Responses of reptiles to fire in transition zones are mediated by bioregion affinity of species

Fire has impact on reptile communities with marked shifts in community composition between burnt and unburnt areas. These shifts are often related to the preference of reptile species throughout early or late post-fire successional habitats. Areas located in transition zones between bioregions harbor complex reptile communities with a mixture of biogeographic affinities. In these biogeographic crossroads, since fire simplifies the habitat structure, we expected simpler (lower alpha diversity) and more similar (lower beta diversity) reptile communities within burnt than within unburnt localities. We have tested this hypothesis in a transition zone between the Atlantic and Mediterranean bioregions in northern Portugal. Reptiles were surveyed in five localities (8 times per locality) along fire edges in which each locality was composed of one burnt and one unburnt transect. In total, 588 reptiles from 10 species were recorded. Unburnt transects had higher alpha and beta diversity and higher relative abundance of non-Mediterranean individuals than did burnt transects. A redundancy analysis also showed contrasting responses of Mediterranean and non-Mediterranean species, the former increasing and the latter decreasing after fire. Our study demonstrates that fire reduced the complexity of the reptile community, with benefits towards Mediterranean species due to its environmental preferences and long evolutionary association to fire. In biogeographic crossroads such as the study area, the retention of long unburnt vegetation is expected to maintain more diverse reptile communities.