Structure and mechanics of intermittent Wetland communities: Bacteria to Anacondas

Freshwater wetlands are highly productive and important features of terrestrial landscapes, yet knowledge of their biotas and understanding of their function has lagged behind that of other ecosystems. Superficially, their communities are known to include bacteria, protists, algae, fungi, higher plants, and invertebrate and vertebrate animals that come together to benefit from the rich resources and oftentimes relatively predator-free space that these habitats provide. The cost of these benefits requires adaptation to a highly variable, though often predictable, hydroperiod. This chapter will focus on wetland habitats that are truly intermittent in their water-balance, and will summarize what is known of the structure of the biota at different trophic levels and how they interact at a dynamic land/water interface. For example, fluctuations in flooding regime are known to cause fluxes in carbon, nitrogen and phosphorus in basin sediments as well as in the water column. Such nutrient pulses can lead to increased productivity followed by anoxia and fluxes of methane in these sediments; significantly, microbes that die during the drying period can represent an important source of carbon upon re-wetting at the same time that phosphorus and nitrogen enter the system. These fluxes produce a range of responses from both prokaryote and eukaryote components of the wetland community. Detritivore and herbivore consumers in wetlands are represented by a rich variety of protists and invertebrates, especially crustaceans and insects, many of which appear to be predictably represented, taxonomically, across wetland types. These groups provide the crucial trophic link between producers and the top predators-although the trophic status of some of the latter is variable. For example, many amphibians that breed in wetlands represent both prey and predator depending on the stage in their life cycle. While salamanders may input large amounts of energy via egg deposition, many larger vertebrate inhabitants of wetlands are seen as net removers of energy from these systems (grazing, predation, etc.), with very little return (chiefly wastes)-although intuitively, they must represent important links between aquatic and terrestrial compartments. However, it must be said that the role of vertebrates in nutrient cycling and energy flow in wetlands is not well understood, and that the consequences of, for example the global decline in amphibian populations, are largely unknown. Coverage of these topics will be global in extent. Future research needs to be focused on piecing together the components of intermittent wetland function through study of: 1) physiological and phenological response to natural (e.g., hydroperiod regime) and human-induced stress by individual taxa; 2) community response to these same factors; 3) trophic function, including bottomup resources and top-down pressures; 4) interaction with, especially energy flow through, permanent sections of wetland, the riparian zone, adjacent woodlands and grasslands, and beyond. © 2009 by Nova Science Publishers, Inc. All rights reserved.

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