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 neighbourin g less flammable individuals and also open recruitment possibilities. We modelled the evolution of flammability using cellular automata to s imulate neighbourhood effects of burning. For plants that survive fire only from unburnt canopies (non-sprouters), increased flammability wo uld cause them to burn to death. Flammability traits can evolve in suc h species only if they result in fire spreading to kill less flammable neighbours and only if they carry additional fitness benefits. In spe cies that resprout from roots or stem bases after fire, flammability c an evolve merely by increasing neighbour mortality but is more likely to do so if the associated traits had other benefits. Most flammabilit y-enhancing traits, both structural and biochemical, are likely to hav e such additional benefits. We predict that flammability traits will b e associated with dense populations where the effect on neighbours is most marked and suggest several tests. Fire has been a key, but neglec ted, evolutionary force. Alteration of the fire regime through the evo lution 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.