 Fire response may also furnish an explanation for the evolution of this species . The differences in fire regime between dune crests and swales would have created different evolutionary pressures , with plants on crests adapting to frequent hot fires by becoming strongly serotinous , and plants in swales adapting to patchier , cooler fires with weaker serotiny . Speciation would be made possible by the much reduced genetic exchange between crest plants and <unk> plants , although evidence suggests that there was some introgression at first . Eventually , however , the need for weakly serotinous plants to produce ripe seed by the bushfire season would have brought forward its flowering season until the flowering seasons no longer overlapped ; thus a phenological barrier to exchange was erected , allowing the two populations to drift independently of each other . 
