Pantanal is a complex of aquatic and terrestrial environments in a permanent shifting interphase. It is difficult to make a clear separation between the biome of dryland, wetland and the waters. With exception of isolated slightly higher stretches, all the terrestrial environments can be subject to flooding, either on a regular, seasonal basis, or exceptionally at high water levels. The rivers are shifting and the baías can occasionally dry out. Terrestrial plants have to cope with both conditions, high groundwater level and extreme drought. Natural fires selected also plants with pyrophytic adaptations. Aquatic organisms face deficient oxygen conditions and very high summer temperatures in the still water and the slow flowing streams; on the other hand they have to be resistant to drought. Practically all the plants are capable of amphibious survival.

Under such conditions, territoriality in animals is rare. Terrestrial mammals and birds follow the changing shorelines of flooded areas, expanding when marshes dry out. Water fowl adapt their roosting and nesting places to the changes in the waterbodies distribution. Fish perform large-scale and long distance migrations, the so-called piracemas. Floating waterplants follow the slow streaming of seasonal vazantes and corixos network.

Pantanal is in a permanent state of successional changes. The sequence of terrestrial plant associations starts with the dry Chaco scrubland, but it doesn't reach the stage of a mature rainforest. The rivers are all slow-flowing depositional streams. An obvious result of all this is the fact the Pantanal is an area of very little endemism, especially among the terrestrial fauna and flora. The present conditions are too fluctuating on a yearly and a secular basis, and they were probably even more so in the longer range of the Pleistocene climatic history.

Brown (1986) considers Pantanal to be first of all a biotic corridor and to a lesser extent a biogeographic barrier separating the surrounding regions. Perhaps the best way to characterize Pantanal is to consider it as a biotic filter situated in the heart of South America. Only the most resistant species of the surrounding biogeographic provinces could adapt to the imprevisible environmental fluctuations of this region.