Evidence clearly suggests that human-driven changes to the earth are having overpowering effects on many species, as well as the species with which they associate. In addition to individual species studies, predicting how species interactions will respond to global change is necessary to best mitigate expected biodiversity losses. We shed light on how orchid mutualisms differ between native and introduced ranges and how mutualisms relate to their potential for range expansion in the face of anthropogenic change, while directly addressing some of the gaps regarding orchid populations, especially in the sub-tropics and tropics. Using a comparative approach we address the role of mycorrhizal specificity in dictating orchid abundances and distributions by taking advantage of two special circumstances: 1) the recent invasion and spread of two introduced orchids in southern Florida each of which has a rarer native congener, and 2) the uphill translocation “assisted colonization” of four rare orchid species in southwest China. We identified mycorrhizal fungi with DNA sequencing using fungal specific PCR primers and by isolating fungi axenically. The degree of mycorrhizal specificity was estimated by generating phylogenetic trees and was defined as both the number of distinct fungal taxa (OTU richness) associated within each species, and the OTU diversity.
In southern Florida, our results showed that the invasive orchids were more generalized in their fungal associations than their native congeners. Native orchid species associated with fewer orchid mycorrhiza taxa (15 OTUs) than did the invasive orchids (24 OTUs), comprising 50% and 78% of the total associations respectively. The invasive species also showed preference for specific basidiomycete genera that are widely available in the invaded habitats only. In southwest China, our results also indicate wide-ranging orchid species were more likely to associate with a greater number (32 OTUs) and more diverse groups of fungi (Shannon diversity (H’) = 1.28) than narrow range species (22 OTUs, H’ = 0.505). However, all translocated orchids were able to establish mycorrhizal relationships with new fungi in the recipient ranges. These findings clarify the potentially strong role of mycorrhizal symbioses in governing distribution in both native and introduced ranges. Understanding the flexibility in these specialized interactions in orchids is urgent, because climate change related phenomena are expected to disproportionately affect those species that depend heavily on other species.