Feeding Ecology and Habitat Use by Two Species of Gymnodactylus (Squamata, Phyllodactylidae) in Atlantic Forest and Caatinga Areas in Northeastern Brazil

In northeastern Brazil, the geckos Gymnodactylus darwinii and G. geckoides coexist in the coastal Atlantic Forest (AF), whereas G. geckoides also occurs in both inland areas of both the Caatinga (CA) and AF where G. darwinii is absent. This study investigates the trophic and spatial niches of G. geckoides in areas without G. darwinii and examines how the two species partition these niches when in sympatry. To this end, we sampled two AF sites—Dunas do Natal State Park (PEDN) and Jenipabu Environmental Protection Area (APAJ)—and one CA site—Seridó Ecological Station (ESEC)—in the state of Rio Grande do Norte. Analyses of diet composition and comparisons with prey availability revealed that in sites where only G. geckoides occurs (ESEC and APAJ), the species primarily selected and consumed termites (Isoptera). In contrast, at PEDN, where both species coexist, G. geckoides exhibited a more generalist diet, mainly selecting Hemiptera and termites, while G. darwinii predominantly consumed termites. The extent to which termites dominated the diet shaped the relationships between lizard size and prey size, with a lack of correlation between lizard size and maximum prey size in populations with greater termite consumption (G. geckoides from ESEC and G. darwinii from PEDN). In the CA site, G. geckoides occupied a generalist spatial niche, whereas in the AF sites it was confined to open habitats (restingas and beach dunes). In contrast, G. darwinii was restricted to forested habitats (tall and short forest), where it occupies soil microhabitats. Despite a moderate overlap in trophic niches when in sympatry, the two species exhibited complete spatial segregation, suggesting that spatial partitioning is the primary mechanism facilitating their coexistence.