When a generalist becomes a specialist: patterns of red fox predation on roe deer fawns under contrasting conditions

Abstract

The red fox (Vulpes vulpes (L., 1758)) functional response to roe deer (Capreolus capreolus (L., 1758) fawn density was investigated in two Norwegian study areas characterized by a 26-fold difference in prey density and contrasting habitat characteristics. In the southern area, characterized by a fragmented agricultural landscape and high prey density, red fox consumption rates were closer to the specialist end in the specialist-generalist continuum of feeding habits. Conversely, in the northern area, dominated by boreal forest and with low prey density, the foxes displayed a type-III functional response typical of archetypal generalist predators. We suggest that differences in the predators' feeding habits reflect differences in prey profitability, which was much higher in the southern area owing to higher prey density and to the openness of the landscape that both favour the hunting of roe deer fawns. Different functional responses produced different predation rates (25% for the southern area and 13% for the northern area) and different temporal patterns (highest predation risk for fawns born at the beginning or at the end of the birth season). Even though the understanding of a predator's functional response is crucial for interpreting predation rates and patterns, much remains to be understood regarding its plasticity in different ecological settings. In the fawn-fox system, this might be the key factor in addressing unsolved questions regarding the adaptive value of reproductive synchrony as an antipredator strategy. Given the flexibility of the functional response and the resulting different impacts of predation with respect to birth synchrony, we suggest that reproductive synchrony evolved primarily in response to habitat seasonality and not as an antipredator strategy. Finally, our results contribute to the debate on the additive or compensatory nature of neonatal predation.Résumé : Nous étudions la réponse fonctionnelle du renard roux (Vulpes vulpes (L., 1758)) au chevreuil d'Europe (Capreolus capreolus (L., 1758)) dans deux aires d'étude en Norvège qui ont des densités de proies qui diffèrent par un facteur de 26 et des caractéristiques d'habitat distinctes. Dans l'aire du sud, dans un paysage agricole fragmenté et avec une forte densité de proies, les taux de consommation du renard roux s'approchent du pôle des habitudes alimentaires spécialisées sur un continuum d'habitudes spécialisées-généralistes. Inversement, dans l'aire du nord dominée par la forêt boréale et contenant peu de proies, les renards ont une réponse fonctionnelle de type III caractéristique des prédateurs généralistes typiques. Nous croyons que les différences dans les habitudes alimentaires des prédateurs reflètent les différences dans les bénéfices probables de la proie qui sont plus importants dans l'aire sud à cause de la densité plus élevée des proies et du paysage plus ouvert qui favorise la chasse aux faons des chevreuils. Les différentes réponses fonctionnelles produisent des taux de prédation différents (25 % dans l'aire du s...

Survival and causes of death of European Roe Deer before and after Eurasian Lynx reintroduction in the Bavarian Forest National Park

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