|dc.description.abstracteng||Tropical mountains are hotspots of biodiversity and refugia for plants and animals, especially in a world of accelerating climatic change (Steinbauer et al., 2018). Biological diversity on tropical mountains is shaped by abiotic and biotic factors. Therefore, elevational gradients provide an opportunity to study effects of different ecological and evolutionary factors over relatively short geographical distances (Körner, 2007). This is a unique opportunity that inspired naturalist to use them as natural laboratories. Along elevational gradients in tropical mountains, multiple ecological questions have been explored, from diversity patterns to trait-environment relationships. Despite scientific advances in our knowledge of elevational gradients, we still lack a comprehensive understanding of numerous aspects of environmental factors and their influence on species diversity and function.
In my thesis, I provide a detailed analysis to understand patterns of tropical plant diversity, particularly vascular epiphytes, and their vulnerability to anthropogenic disturbance at different spatial scales (chapter 1), and the interplay and relative importance of broad- and small-scale environmental gradients as drivers of variation in leaf functional traits of vascular epiphytes (chapter 2). Furthermore, I assembled a publicly available database of epiphyte species diversity, community composition and leaf functional traits based on data from previous chapters, with the aim of contribute and motivate future research on tropical mountains (chapter 3).
In chapter 1, I analysed the response of epiphyte diversity to forest-use intensity from local to landscape scales along a tropical elevational gradient. I studied the effects of forest‐use intensity on alpha, beta, and gamma diversity of vascular epiphyte assemblages in old‐growth, degraded and secondary forests at eight study sites, yielding a total of 120 plots along the elevational gradient. I found that the interactive effects of elevation and forest‐use intensity strongly impacted local‐scale patterns of vascular epiphyte diversity. Alpha diversity did not differ significantly among forest‐use intensity levels. However, gamma diversity was always lower in secondary forests compared to old‐growth forests across the entire elevational gradient. Furthermore, beta diversity was dominated by species turnover along the forest‐use intensity gradient in the lowlands, but declined with increasing elevation, where community composition became increasingly nested. The results in this study highlight a strong interaction between forest‐use intensity and elevation. Further, this study offers a framework to better understand the ecological factors that may determine diversity patterns of epiphytes in an anthropogenic world.
In chapter 2, I examined variation in morphological and chemical leaf traits of 102 vascular epiphyte species along broad- and small-scale environmental gradients, and assessed whether the variation in traits along these gradients were consistent across photosynthetic pathways (CAM and C3). I found that broad- and small-scale environmental gradients explained more variation in chemical traits than in morphological traits. For example, carbon isotope ratio (δ13C) a proxy for water-use efficiency varied systematically across both environmental gradients, suggesting a decrease of water-use efficiency with increasing elevation and an increase with relative height of attachment. Contrary to our expectations, broad- and small-scale environmental gradients explained little of the variation in morphological leaf traits, suggesting that environmental conditions do not constrain morphological leaf trait values of vascular epiphytes. Our findings suggest that analysing multiple drivers of leaf trait variation and considering photosynthetic pathways is key for disentangling functional responses of vascular epiphytes to environmental conditions.
In chapter 3, I compiled a new comprehensive database (BIOVERA-Epi) that contains information on epiphyte species diversity, community composition and leaf functional traits. Moreover, I included data from 120 forest plots distributed along the studied elevational gradient which included six different forest types and three levels of forest-use intensity. In this chapter, I provided information describing two datasets in which, I assembled distribution and frequency data of 271 epiphytes species surveyed along the entire elevational gradient. Further, I measured a set of nine morphological and chemical leaf traits for 102 species surveyed along 45 plots in a section of the elevational gradient. With this chapter, I aim to contribute to future synthetic studies on the ecology, diversity, conservation, and functional plant ecology of tropical epiphyte assemblages in the Neotropics.||de