The Cincinnati metropolitan area has a population of over two million people. The Cincinnati/Northern Kentucky International Airport, as well as several smaller airports, serves this area. The Greater Cincinnati/Northern Kentucky area is located within a climatic transition zone. The southern area of the region, from roughly about the Ohio River, is at the extreme northern limit of the humid subtropical climate; the north part of the region is on the extreme southern cusp of the humid continental climate. Evidence of both humid subtropical climate and humid continental climate can be found here, particularly noticeable by the presence of plants indicative of each climatic region; for example, the Southern magnolia, Crape-myrtle, Aucuba, and Needle palm from the subtropics and the Blue spruce, Maple, and Eastern Hemlock from cooler regions. The wall lizard, introduced from Italy in the 1950s, is an example of fauna in the area that lends a subtropical ambiance to the southern and central area of the region.