What’s in an Ecotone? Lichens living on the edge…

An ecotone is a transition zone between two ecological systems. Ecotones can range in size: in some places ecotones are wide (e.g. forest – grassland ecotones), in other places they are quite narrow (e.g. riparian – arid shrub steppe). In the ecotone, habitats from each ecosystem form a mixed patchy mosaic, often with species assemblages not found elsewhere, and interesting juxtapositions.

From “Ecotone Hierarchies” by James R. Gosz, in Ecological Applications, Vol. 3, No. 3. (Aug., 1993).

Ecotones are important beyond the conceptual wonderings they induce. For land management, monitoring how an ecotone shifts location over a landscape can demonstrate patterns of climatic change and ecosystem health, giving important data for developing strategies to encourage ecosystem resilience.

The study area for our lichen inventory in southeastern Nevada. We marked a tentative ecotone zone for site stratification purposes based on vegetation maps (not shown).

Our lichen biodiversity project in southeastern Nevada is located along the transition zone between the Great Basin Desert and Mojave Desert. As the climate continues to warm in that area, the Mojave biota will continue to shift their ranges northward and uphill into the Great Basin. Part of our lichen biodiversity inventory includes identifying candidate climate change bioindicator species that can be used to monitor the shifting ecotone, before those climatic changes start to impact vascular plants, birds, mammals, and insects.

What’s life like as a lichen in the Great Basin – Mojave ecotone? I’d guess the lichens there find themselves “living on the edge” in the proverbial sense, as well as the literal. Life is probably pretty uncomfortable at times, with many individuals not as genetically equipped to respond to what life throws at them as their mates near the center of their species’ range.  Living on the edge means that adaptation is critical. These lichens are the avant garde. These are the species that are adapting to a changing climate, and giving what they learn (their adapted genome) back to their tribe, thus granting their species a better chance of adapting to future trends in climate and habitat. And that’s a pretty darn awesome contribution.

Lecidea atrobrunnea is abundant in the Great Basin, nearly ubiquitous, and always well developed and fertile. In the ecotone, it struggles – its thallus (lichen body) looks less lustrous, and it is not at all fertile. This is one individual that’s living on the edge. Photo by the wonderful Jason Hollinger.
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