Both biotic and abiotic factors drive species distributions. In the Neotropical alpine, or páramos, novel ecological opportunities have contributed to recent radiations and led to plant communities with high co-occurrence of congeneric species. These species are commonly spatially separated, with some more frequently encountered in mesic areas versus dry slopes. The soil in this mesic microhabitat is characteristically dense, root-packed, and dark. Due to higher moisture and likely greater nutrient availability, soil pathogens may also be more abundant in this microhabitat than on the dry slopes, where the substrate is sandy. As a first step in understanding how edaphic heterogeneity may drive species distributions in the páramos, we compared growth and survivorship of two congeneric grass species in a common garden experiment using substrates representative of both microhabitats. Cortaderia columbiana is a páramo endemic found in both microhabitat types, though is more common in the dry-sandy microhabitat than C. nitida. Cortaderia nitida has a greater altitudinal range than C. columbiana, but is dominantly found in páramos, where it occurs in mesic soil. In a second experiment using autoclaved and non-autoclaved soil, we tested whether release from soil pathogens increases germination rates for these two Cortaderia species.
Results/Conclusions
We did not find significant differences in growth rates across treatments or between species for C. columbiana or C. nitida when grown in field soil or sand. Survival was greater in C. nitida than C. columbiana, regardless of substrate, though both species had greater survival on sand compared with field soil. Germination rates did not differ between autoclaved and non-autoclaved soil for either species. Our data suggest that edaphic conditions play a role in determining the distributions of these species, though in unexpected ways since C. nitida is not common in sandy areas in the páramos and is less abundant than C. columbiana. These data provide insight into how closely related species in the páramos vary in edaphic preferences. In future studies, we aim to test whether facilitative interactions with other plants may better explain these species' distributions and how pathogens may affect survivorship of later life stages.