More than 90% of tropical plant species are animal-pollinated consequently the disruption of pollen dispersal services by anthropogenic deforestation is among the greatest threats to tropical biodiversity. In addition, every 6-8 years a severe El Niño–Southern Oscillation (ENSO) event exposes tropical species to extreme drought conditions, impacting plant phenology, plant-pollinator interactions, and subsequent plant reproduction. Despite the increasing severity of ENSO events and climate change, little is known about the compounding effects of severe climate events and deforestation on tropical plant-pollinator interactions, particularly about how these factors drive inter-annual changes in plant reproduction and gene flow.
To explore these possible impacts, we examined seven populations of a buzz-pollinated, Neotropical pioneer tree, Miconia affinis, that display different levels of deforestation across the Panama Canal region. We compared the reproductive output and pollen-mediated gene flow of adult trees in 2013 (typical year) and 2016 (ENSO year) using microsatellite markers, paternity analyses, and GPS mapping. Specifically, we examined how year, rainfall, phenological synchrony and flowering date, conspecific density, local kinship, mother tree size, and pollinator community diversity influence seed set and pollen dispersal patterns for a common understory tree species across this highly deforested region.
Results/Conclusions
When comparing the ENSO event in 2016 with 2013, we found that M. affinis displayed a phenological shift of one month across six of the seven populations, with an accompanying shift in pollinator community composition. Specifically, pollinator and abundance and diversity did not change significantly across years, but the pollinator species present at the plant during its two-day flowering events differed between years. Moreover, more fragmented landscapes that displayed several asynchronous flowering events were visited by a higher diversity of pollinators than more intact populations that displayed a single synchronous flowering event regardless of year. Further, we documented a significant reduction in reproductive output (seed set) from 2013 to 2016 in five of the seven populations. Molecular analyses indicate that flowering conspecific density plays the most critical role in mediating pollen dispersal patterns across years, while pollinator community composition is less predictive of pollen dispersal distance and diversity. Overall, our results indicate that climate change processes may further compound the negative effects of deforestation on the density of conspecific flowering individuals during extreme climate cycles. These inter-annual changes to plant-pollinator interactions may have critical and long-lasting impacts on plant population viability and genetic structure across fragmented tropical landscapes.