Predicting the impact of shoreline of the future survival of an endemic Hawaiian plant species, Schiedea globosa

Background/Question/Methods

Understanding the connection between habitat modification and species distributions is vital to comprehend species persistence in particular locations. Sea level rise and coastal erosion on the Hawaiian Islands pose an imminent threat to the survival of endemic coastal species. Endemic species often have narrow ecological ranges; thus a modification to their habitat has a potentially significant effect on their future survival. Schiedea globosaoccurs at coastal locations on the four islands of Maui, Molokai, Oahu, and Hawaii. Although not endangered like most species in the genus, it is considered uncommon. Presence and absence data were collected in 2012 and 2013 on Maui and Oahu. Location data along with environmental predictors were used to develop a species distribution model (SDM) and used to predict the impact on S. globosa with changing shoreline.

Results/Conclusions

The environmental predictors used were: elevation, slope, aspect, solar radiation, soil type, and winter and summer rainfall. Logistic regression models in the package R indicate that elevation, aspect, solar radiation and winter rainfall are significant predictors of S. globosa presence (> 42% deviance explained). Winter rainfall varies across sites and does significantly affect occurrence of the species. Model evaluation suggests that these models are better at predicting presences and not absences. Probability maps created from the SDM enabled us to locate additional populations of S. globosa. Combining shoreline data with the habitat suitability map for S. globosa shows that the species could be threatened within the next 50 years unless it is able to migrate inland. Predictive models, such as those developed in this project, are useful to conservation managers because they enable one to make inferences on species sensitivities to future habitat change.