Human-induced effects on the distribution of species and communities of vertebrates at different spatial scales

Different human activities have been observed and predicted to threat present-day and future patterns of biodiversity, with impacts ranging from global to local spatial scales. Anthropogenic impacts on biodiversity can be subdivided into two categories: impacts directly deriving from human activities and those mediated by other taxa, whose detrimental effect is however triggered and enhanced by human action. In particular, three major threats widely recognized as the most important factors affecting biological diversity were analyzed through different modelling approaches: climate change, habitat loss and degradation and invasive alien species. A first case study evaluated the effect of climate change on Mediterranean bird communities through the application of the SESAM framework to model species assemblages. The results highlighted how the effect of climate change on the studied communities may consist in a relevant alteration of their properties, although different modelling implementation leaded to different predicted pathways for these effects to be exerted. While predictions driven by abiotic factors alone suggested a prevalent increase of most of the constituent species distribution, the inclusion of macroecological constraints and assembly rules into the projections leaded to successfully capture dynamics related to interspecific interactions, and provided consistent outcomes with the current knowledge on the studied species. Such discrepancy highlighted the importance of comparing the outcomes of multiple modelling techniques to assess the conservation implications of climate change for species assemblages. The subsequent two case studies assessed the role of traditional forest management and wind farms industries in provoking habitat loss and degradation on vertebrate species in Central Italy. First, I tested the hypothesis that sustainable forest management mimics the dynamics of a natural forest succession more closely than does traditional forestry, causing a less severe long – term impact on the distribution of forest vertebrates. I proposed the first integration of the forest dynamic model “LANDIS – II” with species distribution models in a hybrid modeling framework. The framework was applied on four forest – specialist vertebrates (tiny salamander, slow worm, eurasian nuthatch, and Leisler’s bat) and included three components: Forest Dynamic Model (FDM), Species Distribution Models (SDMs) and Spatial Pattern Analysis (SPA). FDM was used to simulate spatially explicit patterns of forest succession for the current time and for 2050, imposing three alternative forestry scenarios. The simulated forest succession patterns were analyzed through SPA to calculate spatialized landscape metrics that were adopted as environmental predictors for SDMs. Landscape trajectories were calculated on current and future species distributions predicted with SDMs to evaluate the effect of alternative forestry practices on their extension and fragmentation. The results showed how forest management mainly affected the spatial configuration rather than the extension of the predicted species distributions. Sustainable forest management was more favorable than traditional forestry in increasing the extension and reducing the fragmentation of the studied species’ distributions. My results supported the conclusion that conservation – oriented forest management mimicked the dynamics of a natural forest succession more closely than did traditional practices, favoring elements, such as forest unevenness, species richness, aggregation of patches and variability in their distances, which emerged as fundamental characteristics for preserving the long – term persistence of forest vertebrates. To evaluate the potential detrimental effect of wind turbines on bats, a regional-scale model was developed to assess the wind farm impact on bat migration and commuting routes. The model was implemented for the bat Nyctalus leisleri in a region of Central Italy currently undergoing considerable wind farm development. A Species Distribution Model for N. leisleri was generated using the MAXENT algorithm based on 47 presence records (reduced to 19 after the autocorrelation procedure) and 10 environmental variables derived from topographic and land cover maps. The SDM was used to create a map of connectivity using the software UNICOR to identify potential commuting corridors (PCCs). The incidence of each wind farm on bat flight corridors was assessed by overlaying the existing (380) and planned (195) turbine locations onto the PCCs. The results reported that most of the corridors were concentrated in the western part of the region, which hosts the largest suitable areas for the species; most of the existing (54 %) and planned (72 %) wind farms interfered with important corridors connecting the western and the eastern parts of the region. The last two case studies analysed the impacts related to Invasive Alien Species (IAS) on different vertebrate species at different geographical scales, both emphasizing the relevant role of an appropriate level of knowledge to cope with this critical threat to biodiversity. The realized climatic niche of an invasive species can be used to predict its potential distribution in new areas, providing a basis for screening procedures in the compilation of black and white lists to prevent new introductions. I tested this assertion by modelling the realized climatic niche of the Eastern grey squirrel (Sciurus carolinensis). MAXENT was used to develop three models: one considering only records from the native range (NRM), a second including records from native and invasive range (NIRM), a third calibrated with invasive occurrences and projected in the native range (RCM). Niche conservatism was tested considering both a niche equivalency and a niche similarity test. The results showed that NRM failed to predict suitable parts of the currently invaded range in Europe, while RCM underestimated the suitability in the native range. NIRM accurately predicted both the native and invasive range. The niche equivalency hypothesis was rejected due to a significant difference between the grey squirrel’s niche in native and invasive ranges. The niche similarity test yielded no significant results. My analyses supported the hypothesis of a shift in the species’ climatic niche in the area of introductions and leaded to the conclusion that SDMs appear to be a useful tool in the compilation of black lists, allowing identifying areas vulnerable to invasions. However, I advise caution in the use of SDMs based only on the native range of a species for the compilation of white lists for other geographic areas, due to the significant risk of underestimating its potential invasive range. The usefulness of SDMs for the assessment of IAS risk of spread also emerged from the analysis of the potential distribution of the rose-ringed parakeet and the monk parakeet in Central Italy. Psittaciformes play a predominant role among the exotic species deliberately imported by humans all over the world, being the most popular bird pets. When released, they often establish naturalized populations, as they present a wide ecological plasticity and synanthropy. The final case study aimed to statistically reconstruct the actual extent of occurrence (EOO) of the rose-ringed and monk parakeets in Tuscany region through a fixed kernel method, and their potential distribution through a bioclimatic envelope (BIOCLIM), using variables selected from the WORLDCLIM database. BIOCLIM analysis suggested a possible expansion risk for the analysed species in Tuscany, as both were predicted with a huge amount of suitable but not occupied habitat. In particular, the rose-ringed parakeet may colonize the inner part of the region, while the southern part of the region may be exposed to a possible range expansion of the monk parakeet.