Collecting Debt

Have I said "yay for islands!" lately? Well, yay for islands!

This paper, published in the journal Ecography, looks at "extinction debt." So when we look at extinction we see that a majority of the documented extinctions of species are of those that occurred on oceanic islands. Typically these extinctions are a result of habitat destruction and fragmentation associated with human colonization, invasive species, etc. But extinction isn't an instantaneous event. A species can be reduced to a small population but it can take several generations for extinctions to take full effect. The time lag represents an "extinction debt," a 'future ecological cost.' I posted a story called A Little Patch of Home which goes over some of the theory of island biogeography, including the species-area relationship. The methods commonly used for estimating future extinctions are extrapolated from this.

This study takes place in the Azores, a system that has lost >95% of its original native forest during the last 6 centuries in addition to being very isolated and having a significant number of endemic species. The authors used the well-documented historical sequence of deforestation to calculate realistic and ecologically-adjusted species-area relationships. The results showed drastic levels of extinction debt. Over half of the arthropod (insects, spiders, etc.) species might eventually go extinct due to habitat loss. The severity of the deforestation has reduced the opportunities for forest-dependent species to cope with environmental change. The analysis shows that the taxa Araneae (spiders) and Coleoptera (beetles) are at greater risk of extinction than the third studied taxa, Hemiptera (true bugs). This could be because spiders and beetles have more species that are isolated to single islands rather than being found on multiple islands, although this is probably not the only cause. The results suggest the need for caution when thinking about conservation. Generalizing across species based on data for ecologically different taxa is inadvisable. For this reason the authors state that "large-scale conservation efforts need to be implemented if the high extinction debt we have identified is to be deferred or avoided" and that "the conservation of the Azorean natural heritage...will largely depend on establishing an integrated large-scale strategy to manage both indigenous and non-indigenous species while simultaneously protecting the remnants of native habitat and...increasing their extent."

Read more here:
Triantis, Kostas A., et al. (2010) Extinction debt on oceanic islands. Ecography: 33, 285-294. (DOI: 10.1111/j.1600-0587.2010.06203.x)