d'Etudes Biologiques de Chizé, Villiers en Bois, France.
authors.forename: Henri
authors.initials: H
authors.lastname: Weimerskirch
authors.affiliation: Institut de Recherche pour le Développement, Sète, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Bertrand
mesh_terms: D063147:Animal Distribution; D000818:Animals; D001717:Birds / Q000502:physiology*; D004242:Diving; D017753:Ecosystem; D005260:Female; D005399:Fishes / Q000502:physiology; D020387:Food Chain; D008297:Male; D008954:Models, Biological; D010568:Peru; D011156:Population Density; D011235:Predatory Behavior
keywords: Humboldt Current System; central place foragers; foraging ecology; habitat use; predator-prey interactions; spatial distribution