| Summary: | "Many ecological studies focused on predator-prey relationship, but few of them have the possibility to evaluate behavioural response of prey towards a variation in predation risk across space and time. This study was conducted in the Gran Paradiso National Park (GPNP), located in Western Alps. Large predators have been absent for the last 100 years, but since 2007, the presence of a resident wolf (Canis lupus) pack was confirmed. We investigated antipredator behaviour of two prey species: Alpine chamois (Rupicapra rupicapra) and Alpine ibex (Capra ibex). We monitored animals using line-transect sampling, recording for each group localisation, size and composition. We analysed data by means of linear mixed model (LMM). Wolf pack lived in Aosta Valley side of GPNP, while no signs of wolves were found in the Piemont side of the Park. Thanks to this heterogeneous situation we were able to study chamois antipredator behaviour comparing data of the two different sides of the Park. Chamois formed larger groups in areas with than in areas without wolves (LMM: F970.161 = 7.567; P=0.006). Females with kids and mixed groups were larger than adult and sub-adult male groups (LMM: F1128.801 = 262.397; P < 0.001). Moreover, in open habitat (alpine meadow) chamois formed the largest group (LMM: F1454.868 = 13.751; P < 0.001). . To study antipredator behaviour in Alpine ibex, we compared data collected before (2003-2004) and after (2008 – 2010) the recolonisation of the wolf in an area in Aosta Valley side of GPNP. Male group size decreased between the two periods, whereas female group size did not change (LMM: F11,849 = 15,247; P < 0,001) despite ibex population density was about halved from the first and the second period. During “wolf-year”, male groups reduced distance to refuge areas (slope and rocky terrain) whereas female groups (LMM: F37770.131 = 3.712; P = 0.005) did not modify use of safe areas. . Our findings showed different antipredator strategies between and within species in response to a variation of ...
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