a b s t r a c tMany animal pollinated plant species have been introduced to non native regions without their usual pollinators. Nevertheless, some of these alien species managed to establish reproducing naturalized pop ulations, which might negatively affect native plants. Recent studies have shown that many naturalized alien species can readily attract native pollinators. However, it is not known whether alien species that have not established naturalized populations are less successful in attracting pollinators. Therefore, we tested whether flower visitation rates are lower for non naturalized aliens than for naturalized alien and native species. We conducted a comparative study on flower visitation of 185 native, 37 naturalized alien and 224 non naturalized alien plant species in the Botanical Garden of Bern, Switzerland. Our phylogenetically corrected analyses showed that non naturalized alien species received fewer flower visitors than both naturalized alien and native species. Native, naturalized alien and non naturalized alien species were visited by similar flower visitor communities. Furthermore, among the naturalized alien species, the ones with a broader distribution range in Switzerland received a more diverse set of flower visitors. Although it has been suggested that most alien plants can readily integrate into native plant pollinator networks, we show evidence that the capacity to attract flower visitors in non native regions is different for naturalized and non naturalized alien plants. Therefore, we conclude that successful naturalization of alien plants may be related to flower visitation.

Many plant species respond to climate change by phenological shifts, usually with an earlier flowering onset. However, the variability in flowering responses to changed climatic conditions is large, and rare plant species, which are likely to have a low environmental tolerance, may be less able to shift their phenology than common ones. If plant species respond to climate change by shifting their flowering phenology, plant-pollinator interactions may become disrupted. However, it is vital for the reproduction of animal-pollinated plants, and thus for long-term population survival, that plants can attract pollinators. This might be especially difficult for rare species as they may depend on one or few pollinator species. To assess how climatic conditions affect the phenology of common and rare plant species, and whether the plant species attract potential pollinators, we assessed flowering onset and flower visitation in the lowland Botanical Garden of Bern, Switzerland, for 185 native plant species originating from different altitudinal zones. Plants from high elevations flowered earlier and showed more pronounced phenological shifts than plants from lower elevations, independent of species rarity. The probability, number, and duration of flower visits and the number of flower-visitor groups were independent of the altitudinal zone of plant origin and of species rarity. The composition of flower-visitor groups did also not depend on the altitudinal zone of plant origin and on species rarity. Thus, rare and common alpine plants may generally respond to climate change by an earlier flowering onset, and may be able to establish novel interactions with pollinators.