Ecology: Living on the edge of extinction

Greater numbers of species go extinct when areas of their habitat are lost from the edge inwards compared to when they are lost from the centre outwards, finds a study in Nature Communications. Understanding how the shape of habitat destruction affects extinction rates could help global conservation efforts.

Habitat loss is a major cause of species extinction, and is principally associated with human disturbance (for example, through urban expansion or conversion of natural habitat to agriculture), but its impact on different species may vary according to the amount of habitat lost and where each species is found within it. Current methods for estimating extinction of species due to habitat loss typically only take into account the amount of area lost, and not where it is lost within a species' range.

Petr Keil and colleagues investigate the effects of habitat loss on the extinction of birds, mammals and amphibians on four continents (North and South America, Africa and Asia), in regions measuring 4.84 million km2 - large enough to capture the entire natural range of each species. Calculating how many species are lost when this area is successively reduced from its edge inwards compared to its centre outwards, and also when area is lost randomly, they find that inwards destruction is associated with the largest relative extinction of species.

In addition to losing the largest number of species, this scenario is also associated with the greatest loss of evolutionary diversity (how unique a species is) and the greatest reduction in the diversity of different roles that species play within an ecosystem. These findings suggest that species with smaller range sizes found at the periphery of a region (for example, the endangered Ethiopian wolf) are most at risk of extinction from large-scale habitat destruction.