P. siculus is native to south and southeastern Europe, but has also been introduced elsewhere in the continent, as well as North America, where it is a possible invasive species.

A 2008 study[4] detailed distinct morphological and behavioral changes in a P. siculus population indicative of "rapid evolution".

[16] These results complicate how P. siculus fits in with the Island Syndrome hypothesis, which posits that body and head sizes should be higher in insular populations.

However, the Island Syndrome hypothesis also predicts a reduction in sexual dimorphism among insular populations, which was observed.

[8] Its range also includes Bosnia and Herzegovina, Croatia, France, Montenegro, Serbia, Slovenia, and Switzerland, but it has also been introduced to Spain, Turkey, the United States, and Canada.

[1] Populations of P. siculus in North America have been documented from Topeka, Kansas, Long Island, New York, Greenwich, Connecticut, Levittown, Pennsylvania, Joplin, Missouri, and the Greater Cincinnati area of Ohio, Indiana and Kentucky where P. siculus and P. muralis can both be found in very high concentrations and have become so well established that the Ohio Department of Natural Resources now classifies them as a resident species rather than an invasive species because they are so successful and have been present for so long.

Although illegal, it is not uncommon for people in the Greater Cincinnati Area to “trade” P. muralis lizards with people who live in areas with high population of P. siculus (often making trades by live shipment in mail) and then releasing significant numbers of the lizards in their own yards and rock walls.

[20] [21] The species seems to be extending its range from an initial colonization event in western Long Island, presumably by using railroad tracks as dispersal corridors along the middle East Coast.

Common bacterial species include Pantoea, Citrobacter, Morganella morganii, Pseudomonas aeruginosa, Coagulase-Negative Staphylococci, Enterobacter, E. coli, Schewanella, and Providencia.

[4][29] The two islands have similar size, elevation, microclimate, and a general absence of terrestrial predators[29] and P. siculus expanded for decades without human interference, even outcompeting the (now locally extinct)[4] Podarcis melisellensis population.

[29] These population changes in morphology and behavior were attributed to "relaxed predation intensity" and greater protection from vegetation on Mrčaru.

[4] This change in head shape corresponded with a shift in diet: Kopište P. siculus are primarily insectivorous, but those on Mrčaru eat substantially more plant matter.

[4] Additionally, nematodes were common in the guts of Mrčaru lizards, but absent from Kopište P. siculus, which do not have cecal valves.

[4] The cecal valves, which occur in less than 1% of all known species of scaled reptiles,[4] have been described as an "adaptive novelty, a brand new feature not present in the ancestral population and newly evolved in these lizards".

An adult female has also been observed consuming a juvenile Hemidactylus turcicus in 2003, which is the first documented case of predation by P. siculus on a gecko.

[35] The ability of P. siculus to perform different quantitative discrimination tasks may be dependent on the type of stimuli, biological versus non-biological.

A 2009 study found that in one population of P. siculus on Croatian island Pod Mrčaru had significantly high rates of missing toes (55.48%).

Additionally, members of the subpopulation facing higher levels of toe loss had significantly stronger bite forces than other populations of P. siculus.

This relationship is prolonged: the individual that is more aggressive in a dyadic (one on one) encounter can make continued use of a thermally favorable environment over a long period of time.

Regardless of aggression level in an initial encounter, this type of relationship was maintained between the dyad over a long period of time, demonstrating that social behavior is established quickly.

Studies have shown that P. siculus increase tongue-flicking behavior, commonly associated with stress, when exposed to predator scents.

Non-gravid females also spend significantly more time moving slowly when exposed to predator scents than their gravid counterparts.

These results suggest that P. siculus balance the threat of predation while basking with the thermoregulatory needs of embryo development during gravidity.

Lizards from sub-populations facing greater threats of predation achieve higher maximal running speeds.

These behavioral and associated phenotypic changes in these two subpopulations arose rather quickly, highlighting the ability of P. siculus for rapid adaptation.

A 2009 study compared anti-predator behavior in P. siculus juveniles collected from olive tree plantations and vineyards.

Under blue and cyan light, P. siculus is able to correctly orient itself under polarization axes both parallel and perpendicular to the training axis.

Colder mean temperatures in the New York habitat of P. siculus campestris may explain why this population’s activity is limited to the months of April through October.

[1] Because P. siculus is commonly found in agricultural areas, there is a concern about the effects of pesticide exposure on their health and reproductive capabilities.

A 2021 study assessing biomarkers in P. siculus on conventional and organic farms found that those on conventional farms (and therefore likely exposed to pesticides) had higher levels of oxidative stress, indicating that P. siculus can quickly activate antioxidant systems to counteract reactive oxygen species (ROS) formation.