Light diversity: obscuring the observed species

By | October 2, 2015

Yesterday during an iDiv seminar we stumbled across dark diversity. For those unfamiliar with the concept, it has been defined by Pärtel et al. (2011) :

It is possible to specify species that belong to a particular species pool but that are not locally present. We call this unaccounted set of species ‘dark diversity’.

So it is a set of species that we, for whatever reason, expect to be at a locality, but are not observed there.

I raised a concern that, for the sake of completeness, we should also consider light diversity , which would be the set of species that are not in the species pool, but we observe them anyway.


  1. Observations of yet undescribed species.
  2. Observations of vagrant and migrant species (species that do not reproduce at the locality).
  3. Aliens (thanks Marten).
  4. Species from taxonomic groups that are not part of our research, such as a cow in the middle of a botanical plot.

Depending on the context, light diversity could be also called inconvenient diversity, nuisance diversity, Jedi diversity (thanks Dylan), unexpected diversity, surprising diversity, undesirable diversity, avoided diversity, or denied diversity.

In order to make sense, dark diversity requires species pool to be philosophically realistic, i. e. we need to believe in the existence of a real species pool out there in the real world. In contrast, light diversity requires species pool to be nominalistic or conceptual, i.e. it is the species pool that we have in mind, or that we agree on in a broader community.

The idea of light diversity was received with a lukewarm amusement, and I am not sure how useful it could be, but then I am also unsure why we should have dark diversity. Perhaps I should just get back to work, to the usual and dull grey diversity.


Pärtel M., Szava-Kovats R. & Zobel M. (2011) Dark diversity: shedding light on absent species. Trends in Ecology and Evolution , 26 : 124-128.

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4 thoughts on “Light diversity: obscuring the observed species

  1. Aveliina

    Great post, thanks! I love how the idea of "wrong species" has now arisen in parallel in several groups! We have done it as well, stemming also from the concept of dark diversity. After similar brainstorming (wonderful synonyms you have there!), we have termed it "derived diversity". Only exception was that we did not come up with the idea of "cow in the middle of the plot" :). We did not wait too long to publish it as well - take a look to

    I'd be happy to discuss it further!

    Helm A., Zobel M., Moles A.T., Szava-Kovats R. & Pärtel M. (2015). Characteristic and derived diversity: implementing the species pool concept to quantify conservation condition of habitats. Divers Distrib, 21, 711-721.

    Best regards from Tartu,

    1. Petr Keil Post author

      Hi Aveliina,
      Wow, what a coincidence! And thanks for the reference. So derived diversity it is then -- from now on I will respect that, and I will mention and cite your paper alongside the Pärtel et al. TREE paper.

      1. Aveliina

        Coincidence indeed and a clear sign that the concept was "in the air", as has also historically happened with (great ;)) scientific ideas 🙂



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