In a rapidly warming world, tropical biota rely on elevational migrations to locate habitats that fit their ecological and physical requirements. Many tropical plants depend on animal seed dispersers to arrive in and potentially colonize novel upslope environments. This upslope migration is expected to be especially important for lowland species, which will be exposed to extremely warm temperatures over the next century. Using plants from a tropical lowland wet forest in Costa Rica, the objectives of our study were to determine (1) optimal temperatures for the germination of large animal-dispersed seeds, (2) how environmental temperatures in the current elevational distributions of these plant species match their germination temperature optima, and (3) how elevational changes and novel environmental contexts affect transplanted seedling survival in upslope life zones. We used temperature-controlled incubators to assess seed germination success in a range of temperature environments (10 °C—35 °C) for 13 lowland plant species. We also transplanted seedlings of these same species upslope and assessed their survival in native (lowland) and novel (upslope) environments.
Results/Conclusions
Overall, seeds from the tropical lowlands germinated best between 20-30 °C, which are the temperatures they experience most often in the lowlands (min temperature = 20 °C, mean temperature = 25 °C, max temperature = 30 °C). No seeds from any species germinated at the coldest temperature (10 °C). Seeds from all species were able to germinate at the highest experimental temperature (35 °C = “global warming temperature”), with success ranging from 13%-100%. Optimal germination temperatures matched the ambient temperatures along the elevational ranges where all plant species are currently found. Seedling survival in native (lowland) and novel (upslope) elevations was variable (depending on species), but overall seedling survival in upslope habitats implied some potential for upward mobility. The results of this study have implications for understanding and predicting plant ranges in a changing world. Inability to germinate and survive at low temperatures may prevent effective upslope migration of lowland plant species into colder environments, hindering their abilities to outpace the effects of global warming prior to a general upward shift of biomes. Altered plant-animal interactions, especially seed dispersal and predation, will play major roles in redefining tropical plant and animal communities as the world warms.