The network models of the ecosystems

A model of the freshwater graminoid marshes was constructed by Heymans et al. (2002) and consists of 66 compartments, of which three represent nonliving groups and 63 depict living compartments (see reference for details). The three nonliving compartments include sediment carbon, labile detritus, and refractory detritus, all of which are utilized mainly by bacteria and microorganisms in the sediment (living sediment) and in the water column (living POC—Particulate Organic Carbon). The primary producers include macrophytes, periphyton, Utricularia, and other floating vegetation.

Lodge (1994) suggested 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." The source of most fauna in South Florida is from temperate areas further north. Accordingly, the invertebrate component of the graminoid marshes are broken down into eight compartments, consisting of apple snails (Pomacea paludosa), freshwater prawns (Palaemonetes paludosus), crayfish (Procambarus alleni), mesoinvertebrates, other macroinvertebrates, large aquatic insects, terrestrial invertebrates, and fishing spiders. Loftus and Kushlan (1987) described an assemblage of 30 species of fish in the freshwater marshes, of which 16 species are found in the sawgrass marshes.

The Everglades assemblage of herpetofauna consists of some 56 species of reptiles and amphibians. Nine compartments of mammals were identified for the graminoid marshes. Approximately 350 species of birds have been recorded within the Everglades National Park, and just slightly less than 300 species are considered to occur on a regular basis (Robertson and Kushlan, 1984). Sixty percent of these birds are either winter residents, migrating into South Florida from the north, or else visit briefly in the spring or fall. The remaining 40% breed in South Florida (Lodge, 1994), but of these only eight groups nest or breed in the graminoids. Various species of wading and terrestrial birds roost or breed in the cypress wetlands and feed in the graminoid marshes including anhin-gas, egrets, herons, wood storks, and ibises. These birds are explicit components of the cypress network. They feed on the aquatic and terrestrial invertebrate members of the graminoid wetland; however, this capture of prey is represented as an export from the graminoid system and an import into the cypress swamp. Waders were not included as explicit components in the graminoid network.

The cypress swamp model consists of 68 compartments and similar to the graminoid system, the cypress model has three nonliving compartments (refractory detritus, labile detritus, and vertebrate detritus) and two microbial compartments (living POC and living sediment). Ulanowicz et al. (1997), Bondavalli and Ulanowicz (1999) give a breakdown of the construction of the model. The primary producers are more diverse than those found in the graminoids and are represented by 12 compartments, seven of which are essentially terrestrial producers: understory, vines, hardwood leaves, cypress leaves, cypress wood, hardwood, and roots (Bondavalli and Ulanowicz, 1999). These seven compartments ramify the spatial dimension of the ecosystem in the vertical extent—an attribute not shared by the graminoid marshes. Other primary producer compartments include phytoplankton, floating vegetation, periphyton, macrophytes, and epiphytes (Bondavalli and Ulanowicz, 1999).

According to Bondavalli and Ulanowicz (1999), cypress swamps do not possess a distinct faunal assemblage, but rather share most species with adjacent plant communities. Most fauna spend only parts of their lives in the swamp. Benthic invertebrates form the heterotrophic base of the food chain. A high diversity of invertebrates has been recorded in cypress domes and strands, but a lack of data at the species level mandated that they resolve the invertebrates into only five compartments (Bondavalli and Ulanowicz, 1999). Similarly, the fish component of this model could not be resolved into more than three compartments, two containing small fish and a third consisting of large fish (Bondavalli and Ulanowicz, 1999).

The herpetofauna compartments of the cypress model were similar to those of the graminoids. The bird community of the cypress swamps was much more diverse than that in the graminoids. The increased diversity can be traced to the inclusion of wading birds in the cypress model. The wading birds do not roost or nest in the graminoids, although they do feed there; therefore, it was assumed that an export of energy and carbon flowed from the graminoids into the cypress. The 17 bird taxa in the cypress include five types of wading birds, two passerines collections, and various predatory birds (Bondavalli and Ulanowicz, 1999). The mammals of the cypress include all the mammalian compartments of the graminoids, as well as some terrestrial mammals unique to the cypress [shrews, bats, feral pigs, squirrel, skunks, bear, armadillos, and foxes (Bondavalli and Ulanowicz, 1999)]. These species are found mostly in the cypress trees and cypress domes, which extend the spatial extent of the ecosystem into the third dimension.

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