There are at least species of aquatic macrophytes in the Pantanal, exhibiting various degrees of dependence on water.
The most species-rich families are Poaceae 26 species , Cyperaceae 19 , Fabaceae 15 , Onagraceae 15 and Pontederiaceae 12 , and the most species-rich genera are Ludwigia 15 species , Bacopa 12 , Utricularia 11 , Nymphaea 7 , and Polygonum 7 [ 12 ]. Considering only the Pantanal plain, 1, species of phanerogams are known, legumes being the most numerous species , followed by more than grasses [ 28 ].
The phanerogam list could be updated to nearly 2, species [ 29 ]. Because of their adaptations to flooded areas, herbaceous forms are the most numerous around 1, species. They mostly occupy seasonally flooded and grassland habitats [ 28 ]. Because of its central position in South America, the Pantanal is an encounter point for a number of phytogeographic provinces, including Amazonia to the North , the Cerrado to the East , the Atlantic Forests to the South , and the Bolivian and Paraguayan Chaco to the West.
This favors a great diversity of vegetation types.
There is a significant difference between the most humid months and the drier months of the hydrological year in wet biomass of native pastures [ 30 ]. Aquatic plants respond well to flood dynamics [ 12 ]. Many shallowly flooded grasslands dry up and the seasonal aquatics periodically disappear, among them even perennials, such as Pontederia parviflora and Sagittaria guayanensis , as do small annuals like Bacopa spp. Here soils remain waterlogged or retain a high water table, all year round.
This occurs because the area is fed by ground water in the dry season, flowing over an impermeable layer of laterite, making the water ferruginous, or over basalt or sandstone. Plant distribution in cerrado wet grassland and vereda is related to ground-water level [ 31 ], yet in the Pantanal the water table may fall below two meters in the dry season, hence above-ground water level in the wet season is a more important factor. In some parts of the Pantanal landscape these changes in dry phase and aquatic phase are more pronounced, as reflected in the high proportion of opportunistic therophytes [ 32 ] on intermediate ground between floodless and deeply flooded stretches.
Vereda soils are more organic and peaty, acting like a water-storing sponge. These soils are organosoils and gleysoils [ 33 ]. The soils in the Pantanal, even though also hydromorphic vary from pure sand to heavy clay. However, due to the very flat landscape, in the dry period the water table reaches the surface only in low-lying parts, for example in ponds and water courses. Natural pastures of the Pantanal are mainly formed by species such as Axonopus purpusii Mesosetum loliiforme and Panicum laxum covering the open fields and sandy soils of the floodplain.
Other plant species forming homogeneous fields are present, such as the legume Desmodium barbatum and the fura-bucho genus Paspalum. Since these fields of natural pasture remain submerged during the wet season, cattle ranchers are introducing exotic grassland species on the higher ground of the Pantanal. Cultivated pastures have been expanding rapidly in the floodplain to compete with the ranchers located in the upper Cerrado plateaus surrounding the Pantanal.
Two exotic species dominate such pastures: Urochloa decumbens formely Brachiaria decumbens and Urochloa humidicola former Brachiaria humidicola. They aggressively cover the ground and have been widely used to convert natural vegetation into cultivated pastures [ 34 ]. Up to , the Pantanal had lost However, at the current rate of forest loss, the natural vegetation of the Pantanal will have been totally destroyed by , if no measures are taken to combat this trend.
Not only is the Pantanal threatened by loss of natural habitat, but also by more subtle change to existing communities. These will be explored in the following paragraphs.
One potent potential impact is alterations in flooding regimen. This can, in its turn, change the structure and composition of plant communities. This can have collateral impacts on the fauna that depends on that particular kind of vegetation or microhabitat. A single example: a study on the riparian forests of the Paraguay River which studied vegetation mortality after the exceptional flood of found tree mortality rate to be 4. Tree mortality increased with the increase in topographic positions, at community level, suggesting that places where the flooding is less frequent are more affected by extreme floods.
Islands located in dry areas of the Pantanal in the alluvial cone of the Taquari River , have shown alterations in the ecological communities, modifying the local landscape units [ 37 ]. These islands are subjected to floods that cover the local vegetation, depending on the intensity of flooding. According to this study, these floods have been variable in the region year after year since In addition to alterations in the natural vegetation, impacting the local flora and fauna, the inundations also impact the local economy, with deactivation and abandonment of numerous rural properties and human settlements along the river.
The speed of such changes is illustrated by a study [ 38 ] made near the Paraguay River between and In the region the water flow of the Taquari River had become seasonally impounded. This tree can form mono-specific stands, known locally as cambarazais.
The distributary drainage network and the dimensions of the alluvial systems of the Pantanal Basin [22—24] are typical of fluvial megafans . The modern river course has resulted from a major avulsion that commenced during the mid-Holocene, which caused the Nabileque meander belt to be abandoned Fig. The scale is a geologist on the bottom-right of the picture Photos a and c by B. Based on multiple indicators, we favor the lowstand inter- Pantanal wetlands are somewhat different Table 2. Terra Nova 14 3 — Several large rivers enter the Pantanal from the north and east, forming low-gradient megafans draining toward the Upper Paraguay River, which serves as the local base level Fig. The Pantanal Basin is situated in the Upper Paraguay River depression, which is located mostly within west-central Brazil, but it also extends into frontier territories belonging to Bolivia and Paraguay Fig.
These have become locally common due to long-term flooding of old field areas. Frequent and unusual pluri-annual flooding events recorded in the Pantanal have been responsible for the sudden colonization of these trees in seasonally flooded open areas [ 38 ]. During the occurrence of longer dry and wet successive periods, two trends have been observed: 1 during longer dry events some woody plant colonize the seasonally flooded open fields, which usually are covered by herbaceous vegetation; 2 during longer wet events, flood tolerant trees, mainly V.
Changes in the cycles of flood and drought can also affect the Pantanal fauna. The abundant Pantanal crocodilian species Caiman crocodilus yacare exhibits seasonal variations in diet, foraging behavior, and in habitat selection during the hydrological year of the region [ 39 ]. A relationship between rainfall, nesting habitat and fecundity of the Pantanal caiman has been found [ 40 ].
Terrestrial activities of caimans, exhibiting coordinated movement during the dry season in the Pantanal, have been reported [ 41 ]. The ecology of breeding birds is intimately associated with the pulses of water availability, as illustrated below. Most waterfowl species exhibit synchronized reproduction, where huge colonies of birds, such as wood stork Mycteria americana , egrets snowy egret Egretta thula , great white egret Casmerodius albus and the capped heron Pilherodius pileatus and others, such as the spoonbill Ajaia ajaja, concentrate in nesting sites in the gallery forest, during the dry season, to take advantage of the seasonal resources available.
The breeding colonies are formed by hundreds of nesting birds following a pattern of species breeding at the same site or in favoured trees. Colony-based reproduction is successful thanks to the many pairs of eyes that remain vigilant in the frequent presence of predators. Both female and male storks incubate and take care of the hatchlings.
They feed the young about six times a day during the first three weeks. The parents catch prey in shallow waters 15—50 cm deep : mainly fish, molluscs, crustaceans, amphibians, reptiles, and insects. The colonial nesting site is active every year and the young storks born there return 3—4 years later, as adults, to reproduce in the same nesting site.
The birds take advantage of the progressive corralling of fish and invertebrates in ponds. The aggregation of birds in colonies concentrates nutrients via the falling of feces, prey and hatchlings to the ground which, in turn, attracts predators such as caimans, anacondas, wild foxes among others.
As a result, the shallow water of the dry season presents locally high turbidity, elevated levels of nitrogen and phosphate forms, as well as modified dissolved levels of oxygen, enriching the environment with nutrients. Two waves of breeding species are known to use the same trees: a white colony and a black colony.
High densities of black-bellied tree-duck Dendrocygna autumanalis , white-faced tree-duck Dendrocygna viduata, Brazilian duck Amazonetta brasiliensis , and Muscovy duck Cairina moschata are observed. Other common birds are the southern screamer Chauna torquata , and macaws, including the hyacinth macaw Anodorhynchus hyacinthinus.
There is a clear linkage between the flooding regimen of the Pantanal and the availability of food for the adult jabirus to raise their young. The birds need low water, especially in lagoons and ponds, in order to obtain the food they can catch with their specialized beaks. The preferred food is mussum fish Symbranchus marmoratus , which can stay dormant and encapsulated in the mud throughout the dry season, to swim again when the water rises in the rainy season. The jabiru is a specialist in detecting and catching the dormant fish in the muddy bed of the drying pond.
This book provides readers with in-depth insights into the changes in the Pantanal wetland from its formation to the actual and likely future states. It reveals that. PDF | This book provides readers with in-depth insights into the changes in the Pantanal wetland from its formation to the actual and likely future states. It reveals .
They also catch snails Pomacea spp. Jabirus are not present in the Pantanal during the flooding season. They migrate to higher ground to still unknown sites. Unusual rain and flooding occurred during the nesting season dry season of On the Taquari River, an area of km along the river was surveyed and 62 nests monitored in the same year. Only one chick was born. Apparently, the incubating behavior of the parents depends upon the availability of food for the birds, which depends upon the flooding regimen.
Clearly, reproductive success varies with the flooding schedule. Dozens of nests were seen with three young in each nest and no abnormal flooding was reported for that season. The young jabirus are ready to leave the nests in October-November, coinciding with the period of the lowest water.
Different flooding patterns have different impacts on nesting activities. For example, the unusual flooding in July—August in the Taquari area suggests that reproductive activities in that area occurred later than those in the region of Aquidauana and Miranda. Studies [ 42 , 43 , 44 ] report that the stork Mycteria americana also exhibited nest abandonment behavior due to flooding cycles at Rio Vermelho.
Field study has shown that the inter-annual variations in flooding extent can instigate dramatic changes in the number of active jabiru nests. Since the jabiru stork responds negatively to drier conditions in the Pantanal, direct human-induced changes in the hydrological patterns, as well as the effects of global climate change, may strongly jeopardize the population in the region [ 45 ].
Some 40 migratory bird species annually use the Pantanal. Most arrive from the northern hemisphere [ 46 ]. There are inter-American migratory routes connecting bird movements to the Pantanal.