title: The fall and rise of the Icelandic Arctic fox (Vulpes lagopus): a 50-year demographic study on a non-cyclic Arctic fox population.
abstract: In territorial species, observed density dependence is often manifest in lowered reproductive output at high population density where individuals have fewer resources or are forced to inhabit low-quality territories. The Arctic fox (Vulpes lagopus) in Iceland is territorial throughout the year and feeds mostly on birds, since lemmings are absent from the country. Thus, the population does not exhibit short-term population cycles that are evident in most of the species' geographical range. The population has, however, gone through a major long-term fluctuation in population size. Because of the stability in hunting effort and reliable hunting records since 1958, the total number of adult foxes killed annually can be used as an index of population size (N t ). An index of carrying capacity (K) from population growth data for five separate time blocks during 1958-2007 revealed considerable variation in K and allowed a novel definition of population density in terms of K, or N t /K. Correlation analysis suggested that the reproductive rate was largely determined by the proportion of territorial foxes in the population. Variation in litter size and cub mortality was, on the other hand, related to climatic variation. Thus, Arctic foxes in Iceland engage in typical contest competition but can adapt their territory sizes in response to both temporal and spatial variation in carrying capacity, resulting in surprisingly little variation in litter size.
authors.affiliation: The Icelandic Institute of Natural History, Urridaholtsstraeti 6-8, P.O. Box 125, 212, Gardabaer, Iceland. ester@ni.is.
authors.forename: E R
authors.initials: ER
authors.lastname: Unnsteinsdottir
authors.affiliation: Institute of Biology, University of Iceland, Sturlugata 7, 101, Reykjavik, Iceland.
authors.forename: P
authors.initials: P
authors.lastname: Hersteinsson
authors.affiliation: Institute of Biology, University of Iceland, Sturlugata 7, 101, Reykjavik, Iceland.
authors.forename: S
authors.initials: S
authors.lastname: Pálsson
authors.affiliation: Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Angerbjörn
mesh_terms: D000818:Animals; D003411:Arvicolinae; D001717:Birds; D005589:Foxes; D011156:Population Density; D011235:Predatory Behavior
keywords: Carrying capacity; Contest competition; Density dependence; Fecundity; Population dynamics