About the cover
Aerial view from hot-air balloon over a desert grassland in the NamibRand game reserve in Namibia. Desert grasslands in parts of Namibia are punctuated by regularly patterned patches of bare soil known as fairy circles, the origins of which have remained unclear. Corina Tarnita, Juan Bonachela and colleagues use theoretical modelling and image analysis to show that a combination of scale-dependent feedbacks between plants and territorial competition between subterranean social-insect colonies can explain these features. They conclude that multiple mechanisms of self-organization are probably at play in ecosystems across the world. Cover: Lee Frost/Robert Harding/Getty Images.