The northern Maya lowlands, especially the northern portion of the Yucatán peninsula, are notable for their nearly complete lack of rivers (largely due to the absolute lack of topographic variation). Additionally, no lakes exist in the northern peninsula. The main source of water in this area is aquifers that are accessed through natural surface openings called cenotes. With an area of 8,264 km2 (3,191 sq mi), Lake Nicaragua is the largest lake in Mesoamerica. Lake Chapala is Mexico's largest freshwater lake, but Lake Texcoco is perhaps most well known as the location upon which Tenochtitlan, capital of the Aztec Empire, was founded. Lake Petén Itzá, in northern Guatemala, is notable as where the last independent Maya city, Tayasal (or Noh Petén), held out against the Spanish until 1697. Other large lakes include Lake Atitlán, Lake Izabal, Lake Güija, Lemoa, and Lake Managua. Biodiversity Almost all ecosystems are present in Mesoamerica; the more well known are the Mesoamerican Barrier Reef System, the second largest in the world, and La Mosquitia (consisting of the Rio Platano Biosphere Reserve, Tawahka Asangni, Patuca National Park, and Bosawas Biosphere Reserve) a rainforest second in size in the Americas only to the Amazonas. The highlands present mixed and coniferous forest. The biodiversity is among the richest in the world, though the number of species in the red list of the IUCN grows every year. Chronology and culture The history of human occupation in Mesoamerica is divided into stages or periods. These are known, with slight variation depending on region, as the Paleo-Indian, the Archaic, the Preclassic (or Formative), the Classic, and the Postclassic. The last three periods, representing the core of Mesoamerican cultural fluorescence, are further divided into two or three sub-phases. Most of the time following the arrival of the Spanish in the 16th century is classified as the Colonial period. The differentiation of early periods (i.e., up through the end of the Late Preclassic) generally reflects different configurations of socio-cultural organization that are characterized by increasing socio-political complexity, the adoption of new and different subsistence strategies, and changes in economic organization (including increased interregional interaction). The Classic period through the Postclassic are differentiated by the cyclical crystallization and fragmentation of the various political entities throughout Mesoamerica. Paleo-Indian The Mesoamerican Paleo-Indian period precedes the advent of agriculture and is characterized by a nomadic hunting and gathering subsistence strategy. Big-game hunting, similar to that seen in