The historical Everglades system occupied a 9,300 km² basin that extended from the southern shore of Lake Okeechobee south and southwest to the Gulf of Mexico (Hoffman, et al. 1990). The basin can now be divided into three sections: Everglades Agricultural Area, Water Conservation Areas, and the Southern Everglades, which includes the marshes south of Tamiami Trail, including Shark River Slough. The Southern Everglades is still relatively natural and includes much of Everglades National Park. The Everglades National Park occupies an area of 214,000 ha (Gunderson & Loftus, 1993), and is the area used in this study.

Freshwater marsh and wet prairies comprise 33% of all Florida wetlands and 13% of all natural vegetation types (Kautz, et al. 1993). Freshwater marshes are defined as herbaceous plant communities occurring on sites where the soil is usually saturated or covered with surface water for one or more months during the growing season. Wet prairies are characterized by shallower water and more abundant grasses, and usually fewer of the tall emergents, such as bulrushes, than marshes (Moler, 1992).

This category also includes the wet and dry marshes and prairies found on marl areas in south Florida (Moler, 1992). Water enters the Everglades National Park from rainfall or as flow from water conservation areas to the north and from numerous canals east of the park boundary (Roman, et al. 1994). Oligotrophic, nutrient poor waters are characteristic of the interior portions of Everglades National Park (Roman, et al. 1994). In a study on the general limnology of an alligator hole in the Everglades, Kushlan & Hunt (1979) found that the physico-chemical characteristics varied seasonally.

DeAngelis et al. (1998) state that freshwater marshes of the Everglades are relatively oligotrophic and not highly productive, averaging only about 150 g/m²/y in wet prairie areas. However, because of the flood and drought cycle, with rapid decomposition during the dry period, much of the primary production is transferred into the detrital food chain, to fish and aquatic macroinvertebrates, and to higher trophic levels, such as wading birds (DeAngelis, et al. 1998). During flooding, populations of small fish, crayfish, etc., are nourished by detritus and seasonal algal growth and, because they are relatively protected in the shallow marshes from large predatory fish, they reach large numbers. During the dry period, the fish are concentrated into pools and depressions by receding waters (DeAngelis, et al. 1998). There are differences in the fauna of short and long hydroperiod areas: in the short hydroperiod areas, fish and prawn densities are generally lower, whereas the crayfish density is higher (Roman, et al. 1994).

bromeliad

Two distinct communities are evident in this system, and have been modeled separately. These two communities inhabit the short and long hydroperiod areas (Lodge, 1994) that are divided approximately 75:25 in area:

Short Hydroperiod: Marl (mixed) prairie that occurs on thin, calcitic soil over limestone bedrock, which may be exposed as jagged, foot-tall projections called pinnacle rock or dissolved below the surface into pockets or solution holes. Short hydroperiod areas flank both sides of the southern Everglades, and contain low sawgrass, with high plant diversity (100 species) (Lodge, 1994). Most of the marl prairies are dominated by two species: muhly grass and sawgrass, but other species include blackrush, arrowfeather, Florida bluestem, and Elliot’s lovegrass (Gunderson, 1994). Typically, the vegetation is less than 1m tall (Herndorn & Taylor, 1986).

Long Hydroperiod: Deeper marsh community that are developed on peat soil, characteristically with lower plant diversity (Goodrick, 1984), and dominated by maidencane, Tracy’s beak rush or spike rush (Lodge, 1994). This community occurs more commonly in the central Everglades where they lie between sawgrass marshes and sloughs, and is important for fish and aquatic invertebrates, such as prawns. Long hydroperiod areas provide abundant prey for wading birds towards the end of the dry season (March-April). Goodrick (1984) found that beak rush, maidencane, and spike rush comprises 74% of the wet weight biomass at a typical wet prairie.

Gunderson & Loftus (1993) found that rotifers, oligochaetes, snails, chironomids, and microcrustacea are the most numerous primary consumers in the graminoids. Several cyprinodontoids, tadpoles, moorhens and coots and some mammals are also primary consumers. Various fishes, herpetofauna and wading birds prey on the invertebrates and smaller vertebrates. Top level predators include the wading birds, alligator, otter, mink, and raptors. Scavengers include vultures, fishes and many invertebrates. The few specialists and their prey include the limpkin and snail kite – feeding on apple snails; redear sunfish feeding on gastropods; and lepidopterans feeding on specific larval food plants (Gunderson & Loftus, 1993).

Graminoid ecosystems provide valuable habitat for a wide range of animals, including species listed by the U.S. Fish and Wildlife Service as endangered, threatened or of concern. Examples of federally listed species are the Florida panther (Felis concolor coryi) and the eastern indigo snake (Drymarchon corais couperi) (Odum and McIvor, 1990). The Everglades mink (Mustela vison evergladensis) (Layne, 1978), snail kites (Rostrahamus sociabilis), the Cape Sable seaside sparrow (Ammodramus maritimus mirabilis), the sandhill crane (Grus canadensis) and the wood stork (Mycteria americana) are also species of concern that are listed as rare or endangered (Kushlan, 1990).



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