Summary and Conclusions

Abstract

The Pantanal is one of the world’s major wetlands, and it is apparently the largest such environment in the tropical wet-and-dry climatic zone that has been only marginally modified by man and therefore remains largely in its natural state. The fauna is moderately rich, but much less so than the neighboring equatorial region. Its species diversity must be considered relatively low for the tropics since vast numbers of individuals belonging to relatively few species dominate most of the wetland. The net annual production of living organisms approximates zero because nearly all of the organic material produced is consumed again by the living organisms. The gross production rate, however, is extremely high, and large amounts of plant material can be produced during short periods of time at the beginning of the flood period. This situation exists because the extreme annual variations in rainfall result in alternating periods of flood and desiccation, thereby causing seasonal successions of fully terrestrial and fully aquatic biotic communities at some locations and successions of lentic and lotic aquatic communities at others. Where terrestrial and aquatic species successively occupy areas of the floodplain during each annual cycle, the available mineral nutrients required by plants and animals, such as compounds of nitrogen, phosphorus, and calcium, are fully recycled at least twice each year. After the supply has been exhausted by the primary producers, growth stagnates.