Rainfall Increases Alpha and Has No Effect on the Beta Diversity of Animal-Dispersed Shrubs in Panama

Climate patterns affect where plants can grow and survive. In tropical areas, the main form of precipitation is rain, and rainfall has been demonstrated to influence tree species distributions. For this thesis, I examined the relationship between rainfall and the diversity of animal-dispersed tropical shrubs. To do this, I used data on shrub diversity collected in the summer of 2017. Plots were established across the Isthmus of Panama, from the drier Pacific side to the wetter Atlantic side, to survey animal-dispersed shrubs. I analyzed three metrics of diversity that weigh rare and common species differently. The first weighs rare species more, the second weighs rare and common species equally, and the third weighs common species more. I created a model to show how rainfall affects these metrics. I found that rainfall has a significant positive effect on rare and common species which is consistent with other studies on tree species across the same gradient in Panama. Additionally, I investigated the differences between animal-dispersed shrub communities along the rainfall gradient. To do this I used two additional metrics, one that considers only the presence/absence of species in each community while the other considers both the presence/absence and abundances of species. I found differences in animal-dispersed shrub community composition, but the effect of rainfall on the differences was not significant. Overall, I found that rainfall has a great effect on the diversity of animal-dispersed shrubs in Panama but does not explain the differences between communities. These results indicate the effect that rainfall has on the diversity of animal-dispersed shrubs allowing for better predictions of climate change effects on plant communities.