Tropical Deforestation Reduces Plant Mating Quality By Shifting The Functional Composition Of Pollinator Communities

Deforestation can impact the quality of pollen received by target plants (i.e. delivery of incompatible pollen, self-pollen or pollen from closely related individuals). Such reductions in plant mating quality may be direct, when deforestation reduces plant population size and the availability of pollen donors, or indirect, when decreased mating quality results, for example, from shifts in the composition of the pollinator community. As most flowering plants depend on animal pollinators for reproduction, there is a need to understand the direct and indirect links between deforestation, pollinator community composition and plant mating quality.We quantified the direct, pollen donor-mediated and indirect, pollinator-mediated effects of deforestation on mating quality in Heliconia tortuosa, a tropical herb pollinated by low- and high-mobility hummingbirds. We used a confirmatory path analysis to test the hypothesis that deforestation (amount of forest cover and forest patch size) influenced mating quality (haplotype diversity of pollen pools, outcrossing and biparental inbreeding) directly and indirectly through functional shifts in the composition of pollinator communities (proportion of high-mobility hummingbirds).We found that deforestation triggered functional shifts in the composition of pollinator communities, as the proportion of high-mobility hummingbirds increased significantly with the amount of forest cover and forest patch size. The composition of the pollinator community affected mating quality, as the haplotype diversity of pollen pools increased significantly with the proportion of high-mobility hummingbirds, while biparental inbreeding decreased significantly. Although we did not detect any significant direct, pollen donor-mediated effects of deforestation on mating quality, reductions in the amount of forest cover and forest patch size resulted in functional shifts that filtered out high-mobility hummingbirds from the pollinator community, thereby reducing mating quality indirectly.Synthesis. Deforestation primarily influenced plant mating quality through a cascading effect mediated by functional shifts in the composition of the pollinator community. Our results indicate that plant mating quality strongly depends on the composition of local pollinator communities. Functional shifts that filter out highly mobile and effective pollinators may reduce the transfer of genetically diverse pollen loads from unrelated plants. Such shifts may have pronounced effects on plant population dynamics and disrupt genetic connectivity.