Understanding the factors that limit species distribution is a longstanding question in ecology. In land plants, species distribution is simultaneously limited by multiple factors, including climate, dispersal ability, competition, and species' physiological tolerance. The ecological requirements of obligate inter-specific interactions impose additional, often overlooked, limitations. How complex interactions influence plant species distribution has received little attention despite its relevance for species conservation in the face of global change. EpiNet addressed this gap by investigating how two obligate partners, interacting with climate, influence plant distribution in mega-diverse tropical assemblages.
Tropical epiphytic orchids provide an exceptional study model because they depend on two partners to germinate and grow: a host tree and mycorrhizal fungi. I proposed to study tripartite interaction networks of tropical epiphytic orchids with their partners under different ecological conditions. I had three specific goals. First, I investigated whether the diversity of mycorrhizal fungi affect the distribution of orchid species across different types of tropical forests (cloud, temperate and dry forests). Since those forests differ in their climate (temperature, rainfall, and sunlight), I expected them to harbor different communities of orchids, host trees and mycorrhizal fungi. Furthermore, climate can also have an effect on species' traits that are important for survival. For example, roots of epiphytes need to take water from the atmosphere. Therefore, the roots of species growing in dry forests should be especially adapted to drought, and those growing in cloud forests are not expected to be adapted to water scarcity. To assess whether root traits differed significantly between forests, I investigated several root traits related to water conservation and water transport.
Finally, we considered the possibility that orchids might be able to switch their mycorrhizal partners over their lifetimes. Such switches (or temporal turnover) might afford a considerable acclimation potential to the plant. This could enable fairly rapid responses to short‐term fluctuations in growth conditions as well as lasting responses to long‐term climatic trends. Moreover, mycorrhizal replacement is an understudied variable that may influence plant establishment success. I found that we were lacking not only empirical evidence of turnover, but also a unifying conceptual framework to tackle the issue. Therefore, I put forward a theoretical framework that will assist researchers in assessing whether orchids replace mycorrhizal partners or retain them for a lifetime.
