Kill Thy Neighbour: An Individualistic Argument for the Evolution of Flammability

The idea that flammability has evolved in man) tire-prone communities has been criticised for being group-selectionist. However flammability may enhance inclusive fitness if the resulting tires kill neighbouring less flammable indi\iduals and also open recruitment possibilities. We modelled the evolution ot flammabilits usmg cellular automata to simulate neighbourhood effects of burning. For plants that sur\i\e tire only from unbumt canopies (non-sprouters), mcreased flammability would cause them to bum to death. Flammability traits can evolve in such species only if they result in flre spreading to kill less flammable neighbours and only if they carry additional fltness benefits. In species that resprout from roots or stem bases after flre, flammability can evolve merel) by increasing neighbour mortality but is more likely to do so if the associated traits had other beneflts. Most tlammability-enhancing traits, both structural and biochemical, are likely to have such additional beneflts. We predict that tlammability traits will be associated with dense populations where the effect on neighbours is most marked and suggest several tests. Fire has been a key. but neglected, evolutionary force. Alteration o\ the fire regime through the evolution of tlammability. even in a single species contributing heavily to fuel loads, would result in the selective exclusion or admission of other species to an ecosystem depending on the compatibility of their pre-existing traits with fire.