Reptiles are amniote vertebrates (i.e. they lay eggs with a strong calcareous shell) that have a resistant and coated skin: either with great corneous plates forming an armoured carapace (turtles) or provided with simple and numerous epidermal scales made of keratin (lizards and snakes). The majority of reptiles is well adapted for terrestrial life. Being ectothermic animals, their body temperature is obtained and controlled by direct sunlight exposure (heliothermic), or by contact (thigmotaxis) with a slightly heated substratum (rock or soil) or fluid (water). However, some species live in water or close to it.
In the Iberian Peninsula there are two freshwater turtles (known in Portugal as ‘cágados’) and two snakes (water snakes) that use the Mediterranean temporary ponds. These species may be found in the southwest regions of Portugal, namely: the European pond turtle (Emys orbicularis), the Mediterranean turtle (Mauremys leprosa), the viperine water snake (Natrix maura) and the grass snake (Natrix natrix astreptophora).
The fresh water turtles are basically carnivore and frequently scavengers. In temporary ponds and small lagoons they feed on amphibian tadpoles, crustaceans and water vermin. Although having an opportunistic diet, mainly based on animals, they also feed on aquatic plants, especially in summer and in the case of the European pond turtle (Emys orbicularis). This specie has a higher consumption of tadpoles compared to the Mauremys leprosa and it predates exclusively larvae still with minimum sizes.
The Mediterranean turtle is found in Southwest France, Iberian Peninsula and northwest Africa. It is almost continuously present in Southern Portugal, and occupies most of the wetlands, being also a frequent specie in Southwest Alentejo. However, in that region many temporary ponds are being destroyed and transformed into deeper and permanent irrigation pools, which are more frequently colonized by the M. leprosa, since the E. orbicularis is more demanding in terms of habitat quality.
The distribution of the grass snake (N. natrix astreptophora) includes the Iberian Peninsula and Northern Africa. In the Mediterranean region of Portugal, especially the most arid lands of Alentejo and Southwest Portugal, its distribution is discontinuous and it may even be considered a rare species, being found on the riverside galleries and in marshy water environments. Its diet is based (more than 80%) on adult amphibians (e.g. Triturus sp., Discoglossus galganoi, Bufo spinosus, Epidalea calamita and ranidae), and secondarily on fishes, amphibian larvae, vermin, and other vertebrates. The viperine water snake (Natrix maura) is rather more aquatic, abundant and common, and its ecological adaptability basically depends on the occurrence of any kind of fresh water spots, from temporary ponds, to lagoons, rivers and marshes. It easily colonizes artificial means such as cattle drinking pools, dams and irrigation lagoons, as well as any recent water reservoir as long as it has preys. It feeds mainly on fishes and amphibians and that's why it hunts under water.
According to the Habitats Directive governing the LIFE programmes, from the four fresh water reptiles found in the region, only the turtles Emys orbicularis e Mauremys leprosa are found in the annexes II and IV, where they are classified as subject to strict conservation. Having been updated in the IUCN’s list, the Emys orbicularis has the status of ‘Near Threatened'. The main threat that fresh water reptiles face are the destruction and fragmentation of their water habitat by intensive agriculture and fishing. Other potentially negative threats result from the introduction of exotic species, both turtles (e.g. Trachemys scripta) and fish (largemouth bass).