How a drier climate will impact populations of a Neotropical weed (Asclepias curassavica) in Monteverde, Costa Rica

Background/Question/Methods

Central America is among the regions of the world most vulnerable to climate change, and rainfall patterns, especially those in mountainous regions are undergoing large changes.  Rainfall is predicted to decrease dramatically in these areas, and we currently lack an understanding of how such climatic shifts will influence plant populations, especially widespread, weedy plants.  For plants that reproduce throughout the year, changes in rainfall patterns may have season-specific impacts on population growth (λ).  We used demographic data collected every three months from 2011 to 2014 , in conjunction with historic climate data, to examine how climate influences deterministic λ in each season (early wet, late wet, early dry, late dry). We then used future climate predictions and climate-based population projection models to determine and how future changes to climate may impact long-term (stochastic) λ.

Results/Conclusions

We show that two measures of rainfall - mean daily rainfall and  proportion of rainy days - have unique impacts on seasonal patterns in the λ of A. curassavica. Increased proportion of rainy days had a positive influence on λ in early and late dry season late wet season.  In wet seasons, λ is more driven by mean daily rainfall, which has a positive influence on λ  in late wet season, but a negative influence in early wet season.  As a result of these season-specific responses to rainfall, our predictions for stochastic λ under future climate conditions varied depending on which factor (mean daily rainfall or proportion of rainy days) we included in our simulations.  Our most realistic model predicts an increase in population growth for these populations under future climate conditions, due to an increase in survival and fruit production.