Crossing the Divide: An Exploration of Functional Traits in Ferns that Grow Across Terrestrial, Epipetric, and Epiphytic Habitats

Abstract. Plants are characterized by their marked plasticity and ability to alter their functional biology to partition ecological niches. However, there are limits to functional trait exploration especially in complex and stressful habitats. Highly specialized traits may control a species ability to explore within and across habitats. Such may be especially true of epiphytes, whose array of unique traits may constrain their ability to cross establish in epiphytic and terrestrial habitats. In the case of ferns, there are few reported examples of species that can grow across these habitats with regularity. However, this study reports and explores species that exhibit great ecological flexibility growing across a wide range of habitats and growth forms. Specifically, we examine species that grow as 1) terrestrially rooted and epiphytic individuals, 2) nest and non-nest-forming epiphytes; and nest-forming terrestrially rooted individuals, and 3) species that grow as terrestrial, epiphytic, and epipetric individuals. We use natural abundance foliar stable isotope ratios (SIR) of N15 and C13, and %N, to explore intraspecific variation in mineral nutrition and water relations across and within niches. Our results reveal the 1) unreported ability of some species to grow across the epiphytic/terrestrial divide, 2) surprising ability of some species to explore these habitats with little to no shift in functional traits; 3) a potentially new function for the nest in nest-forming epiphytes. Finally, our work highlights the need to consider intraspecific trait variation more carefully when studying ferns that occur across a wide range of habitats.