Influence of chronic anthropogenic disturbances and climate change on Tacinga palmadora (Cactaceae) in the caatinga dry Forest: effects on pollen traits, reproductive success and habitat suitability

Abstract

Tropical ecosystems are degrading at exceptional rates due several factors, including chronic anthropogenic disturbance (CAD) and climate change. Pollination is a key mutualistic interaction that can be affected by disturbance and climate change, due to changes in the quantity and quality of both plants and pollinators, phenological mismatches, and composition of plant and pollinator communities. Within tropical ecosystems, dry forests are considered highly vulnerable to anthropogenic disturbances and climate change due to its high population densities and human activity. The Caatinga dry forest, which harbors one of the largest and most continuous seasonally dry tropical forests, is a region characterized by its highly diversified pollination systems, however, is currently suffering high pressure from CAD and climate change. In this dissertation, I investigated how CAD and climate change influence pollen traits, reproductive success and habitat suitability of Tacinga palmadora, a self-compatible cactus that performs as an important food source for nectar-feeding and fruit-eating animals in the Caatinga dry forest. In the first chapter, I evaluated the effects of increasing CAD and aridity on pollen traits and female reproductive success of T. palmadora at Catimbau National Park. I conducted the experiments in eight plots established within the park and distributed along gradients of CAD and aridity to test for changes on pollen traits (i.e. pollen production, pollen viability, pollen-ovule ratio) and reproductive success (i.e. fruit- and seed-set). While pollen traits were negatively associated with increasing CAD and aridity, the seed-set by open pollination was positively associated with increasing CAD, while the fruit-set by open pollination was positively associated with increasing aridity. My results suggest that even though pollen traits are becoming less attractive to pollinators by increasing CAD and aridity, pollination is maintained or even increased in the most arid and disturbed areas of the park. Thus, in terms of pollination effectiveness, plant populations of T. palmadora might be adapted to disturbance and aridity. In the second chapter, I evaluated the effects of climate change on the range and distribution of suitable habitat for T. palmadora within the Caatinga dry forest. I modeled the species distribution (current and future) considering (i) usual climatic variables only and (ii) adding plant-pollinator interactions to the model. I used the CCSM4 and MIROC-ESM models for both intermediate (RCP4.5) and highest predicted (RCP8.5) GHG emission projections. Models including interaction with pollinators showed better performance and suggested that the suitable areas for T. palmadora will most likely be reduced in both scenarios of climate projections. Even though T. palmadora might be still adapted to CAD and aridity regarding its pollination, habitat suitability of the species might decrease in the future. Considering that the Caatinga dry forest is currently the least protected of all major ecoregions in Brazil, future conservation strategies are essential for the persistence and survival of this functionally-important plant species.