Network analysis of the South Florida Everglades graminoid marshes and comparison with nearby cypress ecosystems

Network analysis (NA) is used to compare two ecosystems with different spatial extents to understand the different patterns and dynamics that arise. NA allows one to study the system at different scales: At the level of bilateral interactions, input-output structure matrices are calculated to look at the direct and indirect effects that one flow has on another: at the functional level, the food web is mapped into a concatenated trophic chain, and till simple, directed biogeochemical cycles are identified and separated froth the supporting dissipative flows; and at the system's level global variables describe the state of development of the total network. The systems in question are the Everglades graminoid marsh and the adjacent cypress swamp. The graminoid marsh is essentially a two-dimensional system, with reduced diversity of primary producers. and a more focussed dependency of higher trophic levels on one particular primary producer. the periphyton. Although the cypress swamp system contains most of the same flora and fauna as the graminoids, it extends into a third dimension, and contains additional forms of terrestrial vegetation that increase the diversity of primary production, and thereby the resilience of the ecosystem. The importance of detritus to both systems is marked, although recycling within detritus is far more important in the graminoids than in the cypress. The linkages to higher trophic levels are relatively fewer in the graminoids. and the diversity of interactions between the detritus and higher trophic levels is much higher in the cypress. Overall, the presence of a third dimension imparts diversity and resilience to the cypress system, although the faster turnover rates of the graminoids make them more productive. (C) 2002 Elsevier Science B.V. All rights reserved.