Many tropical plants rely on seed dispersers to colonize new environments they may face under climate change. In a warming world, tropical biota will rely on elevational migrations to locate habitats that fit their ecological and physical requirements. The objectives of our study are to determine (1) if upslope biotic or abiotic barriers currently exist to prevent plant range expansions, (2) if seed dispersers can move seeds into novel habitats to track or outpace global warming, and (3) how elevational changes and novel environmental contexts affect subsequent seedling survival. We are investigating if pre- and post-dispersal barriers exist to delimit the ranges of plants on tropical mountains in the Los Tuxtlas Biosphere Reserve, Mexico and Braulio Carillo National Park, Costa Rica. Using upslope transplant experiments of seeds and seedlings at multiple elevations, we are assessing seed dispersal/predation, seed germination success, and seedling survival in native and novel habitats. Supplementing field experiments with laboratory work, we are using temperature-controlled incubators to assess seed resilience to novel temperature environments.
Results/Conclusions
Astrocaryum mexicanum seeds were preferentially removed and eaten by squirrels (Sciurus deppei) and mice (Heteromys desmarestianus) in lowland forests (native habitat), but not in highland forests (novel habitat). Alternately, Nectandra ambigens seeds and seedlings suffered high mortality via rodent seed predation (by Peromyscus mexicanus) in the highlands compared to their natural habitat in the lowlands. Field germination of all seed species in transplanted, upslope habitat did not differ from germination success in the lowlands. In the lab, lowland seeds were able to germinate at high temperatures (up to 35° C), but were not able to germinate at temperatures below 20° C. The results of this study have implications for understanding and predicting plant ranges in a changing world. Some species do not face post-dispersal barriers to upslope migration and may be able to colonize novel habitat to outpace global warming. However other species face pre-existing biotic barriers to survival at high elevations. If plants are unable to colonize novel highland habitats as biomes shift upward, these barriers will prevent successful elevational migration, resulting in lowland biotic attrition. Altered plant-animal interactions, especially seed dispersal and predation, will play major roles in redefining tropical plant and animal communities as the world warms.