Does generalism drive pollinators' abundance, persistence and regional distribution? Insights from an ecological model

The functioning of plant-pollinator mutualistic networks is crucial for ecosystem service provisioning and biodiversity maintenance. However, multiple drivers of global change are causing an alarming decline of wild pollinators abundance and richness. We propose an ecological, process-based mathematical model describing the dynamics of pollinators and plants, properly mediated by reward resources. Our model explicitly accounts for the main interactions of both facilitative and competitive nature that occur both within and between the two guilds. We apply our model to a broad set of real communities in fragmented landscapes to investigate the mechanisms that link the architecture of the interaction networks, the pollinators temporal persistence and abundance at the community level, and their rarity at the landscape level. Our results suggest that few generalist pollinators form a core of abundant, persistent and widely distributed species, while a lower number of mutualistic partners is generally associated with low abundance, low persistence and high turnover between patches. Specialists, however, are crucial to maintaining high levels of biodiversity within the community. This finding highlights the importance of ecological connectivity, through which local extinctions can be counter-balanced by recolonizations. Our analysis shows how a mechanistic model accounting for the structure of plant-pollinator networks can serve as a tool to investigate important ecological mechanisms driving community composition, dynamics and the resulting species distribution patterns.