The influence of landscape heterogeneity and species interactions on the distribution of an epiphytic orchid and its genetic variation
Kartzinel, Tyler Ryan
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Multiple historical and ecological factors influence species distributions. The relative influence that these factors have on species distributions must be examined in order to understand the fundamental patterns and processes of evolutionary ecology or anticipate the consequences of environmental change. I assess the relative influence of landscape heterogeneity and species interactions on the distribution of an epiphytic orchid and its genetic variation at multiple spatial scales in Costa Rica. Pairing molecular techniques with field experiments, I ask 1) how did the historic distribution of populations in narrow mountain habitats influence patterns of gene flow and genetic structure; 2) are spatial or environmental distances associated with variation in the communities of symbiotic mycorrhizal fungi upon which the orchids rely; and 3) does environmental heterogeneity or a paucity of established conspecific plants limit the germination of seeds in disturbed agricultural landscapes? First, I used neutral nuclear and chloroplast genetic markers to infer historic patterns of gene flow and identify their contribution to genetic structure. Pollinators contribute substantially more to gene flow among groups of populations in geologically distinct mountain ranges than wind-dispersed seeds, contrary to expectations based upon the dispersal traits of orchid pollen and seed. Second, I used genetic barcodes to characterize variation among communities of symbiotic mycorrhizal fungi. The composition of diverse mycorrhizal communities varied among populations, suggesting that taxonomically distinct fungi can fulfill similar symbiotic functions. Third, I used a seed sowing experiment to determine whether the probability of seed germination increases with seed deposition in close proximity to established conspecific plants or in particular environmental conditions. I found no significant influence of proximity to adults, but that diverse native trees and trees with more closed canopies were significantly more favorable hosts than commonly cultivated tree species or trees that had more open canopies. Together, these studies provide insights into the relative influence of landscape characteristics and species interactions on the distribution of an epiphytic orchid and its genetic variation at multiple spatial scales. Actionable information is provided for conservation planning during the current period of unprecedented environmental change.