Abstract
Two species of rock lizards, the parthenogenetic D. dahli and the sexually reproducing D. portschinskii, coexist in a rocky outcrop in an area of ca. 1 ha, in the vicinity of Tbilisi, Georgia; the location has been well-known since the middle 1960s. The population density of the parthenogenetic lizard is five times higher than that of the sexual breeder. We studied the distribution of active lizards in space and time over three consecutive years, during the spring and autumn activity periods, to explore spatial and temporal differences between the species on a fine spatial scale. We studied the influence of temperature, humidity, and quantitative characteristics of the surface and the distance from permanent water source on the spatial distribution of D. dahli and D. portschinskii. Darevskia portschinskii was less dependent on the distance from the water source and more evenly distributed in space and time than D. dahli. Despite potential competitive interactions, the species did not avoid each other on the microhabitat scale, suggesting that the observed ecological differences are not caused by a niche shift. More individuals of the sexual breeder than individuals of the parthenogen were found in suboptimal habitats. This feature may increase the evolutionary success of D. portschinskii in a long-term perspective.
Highlights
Comparing ecological niches of closely related species is a challenging task
We examined whether ecological niches of D. dahli and D. portschinskii are displaced on a microgeographic scale and what can be the reason for the differences: type of territorial behavior, population density, or competition
Darevskia dahli were recorded at 78 out of 108 studied plots, and D. portschinskii at 40 plots (Fig. 3)
Summary
Comparing ecological niches of closely related species is a challenging task. In the case of the presence of a competitor, the space occupied by a population can be shifted, as well as the activity dynamics (Schoener 1983; Abrams 1986; Pfenning and Pfenning 1992; Pianka 2011; Carvalho and Cardoso 2020). This process affects empirically estimated tolerance limits and response curves (Huey and Stevenson 1979; Kassahn et al 2009) can be different, dependent on the species composition in a biological community (Petren et al 1993; Pianka 2011; Frishkoff et al 2015). Competition is a significant force causing character displacement and, organismal evolution (Grant 1972; Pfenning and Pfenning 2010)
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