Species interactions and climate change
Although the Earth's climate has changed throughout its history, the current rate of change has been unprecedented during the last 65 million years. This fact, together with the loss of natural habitat, may weaken the ability of species to respond to change through migration, adaptation and acclimation. Moreover, individuals, populations and species do not exist in isolation. Therefore, one of the main challenges in biodiversity studies is to explain how interactions among species might affect a response to a changing climate. This question was addressed by the EU-funded EPACS (Ecological process and climate change) project, which used interactions between lichens as a study system. Lichens are a symbiotic association between a fungus, which builds the lichen structure, and algae or cyanobacteria (called a photobiont). The photobiont produces food in the form of carbohydrate through photosynthesis. The EPACS study focused on lichen epiphytes, which are found growing on trees in Europe's oceanic temperate rainforests. Scientists investigated several hypothesised interactions involving lichen-fungus and the photobiont, which are relevant to climate change impacts on biodiversity. Researchers successfully developed and tested microsatellite biomarkers for two closely related lichens with similar environmental requirements but different forms of reproduction. The results support the hypothesis that the species that reproduced sexually (Nephroma laevigatum) had greater genetic diversity than the species that reproduced asexually (N. parile). An additional hypothesis was that lichen-fungus combine with photobiont types that optimise ecological fitness in a local environment through a process known as selectivity. This is a potential route for acclimation among lichens. A gene region that is variable among different strains of the photobiont (Nostoc) was tested to determine whether Nephroma species show selectivity in different conditions and habitats. EPACS also showed that spore-dispersed lichen-fungus (N. laevigatum) depend on the prior colonisation of habitat by an asexual species, which 'seed' the photobiont into the habitat. The ecologically similar but asexually dispersed lichen-fungus N. parile showed no such dependency. This contrasted with the traditionally held assumption that spore-dispersed lichen-fungi can migrate more easily in the face of climate change. Project results demonstrated how species interactions can alter expectations under climate change at two levels. These are the interaction of fungus and photobiont to create a lichen and the interaction among lichens in an epiphyte community. This valuable information will be used to improve management plans for key European temperate rainforest sites.
Keywords
Species interactions, climate change, migration, adaptation, acclimation, ecological process