Insights on wild boar behaviour, ecology, and impacts in Mediterranean areas

Wild ungulates play crucial roles in food webs, generating effects propagating across trophic levels, which can intensify at high population densities. Understanding their ecology and behaviour, as well as the determinants of their impacts, is essential to address effective management actions. This is particularly relevant in recent decades, because ecological perturbations are increasingly reshaping interspecific interactions and animal responses to external pressures. I focused on the wild boar Sus scrofa, a widespread ungulate whose foraging activity, especially rooting, can markedly affect ecosystems. By combining long-term data from morphometric measurements, camera trapping, faeces counts, rooting estimates, and statistical modelling, I investigated the main drivers of wild boar body mass variations (Chapter 2), diel activity rhythms (Chapter 3), and rooting intensity (Chapter 4) and distribution (Chapter 5). Also, I assessed its potential impacts on natural/seminatural habitats (Chapters 4 and 5) and medium-to-large sized mammal communities (Chapter 6). These investigations were focused on Mediterranean habitats, mainly during the harshest season (i.e., summer), when seasonal constraints may affect wild boar phenotypic traits and amplify local impacts. In Chapter 2, a 16-year analysis of culled males and trapped females showed that adult/yearling body mass in summer was reduced by aridity and high population density, and increased with ecotones in wild boar home range and in rainy-mild years. In Chapter 3 wild boar daily activity during summer was higher near persistent water resources and agricultural lands, decreasing in sites more visited by humans. Females with offspring were more diurnal than females without offspring and males, likely to reduce predation risk for their young. Nocturnality increased with increased temperatures over the previous 24h, close to crops, and in open habitats, especially in brighter nights. In Chapter 4 three-year seasonal surveys in EU-protected grasslands, and in Chapter 5 six-year intensive summer surveys in heterogeneous habitats, revealed that rooting intensity increased with population density, rainfall, and near woodland, and decreased in rocky and steep terrains, heterogeneous landscapes, and far from roads/railways. Rooting peaked in autumn/winter. In Chapter 6, the fine-scale richness of medium-to-large sized mammals across 21 Mediterranean protected areas showed no negative association with the spatial variation of wild boar visitation rate. Yet, support to species-specific responses emerged: Martes spp., red fox Vulpes vulpes, and European brown hare Lepus europaeus decreased their site-use in sites with higher wild boar detection rates, whereas the opposite relationship was found for badger Meles meles, crested porcupine Hystrix cristata, roe deer Capreolus capreolus, red deer Cervus elaphus and fallow deer Dama dama. While positive or negative co-occurrence in the same habitat because of factors independent from interactions with wild boar cannot be ruled out, biological support may be expected to (i) resource competition and habitat degradation by high wild boar activity negatively affecting site-use of small herbivores (hare) and predators of small rodents (red fox and martens), and to (ii) wild boar digging facilitating the access to underground resources for semi-fossorial species (badger and porcupine). Overall, my results highlight the remarkable behavioural plasticity of wild boar and show that the intensity of activity is strongly context-dependent, whereas perceived impacts on other species may be species-specific. In their native distribution range, wild boar are integral components of ecosystems and can play important functional roles, although negative impacts on the conservation status of endangered species or habitat may emerge, which makes it necessary to maintain their populations at ecologically sustainable levels. Behavioural responses to climate change, however, may reshape interspecific interactions and increase the likelihood of human–wildlife conflicts, underscoring the need for targeted monitoring and adaptive management. Management actions should promote landscape heterogeneity and focus on attractive habitats, such as grasslands and productive areas adjacent to woodlands, particularly following rainy and mild years.