I discovered this unpublished post today, originally written in the Spring:
A while ago I wrote a wikipedia article on extinction debt. Frankly, researching this topic scared the hell out of me. Extinction debt began as a fairly obscure theoretical concept that emerged out of mathematical modeling exercises in ecology that showed that it could take tens or even hundreds of years for species to go extinct (Timan et al. 1994). At first blush, this might seem like good news - maybe we have a long time to prevent extinctions. However, it's also bad news, because if this is true, many of the species alive today are committed to extinction due to our actions in the past.
Many of the species we see in nature today are no longer really supported by their remaining habitat. Standing trees may live, but if their habitat can't support new seedlings, we'll lose them in a generation. Some animals might go through boom-and-bust cycles that . These are the living dead.
Eventually scientists began to figure out how to measure which species are zombies and how long to they are likely to last. More than 50% of insects currently on the Azores islands are expected to go extinct because of past deforestation. African countries can expect to lose 30% of primate species. (Kuussaari 2009 reviews many of these studies)
An interesting corollary to extinction debt is "dark diversity," a concept introduced Meelis Partel, Robert Szava-Kovats and Martin Zobel in TREE earlier this year. Dark diversity refers to the missing species in an ecosystem. The diversity in any locale draws on some but not all of the "pool" of species available in the region. Why? Sometimes it's because species are incompatible with each other, sometimes because physical barriers prevent species from colonizing a location, but often because species have been lost due to human impacts. They took a crack at estimating dark diversity globally:
This map shows the ratio of plant species to the "dark" or "missing" species. In red areas, there are a lot fewer species on the ground than one would expect. We can infer - but not yet prove - that a lot of the species in the red areas have been lost.
It's not normally my style to be all gloom and doom, but this is freaking me out.Pärtel, M., Szava-Kovats, R., & Zobel, M. (2011). Dark diversity: shedding light on absent species Trends in Ecology & Evolution, 26 (3), 124-128 DOI: 10.1016/j.tree.2010.12.004