Karl M. Wantzen

Biodiversity and its conservation in the Pantanal of Mato Grosso, Brazil

Abstract.The Pantanal of Mato Grosso, Brazil, is famous for its luxurious plant and animal life. We combine a literature review with recent work and show that species diversity is large but that most major plant and animal groups contain a large number of not wetland-specific species that depend on permanently terrestrial habitats within the Pantanal, or are restricted to dry areas during the low water period. These species occur also in the neighbouring biomes of Cerrado, Amazon Forest or Chaco. Until now, very few endemic species have been described, however, there are large populations of species in the Pantanal that are considered rare or endangered in South America. The number of trees adapted to long term flooding is low in comparison with the Amazon River floodplain. We hypothesize that the reason for the lack of local endemisms and the occurrence of a large number of species with a large ecological amplitude is the climatic instability of the region of the Pantanal, which suffered severe drought during glacial periods. The instability of the actual climate, which is characterized by multi-annual wet and dry periods, has a strong impact on distribution, community structure and population size of many plant and animal species and hinders spatial segregation of populations. The dependence of the system on the flood pulse makes the Pantanal very vulnerable to human induced changes in hydrology and the predicted changes in global climate.

Ecological effects of water-level fluctuations in lakes: an urgent issue

Water-level fluctuations (WLF) affect the ecological processes and patterns of lakes in several ways. Aquatic habitats and feeding or breeding grounds are gained or lost, as light, climate and wave impacts change to mention only a few phenomena. While the phenomenon of WLF has been studied in many rivers (better known as flood pulse, Junk & Wantzen, 2004) and environmental flows (Coops et al., 2003), so far it has not received due attention in lakes (Coops et al., 2003). A potential reason for why WLF in lakes have been overlooked for such a long time may be that central Europe and North America—the cradles of limnological research—are situated in landscapes which have been shaped by man for long time. Most central European lakes have been regulated since the middle ages; therefore, naturally fluctuating lakes such as Lake Constance (Fig. 1) are rare today.

Detritus processing by invertebrate shredders: a neotropical–temperate comparison

Abstract Leaf litter is a major component in the organic matter budgets of streams worldwide. Shredding invertebrates are widely considered to be of central importance for the breakdown of allochthonous organic material in temperate-zone streams. However, various authors report an absence of this group in tropical streams. Various phenomena, including hydraulic disturbance, chemical leaf quality, and biotic control through macroconsumers, may cause variable shredder performance in streams. Our paper discusses the hypothesis that biogeographic distribution and the life-cycle strategies of the shredders are additional factors affecting the contribution of invertebrates to lotic decomposition processes. As a case study, we analyzed the type of organic matter inputs, the community of benthic invertebrate shredders, and the decomposition of temperate zone leaves (alder, Alnusglutinosa) in the Breitenbach (BRB), a temperate stream in Hesse, Germany, and in the Córrego Tenente Amaral (CTA), a neotropical Cerrado stream in Mato Grosso, Brazil. Quantities of natural leaf-litter inputs were comparable in the 2 systems (CTA: 820 g m−2 y−1, BRB: 700 g m−2 y−1), but the diversity of trees varied from 60 species/ha in CTA to 5 in BRB. Several shredding species were found in CTA, but in very low abundances. Larvae of the shredding calamoceratid caddisfly Phylloicus sp. were found only in lateral pools and not in the stream channel at CTA. Earlier decomposition experiments with naturally fallen native leaves did not indicate any importance of shredders at CTA, but green leaves of A. glutinosa were rapidly consumed by mining chironomids (Stenochironomus sp.). Decomposition rates were faster in CTA (–k = 0.035 ± 0.006) than in BRB during wintertime (0.0095 ± 0.0021). We conclude that detritivorous neotropical insects may have 2 different species traits. Either they have mass occurrences during short periods when their food source is available and they must be adapted to a secondary, permanently available resource on which they can survive for the rest of the time (facultative specialists), or they are restricted to the few sites that provide a permanent food source (localized specialists). Apart from these special cases, however, the community in the neotropical stream was largely composed of omnivores.

Seasonal isotopic shifts in fish of the Pantanal wetland, Brazil

Abstract. Seasonal inundations shape the floodplain characteristics of the Pantanal, a large wetland in Central South America. In the first study combining stable carbon and nitrogen isotope analysis with classical stomach content analysis in this region, we investigated the influence of the annual inundation on diet and isotopic composition of floodplain fish. Apart from potential food items, 33 fish species from the Coqueiro Lake were analyzed, 10 of which were present during both the wet and dry season 1999. A δ13C and δ15N plot of the floodplain ecosystem allowed us to assess a foodchain of 3–4 trophic levels. However, the wide overlap of nitrogen values suggested that the organisms act on trophic continua rather than on distinct levels. The foodweb was based mainly on C3-plant carbon. However, fish species capable of feeding on terrestrial invertebrates (e.g., Brycon microlepis) had δ13C values above –25‰, indicating 13–30% intake of C4-plant based carbon during the flooding period. The novel use of vector coordinates and 2-dimensional ANOVA showed that the seasonal isotopic shifts of δ13C and δ15N were highly significant for some feeding guilds. δ15N values increased from the wet to dry season in most fish species, and these shifts were highly significant for omnivores (Astyanax bimaculatus, Triportheus nematurus, Tetragonopterus argenteus and Moenkhausia dichroura), and significant for invertivores (Gymnogeophagus balzanii and Poptella paraguayensis) and carnivores (Serrasalmus spilopleura). Average carbon isotope ratios decreased at the same time in the herbivores (Methynnis mola: 3.4‰) and detritivores (Psectrogaster curviventris: 5.3‰), but they did not change in the hypostomatic herbivore Sturisoma robustum. We explain these shifts by abundant and variable food sources during the inundation period and increasing carnivory and starvation during the dry season when the lake is confined to its central basin. Isotopic shifts between seasons were more prominent in less specialized species of omnivores, invertivores and some carnivores, whereas more specialized herbivores and detritivores appeared to be more influenced by changes in the carbon isotope ratio of the diet affected by biogeochemical processes such as respiration and methanogenesis. A general model for the interpretation of isotope data of floodplain fish considering different time-scales is given.

An extension of the floodpulse concept (FPC) for lakes

This paper delivers a conceptual framework for the ecological functioning and biodiversity patterns of lakes that is based on the floodpulse concept (FPC). The specific characteristics of rivers and lakes considering water-level fluctuations are compared, with respect to catchment linkages, temporal patterns, and hydraulic forces of flooding and drawdown. The influences of floodpulses on element cycles, biodiversity, and adaptations of lake biota are analyzed, and the importance of multi-annual flooding cycles is highlighted. The degree by which these water-level fluctuations influence lake ecosystems strongly depends on lake morphology, where shallow lakes or those with large shallow margins are the most sensitive. Although floodpulses play a major role for ecosystem services such as lake management and climate change mitigation schemes, this issue is only scarcely dealt with. Tenets of the extended FPC for lakes are formulated in order to overcome this problem.

Leaf-litter decomposition in an Amazonian floodplain stream: effects of seasonal hydrological changes

Abstract Decomposition of allochthonous material is a central process in organic matter budgets of low-order streams. Shredding invertebrates contribute substantially to the decomposition of leaves in northern-temperate-zone streams, but their role in tropical streams is less clear. Hydrology has an overarching control on ecological processes in streams, especially on floodplains, where flooding of the mainstem river may cause backflooding in the tributaries. Decomposition experiments with leaves of Cecropialatiloba, Tessariaintegrifolia, and Symmeriapaniculata were used to assess the importance of hydrology and benthic invertebrates to decomposition in a neotropical floodplain stream. Leaf breakdown rates and leaf-associated aquatic invertebrate assemblages were compared among leaf types in a typical 1st-order stream of the Amazonian whitewater floodplain forest near Leticia, Colombia. The stream hydrograph was influenced by regular rainfall throughout the year and by seasonal backflooding from the Amazon River. Stream discharge was more variable when the Amazon was low (flashy-discharge phase [FDP], September–November) than during the high-water period (backflooded phase [BFP], March–April). Cecropialatiloba and T. integrifolia decomposed much faster than S. paniculata; however, breakdown rates (mean k ± SD = 0.031 ± 0.003, 0.029 ± 0.006, and 0.010 ± 0.003, respectively) were significantly higher during FDP than during BFP (k = 0.009 ± 0.002, 0.009 ± 0.002, and 0.001 ± 0.003, respectively). Thirty-nine taxa of benthic invertebrates (mainly Chironomidae, Trichoptera, and Ephemeroptera) were identified from the litterbags. The tough leaves of C. latiloba were most densely colonized. Most invertebrate taxa (60%) were collectors, whereas shredders were very scarce (0–5%). The proportions of functional feeding groups did not differ significantly between leaf species and hydrologic period. Our results indicated that irregular hydrological pulses in these Neotropical streams had a significantly stronger impact on leaf breakdown than leaf-associated invertebrates.

Organic Matter Processing in Tropical Streams

Organic matter derived from many sources provides a basis for stream food webs. In terms of weight, leaves from the surrounding land constitute the largest allochthonous source of energy for stream consumers, but other items, including fruits, flowers, wood and twigs, and terrestrial insects, are also important. Timing of allochthonous inputs can vary markedly due to the phenology of the riparian vegetation, retention mechanisms in the aquatic-terrestrial transition zone, and local climate (especially the incidence of high-rainfall events), but seasonality of litter inputs is different, and often much less marked, than is typical of streams in temperate latitudes. As in such streams, litter decomposition rates depend on the interaction of physical factors (flow, temperature), water chemistry (dissolved nutrients), and biological agents (micro-organisms and detritivores – especially shredding invertebrates). Because vascular plant biodiversity in the tropics is high, varied leaf characteristics (hardness, phenolic content, and other aspects of leaf chemistry) contribute to great variability in breakdown rate: fast-decomposing leaves persist for a few days only, whereas highly recalcitrant species take well over a year to decompose. In all the above cases, the decomposition process includes an initial rapid leaching phase when water-soluble compounds are lost, followed by colonization by micro-organisms (fungi and bacteria), and subsequent mechanical breakdown of the leaf structure by invertebrate shredder and hydraulic forces. Undecomposed leaves are sometimes exported downstream during flood events, and thence deposited in water-logged riparian zones or, in some cases, forming dense accumulations of peat that are important as carbon sinks and as habitat for specialized biota. Recent research indicates that the role of invertebrate shredders in processing organic matter in tropical streams is less than in temperate latitudes, and there may be a higher proportion of material that is recalcitrant and/or exported from streams (or stored as peat) before it is decomposed completely. Autochthonous energy sources may be particularly important to consumers in tropical streams, and there is some evidence of a lesser reliance on allochthonous organic matter than in temperate streams.

Stable carbon and nitrogen isotope signatures of decomposing tropical macrophytes

The Pantanal of Mato Grosso, Brazil, is a large, seasonal wetland, which exhibits high macrophyte productivity at the beginning of the rainy season, when the floodplain becomes flooded. During inundation, from December through May, there is rapid turnover of decomposing macrophyte litter, which is subsequently colonized and consumed by various organisms. In this paper, the variation in the carbon and nitrogen isotope signatures of decomposing macrophytes and detritus was determined to provide an isotopic baseline for the elucidation of higher trophic levels. Seven abundant macrophyte species, Cyperaceae sp., Pontederia lanceolata, Cabomba furcata, Salvinia auriculata, Eichhornia crassipes, Nymphaea amazonum and Paspalum repens, were exposed in mesocosm decomposition experiments lasting 21 or 100 days. Stable isotope ratios of carbon and nitrogen and the atomic C/N ratios were determined for decomposing plant material, particulate organic matter (POM), the microbial film, and aquatic invertebrate larvae. The δ13C values for the macrophytes did not change during decomposition. However, the variability of δ15N was high (range of ± 6 ‰) due to microbial activity. There was no consistent difference in the isotopic signatures of macrophytes and POM. C/N ratios decreased from 17 to 50 in macrophytes, to 7 to 12 in POM. The isotopic signatures and C/N ratios of the microbial film were the same as those of POM. We concluded that heterotrophic processes did not fractionate stable carbon isotopes but caused an increase in the variability of stable nitrogen ratios and a change in the C/N ratios in our experimental system. Therefore, it was not possible to distinguish fresh and senescent material or even POM when used as a food source. The δ13C values of the aquatic larvae were closely coupled to those of the carbon source provided.

Benthos of a large neotropical river: spatial patterns and species assemblages in the Lower Paraguay and its floodplains

We studied the composition and spatial structure of benthic invertebrate assemblages and their physical and chemical environment on a 331 km long section of the Lower Paraguay River between Asuncion (Paraguay) and the rivers confluence with the Parana River near Corrientes (Argentina). Applying the same methods used in former studies in the Upper Paraguay and Parana Rivers, we sampled bottom fauna, bed sediments and water at ten riverine stations, two tributaries, and six floodplain lake sites. Seventy-six taxa, mostly oligochaetes (18 species) and chironomids (17 species), were identified. There was a clear distinction between central sites, river banks, and floodplain habitats. Highly significant regressions between sediment composition and biotic parameters were obtained (clay/diversity, R = 0.60, p < 0.0001; silt/diversity, R = 0.61, p < 0.0001; organic matter/diversity, R = 0.63, p <0.0001; coarse-middle sand/density, R = 0.75, p = 0.001). Central channel sites were dominated by the psammophilous oligochaete Narapa bonettoi, which attained densities of 10-3,500 ind. m -2 . The river banks had higher diversity indices, but lower average densities than the main channel center. Some sites with solid substrates were densely colonized by an invading mollusk species, Limnoperna fortunei, which had maximum densities of 13,500 ind. m -2 . Diversity was highest in the floodplain lakes (Shannons H = 2.4 ± 0.67) compared with banks (H = 1.79 ± 0.77) and central sites above the confluence of the Bermejo River (H = 0.89 ± 0.35). This tributary carries large amounts of fine sediments and organic matter into the Paraguay River, thereby reducing biodiversity and abundance of Narapa bonettoi. The faunal composition of the Lower Paraguay was more similar to that of the Middle Parana than to that of the Upper Paraguay. From this and former studies, two general patterns of river ecology become apparent: 1) naturally flowing sand-bed rivers can have continuous species assemblages over very long distances, characterized by few, well-adapted species that occur in high densities, but contribute relatively little biomass to the riverine foodweb; and 2) the biodiversity in the floodplain water bodies is higher than in the river channel as a result of the greater habitat diversity.

Tropical Stream Conservation

Publisher Summary This chapter focuses on the conservation issues that are relevant to most tropical regions and stream types. It also reviews the major factors impacting tropical streams. Conservation issues affecting tropical streams are complex and result from particular combinations of socio-economic factors and ecological responses. It reveals that the major factors impacting tropical streams are mainly over-fishing, deforestation, and water abstraction for irrigation and human consumption, pollution, and alterations in riverine connectivity. Most tropical regions have annual population growth rates of nearly 3% and this rapid pace of growth is commonly followed by over-exploitation of natural resources. The problem of over-exploitation of natural resources by developing countries is exacerbated by over-consumption in developed nations. On the other hand, the ecological factors include the increased rate of erosion of land after clearance for agriculture. Tropical streams located in coastal areas and island streams tend to be dominated by migratory fishes and shrimps that must pass their immature stages in estuaries or coastal waters. Deforestation is a major environmental problem in tropical regions, where rates of tropical forest loss currently exceed 1.25×105 km2 yr-1. Removal of catchment vegetation, in particular riparian vegetation, alters water movement from land to stream, resulting in increases in erosion and sedimentation in the channel. Loss of longitudinal and lateral riverine connectivity is one of the main results of river regulation, damming, and water abstraction. The case study shows that the abandonment of agriculture in Puerto Rico has had a positive effect on water quality, as chemically loaded runoff into streams has decreased.