Evolution of Plant-Pollinator Relationships: Effects of alien species on plant–pollinator interactions: how can native plants adapt to changing pollination regimes?

Invasive alien species are of major concern in the management and conservation of habitats and species worldwide. Recent research has highlighted the importance of alien species' integration into plant-pollinator interactions, and its possible consequences for native species. Here we focus on the implications of alien plant and animal invasion for the pollination and reproductive success of native plants. We review the different mechanisms by which native plants might adapt to novel pollination regimes imposed by invading plants and animals, mainly changes in flower morphology and attractiveness, changes in blooming time and location, and shifts to reproductive modes that are independent of animal visitation. These adaptations may allow some native plant species that are negatively affected by invasive species to survive alongside the invaders. However, not all native plant populations and species are equally likely to undergo such adaptation. We outline the main factors that are likely to affect the potential for such adaptive processes across different taxa and ecosystems, and highlight the need to evaluate these factors in future research. Understanding the mechanisms by which native plants adapt to changing pollination regimes and the main characteristics that allow them to do so may provide an important tool for managing and conserving diversity and functionality in pollination networks. Invasive alien species are a major concern in the management and conservation of habitats and species worldwide (Crooks 2002; Bax et al. 2003; Levine et al. 2003; Vila et al. 2010). The direct effects of these species may further cascade in the ecosystem and affect interand intraspecific ecological interactions. The introduction of alien plants and animals can have severe consequences not only for individual native plant and pollinator species, but also for their ecological interactions through plant-pollinator networks (Morales and Traveset 2009; Dohzono and Yokoyama 2010; Schweiger et al. 2010). Integration of alien plant and pollinator species into pollination networks inevitably creates new interactions and may also affect the strength and quality of existing ones. These changes are open niches for novel evolutionary adaptations of both alien and native species (Mooney and Cleland 2001). However, research in this topic is very limited, and has focused mostly on adaptations of alien plant species to pollinator-independent reproduction modes (Barrett et al. 2008). We know of no study investigating adaptations of native plant and pollinator species to invaders, and the ecological and possibly evolutionary consequences of these adaptations in the context of plant-pollinator networks. Such adaptations might have far-reaching ecological and evolutionary implications, as has been shown in plant-herbivore and predator-prey interactions (Cox 2004). Here we outline the main effects of species invasions on plant-pollinator interactions, and deduce the main adaptive mechanisms that native plant species can exhibit in response to changes in