Biologists and conservationists usually deal with species found in a specific location. For example, they might count all the species found in a square kilometer.
A new theory, published by University of Tartu ecologists in the March issue of “Trends in Ecology & Evolution”, considers the absent species in nature as important as the existing ones.
UT Professor of Botany Meelis Pärtel, Professor of Plant Ecology Martin Zobel and researcher Robert Szava-Kovats call species in the region that are absent, but that could potentially inhabit those particular ecological conditions, ‘dark diversity’.
Cosmology has used a similar term, ‘dark matter’, for decades to describe matter that can’t be seen or sensed but still makes up 80% of our universe. This dark matter interacts with visible matter such as stars and planets. A similar kind of interaction is going on in ecosystems.
For instance, nemoral forests are usually home to liverleaves. “If liverleaves are for some reason not present in the forest, this could be a sign of something not being right. The missing liverleaves are an example of dark diversity – they should be present in the forest, but for some reason, they are not,” illustrates Pärtel. The dark diversity species may have been present in an ecosystem and may return if favourable conditions are met.
Only a couple of decades ago, Estonia was home to a distinctive type of meadow ecosystems called alvars, but management of these meadows was ceased. The meadows started to overgrow and many of their plant species are now starting to disappear.
“If we would clear the meadows of brushes and start to use them as pastures, the missing species would probably return. But today they are part of the dark diversity,” Pärtel added.
This dark biodiversity cannot be directly measured, however its size can be assessed. “Just as dark matter is important to understanding the structure of galaxies, dark diversity is necessary to understand ecosystems. Dark diversity allows one to assess whether the biodiversity under observation is regulated by local and ecological, or regional and evolutionary processes. Large dark diversity is a sign of reduced local biodiversity as well as the potential for restoring a damaged ecosystem,” Pärtel explained.
If dark diversity in an area remains high, there is a possibility for the missing species to return.
The concept of dark diversity has been listed in Faculty1000, a portal specializing in post-publication peer review of the most important natural and medical science articles.
Pärtel M, Szava-Kovats R, & Zobel M (2011). Dark diversity: shedding light on absent species. Trends in ecology & evolution (Personal edition), 26 (3), 124-8 PMID: 21195505