1 2 2,3 MARTIN H. IRIONDO, JUAN CESAR PAGGI, AND MARIA JULIETA PARMA 2 The great Parana basin (2,600,000 km) covers a large portion of the Neotropical Realm, extending from the Andes to the Atlantic coast and c- necting the central regions of South America along 2,200 km in a north-south direction. Most of the basin is under subtropical climates, which range from desertic in the west to humid in the east. The Middle Parana is a broad, complex floodplain extending 600 km in the heart of the interior lowlands of the continent. This system of river channels, shallow lakes, islands, and wetlands...