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) states that freshwater marshes of the Everglades are relatively oligotrophic and not highly productive, averaging only about 150 g.m^-2.y^-1 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. They reach large numbers because they are relatively protected from large predatory fish, in the shallow marshes. 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).

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.

General categories of marsh vegetation include sawgrass marsh, wetland prairies, sloughs, ponds and creeks (Lodge, 1994). Busch et al. (1998) grouped marsh vegetation into associations dominated by:

1. Sawgrass (Cladium jamaicense) (Short hydroperiod — Daoust & Childers, 1999),
2. A group of emergents including Eleocharis cellulosa, Sagittaria lancifolia, and Rhyncospora tracyi (Long hydroperiod — Daoust & Childers, 1999),
3. Taxa associated with algal mats (Utricularia spp. and Bacopa caroliniana), and
4. The grasses Panicum hemitomon and Paspalidium geminatum (Long hydroperiod — Daoust & Childers, 1999).

Sawgrass covers 65 — 70% of the Everglades marsh, in nearly mono-specific stands or in association with a variety of other macrophyte species (Loveless, 1959). The sawgrass marsh community consists almost exclusively of Cladium jamaicense, which comprised on average 96.8% of the total plot aboveground biomass (Daoust & Childers, 1999). Only two other species were found to coexist with C. jamaicense — Peltandra virginica and Pontederia cordata. Eleocharis spp. was most abundant within the wet prairie community, comprising on average 61.2% of the total aboveground biomass throughout the year. Three other species, Hymenocallis palmeri, Panicum hemitomon, and Sagittaria lancifolia, were also found to co-occur within the wet prairie — long hydroperiod community (Daoust & Childers, 1999).

Caprio & Taylor (1984) and Olmsted et al. (1980) report that Muhlenbergia prairies are found in areas with the shortest hydroperiod (2-4 months). The dominant plant species in these prairies are the graminoids, Cladium jamaicense, Rhychospora tracyi, Muhlenbergia filipens, and Schizachyrium rhizomatum. A periphyton mat also covers the soil of these prairies. This relatively short hydroperiod results in a dry soil surface during most of the dry season (Caprio & Taylor, 1984).

According to Trexler (FIU, pers. comm.) the floating mat includes all non-rooted plants (and a few that may or may not be rooted) and algae. It also includes algal mats (periphyton) that float up from the bottom surface and may be suspended at mid water, or near the bottom, depending on the time of year and time of day (as the algae photosynthesize they accumulate bubbles which make them float, and at night they sink). The vascular plants included in the floating mat consist of two species: Utricularia chara and Utricularia bacopa (not common). Utricularia is a carnivorous plant that generally occur in nutrient-poor habitats that are sunny and moist (at least in the growing season), where they are often dominant (Givnish, 1989).

Periphyton is defined as an assemblage of attached microorganisms (primarily algae) which form living biofilms on the free surface of submerged substrates (Swift & Nicholas, 1987). Both plant stems and the surface of the marsh are covered with a complex association of numerous types of algae. Where it grows on the soil surface, it is commonly called an "algal mat" (Lodge, 1994). Gaiser et al. (1998) found that floating mat communities contained a matrix of Utricularia purpurea, cyanobacterial filaments (mostly Schizothrix hofmanni and Scytonema calcicola), and other associated algae, bacteria, fungi, and invertebrate animals. They found that the organic portion of the periphyton mat (excluding the Utricularia and invertebrates) comprise on average ~41% of dry biomass and consisted of mostly senescent and a lesser quantity of living material (Gaiser, et al. 1998).

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).

Lodge (1994) suggests that the Everglades does not have a great diversity of freshwater invertebrates due to its limited type of habitat and its nearly tropical climate, which many temperate species cannot tolerate. Gunderson & Loftus (1993) also found that aquatic invertebrates are generally depauperate in the Everglades: there are no stoneflies and only two mayflies (Berner & Pescador, 1988), a few snails (Thompson, 1984), and one amphipod, while chydorid cladocerans, odonates, and dipterans are diverse.

The Florida applesnail (Pomacea paludosa) is an important freshwater mollusk in the Everglades. It is found in Florida’s wetlands, lakes, and rivers. The Florida applesnail is important, due to its predation by a variety of wildlife including young alligators and numerous birds (Kushlan, 1978). The most publicized example is the snail kite, a hawk-like bird that feeds exclusively on the applesnail and is thus completely dependent upon water levels that maintain the snail’s habitat. The limpkin, a wading bird, which is related to cranes, is also heavily dependent on the applesnail (Lodge, 1994).

There is only one species of crayfish that lives in the Everglades, Procambarus alleni. P. alleni is endemic to the Florida peninsula and is adapted to the motionless waters of marshes and to the alternating wet and dry seasons of the region. It lives in underground burrows during the dry season and browses on algae and small invertebrates over the marsh bottom during the wet season. Crayfish are important prey for largemouth bass, pig frogs, young alligators, and wading birds, particularly the white ibis (Kale, 1978). Because of its reproductive timing, P. alleni is one of the first abundant prey species in the Everglades early in the wet season (Franz & Franz, 1990). Crayfish make up a substantial proportion of the diets of great egrets, tricolored herons, and little blue herons, especially during the early part of the nesting season (Frederick & Callopy, 1988).

Another important decapod crustacean in the Everglades is the freshwater prawn, Palaemonetes paludosus. Much smaller than the crayfish, these shrimps can reach very high densities during the wet season (Kushlan & Kushlan, 1980). Unlike the crayfish, it appears that the population numbers and biomass swells in the later stages of the wet season, as the current year’s larvae enter the adult shrimp-population (Beck & Colwell, 1976). The shrimps feed primarily on algae, vascular plants, detritus and small aquatic insects, with algae being the largest diet component (Beck & Colwell, 1976). These organisms are prey items of larger fish, and many of the birds that also feed on crayfish.

Aquatic insects are important in the food chain of the Everglades, as they are in all freshwater habitats (Rader, 1994). Numerous insects (e.g. water scavenger beetles, water boatmen, and giant water bugs) are totally aquatic but have retained the ability to fly and will attempt to relocate if their environments dry up. Most species that inhabit aquatic habitats, however, live in the water only as larvae and emerge to live in the air as adults. Prominent examples are mosquitoes, mayflies, damselflies, and dragonflies. Their dual lifestyles represent a significant transfer of energy from aquatic to terrestrial environments, where flying insects are important in the diets of many birds (Pennak, 1978).

Loftus & Kushlan (1987) found an assemblage of 30 species of fish in the freshwater marshes, all of which occurred in the spikerush or wet prairie habitat. Of these 30 species only 16 species are found in the sawgrass marshes (Loftus & Kushlan, 1987). Small species of killifishes (Cyprinodontidae), livebearers (Poeciliidae), and juvenile sunfishes (Centrarchidae) were the common inhabitants of spikerush and sawgrass habitats. The killifishes and livebearers are short-lived, rapidly growing species (Haake & Dean, 1983), which respond to favorable conditions with rapid increases in population. The deeper, open-water alligator holes were used by larger fishes such as Florida gar, yellow bullhead, and adult sunfishes, although smaller species including mosquitofish and sailfin molly are also common (Loftus & Eklund, 1994). Loftus et al. (1998) found that the majority of common species in the marsh were omnivorous, while a smaller number were mainly herbivorous, detritivorous or predators on fishes and decapods. Most species of Everglades fishes acted as predators on aquatic insects and crustaceans which are major trophic links between primary and secondary production in this system. The sailfin molly was the only strict herbivore in the piscifauna but the flagfish, sheepshead minnow, least killifish, and large mosquitofish also took high proportions of algae, in addition to animal prey (Loftus et al. 1998).

Freshwater fish are a mainstay of the Everglades food chains. They provide the diet for alligators, otters, wading birds, and other predators (Dineen, 1984; Loftus & Eklund, 1994; Loftus & Kuslan, 1987). Herbivorous species include the golden shiner, sailfin molly, least killifish, and flagfish. Other fishes, such as golden topminnows, marsh killifish, mosquitofish, bullheads, redear sunfish, and bluegills, feed on invertebrates, many of which grazes on plants. Adult Florida gar, warmouth and largemouth bass feed principally on other fishes, and in turn, all of these fishes are the vital food supply for other predators (Hunt, 1952).

The Everglades assemblage of herpetofauna include 56 species of reptiles and amphibians, excluding the American alligator (Dalrymple, 1988) and Diffendorfer et al. (1999) classified them into nine functional groups. The herpetofauna include the alligators (Alligator mississippiensis), snakes, turtles, salamanders, salamander larvae, large frogs, medium frogs, small frogs, tadpoles and lizards. The species composition of the herpetological assemblage varies across the different habitat types (Diffendorfer, et al. 1999). Marshes contain four turtle species absent in the wet prairie and drier upland areas, while upland areas contain four frogs and lizards adapted for the drier conditions that do not occur in the marsh (Diffendorfer, et al. 1999). Wet prairie has the highest species richness, because many species found in both the marsh and upland also use prairies. During wet periods, marsh species move into the wet prairie, while upland species utilize the wet prairie when it is dry (Dalrymple, 1988).

Raccoons (Procyon lotor) and marsh rabbits (Sylvilagus palustris) are probably the most commonly seen mammals in Everglades National Park (Humphrey, 1992, Layne, 1984). Otters (Lutra canadensis), which are more at home in water than on land, are reasonably common but are usually seen only in the dry season (Lodge, 1994). Gunderson & Loftus (1993) found that carnivores compose nearly 50% of the 17 mammals known from true Everglades habitats and rodents are the most abundant mammals. Sowder & Woodall (1985) found no cotton mice (Peromyscus gossypinus) or cotton rats (Sigmodon hispidus) in the melaleuca strands they studied, but they do occur in the other parts of the graminoids. Gaines et al. (1995) found that rice rats (Oryzomys) move between hammock islands — indicating that they would also occur in the graminoids — even if they are only in transit. Other rodents include the exotic house mouse (Mus musculus) and the muskrat (Neofiber alleni) or Florida water rat (Burt & Grossenheider, 1961). Species that do not occur in the graminoids, but do occur in the Cypress, are the bats, feral pigs, squirrels, skunks and foxes.

Opossums (Didelphis virginiana) are the only marsupials in the graminoids, and North America (Burt & Grossenheider, 1976). Opossums are about the size of a house cat and prefer farming areas, but they also occur in woodlands and along streams. They are usually active only at night (Burt & Grossenheider, 1976).

Everglades mink (Mustela vison evergladensis) is a rare animal, but they are found in the true Everglades region of South Florida (Layne, 1978). Most mink collected by Smith (1980) were obtained during the wet season, with very few data gathered during the dry season. Smith (1980) speculates that the population density of mink could have been enhanced due to the presence of canals and levees. Smith & Cary (1982) found that runways of mink were generally in sawgrass habitat within 3 m of the edge of the levee and appeared to be used frequently. Humprey (1982) suggests that mink retreat from marshland as it dries, and most move to permanent ponds in the late dry season, which concentrates them during this time, making for higher densities during the dry season. The swim very well and can remain under water in search of prey for several minutes (Layne, 1978).

The rarest mammal in the Everglades is the Florida panther (Felis concolor), whose preferred prey is white-tailed deer (Odocoileus virginianus) (Lodge, 1994). Smith & Bass (1994) report that whereas sub-adults and non-breeding female panthers feed almost exclusively on small prey, such as raccoon, marsh rabbit and alligator, breeding females prey primarily on white-tailed deer. In the Everglades, female white tailed deer make greater use of prairie habitat, than do males, who prefer to stay in the hummocks (Miller 1993). Labisky et al. (1995) report that bobcat (Lynx rufus) predation on adult deer is common in the Everglades (MacDonald, 1997).

Approximately 350 species of birds have been recorded within the Everglades National Park, and just under 300 species are considered to occur regularly (Robertson & Kushlan, 1984). Sixty percent of these birds are winter residents, migrating into South Florida from the north, or are hurried visitors, stopping only briefly in the spring or fall. The remaining 40% of the species of birds breed in the area. Approximately 116 species of birds breed in southern Florida (Lodge, 1994). According to Gunderson & Loftus (1993) only 70 species are know to breed in the Everglades - mostly on the tree islands and in thickets. Thus, they do not truly reside in the graminoid marshes, but only feed there.

Water birds that breed or roost in the graminoids are the pied-billed grebe (Podilymbus podiceps), least bittern (Ixobrychus exilis), fulvous whistling duck (Dendrocygna bicolor), green-winged teal (Anas crecca), mottled duck (Anas fulvigula), mallard (Anas platyrhynchos), blue winged teal (Anas discors), northern shoveler (Anas clypeata), ring necked ducks (Aythya collaris) and the ruddy duck (Oxyura jamaicensis) (Stevenson & Anderson, 1994).

Just over 70 species of land birds breed in southern Florida, but relatively few of them breed in the marshes. Land birds are those types of birds that normally live in terrestrial habitats and have no obligate dependence on aquatic or marine habitats, e.g. hawks, vultures, kites, doves, owls, woodpeckers, and songbirds (passerine birds). Some misfits within the land bird category include the osprey and the bald eagle, both of which are seen regularly in the Everglades, but neither breeds in the graminoids themselves (Lodge, 1994).

The terrestrial birds include the two Accipitridae: the snail kite (Rostrhamus sociabilis) and the northern harrier (Circus cyaneus) (Stevenson & Anderson, 1994) and the Caprimulgiformes: the common nighthawk (Chordeiles minor) (Werner & Woolfenden, 1983). The Gruiformes are a heterogeneous assemblage of birds often living in marshy places and are characterized by their long legs and lack of a crop (Stevenson and Anderson, 1994). There are various species in the graminoids: king rails (Rallus elegans), common moorhens (Gallinula chloropus), American coots (Fulica americana), limpkins (Aramus pictus) and Sandhill cranes (Grus canadensis pratensis) (Stevenson & Anderson, 1994).

The endangered Cape Sable seaside sparrow (Ammodramus maritimus mirabilis) breeds in marl prairies on either side of the Shark River Slough, that are typified by dense mixed stands of graminoid species, naturally inundated by freshwater for two to four months annually (ANON, 1997). They share their range with some of the passerines, such as marsh wrens, common yellowthroats, red winged blackbirds and clapper rails (Stevenson & Anderson 1994). Almost the entire range of the Cape Sable seaside sparrow (an endemic subspecies of the seaside sparrow) is the southern Everglades and Big Cypress Swamp areas in the Everglades National Park.

The omnivorous passerines that breed and roost in the graminoids include the red winged blackbirds (Agelaius phoeniceus), common yellowthroat (Geothlypis trichas), swamp sparrow (Melospiza georgiana), bobolink (Dolichonyx oryzivorus), eastern meadowlark (Sturnella magna), boat-tailed grackle (Quiscalus major), common grackle (Quiscalus quiscula), western kingbird (Tyrannus verticalis), tree swallow (Tachycineta bicolor), blue jay (Cyanocitta cristata), fish crow (Corvus ossifragus), blue-gray gnatcatcher (Polioptila caerulea), northern mockingbird (Mimus polyglottos), white-eyed vireo (Vireo griseus), yellow rumped warbler (Dendroica coronata) and the cardinal (Cardinalis cardinalis) (Stevenson & Anderson 1994). The predatory passerines include the eastern phoebe (Sayornis phoebe), loggerhead shrike (Lanius ludovicianus) and the palm warbler (Dendroica palmarum) (Stevenson & Anderson 1994).

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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