LB 8-61 - The effects the duration of the dry season on pollinator diversity and abundance and fruit set of two seasonally dry forests tropical tree; Tabebuia rosea and Handroanthus ochraceous.

Seasonally dry tropical forests (SDTF) are the most endangered major tropical ecosystems worldwide. Ongoing climate change and the concomitant decline in pollinators and pollinator services threaten these ecosystems even more. Regional projections of the Intergovernmental Panel for Climate Change (IPCC) indicate that most arid and semi-arid regions worldwide, including SDTF, will experience climate changes leading to reductions in annual precipitation and more severe dry seasons. These climate change projections are of particular concern for SDTF, where water availability determines competitive interactions among plants and the interactions of plants with their pollinators, herbivores, seed dispersers, and pathogens. However, little is known about how climate change will affect the phenology of SDTF trees and their pollinators and how those effects will impact their geographical distribution, abundance, and diversity. In this study, we determine the effect of climate change on the reproductive biology of two seasonally dry tropical forest trees; Tabebuia rosea and Handroanthus ochraceous. We studied the pollinator communities visiting the dry season flowering T. rosea and rain-induced flowering H. ochraceous trees in two locations in NW Costa Rica, El Pelón de la Bajura and Hacienda La Pradera del Norte. These two locations differ in the duration of their dry season, which typically lasts longer at El Pelón. Although the dry season started nearly at the same time in both locations in 2015, the rainy season at Pelón started three weeks later than at La Pradera, thus delaying the flowering of H. ochraceous trees. The longer dry seasons resulted in a lower abundance and diversity of pollinators visiting trees that flower at the onset of the rainy season. Our data revealed that the diversity and abundance of pollinators visiting T. rosea trees (0-4 scoring scale based on the number of bees counted for each species) and the amount of pollen deposited onto stigmas (0-3 scoring a scale-based abundance of pollen on stigma) was similar in both locations. In contrast, there was lower diversity and abundance of pollinators visiting H. ochraceous trees at El Pelón, and most flowers of H. ochraceous trees had no pollen deposited onto their stigmas. Moreover, the difference in the timing of the flowering phenology also affected the fruit production of H. ochraceous trees, where trees at Pelón were five times less likely to produce fruits than trees at La Pradera, suggesting a mismatch between their flowering and their pollinators.