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The recent Europe-wide increase in wild boarSus scrofa, Linnaeus, 1758 abundance is undoubtedly due to many different factors, the relative importance of which differs from region to region. In Aragón (northeastern Spain), wild boar enlarged its distribution area eight times in the 1990s as compared with the century before, occupying the whole region. We studied wild boar abundance along an environmental gradient in Aragón to determine which factors are most responsible for its variation. Relative abundance of wild boars was estimated by catch-effort methods in 134 hunting estates (sampling units) for 5 consecutive hunting seasons. To characterise the environmental conditions, we quantified landscape composition and structure, topographical factors and climatic factors. Hunting pressure indices were also calculated for our sampling units. The average wild boar catch per hunting activity and per 100 km2 ranged from 0.72 to 16.31. Our results suggest thatwild boar abundances are affected by landscape structure, mainly by landscape diversity. In addition, lowland arid agrosystems (characterized by high temperatures and open juniper woodlands with little food availability) constrain the abundance of wild boar populations in spite of their wide plasticity to colonize new habitats.
We studied the age-structure and the reproductive parameters in two samples of red foxesVulpes vulpes (Linnaeus, 1758) from two contiguous areas in the Ebro valley (NE Spain) differing in the level of deliberate culling and in the habitat quality. Percent of juvenile foxes in the semiarid steppe (under higher persecution) was lower (53%) than in the irrigated highly productive “vegas” (67%). Conversely, foxes in the “vegas” (more favourable habitat) had a larger litter size (3.9 ± 0.23 cubs per female) and a higher amount of barren vixens (19.3%) than in the steppe (3.3 ± 0.12 cubs per female, and 1.7% of barren vixens). In this study, migration due to juvenile dispersal does not hide the effects of the habitat on fox population dynamics, despite the proximity between both areas. The results are discussed in relation to previous studies on red fox population dynamics.
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