The first three reports emphasized the individual characteristics of the cypress, mangrove and Florida Bay ecosystems. With the characterization of the last community, the graminoids, now having been completed, intersystem comparison becomes feasible. The fact that the series cypress—graminoid-mangrove-bay form a gradient from terrestrial, fresh water, estuarine to marine habitats make this comparison even more interesting.

In the graminoid system, the breakdown of carbon to the detritus is very important, which is similar to the importance of detritus in the cypress and mangrove systems. However, unlike the latter two systems, the recycling of detritus in the graminoids seems not to be important. Most of the carbon simply sinks out of the system. Conversely, the periphyton seems to be much more important to the higher trophic levels of the graminoids than is the case in the other systems. This is all borne out by the various analyses as discussed below:

The dependency of the consumers upon primary producers is very different in the graminoids than in the other systems. In the mangrove system (Ulanowicz, et al. 1999), the consumers depend mostly on carbon from the detrital compartments. In the cypress system, most of the consumers depend on the grazing chain, and the importance of periphyton increases in that system during the dry season (Ulanowicz, et al. 1997). This summer dependency upon periphyton is similar to, although not as spectacular as, the dependencies on periphyton by the higher trophic levels of the graminoid system (Figure 1). In the Florida Bay marine system the dependency on detritus returns to lower values (Ulanowicz, et al. 1998). One is led to speculate whether the rigors of the physical environment in the mangroves (osmolarity) might not somehow occasion the greater reuse of detritus in that system?

The analysis of beneficial predators and malefic prey in the graminoids indicates that the living POC and living sediment compartments benefit the most from some of their predators (Table 3). In addition, graminoid living POC is the compartment that is malefic to the most predators (Table 4). This is not the case in the cypress system, where living POC and living sediment benefit at most from only 3 predators (Ulanowicz, et al. 1997), or in the Florida Bay system, where bacteria is not malefic to any of its predators (Ulanowicz, et al. 1998). In the mangrove system, however, bacteria in the sediment is malefic to most of its predators (Ulanowicz, et al. 1999). Thus, with regard to malefic prey species, it seems that the bacterial components of the graminoid and mangrove systems impact the rest of their systems in a negative way, even though bacteria are affected positively by most of their predators in the graminoids. One is led to conclude that the sediment is a natural sink for carbon in the graminoid system.

The extremely high detritivory:herbivory ratios in the graminoids (29:1 in the wet season and 45:1 in the dry season) normally would indicate that recycling is important in this system. The concomitant low FCI values (2.4 - 4.3%) indicate, however, that cycling really isn’t that important in the graminoids. This apparent paradox is resolved by concluding that much of what is produced by the primary producers seems to be shunted into the detritus (sediment carbon, labile and refractory detritus), where it is consumed by the bacteria that help make up the living POC and living sediment. Further study of the total dependency analysis reveals that the carbon in the bacteria is not recycled to higher trophic levels, but seems to be deposited as peat. This accords with the other observation that most of the higher trophic levels seem to depend on periphyton instead of detritus or bacteria.

The analysis of cycles also lends support to the theory that cycling in the graminoids is confined mostly to the sediment and water column detritus. Sediment carbon (ETL 1) is at the crux of most of the recycling, and most carbon is recycled among the sediment carbon (ETL 1), living sediment (ETL 2), refractory detritus (ETL 2) and labile detritus (ETL 2) (Figure 6). That is, the detritus-microbial loop accounts for 96% of the recycling in the graminoids and incorporates only compartments at the first and second trophic levels. The link between the detrital cycle and the higher trophic levels is quite weak. The largest such cycle consists of the mesoinvertebrates feeding on living sediments and sediment carbon (± 1.1 gC/m²/yr in the wet season and 0.7 gC.m^-2.y^-1 in the dry season). When incorporating the water column detritus, the most significant loop (labile detritus-mesoinvertebrate-Utricularia) shows only marginal activity (0.5 gC.m^-2.y^-1 in the wet season and 0.4 gC.m^-2.y^-1 in the dry season). All signs seem to point to a weak interaction between the microbial loop and the upper trophic levels in the graminoid system.

When comparing the key players that effect recycling in the graminoids with their counterparts in the Florida Bay system (Ulanowicz, et al. 1998), it becomes evident that the links with the higher trophic levels are more visible in the latter system. In the Florida Bay water column, for example, the main recycling pathways include pelagic flagellates (ETL 2.1), zooplankton (ETL 2.5) and pelagic ciliates (ETL 2.6), and benthic recycling includes meiofauna (ETL 2.3) and benthic ciliates (ETL 2.4). Similarly, in the mangrove ecosystem the key players in recycling carbon are sediment carbon (ETL 1), bacteria in the sediment (ETL 2), flagellates in the sediment (ETL 2.5), ciliates in the sediment (ETL 2.66) and meiofauna in the sediment (ETL 2.74). All such links towards the higher trophic levels remain in the distant background in the graminoid ecosystem.

The fact that the graminoid ecosystem is being used as a feeding ground by many of the migratory species that reside in the cypress and mangrove systems, has influenced how we cast the graminoid model and, consequently, has affected the model properties vis-à-vis its counterparts. The analysis of beneficial predation provides good examples of the differences engendered thereby. For example, there are 13 beneficial predators in the graminoid wet season and 17 in the dry season. This is much fewer than the instances of beneficial predation in the cypress, mangrove and Florida Bay systems, where examples of beneficial predation were far more in evidence. There were 78-67 (wet-dry) beneficial predators in the cypress, 208-218 beneficial predators in the mangrove system and 282-294 in Florida Bay. This reduction in the instances of beneficial predation in the graminoids derives from the exclusion of the wading birds, and of other birds that do not roost there, but still feed in the grassy prairies.

Even though the graminoid ecosystem is represented by fewer compartments (66 vs. the 128 for Florida Bay), it is far more active than either the cypress, the mangrove or the Florida Bay community (Table 6). Its total system throughput is an order of magnitude larger than that of any of the other three systems, and its development capacity is similarly higher than that of the other systems. Furthermore, the leading index of development (the ascendency:capacity ratio) also indicates that the trophic relationships in the graminoid ecosystem are more clearly defined than they are in the other three systems.

The insights gained from this comparative exercise should serve the ATLSS modelers well as they begin their task of executing this most complex of all ecosystem simulations.

During the past year several individuals have been most generous in devoting their time and data to the construction of the graminoid ecosystem networks. These include Joan Browder, George Dalrymple, James Layne, Len Scinto, Joel Trexler and Wilfried Wulff. We sincerely appreciate their help with this daunting task.


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