Diverging temporal and thermal niche dimensions favor syntopy of Tropidurus hispidus and Tropidurus semitaeniatus (Squamata: Tropiduridae)

Abstract

Divergences in ecological niche dimensions favor the coexistence of species in syntopy. Supposedly, closely related species face stronger pressures to differ in dimensions of niches. Integration among temporal, spatial and thermal niche dimensions is relevant for lizards because it allows proper regulation of body temperatures, which has consequences for their physiology and ecology. Here, we investigated temporal (daily activity) and thermal (body and microhabitat temperatures) niche dimensions and thermoregulation of Tropidurus hispidus and T. semitaeniatus. We hypothesized that divergences of niche dimensions would favor their local coexistences (syntopy). Tropidurus hispidus and T. semitaeniatus had similar lengths of daily activity cycles, but differed in movement rates along the day (start of the activities; hours of activity peaks; periods of greater inactivity). Activity rates and body temperatures of the lizards reflected phylogeny and thermal conditions. For both species, microhabitat temperatures and sunlight were sources for thermoregulation. Tropidurus semitaeniatus used warmer microhabitats than T. hispidus, but the species had similar body temperatures. Body sizes did not influence body temperatures, presumably because of effective behavioral thermoregulation allowing maintenance of body temperatures under appropriate ranges. Levels of active or passive thermoregulation varied depending of the thermal source (air and substrate temperatures). To thermoregulate, lizards raised up or brought down their bodies and increased or decreased levels of body flattening over substrates and shuttled across microhabitats with different temperatures and levels of sunlight. Along the day, T. hispidus used mainly partially shaded microhabitats and T. semitaeniatus used mostly full sunlight. Temporal and thermal niche dimensions of T. hispidus and T. semitaeniatus differed in ways that favor their syntopy.