KILL THY NEIGHBOR - AN INDIVIDUALISTIC ARGUMENT FOR THE EVOLUTION OF FLAMMABILITY

The idea that flammability has evolved in many fire-prone communities has been criticised for being group-selectionist. However flammability may enhance inclusive fitness if the resulting fires kill neighbouring less flammable individuals and also open recruitment possibilities. We modelled the evolution of flammability using cellular automata to simulate neighbourhood effects of burning. For plants that survive fire only from unburnt canopies (non-sprouters), increased flammability would cause them to burn to death. Flammability traits can evolve in such species only if they result in fire spreading to kill less flammable neighbours and only if they carry additional fitness benefits. In species that resprout from roots or stem bases after fire, flammability can evolve merely by increasing neighbour mortality but is more likely to do so if the associated traits had other benefits. Most flammability-enhancing traits, both structural and biochemical, are likely to have such additional benefits. We predict that flammability 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 of the fire regime through the evolution of flammability, 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.