Introduced mammals can cause extinction of native species due to replacement competition, disease, predation or hybridization. We studied the colonization of Piedmont (NW-Italy) by American grey squirrel (Sciurus carolinensis) and its effect on the native red squirrel (Sciurus vulgaris). Presence/absence data (2x2 km squares), of both species were (re)constructed using questionnaires, literature, existing databases, unpublished information, and direct monitoring with hair-tubes. In 1970 red squirrels were still widespread and greys were restricted to forests near the introduction site. By 1990, grey squirrels had increased their range to 220 km 2. , which coincided with the disappearance of native squirrels from 33 squares inside this range. The invasive species continued its spread occupying an area of 2,016 km 2 in 2010; within this area red squirrels went extinct in 88 squares. Overall, from 1970 to 2010 red squirrel went extinct in 62% of 2x2 km squares (ca. 1,689 km 2 ), and were replaced by grey squirrels. The spread of the alien species was slow in the first twenty years, but doubled in the successive two decades. Nevertheless spread was slower than in Ireland and England. Grey squirrel adapt to climate and habitats in both North and South Europe, causing extinction of the native red squirrel. A EU LIFE co-funded project with the aim to control the grey squirrel in North Italy and recent trade-restrictions and trade-ban are a first step in reducing the risk of grey squirrels invading other countries, but their effectiveness will have to be evaluated.

To assess competition for trophic resources within a guild of ungulates, we studied the food niches of sympatric ungulates in an alpine area of the Italian Western Alps and evaluated the extent of their dietary overlap, especially with regard to the presence of the introduced mouflon Ovis musimon. The roe deer Capreolus capreolus had the most diverse diet including dicotyledons, young sprouts of trees and an unusually high percentage of graminoids. The red deer Cervus elaphus and chamois Rupicapra rupricapra mainly consumed graminoids, supplemented with dicotyledonous herbs and woody plants. The mouflon was a grass feeder, with graminoids representing the majority of items ingested in all seasons. Among the native species, we recorded a high overlap of feeding choices between red deer and chamois, which frequently used the same areas and are both intermediate feeders.The mouflon showed considerable dietary overlap with the chamois and red deer in all seasons, while the similarity with roe deer was low. High food-niche overlap can imply competition but only if resources are limited and the species use the same habitats.

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We used radiotelemetry to investigate resting sites habitat selection by introduced eastern cottontail (Sylvilagus floridanus) and native European hare (Lepus europaeus) under sympatric conditions. We tracked 24 hares and 34 cottontails in a protected area of northwestern Italy. Hares were found in different sites every week, while cottontails used the same site for two weeks, and occasionally for longer. It is supposed that this periodic nest switching reduces the risk of predation and parasitism. Hares and cottontails forms were located in different habitats and characterized by dense vegetation cover near the ground. This cover increased from winter to summer in both species, while in autumn it continued to increase in cottontails only, and decreased in hares. Cottontails selected shrubby habitats near the river, and avoided crop fields in all seasons. Hares were more adaptive in their search, using high herbs and shrubs all year round, wheat fields in spring, maize in spring and summer, and stubbles in winter. Arguably, partial niche differentiation is necessary to allow the coexistence of similar species. In our study area, hares and cottontails differentiated in the use of resting sites habitats, presumably so as not to compete in this part of their ecological niche.

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