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The influence of climate variability on polar bear (Ursus maritimus) and ringed seal (Pusa hispida) population dynamics

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Unusually high polar bear (Ursus maritimus Phipps, 1774) predation on ringed seal (Pusa hispida (Schreber, 1775)) pups and increased survival of polar bear cubs during mild springs is documented in published articles. Strong predation on newborn ringed seal pups in early spring, however, is likely to lower the overall energy intake of polar bears if ringed seal pups are their main food, because the energetic value of ringed seal pups increases 7–8 times during the 6 week lactation period. So although hunting success in early spring increases cub survival during the period after den emergence,when they are most vulnerable, it is likely to increase the number of starving bears later in the season. This negative-feedback effect of strong spring predation will not occur in areas where other seal species are abundant during summer, and polar bears in such areas are likely to exhibit population growth during periods with milder springs, at least until the ringed seal population has been depleted. Long time series of population estimates that can be used to test this hypothesis do not exist, but it is strongly supported by catch statistics for polar bears and ringed seals from east Greenland.

La littérature scientifique signale que, lors de printemps doux, il y a une prédation anormalement élevée des petits du phoque marbré (Pusa hispida (Schreber, 1775)) par l'ours polaire (Ursus maritimus Phipps, 1774) et une survie accrue des oursons de l'ours polaire. Cependant, une forte prédation de nouveaux-nés du phoque marbré risque de diminuer l'ingestion globale d'énergie chez les ours polaires, lorsque les jeunes phoques marbrés constituent leur nourriture principale, parce que la valeur énergétique des jeunes phoques marbrés augmente d'un facteur de 7–8 durant les 6 semaines de la longue période d'allaitement. Ainsi, alors que le succès de la chasse tôt au printemps augmente la survie des oursons durant la période difficile qui suit l'émergence du terrier, il risque d'accentuer la disette chez les ours plus tard dans la saison. Cet effet de rétroaction négative de la forte prédation printanière ne se produira pas dans les zones où d'autres espèces de phoques sont abondantes durant l'été; dans ces sites, les ours polaires sont susceptibles de connaître une croissance de population durant les printemps doux, au moins jusqu'à ce que la population de phoques marbrés soit réduite. Il n'existe pas de longues séries chronologiques de données pour évaluer cette hypothèse, mais les statistiques de capture des ours polaires et des phoques marbrés dans l'est du Groenland l'appuient fortement.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2006

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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