Rekindling an old flame: A haploid model for the evolution and impact of flammability in resprouting plants

Using a two-locus diallelic population genetic model, we studied the evolution and impact of flammable traits in resprouting plants. A 'flammability locus' determines the flammable character of a plant and the frequency of alleles at this locus affects the probability that any plant in the population will burn. A linked 'disturbance locus' determines how a plant fares in the presence or absence of fire. Thus, the frequencies of alleles at the flammability locus influence evolution at the disturbance locus. The evolution of flammability-enhancing alleles is influenced by asymmetries in the genotypic fitnesses as well as by the base flammability of the population and the genetic structure of the system (with tighter linkage increasing the possibility that the population becomes more flammable). We demonstrate that stable polymorphisms of plants differing in flammability alleles are possible. The magnitude of the organism's impact on the flammable character of the environment influences where such polymorphisms are expected. Furthermore, predictions concerning the evolution of alleles at the disturbance locus based solely on fitness asymmetries may fail due to the influence of plants on their environment. Unusual population dynamics, including stable and unstable cycles of genotypes, are also presented. The relation of this model to the Mutch hypothesis and the recently developed theories of 'niche construction' and 'ecosystem engineering' is discussed.