Leaf-based miniature ecosystems reveal processes behind rainforest biodiversity
Although they normally pass unnoticed, entire communities of living organisms can be found on the surface of leaves in tropical rainforests. These communities, known as epiphylls, are extremely diverse and include bryophytes (mostly liverworts), algae, fungi, bacteria and cyanobacteria, with more than 100 species on a single leaf. As with other tropical biotic communities, it is not clearly understood why these epiphyll communities are so diverse or how biodiversity is maintained. Testing biodiversity in tropical rainforests can be challenging because of the slow dynamics of tree communities. By focusing on bryophytes and lichens, scientists can test biodiversity theories in an ecological system with much faster dynamics and easier replication than tropical rainforests, while maintaining similarly high levels of biodiversity. The EU-funded EPIDYN project is the first study to explicitly address species interactions and community dynamics among epiphyll species within single leaves. “Due to the ephemeral character of their substrate and the small scale and relatively fast dynamics, epiphyllous communities offer an ideal system for studying primary succession and mechanisms explaining biodiversity maintenance in relation to environmental variables,” says project coordinator Maaike Bader.
Effect on ecological succession
A research fellow supported by the Marie Skłodowska-Curie Actions programme conducted research on Barro Colorado Island in Panama, monitoring leaves under different light and moisture conditions – the main limiting factors for bryophytes and lichens in tropical rainforests. By studying the species composition and spatial patterns on the leaves, they determined the order of their arrival and establishment and the interactions between the different organisms, enabling better understanding of the drivers behind community structure in epiphylls. The team found that the succession of species on the leaves was characterised by an accumulation of species rather than a replacement of ‘weaker’ colonisers by more competitive species. “This differs from the classical model of species succession in plant communities,” Bader points out. Also, at the forest scale different successional stages (closed forest and forest gaps) differed in the species composition of the epiphyll communities, indicating the importance of forest dynamics for biodiversity. “We thus showed that habitat dynamics and succession processes at very different spatial scales interact to create these highly diverse ecosystems,” observes Bader.
A better understanding of epiphylls
These results will help understand how epiphylls from evolutionary and morphologically very different taxonomic groups (e.g. lichens and liverworts) grow together to form small-scale biotic communities. Bader explains: “Following the spatial patterns on the leaves through time, we saw that these changed from being mostly random on young leaves to more organised on older leaves, indicating a shift from random processes (chance arrival) to more deterministic processes, for example competition.” By following community dynamics on a highly replicated set of miniature habitat patches, EPIDYN is expected to add not only to understanding of epiphyll communities, but more generally to community ecology of sessile organisms. “We are still far from fully understanding the functioning of epiphyll communities, but it is important that they are not overlooked or forgotten when thinking about biodiversity and ecosystem functions,” Bader concludes.
Keywords
EPIDYN, epiphyll, biodiversity, rainforest, succession
