The diverse effects of habitat fragmentation on plant-pollinator interactions

Habitat fragmentation affects a wide variety of biological variables including species' abundance and richness (population demography), phenology, male and female reproductive fitness, and it also affects the degree of specialization versus generalization of pollination networks. Evidence is accumulating that suggests that habitat fragmentation can have significant impacts on plant-pollinator interactions. In this article, we review the literature on habitat fragmentation effects on plants, pollinators, and the pollination network. We also discuss pollination network mechanisms that may be affected by habitat fragmentation. Habitat fragmentation isolates populations and affects ecological properties at both population and community levels. Evidence shows that habitat size and connectivity directly or indirectly influence the abundance of both plant and pollinator species. In general, plant and pollinator diversity and population size decrease with the decreasing size and habitat connectivity. Habitat fragmentation of plant communities can shift plant phenological patterns, contract flowering periods and increase the risk of local pollinator extirpation. Fragmentation has the potential to influence pollination dynamics by altering pollinator or plant densities and by altering pollinator behavior. However, evidence for the impact of habitat fragmentation on plant species' flowering phenology is relatively limited, and little is known about the effect of habitat fragmentation on the phenology of pollinators. Habitat fragmentation also leads to reduced reproduction in many species. In contrast, other species showed neutral or positive responses to habitat fragmentation in female reproductive fitness, especially in plants regularly affected by pollen limitation and pollination limitation which lead to plants' experience selection for increased autogamy in isolated habitats. Habitat fragmentation often leads to the extirpation of specialist species and results in an influx of generalists. However, studies have shown that pollinators tend to be more generalized as habitat fragmentation increases. The reason is that habitat fragmentation changes the composition of the flora, and scatters floral resources, so any remaining pollinators may need to behave as generalists in order to survive. However, the knowledge of potential ecological consequences of habitat fragmentation is limited, especially regarding the effects on a long-term scale and at landscape scales. We propose experiments involving long-term monitoring, permanent samples of flowering plants, pollinators, and their interactions at large spatial and temporal scales.