Parapatry and niche complementarity of Peruvian Desert geckos (Phyllodactylus): the ambiguous role of competition.

The Sechura Desert of Peru is among the most arid, barren regions of South America. Four species of nocturnal geckos (Phyllodactylus) are parapatric in part of the desert. By comparing niche associations of these species in allopatry and parapatry, I attempt to determine whether the observed parapatric distributions and niche dimension complementarity are related to competition - as is frequently assumed. While parapatry suggests a role for competition, distributional patterns can alternatively be related to adaptations of geckos to different physical environments (sandy desert and rocky foothill) that abut in the study area. Niche complementarity might also be a result of competition, but potentially contradictory evidence suggests that niche complementarity might instead be the result of adaptations developed in allopatry and having no relationship to competition. The ambiguity of these interpretations sets limits on the significance of this kind of evidence: in the absence of attempts to falsify alternative explanations, observations of parapatry or of niche dimension complementarity do not demonstrate conclusively the impact of competition as a force structuring communities.