Conceptual ecological models, as used in the Everglades restoration program, are non-quantitative planning tools that identify the major anthropogenic drivers and stressors on natural systems, the ecological effects of these stressors, and the best biological attributes or indicators of these ecological responses. Conceptual ecological models can be used with any ecological restoration and conservation program and can become the primary communication, planning, and assessment link among scientists and policy-makers. A set of conceptual ecological models has been developed for South Florida restoration as a framework for supporting integration of science and policy and are key components of an Adaptive Management Program being developed for the Comprehensive Everglades Restoration Plan. Other large-scale restoration programs also use conceptual ecological models. This special edition of Wetlands presents 11 South Florida regional models, one total system model for South Florida, and one international regional model. This paper provides an overview of these models and defines conceptual ecological model components. It also provides a brief history of South Florida's natural systems and summarizes components common to many of the regional models.

A conceptual ecological model of the effects of the major anthropogenic stressors on the Everglades ridge and slough system was developed as a planning tool for designing and assessing the Everglades restoration program. The pre-drainage Everglades ridge and slough system was an expansive, hydrologically integrated, long-hydroperiod, low-nutrient freshwater marsh, characterized by low-velocity sheet-flow, long-term water storage capacity, moderate-to-deep organic soils, and alternating sawgrass ridges and more open-water slough communities. Depth, distribution, and duration of surface flooding in this environment largely determined vegetation patterns, as well as distribution, abundance, seasonal movements, and reproductive dynamics of all aquatic and many terrestrial animals. Drivers on the system are urban and agricultural expansion, industrial and agricultural practices, water management practices, and human influences on species composition. These drivers lead to five major ecosystem stressors: reduced spatial extent, degraded water quality, reduced water storage capacity, compartmentalization, and exotic species. Attributes that are affected by these stressors and can be used as indicators of restoration success include periphyton, marsh plant communities, tree islands, alligators, wading birds, and marsh fishes, invertebrates, and herpetofauna.

About 190,000 ha of higher-elevation marl prairies flank either side of Shark River Slough in the southern Everglades. Water levels typically drop below the ground surface each year in this landscape. Consequently, peat soil accretion is inhibited, and substrates consist either of calcitic marl produced by algal periphyton mats or exposed limestone bedrock. The southern marl prairies support complex mosaics of wet prairie, sawgrass sawgrass (Cladium jamaicense), tree islands, and tropical hammock communities and a high diversity of plant species. However, relatively short hydroperiods and annual dry downs provide stressful conditions for aquatic fauna, affecting survival in the dry season when surface water is absent. Here, we present a conceptual ecological model developed for this landscape through scientific concensus, use of empirical data, and modeling. The two major societal drivers affecting the southern marl prairies are water management practices and agricultural and urban development. These drivers lead to five groups of ecosystem stressors: loss of spatial extent and connectivity, shortened hydroperiod and increased drought severity, extended hydroperiod and drying pattern reversals, introduction and spread of non-native trees, and introduction and spread of non-native fishes. Major ecological attributes include periphyton mats, plant species diversity and community mosaic, Cape Sable seaside sparrow (Ammodramus maritimus mirabilis), marsh fishes and associated aquatic fauna prey base, American alligator (Alligator mississippiensis), and wading bird early dry season foraging. Water management and development are hypothesized to have a negative effect on the ecological attributes of the southern marl prairies in the following ways. Periphyton mats have decreased in cover in areas where hydroperiod has been significantly reduced and changed in community composition due to inverse responses to increased nutrient availability. Plant species diversity and community mosaics have changed due to shifting gradients to more terrestrial or more aquatic communities, displacement of native communities by non-natives, expansion of woody plants, high-intensity dry season fires, tree-island burnout, and reduced microtopography resulting from alligator population decline. Cape Sable seaside sparrow populations are threatened by nest destruction resulting from extended hydroperiods, drying pattern reversals, and high intensity dry season fires, as well as by the expansion of woody plants into graminoid wetland habitats. Populations of marsh fishes and associated aquatic fauna that constitute the aquatic prey base for higher vertebrates have decreased in density and changed in species composition and size structure due to loss of wetland spatial extent, shortened hydroperiod, increased drought severity, loss of aquatic drought refugia in solution holes and alligator holes, and spread of exotic fishes. American alligator populations have declined in the Rocky Glades, and alligator holes have filled with sediment, as a result of shortened hydroperiod and increased drought severity. Habitat options for wading birds to forage during the early dry season and during unusually wet years have been reduced due to loss of spatial extent and shortened hydroperiod.

A brackish water ecotone of coastal bays and lakes, mangrove forests, salt marshes, tidal creeks, and upland hammocks separates Florida Bay, Biscayne Bay, and the Gulf of Mexico from the freshwater Everglades. The Everglades mangrove estuaries are characterized by salinity gradients that vary spatially with topography and vary seasonally and inter-annually with rainfall, tide, and freshwater flow from the Everglades. Because of their location at the lower end of the Everglades drainage basin, Everglades mangrove estuaries have been affected by upstream water management practices that have altered the freshwater heads and flows and that affect salinity gradients. Additionally, interannual variation in precipitation patterns, particularly those caused to El Niño events, control freshwater inputs and salinity dynamics in these estuaries. Two major external drivers on this system are water management activities and global climate change. These drivers lead to two major ecosystem stressors: reduced freshwater flow volume and duration, and sea-level rise. Major ecological attributes include mangrove forest production, soil accretion, and resilience; coastal lake submerged aquatic vegetation; resident mangrove fish populations; wood stork (Mycteria americana) and roseate spoonbill (Platelea ajaja) nesting colonies; and estuarine crocodilian populations. Causal linkages between stressors and attributes include coastal transgression, hydroperiods, salinity gradients, and the “white zone” freshwater/estuarine interface. The functional estuary and its ecological attributes, as influenced by sea level and freshwater flow, must be viewed as spatially dynamic, with a possible near-term balancing of transgression but ultimately a long-term continuation of inland movement. Regardless of the spatio-temporal timing of this transgression, a salinity gradient supportive of ecologically functional Everglades mangrove estuaries will be required to maintain the integrity of the South Florida ecosystem.

The Big Cypress region of southwest Florida is a diverse mosaic of upland pine flatwoods and hardwood hammocks, herbaceous wet prairies and marshes, and forested wetlands. Besides large natural landscapes, it includes extensive areas of residential and agricultural development. Dominant natural controlling factors are hydrology on the low relief land surface and fire in a subtropical environment with a strong wet-dry seasonal cycle of rainfall. Human influences on the Big Cypress ecosystem are all associated with extensive residential and agricultural development. Lowered water levels and shortened hydroperiods cause shifts to drier communities, which leads to habitat loss and more intense fires. Higher nutrient concentrations associated with agriculture and more mineralized ground-water inputs from a variety of sources favor nuisance and exotic plant species. Fragmentation of the plant community mosaic interferes with seasonal expansion and contraction of wetland water bodies and associated seasonal movements of animal populations. Fragmentation also interferes with wildlife movements and the natural spread of fire across the landscape. Disturbed environments along edges created by fragmentation facilitate invasion of natural plant and animal communities by exotic species. Efforts to eradicate fire have eliminated large areas of early successional communities, while creating high fuel loads that ultimately result in very destructive fires. The spread of exotic plants is resulting in the replacement of large areas of native plant communities, but the effects of exotic animal invasions on native animal populations are poorly known. The objective of this paper is to present a conceptual model of the major human influences on the Big Cypress region, and how they affect natural processes and selected components of the ecosystem.

Biscayne Bay is a naturally clear-water bay that spans the length of Miami-Dade County, Florida, USA. It is bordered on the east by barrier islands that include Miami Beach and is an almost completely urban bay in the north and a relatively natural bay in the south. Planned water management changes in the next few years may decrease freshwater flows to the bay from present sources, while offering reclaimed wastewater in return. In addition, a project is planned to restore the former diffuse freshwater flow to the bay through many small creeks crossing coastal wetlands by redistributing the water that now flows into the bay through several large canals. To guide a science-based, adaptive-management approach to water-management planning, a conceptual ecological model of Biscayne Bay was developed based upon a series of open workshops involving researchers familiar with Biscayne Bay. The CEM model relates ecological attributes of the bay to outside forcing functions, identified as water management, watershed development, and sea-level rise. The model depicts the effects of these forcing functions on the ecological attributes of the bay through four stressors. The hypothesized pathways of these effects include salinity patterns, water quality, sediment contaminant concentrations, and physical impacts. Major research questions were identified with regard to uncertainties explicit in the model. The issues addressed include, for example (1) the quantitative relationship between upstream water management, rainfall, and flow into Biscayne Bay; (2) the salinity gradient required to restore the historical estuarine fish community; (3) the potential effect of freshwater inputs on benthic habitats; (4) the effect of introduced nutrient and contaminant loads, including the effects of reclaimed wastewater.

Florida Bay is a large and shallow estuary that is linked to the Everglades watershed and is a target of the Greater Everglades ecosystem restoration effort. The conceptual ecological model presented here is a qualitative and minimal depiction of those ecosystem components and linkages that are considered essential for understanding historic changes in the bay ecosystem, the role of human activities as drivers of these changes, and how restoration efforts are likely to affect the ecosystem in the future. The conceptual model serves as a guide for monitoring and research within an adaptive management framework. Historic changes in Florida Bay that are of primary concern are the occurrence of seagrass mass mortality and subsequent phytoplankton blooms in the 1980s and 1990s. These changes are hypothesized to have been caused by long-term changes in the salinity regime of the bay that were driven by water management. However, historic ecological changes also may have been influenced by other human activities, including occlusion of passes between the Florida Keys and increased nutrient loading. The key to Florida Bay restoration is hypothesized to be seagrass community restoration. This community is the central ecosystem element, providing habitat for upper trophic level species and strongly influencing productivity patterns, sediment resuspension, light penetration, nutrient availability, and phytoplankton dynamics. An expectation of Everglades restoration is that changing patterns of freshwater flow toward more natural patterns will drive Florida Bay's structure and function toward its pre-drainage condition. However, considerable uncertainty exists regarding the indirect effects of changing freshwater flow, particularly with regard to the potential for changing the export of dissolved organic matter from the Everglades and the fate and effects of this nutrient source. Adaptive management of Florida Bay, as an integral part of Everglades restoration, requires an integrated program of monitoring, research to decrease uncertainties, and development of quantitative models (especially hydrodynamic and water quality) to synthesize data, develop and test hypotheses, and improve predictive capabilities. Understanding and quantitatively predicting changes in the nature of watershed-estuarine linkages is the highest priority scientific need for Florida Bay restoration.

The Caloosahatchee Estuary is a large estuarine ecosystem, located on Florida's lower west coast, that supports a productive and diverse floral and faunal community. Major modifications to the hydrology of the Caloosahatchee watershed through water management, including water releases from Lake Okeechobee into the Caloosahatchee River, along with land-use transformations, increased development, and dredging for navigation, have resulted in alterations within the estuary. Changes in estuarine salinity, flows, and nutrient inputs, along with physical alterations to the estuary as a result of these stressors, can affect estuarine fishes and manatees, as well as benthic communities including several species of bivalves, such as oysters, scallops, and clams. Additionally, the submerged aquatic vegetation and mangrove shoreline habitat are affected through a variety of processes associated with these changes. As a result, these estuarine attributes can be used as indicators of restoration success.

The St. Lucie Estuary is one of the largest brackish water bodies on the east coast of Florida, USA and a major tributary to southern Indian River Lagoon. The Indian River Lagoon is a biogeographic transition zone, rich in habitats and species, with the greatest species diversity of any estuary in North America. Habitats and species diversity in the lagoon system are believed to be affected by the decline in water and sediment quality. The health of the system is being affected by water management and land-use development in this rapidly growing area of South Florida. These affects are expressed through the six major stressors identified in this conceptual ecological model. The model diagram and its associated text describe the effects of these stressors on the key ecological attributes of the system and are a way to describe both the well-known linkages and pathways between these stressors and the detrimental impacts they have on the ecology of the system. This model also provides a means to describe some of the uncertainties and associated research that will be needed to fine tune our understanding of some of the more complicated ecological interactions and interdependencies in order to carry out effectively the goals and objectives of Everglades restoration in this system and adaptively manage the restoration into the future.

With a surface area of nearly 1,800 square kilometers, Lake Okeechobee is a prominent central feature of the South Florida aquatic ecosystem. The lake provides regional flood protection, supports a prized recreational fishery, provides habitat for migratory waterfowl and regional wading bird populations, and is a source of fresh water for irrigation, drinking, and restoration of downstream ecosystems. The main stressors on Lake Okeechobee are (1) large inputs of phosphorus from agricultural and other anthropogenic land uses in the watershed, (2) unnatural variation in water levels due to channelization of inflows and dike containment, and (3) rapid expansion of non-native plants. Ecological effects are complicated due to three distinct in-lake zones with different water chemistry, physical properties, and biota. A central pelagic zone has turbid, nutrient-rich water and phytoplankton dominance; a shallow south and western near-shore zone has submerged plant or phytoplankton dominance (at low vs. high water levels, respectively); and a western littoral zone is dominated by emergent wetland plants. Changes in water level influence the flow of nutrients between zones, thereby creating a synergistic effect between stressors. Under high water conditions, there is considerable advective transport of nutrients from the pelagic zone into the littoral zone. Under low water conditions, the littoral zone is cut off hydrologically and is a rainfall-driven oligotrophic wetland. Low water also facilitates drying and wildfires in the littoral zone, which in turn has an influence on expansion of non-native plants and recovery of native plants from buried seed banks. All of these factors influence fish, wading birds, and other animals, which depend on littoral and near-shore plant communities for nesting and foraging habitat. This paper describes our current knowledge of these complex processes, the lake's expected responses to ongoing and planned restoration programs, and key areas of uncertainty requiring future research.

Historically, the Loxahatchee River watershed included an area of more than 560 km². The drainage basin was comprised primarily of pine flatwoods interspersed with cypress sloughs, hardwood swamps, marshes, and wet prairies. Rain falling on the basin was directed through natural topography into wetlands, treated by natural biological and chemical action, and slowly released to the receiving water bodies, the Loxahatchee River and Estuary and the Indian River Lagoon. Today, approximately 434 km² of the original watershed drain to the Atlantic Ocean through Jupiter Inlet. The watershed still includes substantial amounts of upland, freshwater wetland, riverine, and estuarine habitats, but large areas have been developed for urban and agricultural land uses. Development in the watershed, stabilization of the inlet, and dredging of the estuary and river have resulted in saltwater intrusion in the river, destruction of riverine cypress forest along the river, and upstream migration of seagrasses and mangroves. A conceptual ecological model, in the risk assessment framework, was developed for the Loxahatchee system to characterize the wetland, riverine, and estuarine components of this complex and diverse system. This model was developed as a means to build understanding and consensus among scientists and managers regarding the linkages between ecological stressors and attributes in the Loxahatchee river system. These relationships lead to development of a set of working hypotheses that explain how observed shifts in the distribution of riverine floodplain plant communities, oysters, seagrasses and other key species are related to increases in salinity in the river and estuary that have occurred during the past century in response to changing land use, climate change and water management practices. Basic and applied research is needed to address questions related to ecosystem structure and mechanisms that control the abundance and distribution of plants and animals in this system.

The Lake Worth Lagoon is a major estuarine water body located in Palm Beach County, Florida whose remaining natural resouces need to be protected. The lagoonal ecosystem has been stressed through the past one hundred years due to many anthropogenic influences. Altered hydrology of the system allows massive freshwater discharges into the lagoon, which exit via two ocean inlets and influence continental reef systems. These discharges carry large influxes of nutrients, suspended and dissolved organic matter, contaminants, and toxins into the lagoon, affecting the flora and fauna. Additional pressures in this urbanized coastal area include boating and fishing pressures, as well as loss of natural habitat through physical alterations to the system. A conceptual ecological model of the cause-and-effect relationships of flora and fauna to human-induced and natural conditions within the system was developed. The model consists of ecosystem external drivers and ecological stressors, ecological attributes, and ecological effects, and presents research hypotheses, including the effects of altered volume, timing and distribution of fresh water relative to seagrasses, macroinvertebrates, salinity, fishes, nutrients, toxins, suspended solids, and dissolved organic loads that will assist in the development of a quantitative hydrodynamic model for this system.

The total South Florida ecosystem encompasses all natural areas that were once interconnected and embedded within the vast Everglades basin that originally extended from coast to coast and from the upper Kissimmee basin headwaters to Florida Bay, Biscayne Bay, the Gulf of Mexico, and Caloosahatchee and Indian River Lagoon estuaries. Restoration of this system will be successful once defining characteristics of the pre-altered system are recovered. Defining characteristics of the ecosystem are 1) abundant large vertebrates and aquatic prey bases, 2) animals with large spatial requirements, 3) healthy, dynamically sustainable estuaries, 4) oligotrophic freshwater wetlands, and 5) complex landscape mosaics and interactions. These defining characteristics have been altered by three external drivers that create stressors on the system: water management, land-use management and development, and climate change and sea-level rise. Stressors on the South Florida ecosystem include loss of spatial extent; loss of connectivity; altered geomorphology and topography; altered volume, timing, and distribution of regional hydropatterns; input of nutrients; altered fire patterns; and introduction and spread of exotic plants and animals. The Total System Conceptual Ecological Model links stressors to changes in the defining characteristics through major working hypotheses of cause-and-effect relationships. The linkages (ecological effects) relate to hydroperiod and depth patterns, sheet flow, salinity gradients, nutrient status and dynamics, fire patterns, habitat availability, and marsh aquatic fauna prey bases. For each defining characteristic, key ecological indicators are identified to collectively track the decline and restoration of the ecosystem.

Located on the Caribbean Coast in the State of Quintana Roo, the Sian Ka'an Biosphere Reserve (RBSK) is one of Mexico's largest protected areas. The ecosystems of Sian Ka'an and the Greater Everglades are similar in many respects. The natural systems of Quintana Roo, Mexico and Florida's Greater Everglades and adjacent coastal ecosystems support economically important fisheries and tourism industries. Both systems are threatened by growing human populations and associated development, as well as other stressors on the ecosystem, including unsustainable uses, agricultural and urban development, and increased extraction of natural resources. Valuable lessons in ecosystem ecology and management are being learned from the South Florida Ecosystem Restoration Initiative (SFERI) that can and should be applied to the Sian Ka'an Biosphere Reserve. Conceptual ecological models have been used in Greater Everglades ecosystems to communicate major issues in restoration and to identify attributes and biological indicators for evaluating alternative restoration plans and for designing monitoring and assessment programs. The conceptual ecological model for RBSK is a conservation model rather than a restoration model; it does not explain effects that have already occurred but, rather, hypothesizes effects that, based on experience, are likely to occur. Stressors in the Sian Ka'an Conceptual Ecological Model are driven by local and national societal needs and not natural drivers. Attributes identified were similar to those in Greater Everglades systems and included hydrology and water quality, upland, wetland and coastal fauna, and vegetation patterns. Visual aesthetics also were identified as significant. Linkages between stressors and attributes are being used to design and communicate science and management needs for the Reserve.