When climate change results in sub-optimal conditions for population persistence, populations can respond in three ways. Populations can (1) adapt and persist locally, (2) go locally extinct due to physiological constraints or unfavorable biotic interactions, or (3) shift their range and colonize sites with more favorable conditions. Theory predicts that many mountain species will shift their range upward and have higher colonization rates at higher elevations; yet, this prediction may be less applicable to species with strong dispersal constraints. Passive asymmetric dispersers such as wind-dispersed epiphytes may be particularly vulnerable to climate change. Long-distance dispersal in these epiphytes depends exclusively on wind direction. Therefore, range expansion will have limited options if advection sources drive dispersal in an unfavorable direction. In this study, we follow a process-based approach to leverage long-term data on a rare orchid Lepanthes rupestris to understand the contributions of dispersal potential, climate and biotic interactions as drivers of local colonization and extinction dynamics. Specifically, we ask: (1) What are the drivers of local colonization-extinction dynamics in this species? (2) Is the population shifting, adapting or going extinct as a response to changes in climate?
Results/Conclusions
We compared multiple occupancy models that vary in the covariates used to explain local colonization and extinction of L. rupestris. The most parsimonious model included asymmetric connectivity, species interactions (moss area) and minimum temperature as important drivers of colonization, and species interactions (moss area) and maximum temperature as important drivers of extinction. This model predicted that colonization increases with increasing asymmetric connectivity and moss area. Local extinction decreased with decreasing moss area. In addition, local colonization decreases with increasing minimum temperature and local extinction increases with increasing maximum temperature. The predicted equilibrium occupancy at year 2100 based on IPCC climate change scenarios suggests that the population will go extinct (y* <0.01) under most scenarios. Therefore, between stay and adapt, go extinct, or expand its range our results suggest that the metapopulation will go extinct. This failure to adapt to local challenging conditions is likely due to an asymmetric dispersal pattern that does not allow to colonize upward because the wind blows in the opposite direction (downward). Also, increasing temperature may shift the interaction between the orchid and moss from facilitation to competition increasing local extinction. Our results emphasize the vulnerability of asymmetric dispersers, particularly epiphytes, to climate change.