EPIDYN · Life on a leaf: species interactions and community dynamics in epiphyll communities

Life on a leaf: species interactions and community dynamics in epiphyll communities

Global climate change (GCC) is among the greatest threats to planet Earth. GCC influences all ecosystems, initiates negative and irreversible processes, and causes biodiversity loss. Biodiversity in particular plays an important role in ecosystem function over time. Furthermore, it plays a critical and widely recognized role in human wellbeing in terms of biological resources, recreation and cultural value. The failure of clear predictions of the consequences of biodiversity loss is due in part to the lack of a theoretical and empirical foundation incorporating the aspect of species interaction. Species dynamics are key processes in the structuring of ecological communities. The highest biodiversity worldwide has been found in tropical forests, where bryophytes and lichens represent a significant amount of diversity and cover. In spite of this, due to their relatively small size and challenging identification, these organisms have been largely neglected in many ecological studies. Tree and shrub leaves that harbour epiphyll communities (bryophytes, lichens, algae and fungi) in miniature ecosystems are an interesting model system in which to study ecological processes, precisely because epiphyll community dynamics happen quickly, during the life-span of the leaf, ensuring economy both in terms of time and resources. Due to the ephemeral character of their substrate and the small scale and relatively fast dynamics, epiphyllous communities offer an ideal system to study dynamics of primary succession and mechanisms explaining biodiversity maintenance (BM) in relation to environmental variables. Taking a closer look, epiphyll communities can be extremely diverse, with up to 80 species of lichens on a single leaf, plus numerous species of bryophytes (mostly foliose liverworts), algae, fungi and bacteria. As in other tropical biotic communities, it is unknown why these epiphyll communities are so diverse or how biodiversity is maintained. Theoretical models of BM range from ‘neutral theories,’ where random processes explain the high degree of coexistence without counting on different species responses to the environment, to niche-based models, where interactions between species and the environment play a more central role in BM. When a new area is first colonized by plants—for example in primary succession—the course of succession may be a chance process depending on what species happen to arrive first (the ‘priority effect’); or at the other extreme, it may be highly deterministic with very specific roles (e.g. first colonizer, late-successional) or niches for each species. In all these models of BM, species interaction plays an important role, but the predicted outcomes of the interactions differ. While the priority effect implies that the first species to arrive will dominate, models including species-specific niches allow for a range of interactions, both negative (competition) and positive (facilitation). In this project, we aim to determine which are the most appropriate theoretical models for describing species interactions and successional dynamics in epiphyll communities (liverworts, lichens, algae and fungi) and how the relative role of each model depends on environmental conditions.

Data: CORDIS, © European Union