Andamento di ampiezza e posizione di nicchia e tratti specifici dei coleotteri carabidi lungo gradienti altitudinali nelle Alpi italiane occidentali.

Given the continuing loss of species and the environmental changes we are facing, understanding the mechanisms underlying spatial variation in species distribution is a fundamental and increasingly urgent aim in ecology. Carabids can be considered good candidates as ecological indicators because they are sensitive to habitat heterogeneity and land use, and they are relatively easy to study. They are appropriate organisms to examine using the elevation gradient approach in order to draw inferences about potential impacts of future environmental change. This thesis aims to assess whether there are any effects of elevation on niche breadth and niche position and whether these effects are modulated by species traits. We analysed pitfall trapping data collected from 182 points in the Western Italian Alps, consisting of the presence of carabid species collected along several elevation gradients, in addition to habitat, climate and topographic measures taken at each sampling point. At first, we evaluated the relationship between species richness and elevation. Then, using CCA (canonical correspondence analysis) we estimated the values of niche breadth and niche position for each sample location for each species. Finally, General Linear Models (GLMs) were used to analyse (i) variations in niche breadth with elevation, (ii) variations in niche position with elevation, and, (iii) the extent to which species traits modulate the responses of niche breadth and niche position to elevation. Species richness showed a bell-shaped distribution, marking first an increase (until 2500 m a.s.l.) and then a decrease. Niche breadth showed a positive linear effect in relation to standard deviation elevation, meaning that species occurring across a wider elevation range have a wider niche breadth, and may be therefore considered more resilient. Niche positions showed an inverse non-linear effect of elevation, suggesting that species become more specialised at both lower and higher elevations. Finally, we found no evidence of interactions between elevation and species trait on niche breadth and niche position, result that might be either distorted by the sample size or indicate that there are no ecological effects of these variables. Further investigations are therefore needed in this particular field, to understand which could be the main biotic and abiotic factors shaping niche breadth and niche position of carabid beetles along elevation gradients.