Invasions by nonnative species can threaten Everglades restoration, displacing native species and transforming large expanses into ecosystems that differ radically from their historical structure, functioning, and provision of ecosystem services. Melaleuca (Australian paperbark, Melaleuca quinquenervia), Brazilian pepper (Schinus terebinthifolius), Australian pine (Casuarina spp.), and Old World climbing fern (Lygodium microphyllum) together infest hundreds of thousands of acres of the Everglades region and foster frequent, hot fires that destroy native plants in the “River of Grass” and tree islands, facilitating dominance by exotic vegetation (Schmitz et al., 1997). The Burmese python has quickly become the top carnivore in the Everglades food web, eating not only alligators but virtually all vertebrates it can reach. Its invasion of the Everglades has coincided with ~90 percent declines in populations of bobcats, raccoons, and opossums and a 100 percent decline of rabbits (Dorcas et al., 2012).
The extent to which invasions hinder restoration depends on how restoration is defined. As noted in Chapter 2, different agencies define “restoration” differently, as is revealed in the specific goals. The South Florida Ecosystem Restoration Task Force (Task Force) describes three goals for Everglades restoration, of which the second is “Restore, preserve, and protect natural habitats and species” (SFERTF, 2000). The Comprehensive Everglades Restoration Plan (CERP) defines the goal of Everglades restoration as “restoration, preservation, and protection of the South Florida Ecosystem while providing for other water-related needs of the region, including water supply and flood protection.” The Programmatic Regulations that guide implementation of the CERP state that the desired hydrologic and biological characteristics include resilient plant communities and an abundance of native wetland animals (DOI and USACE, 2005). Substantial establishment by nonnative species is certainly incompatible with the Task Force goal, and establishment of at least some highly aggressive nonnative species is incompatible with the CERP goal. A senior DOI official succinctly summarized the problem: “an Everglades landscape teeming with
exotic species is not a restored Everglades” (S. Estenoz, DOI, personal communication, 2013).
This chapter details the status and trends of nonnative species invasions of the Everglades ecosystem, discusses some of the challenges for managing these nonnative species in the context of Everglades restoration, and suggests ways of addressing these challenges.
EVERGLADES INVASIVE SPECIES AND THEIR IMPACTS
Invasive species are increasingly common around the globe, and the impacts of nonnative species are quite variable because they depend upon characteristics of the species itself and the ecosystem it invades. Ecological changes induced by these invaders range from no immediately discernible impacts to dramatic effects limited to particular native species or specific groups of them, to broad-scale habitat transformation with attendant changes in ecosystem structure and functioning. This section reviews the effects of invasive species in the Everglades.
Some biological invasions affect particular native species or specific groups of them. For instance, the newly invading redbay ambrosia beetle (Xyleborus glabratus; Figure 6-1) attacks a native plant species, swamp bay (Persea palustris), infecting trees with the deadly laurel wilt fungus (Raffaelea sp.) (Fraedrich et al.,
FIGURE 6-1 Laurel wilt damage to swampbay trees on an Everglades tree island (left), which is caused by the laurel wilt fungus carried by the nonnative redbay ambrosia beetle (right). Note the scale: the adult insect is less than 3 mm long.
SOURCES: Photographs courtesy E. Allen, SFWMD (left) and J. A. MacGowan, Mississippi Entomological Museum (right).
2008; Rodgers et al., 2014a). Ecological impacts may spread beyond swamp bay to species that depend on it for food, habitat, or other services (Chupp and Battaglia, 2014; Kendra et al., 2013). Other trees in the laurel family (Lauraceae), such as avocado, are also at risk (Mayfield et al., 2008; FDACS, 2012).
Other biological invasions affect ecosystem processes (such as fire regimes or nutrient or hydrologic cycles) or ecosystem structure, so they automatically affect many native species. For instance, melaleuca and Old World climbing fern both greatly affect the fire regime in parts of the Everglades. The altered fire regime then adversely affects marshes, sawgrass prairies, and tree islands, with follow-on effects on species that may occupy these habitats, such as epiphytes and various rare plants (Serbesoff-King, 2003).
Further complicating both understanding and management of nonnative species is the fact that they can interact synergistically with one another to exacerbate impacts, a phenomenon known as invasional meltdown (Simberloff and Von Holle, 1999). For example, nonnative fig trees were present for a century in South Florida as ornamentals, restricted largely to residential areas and not an invasive problem in the Everglades until the 1990s. This restriction was caused by the fact that each fig species can be pollinated only by a particular fig wasp species, and the nonnative fig species present in Florida lacked their fig wasps. However, beginning in the 1980s, the nonnative fig wasps of three of these fig species arrived (by unknown means) in Florida, and at least one of the figs, Ficus microcarpa, is now an invasive pest in parts of the Everglades (Kauffman et al., 1991).
The case of the figs and fig wasps also exemplifies another complication in assessing invasion threats and prioritizing management activities—many introduced species that ultimately become widespread, highly damaging invaders can remain restricted and innocuous for an extended period, even for decades, before spreading across the landscape (Crooks, 2011). In South Florida, Brazilian pepper was introduced at least as early as the 1880s but did not explode across the region until the 1950s (Ewel, 1986). Melaleuca was similarly present long before it became a major vegetation element (Ewel, 1986). For Brazilian pepper and melaleuca, the reason for the lag between introduction and widespread invasion is not known with certainty. The rather sudden explosion of Brazilian pepper in the 1950s might even have resulted from hybridization between two separate earlier introductions that differed genetically (Mukherjee et al., 2012). However, whether the reasons for a lag and its termination are known (as with the fig) or not (as with Brazilian pepper and melaleuca), the frequency of such invasion lags cannot be doubted (Crooks, 2011). These lags, in turn, challenge attempts to classify a newly discovered introduction as likely innocuous or potentially threatening.
Invasion of nonnative species is often accompanied by structural, func-
tional, and biogeochemical changes in the community. Invasion by melaleuca has transformed prairies of sawgrass and muhly grass into forests almost wholly composed of melaleuca (Bodle et al., 1994), while Australian pine (Casuarina spp.) dominates formerly treeless beaches (Schmitz et al., 1997). Invasion by these plants affects the native animal community; for example, Australian pine interferes with nesting of endangered sea turtles (Wheeler et al., 2011). Similarly, spread of the Burmese python (Python bivittatus) threatens the entire food chain, challenging even the American alligator for the apex position. This top predator is spreading quickly, leading to dramatic declines in mammal populations (Dorcas et al., 2012), and native bird populations may also be at risk (Dove et al., 2011). Table 6-1 highlights several potential impacts of invasive species on CERP performance measures in the Greater Everglades region.
Following their removal, some of those changes linger, leaving legacies of unknown longevity and impacts. For example, substantial remains of melaleuca trees persist on tree islands and other areas in the Everglades where trees were girdled and died in place (Figure 6-2). Such legacies may negatively influence subsequent regeneration of native species and/or facilitate reinvasion of nonnative species (D’Antonio and Meyerson, 2002). Areas with seedbanks of per-
TABLE 6-1 Examples of Potential Invasive Species Threats to CERP Performance Measures
Potential Threat or Risk
Distribution, Size, Nesting and Condition
Argentine black and white tegu
Reduced reproduction due to egg and hatchling predation
Direct competition for food resources
Direct predation by pythons
American Crocodile –
Argentine black and white tegu
Reduced reproduction due to egg and hatchling predation
Direct competition for food resources
Direct predation by pythons
Marl Prairie Cape Sable
Seaside Sparrow Habitat
Degradation nesting habitat due to changes in plant community structure and fire regimes
Prey-Based Freshwater Fish
Density Performance Measure
Nonindigenous freshwater fish
Reduced native small dish density due to predation or competitive interactions
Ridge and Slough
Old World climbing fern
Alteration of plant community structure, microtopography, and fire regimes
Displacement of native plant community
Alteration of fire regimes
Loss of wildlife habitat
SOURCE: RECOVER (2014a).
FIGURE 6-2 Stands of melaleuca in the Everglades, after control efforts using ground-based herbicide application.
SOURCE: Photograph courtesy of D. Policansky, National Research Council.
sistent, viable propagules of nonnative species are particularly vulnerable to reinvasion. Unfortunately, very little is known about these legacies and potential impacts on restoration success in the Everglades. Sites where nonnative species have been removed may remain altered by their legacies and require additional rehabilitation to achieve long-term restoration goals.
In many cases, the effects of invaders are currently unknown. For example, nonnative fishes are quite abundant in certain areas, exceeding 6 percent at 12 sites in Everglades National Park (RECOVER, 2014a). Yet no studies have documented and quantified their effects on native fish species or on various
CERP performance measures (e.g., freshwater fish density, wading birds nesting and foraging).1 Once established, removal of nonnative fishes is “problematic,” although options may exist to prevent future introductions or limit their spread (RECOVER, 2014a).
In this section, some of the more significant Everglades invaders are discussed, focusing on some of the most damaging ones or ones with unknown potential to be damaging, to illustrate the types of impacts that can occur. The types of treatments that have been used to manage them and the efficacy of available treatments are summarized. Appendix B contains descriptions of other invasive species in the Everglades, and extensive lists of invasive plants and animals are provided in the 2014 System Status Report (RECOVER, 2014a).
Many nonnative plants are pervasive pests in the Everglades (reviewed in Junk et al., 2006). There are approximately 250 nonnative plant species in aquatic, wetland, and terrestrial habitats of the Everglades, constituting 16 percent of the flora (Long, 1984). Currently, 75 species are listed as priorities for control by the South Florida Water Management District (SFWMD), with a particular emphasis on species able to displace natives and transform ecosystem structure and functioning (Rodgers et al., 2014a). Of the 75 priority species, 12 are considered particularly high priority because they are believed to threaten the success of the mission of the SFWMD (Rodgers et al., 2014a), and four of these are systemwide priorities, described in detail in the sections that follow. Table 6-2 summarizes the status and trends of all 12 high-priority species, along with two others that have been targeted for early detection and rapid response (EDRR). Appendix B provides some additional details of invasion history and impacts of these and other invasive species.
Melaleuca is a highly invasive tree native to Australia, New Guinea, and New Caledonia. It readily establishes in sawgrass prairies and tree islands (Davis et al., 2005b), converting these communities into low-diversity forests with highly altered structure and functioning (Schmitz et al. 1997, Serbesoff-King, 2003). Melaleuca can drive changes in soil chemistry, depth to the water table, nutrient cycling, and perhaps most importantly, fire regime. Native sawgrass communities are adapted to frequent, low-intensity fires, but when melaleuca-dominated areas burn, the fires are much more intense as the essential oils in
TABLE 6-2 High-Priority Invasive Plants in the South Florida Water Management District
|Species||Areal Extent||Ecological Impacts||Treatment Availability||Systemwide Trends|
|Melaleuca||10,035 canopy acres in ECISMA, systemwide||Displaces native vegetation, alters plant community structure, changes soil chemistry, alters fire regime||Integrated mechanical, herbicide, biocontrol—effective with continued maintenance management||36% decrease since 2010-2012|
|Brazilian pepper||22,145 canopy acres in ECISMA, systemwide||Displaces native vegetation, reports of allelopathy (chemicals produced by plant affect other vegetation), alters fire regimes||Mechanical, herbicide, prescribed burning (in low-density areas); expensive to manage successfully||16% increase since 2010-2012|
|Old World climbing fern||5,927 canopy acres in ECISMA, systemwide||Displaces native vegetation, alters fire regime||Mechanical; herbicide effective but affects nontarget species; biocontrol efforts promising||69% increase since 2010-2012|
|Australian pine||1,869 canopy acres in ECISMA, systemwide||Alters habitat for nesting sea turtles and small mammals; limits regeneration of native species||Mechanical and herbicide methods effective but require repeat; biocontrol agents under development||Spatial distribution constant; 94% increase in canopy acres since 2010-2012|
|Water hyacinth||Acreage unknown; significant infestations in Kissimmee Basin and Lake Okeechobee||Displaces native aquatic species; clogs waterways||Herbicide, biocontrol||Unknown; monitored in public waters; treated as needed and resources allow|
|Hydrilla||Acreage unknown; significant infestations in Kissimmee Basin and Lake Okeechobee||Displaces native aquatic species; clogs waterways||Herbicide effective but recent detection of resistance; mechanical harvesting||Unknown; monitored in public waters; treated as needed and as resources allow|
|Air potato||Acreage unknown||Shades and displaces native species||Herbicide; biocontrol partially effective; other agents under development||Unknown|
|Shoebutton ardisia||Acreage unknown; high densities in southern Everglades and eastern part of ENP||Shades and displaces native species in a wide range of habitats||Mechanical cutting followed by herbicide||Unknown; difficult to detect aerially|
|Species||Areal Extent||Ecological Impacts||Treatment Availability||Systemwide Trends|
|Torpedograss||9,000 acres in marshes of Lake Okeechobee||Displaces native species; readily invades disturbed areas||Herbicide; no biocontrol agents approved||Unknown; no systemwide monitoring|
|Downy rose myrtle||Unknown coverage; mostly coastal counties||Displaces native species||Mechanical cutting, herbicide; biocontrol agent under testing and development||Unknown; difficult to assess aerially|
|Cogongrass||6,900 acres in the SFWMD||Displaces native species in wide range of habitats; alters fire regimes and nutrient cycling||Herbicide, mechanical, prescribed fire; no biocontrol agents approved||Unknown, appears to have spread recently|
|Water lettuce||Acreage unknown; significant infestations in Kissimmee Basin and Lake Okeechobee.||Displaces native aquatic species; clogs waterways||Repeat application of herbicide; biocontrol agents ineffective||Unknown; monitored in public waters; treated as needed and as resources allow|
|Tropical American water grass||Restricted mainly to Lake Okeechobee||Displaces native aquatic species||Herbicide||Unknown; some expansion on Lake Okeechobee marsh|
|Black mangrove||Limited and contained distribution||Not fully understood; threat to diversity and function of native mangroves||Mechanical||EDRR reduced occurrence, likely to eradicate|
|Mile-a-minute||Limited and contained distribution||Shades out and blankets native vegetation||Herbicide||EDRR reduced occurrence, eradication may be possible|
NOTE: The acreage numbers presented here are compiled from multiple sources, some with sampling over the entire South Florida Water Management District, which, at 4,662,000 ha, is much larger than the 728,000-ha Everglades Cooperative Invasive Species Management Area (ECISMA), representing all state and federal conservation lands within the Everglades Protection Area, Miccosukee and Seminole lands, Broward County, Palm Beach County, and Miami-Dade County. Sampling methods and time frames of measurement may also differ. EDRR = early detection and rapid response; ENP = Everglades National Park.
SOURCE: Rodgers et al. (2014a,b); R. Johnson, NPS, personal communication, 2014.
the foliage become explosive, killing nearby sawgrass and many other native members of the community (Center et al., 2012). Melaleuca seeds are liberated by fire, and millions of seeds are released during the high-intensity fires. Thus, melaleuca is a habitat transformer (Gordon, 1998). Rodgers et al. (2014b) report that melaleuca infested over 40,000 acres of the Everglades Cooperative Invasive Species Management Area (ECISMA; which consists of all state and federal conservation lands within the Everglades Protection Area, Miccosukee and Seminole lands, Broward County, Palm Beach County, and Miami-Dade County) in 2010-2012, including more than 10,000 canopy acres.2
Melaleuca has been treated in many areas with mechanical removal, herbicide (Silvers et al., 2007), and most recently with several biocontrol agents—natural enemies of melaleuca imported from its native range (Franks et al., 2006). These insects reduce its seed production, growth, and density, and increase its susceptibility to fire and herbicides, leading to greater native species diversity in some targeted areas (Rayamajhi et al., 2009). Control efforts have been quite successful, and abundance of melaleuca has been dramatically reduced to maintenance control levels in many areas of the Everglades (Figure 6-3; Center et al., 2012; Rodgers et al., 2013), although not systemwide to date. With combined control efforts, there was an estimated 36 percent decrease in canopy acres in the ECISMA between 2010 and 2012 (Rodgers et al., 2014a). Untreated plants can flower within a year of establishment, replenishing the seed bank, which enables melaleuca to reinvade treated areas readily. Although biocontrol efforts have slowed the rate of new invasions, frequent monitoring and retreatment are necessary to achieve maintenance control of this species.
Brazilian pepper is highly invasive and widely distributed in the Everglades (Ewe and Sternberg, 2002) with the highest spatial coverage of nonnative plant species (see Figure 6-2). The growth form of Brazilian pepper is quite plastic, and it can occur as a shrub, small tree, or even vine depending on environmental conditions (Spector and Putz, 2006). On tree islands and other areas where it dominates the canopy, understories support few if any native species (Rodgers et al., 2013). It is highly fecund, producing thousands of seeds each year (Ewel et al., 1982). Its rapid growth rates, vigorous sprouting capacity, and reported ability to produce chemicals that inhibit other plant species (Morgan and Overholt, 2005) enhance its capacity to displace native species and become dominant.
2 Canopy acres represent the area of ground covered by foliage of a particular invasive species. Infested area is defined as the acreage encompassed after drawing a line around the perimeter of the areas of infestation (the canopy cover of the plants) excluding areas not infested (Price, 2009).
FIGURE 6-3 Areas with melaleuca infestations, 1995-2010. Darker shades indicate denser coverage of melaleuca.
SOURCE: J. Eckles, Florida Fish and Wildlife Conservation Commission, and L. Rodgers, SFWMD, personal communication, 2013.
If allowed to continue to spread across the Everglades, Brazillian pepper could significantly affect CERP performance measures, such as ridge-and-slough sustainability (RECOVER, 2014a).
Fire can be used to manage low densities of Brazilian pepper. However, in high-density stands, fire has much less impact, and Brazilian pepper can drive a fire suppression feedback that leads to further invasion (Stevens and Beckage, 2009). Brazilian pepper is particularly difficult to control in nutrient-rich conditions. For example, the Hole-in-the-Donut within Everglades National Park had perhaps the most expansive infestation of Brazilian pepper. This area was heavily disturbed and had elevated soil nutrient availability from previous farming practices (Li and Norland, 2001). Restoration required removing the soil substrate, which had been highly modified by rock plowing (Ewel, 2013), down to the bedrock to promote reestablishment of native vegetation (Smith et al., 2011). Mechanical removal and herbicides can also control this species to some degree. In the Picayune Strand CERP project, massive mortality of Brazilian pepper occurred followed flooding of plot PC26 (RECOVER, 2014b). Biological control agents have been tested, but to date, none have been released. Currently, a gall-producing potential biocontrol agent is under testing and development. Brazilian pepper is not under maintenance control and is still spreading. This species infested 74,225 acres in the ECISMA area and there was an estimated 16 percent increase in canopy acres during the period 2010-2012 (Rodgers et al., 2014a).
Three species of Australian Casuarina are highly invasive in the Everglades. Casuarina equiseitfolia is the most common and widely distributed of the three and threatens coastal areas and beaches because it tolerates arid conditions and saline soils with limited fertility. It is limited by long hydroperiods, occurring mostly on better drained soils and in some short-hydroperiod sawgrass habitats. C. glauca and C. cunninghamiana are often found on disturbed sites in upland habitats adjacent to coastal communities. Left unchecked, C. equisetifolia can dramatically alter the structure and functioning of many coastal areas of the Everglades. For example, the root structures and fallen “needles” of the Australian pine on invaded beaches inhibit nesting by loggerhead and green sea turtles (Wheeler et al., 2011). Also, the heavy litter layer that develops under dense Australian pine canopies can impede regeneration of other plant species.
Mechanical removal has proven difficult because these species have tremendous sprouting capacity. Controlled burning is not effective (Doren and Jones, 1997), and herbicide applications are expensive. An effective biological control agent is being sought (Wheeler et al., 2011); recent discovery that Australian
pine species are hybridizing in the Everglades may further complicate this search. Australian pine is currently relatively low in abundance compared with melaleuca and Brazilian pepper (Figure 6-4). Australian pine is considered to be at maintenance control levels in most areas of the Everglades (Rodgers et al., 2013). During 2010-2012, Australian pine infested 10,325 acres in the ECISMA area. Although its spatial distribution has remained relatively constant, there was an estimated 94 percent increase in canopy acres during this period (Rodgers et al., 2014a). This dramatic increase in abundance indicates that monitoring and control remain warranted.
Old World Climbing Fern
Old World climbing fern is native to Africa, southeast Asia, and Australia and is highly invasive in the Everglades (Volin et al., 2004). Its tiny, numerous spores disperse readily, and it poses a great risk to upland, marsh, and coastal habitats alike. Rapid growth where light is not limiting, as in canopy gaps (Lynch et al., 2011), and its twining growth form enable it to cover whole forest stands rapidly (Figure 6-5). Once established vertically in the stand, it alters the fire regime by extending “flame ladders” into the canopy not normally exposed during low-intensity ground fires. Burning fern mats can be dislodged and carried long distances to ignite new outbreaks. Between 1995 and 2010, Old World climbing fern expanded from 1 percent to 10 percent of the ECISMA (F. Laroche, SFWMD, personal communication, 2013). Figure 6-6 shows a lower rate of continued expansion between 2003 and 2013.
Successful chemical control requires contact of the herbicide with all foliar surfaces, and repeated applications of herbicide are often necessary. Because the fern is most commonly found twining around other species, herbicide application may have undesirable effects on surrounding nontarget native species (Hutchinson and Langeland, 2012). Several biocontrol agents have been introduced, and others are still in development. The most successful one to date has been the brown Lygodium moth (Neomusotima conspurcatalis), which was introduced in 2008 and is now established in the field. Its larvae can radically reduce coverage of the fern. Despite these control efforts, this highly aggressive invader remains widespread and is not currently under maintenance control (Figure 6-5; Rodgers et al., 2013). Old World climbing fern infested 24,619 canopy acres in the ECISMA during 2010-2012 and has increased 69 percent in canopy cover since that period (Rodgers et al., 2014a).
At least 192 nonnative animal species are established in the Greater Ever-
FIGURE 6-4 Aerial extent of melaleuca, Brazilian pepper, Australian pine, and Lygodium in the Everglades. The colors represent the percentage of mapped polygons within the grid cell containing the species.
SOURCE: Rodgers et al. (2014b).
FIGURE 6-5 Old World climbing fern completely blanketing a tree island in the Arthur R. Marshall Loxahatchee Wildlife Refuge.
SOURCE: Photo courtesy of Tony Pernas, National Park Service.
glades. Particularly noteworthy species are discussed below, with information on these and other species listed as high priority for management (Rodgers et al., 2014a) given in Table 6-3. These and several other noteworthy animal invaders are detailed in Appendix B. Those that have drawn particular attention (some of which have been the focus of specific management efforts) tend to be either large, flashy predators such as the Burmese python or Nile monitor (Varanus niloticus) or insect species, such as the redbay ambrosia beetle, that attack or
FIGURE 6-6 The spread of Old World climbing fern between 2003 and 2011. Darker shades indicate more dense coverage.
SOURCE: RECOVER (2014a).
spread pathogens to plant species of special concern. Even for these nonnative animal species, the impact on Everglades species and ecosystems cannot be determined quantitatively without intensive research.
Whereas certain plant species (e.g., Brazilian pepper, melaleuca) overgrow vast areas, so that at least some aspects of their impact are readily evident, animal impacts are generally not as obvious. Even if one sees a Burmese python eating an alligator or a Mexican bromeliad weevil (Metamasius callizona) eating a bromeliad, the impact on the population of the prey or host species can be determined only by substantial research. The great majority of established nonnative species have not been studied in detail in the Everglades. Therefore, great caution is warranted in determining which nonnative species pose threats
TABLE 6-3 Noteworthy Invasive Animals in South Florida
|Species||Areal Extent||Ecological Impact||Treatment Availability||Trends||Priority Statusa|
|Burmese python||Spreading northward beyond Alligator Alley||Depresses populations of many prey species||Licensed hunting, extremely limited success||Unknown, population likely increasing within range||Priority|
|Argentine black and white tegu||Established and spreading in Dade||Attacks many prey species; population impact unknown||Traps||Population increasing within range||Priority|
|Nile monitor||Several areas of South Florida||Likely predator but impacts unknown||Snares, traps, hunting||Unknown||Priority|
|Spectacled caiman||Dade and Broward||Likely predator but impacts unknown||Hunting||Unknown||Priority|
|Wild hog||Throughout region||Greatly disturbs vegetation by rooting; may prey on accessible eggs and animals||Hunting and trapping, but limited because valued game animal||Unknown||Priority|
|Feral house cat||Throughout region||Attacks many prey species, including birds, mammals, reptiles, and amphibians||Trapping, but limited because cannot use lethal means||Unknown|
|Lionfish||Entire Atlantic and Gulf coasts of Florida||Attacks and locally eliminates reef fish||Spearing on single corals; no regional management methods||Rapidly increasing abundance|
|Redbay ambrosia beetle||Throughout region||Vectors laurel wilt, which devastates redbay and swamp bay||None||Unknown||Priority|
|Gambian pouched rat||Grassy Key||Unknown||Trapping, but unable to eradicate because cannot trap on private property||Stable||Priority|
|Northern African python||Small region of Dade County||Unknown||Intense hunting||Unknown||Priority|
|Oustalet’s chameleon||Small region of Dade County||Unknown||Intense hunting||Unknown||Priority|
|Veiled chameleon||Lee and Dade||Unknown||Hunting||Unknown||Priority|
|Species||Areal Extent||Ecological Impact||Treatment Availability||Trends||Priority Statusa|
|Cuban tree frog||Throughout region||Unknown||None||Unknown||Priority|
|Cane toad||Throughout region||Unknown||None||Unknown|
|Purple swamp hen||Entire region except possibly west coast||Aggressive and eats eggs and young of waterfowl||None||Unknown||Priority|
|Asian swamp eel||Miami and Tampa regions; Everglades National Park||Unknown||Electrofishing or toxicants possible in isolated areas||Unknown, but common||Priority|
|Mayan cichlid||Southern part of region||Unknown||Electrofishing or toxicants possible in isolated areas||Unknown|
|Pike killifish||Much of region||Unknown||Electrofishing or toxicants possible in isolated areas||Unknown|
|Black acara||Southern part of region||Unknown||Electrofishing or toxicants possible in isolated areas||Unknown|
|Island apple snail||Throughout region||Believed to outcompete native apple snail; may aid snail kite||None||Unknown||Priority|
|Giant African land snail||Miami||Eats wide variety of cultivated and natural vegetation; economic damage||Hand collecting; poison||Slated for eradication||Priority|
|Mexican bromeliad weevil||Throughout region||Attacks native bromeliads; threatens populations of two species||None||Unknown||Priority|
|Rugose spiraling whitefly||Dade County and Florida Keys||Attacks many plant species; population impact unknown||None||Unknown|
aIncluded in a list of species prioritized for SFWMD management in Rodgers et al. (2014a).
SOURCE: Rodgers et al. (2013, 2014a).
and in predicting the nature and extent of those threats, particularly given the subtlety and frequent delay of invasive impacts.
Several animal invaders that have attracted the most attention are presented below; these are but a small fraction of recorded nonnative animals in South Florida. In most cases, research has not been sufficiently extensive and detailed to confirm the extent of the threats they pose, but in each case, existing observations and data suggest impact is likely great. Appendix B details the history and potential impacts of several other notable invasive animals.
The Burmese python is established in wide areas of the Everglades (Figures 6-7 and 6-8), although the population size, believed to be large, can be at best estimated only with very wide confidence limits. It is believed that even skilled herpetologists can detect at most 1 percent of those in areas they search,
FIGURE 6-7 A Burmese python in Everglades National Park.
SOURCE: Photograph courtesy of Catherine Puckett, U.S. Geological Survey.
FIGURE 6-8 Approximate distribution of Burmese pythons in South Florida from the 1990s to 2010, indicating rapid spread throughout the area.
SOURCE: Dorcas and Willson (2011).
and that the population in South Florida is in the tens of thousands (Dorcas and Willson, 2013). By virtue of its massive size and position as top carnivore in the food web, the python has attracted enormous attention in South Florida. A precipitous decline in populations of many mammal species in the Everglades was correlated with the arrival and spread of the Burmese python (Dorcas et al., 2012), although population declines of nonprey species suggest other factors may also have played roles (F. Mazzotti, University of Florida, personal communication, 2013). The Burmese python likely affects several CERP performance
measures, such as juvenile crocodile survivorship, various aspects of alligator population status, and wading bird survivorship (Dorcas and Willson, 2011).
The Burmese python is monitored along several defined routes that cover a small fraction of the Everglades, as well as less systematically by reptile enthusiasts (Rodgers et al., 2014a); however, no estimate of population size is possible with existing data. Development of an attractant and means of detection are recognized as critical needs, but limited resources have hamstrung control efforts (Rodgers et al., 2013). Contracted research to develop an attractant possibly based on pheromones was terminated by the contractor (F. J. Mazzotti, University of Florida, personal communication, 2013). Because this is a promising avenue for control, delays in this research are crippling. A promising trial using highly trained dogs for detection (Romagosa et al., 2011) also has not been followed up. The tremendous amount of press received by this invasion has led to many unorthodox proposals for management, such as enlisting consultants from the Irula tribe, a small group from southern India who traditionally hunt snakes. The Florida Fish and Wildlife Conservation Commission (FWC) has a permit program to allow trained hunters to capture Burmese pythons and other nonnative reptiles.3
Argentine Black and White Tegu (Tupinambis merianae)
This predaceous lizard (Figure 6-9), which can reach 4 feet in length, recently became established and is spreading from a small area in Dade County. It poses a threat of unknown magnitude to ground-nesting birds and reptiles (Rodgers et al., 2013). It also is established in Hillsborough and Polk counties in Florida, and has reproduced in Miami-Dade County (Florida Fish and Wildlife Conservation Commission, 2012; Pernas et al., 2012). They were first noticed in Everglades National Park in 2009 (Tony Pernas, NPS, personal communication, 2014), and their presence in the wild is likely due to releases of unwanted pets. ECISMA has coordinated a monitoring effort but lacks resources for an adequate rapid response team (Rodgers et al., 2014a). As is often the case with nonnative animals, no reliable information is available on the number of individuals in the wild. According to the Florida Fish and Wildlife Conservation Commission (2012), the current approach to reducing tegu numbers in the wild is targeted trapping and removal, and additional trapping efforts are under way to contain the invasion east of Everglades National Park (R. Johnson, DOI, personal communication, 2014).
FIGURE 6-9 Argentine black-and-white tegu.
SOURCE: Photograph courtesy of David Policansky, National Research Council.
Wild Hog (Sus scrofa)
Wild hogs (Figure 6-10) are damaging invaders worldwide, inflicting many kinds of ecological and economic damage to varying degrees in different locations (Barrios-Garcia and Ballari, 2012). Furthermore, they can interact with other introduced species, such as mutalistic mycorrhizal fungi and invasive plants, to generate invasional meltdowns—that is, much greater impacts than each species could have produced on its own (Nuñez et al., 2013). Wild hogs are
FIGURE 6-10 A wild hog in the Everglades.
SOURCE: National Aeronautics and Space Administration.
in all of Florida’s 67 counties, but information on local numbers and distribution is difficult to obtain. Their impact is apparent in the Everglades, with large areas disturbed by their rooting. Some hog control, mainly by trapping and hunting through contracts given to trappers, is undertaken on particular SFWMD lands, but there is no high-level coordination of such activities, and this is recognized as a need (Rodgers et al., 2013, 2014a). Aggressive hog control is controversial because hogs are a valued game species; the contribution of hunting to control of hog populations is unstudied. Hogs are also a major prey item for the endangered Florida panther (Maehr et al., 1990), and improved habitat for this prey species has been offered as one benefit from the Picayune Strand restoration project (see Chapter 4). These conflicting views on the desirability of hog control greatly complicate an effective management response.
Feral House Cat (Felis catus)
Feral house cats are damaging invaders worldwide, killing approximately 2 billion birds and 12 billion mammals annually in the United States alone (Loss et al., 2013). Their impact in Florida is similarly substantial (Feral Cat Issue Team, 2003), and they are a major predator of birds and mammals (and perhaps other animals as well) in the Everglades, although the committee knows of no specific estimate. Feral cats trapped in the Everglades may be neutered and released, but they are not killed, as cat control generally is viewed through the lens of animal welfare rather than as a conservation issue. Despite the damage feral cats can cause, they are frequently overlooked in lists of priority invasive species (e.g., RECOVER, 2014a; Rodgers et al., 2014a).
Asian Swamp Eel (Monopterus albus complex)
Asian swamp eels are large, carnivorous eels first reported in the wild in Florida in 1997 (Kline et al., 2013). They appear to have been introduced more than once, and because they have some degree of salinity tolerance, apparently variable across populations, swamp eels have the ability to invade estuaries as well as freshwater. They are opportunistic predators and get quite large (up to at least 4 feet; see Figure 6-11), and they also tolerate desiccation, pollution, and low temperatures (Schofield and Nico, 2009). Therefore they have the potential to be invasive as well as to affect ecosystem structure. Relatively little is known about their distribution in South Florida.
FIGURE 6-11 Wood stork with swamp eel, which it ate; at Royal Palm, Everglades National Park, 2013.
SOURCE: Photograph courtesy of Theron Mays.
Lionfish (Pterois volitans and P. miles)
Lionfish, native to the Indo-Pacific region, are now widely distributed in the Caribbean and southeastern United States. They are highly predaceous, greatly lower the population density of their prey, and outcompete native reef fish (Albins and Hixon, 2008, 2011). Lionfish also invade estuaries, including that of the Loxahatchee River (Jud and Layman, 2012), and a preliminary study shows a major impact on estuarine invertebrates (Layman et al., 2014). In addition, their venomous spines can cause extremely painful injuries to people who come in contact with them. Lionfish are numerous in coral regions of South Florida (e.g., Florida Keys, Biscayne Bay). They are currently managed in South Florida on a coral-head-by-coral-head basis as opposed to a regionwide basis, and the public is encouraged to capture them by angling or spearfishing and to use them as food. There is no evidence that this approach has hindered their spread or lowered their density, except perhaps locally.4 They appear to be rapidly increasing in abundance and impact (Ruttenberg et al., 2012).
Island Apple Snail (Pomacea insularum)
The island apple snail is much larger than the native apple snail, P. paludosa, which is the main food of the endangered Everglades snail kite (Rostrhamus sociabilis). Evidence strongly suggests that the island apple snail outcompetes the native apple snail (Barnes et al., 2008), and also that the snail kite has lower net energy balance when feeding on the island apple snail (Cattau et al., 2010). However, Pias et al. (2012) report some initial behavioral adaptations by the kite to the island apple snail. The island apple snail consumes a wide range of aquatic plants as well as other food sources and is capable of completely defoliating lush ecosystems (RECOVER, 2014a). In a single cell of STA-1E, a major increase in the population of this snail in 2013 devastated submerged vegetation. The event was correlated with large increases of total phosphorus in outflow concentrations, such that the cell had to be taken offline for rehabilitation (Figure 6-12; L. Gerry, SFWMD, personal communication, 2014). RECOVER (2014a) reported that as of 2012, the island apple snail was well established in the northwestern littoral zone of Lake Okeechobee and spreading southward. There is little coordination of monitoring and little research on impacts and possible control measures (Rodgers et al., 2014a).
FIGURE 6-12 Island apple snail with egg cluster (left). Egg clusters of nonnative apple snails in STA-1E, showing the extreme density of clusters and reproductive potential of this species. Native apple snails have white eggs.
SOURCE: Photograph courtesy of Delia Ivanoff, SFWMD.
Redbay Ambrosia Beetle (Xyleborus glabratus)
The redbay ambrosia beetle (Figure 6-1) and its associated fungus, laurel wilt (Raffaelea lauricola), have spread widely throughout the southeastern United States since 2002 (Fraedrich et al., 2008; Kendra et al., 2013), including to parts of the Everglades by 2010 (Rodgers et al., 2014a). It attacks some native (e.g., swamp bay, redbay) and nonnative (e.g., avocado) members of the laurel family and may also affect species that are restricted to feeding on such species, including the Palamedes swallowtail butterfly (Papilio palamedes) (Lederhouse et al., 1992). The fungal disease threatens tree island habitat where redbay is a dominant species. There is also great potential for loss of cultural resources because redbay is used extensively by local tribes. There is coordinated monitoring of the recent dramatic spread of the disease (see Figure 6-13) but little research on impacts on native species (other than redbay) in the Everglades or on management methods.
FIGURE 6-13 Distribution and abundance of laurel wilt-infected swamp bays in the central Everglades in 2011 and 2013.
SOURCE: RECOVER (2014a).
MANAGING INVASIVE SPECIES IN THE EVERGLADES
Management approaches differ for species at different stages of the invasion process. Biological invasions typically begin with the arrival of a small number of individuals (propagules) that establish a population that grows slowly at first. After this initial period, which varies in length depending on the species and environmental conditions, population numbers increase rapidly until some environmental limit is reached (e.g., fewer and fewer habitats are available as more
and more are occupied) and population growth slows, eventually leveling off. The resulting sigmoid curve (Figure 6-14) can be used to determine management costs and strategies.
Although eradication often is possible with early detection of new arrivals, most of the species listed as priorities (Tables 6-2 and 6-3) are in advanced stages of invasion. Eradication in such cases is always more expensive and difficult and may not even be possible with current technology. In cases where eradication is highly unlikely, containment and long-term management are the pragmatic strategies. Thus, continued presence of some nonnative species on the landscape is a reality in the modern Everglades. The following sections outline efforts in South Florida with regard to prevention, early detection and rapid response, eradication, and maintenance management (including containment and long-term management).
FIGURE 6-14 The invasive species invasion curve.
SOURCE: South Florida Ecosystem Restoration Task Force, 2013.
A number of state and federal laws are designed to prevent the introduction of potentially invasive nonnative species into the United States. Two primary federal laws restrict the import of certain nonnative species into the United States: (1) the Lacey Act (18 U.S.C. § 42 and 16 U.S.C. §§ 3371 et seq.) and (2) the Plant Protection Act (7 U.S.C. §§ 7701 et seq.).
The Lacey Act prohibits the importation of certain specified fish and wildlife that the Department of the Interior (DOI) designates as injurious to humans, agriculture, wildlife, and “wildlife resources” of the United States. The law has limited effect in that the only species that can be listed as injurious are certain classes of animals. In practice, the Lacey Act has been applied only in a reactive way (Fowler et al., 2007). For example, the DOI’s list of injurious species includes only ones that have already become a problem. The DOI does not list species that may, but have not yet, become problematic. To date, only about 239 species have been included on the list. Several of the invasive animal species in the Everglades are on the DOI list of injurious species. For example, the list currently includes four species of constrictors (Burmese python, northern African python, southern African python, and yellow anaconda). The DOI has proposed listing four additional species of constrictors. Many animal species that are considered to be invasive in the Everglades, including the Argentine black and white tegu, are not included on the list. Because the list is limited in scope and because it contains only species that have already become problematic, the Lacey Act as currently implemented is not particularly useful at ensuring that new, potentially invasive species releases are prevented in the Everglades.
Under the Lacey Act, states are permitted to adopt and enforce laws related to invasive animals, provided such laws are not inconsistent with federal law. Florida law prohibits the importation for sale or use or release within Florida of any wildlife not native to Florida unless specifically authorized by the FWC. However, by regulation, the Commission has limited this prohibition only to the import, sale, possession, or transport of any live specimens that it lists as “conditional non-native species.” In recent years, the FWC has listed the Burmese python, reticulated python, northern African python, southern African python, scrub python, amethystine python, green anaconda, and Nile monitor as “conditional non-native species,” and thus, the prohibition now applies to each of these reptile species. The FWC regulations also encourage persons possessing unwanted nonnative species, such as pet pythons, to turn over the animals to the FWC by providing amnesty.
The Plant Protection Act authorizes the U.S. Department of Agriculture (USDA) to prohibit or restrict the importation and interstate movement of certain organisms that USDA determines to be plant pests or noxious weeds. The
Act imposes significant restrictions on species listed as “noxious weeds.” USDA can list species as noxious weeds if the species can directly or indirectly injure agriculture or the natural resources of the United States, public health, or the environment. As with the Lacey Act, species typically are listed as noxious weeds only after they have become a problem. Many of the invasive plant species in the Everglades are listed as noxious weeds, including melaleuca, hydrilla, water hyacinth, and feathered mosquito fern. In addition, the Plant Protection Act regulates the interstate movement of noxious weeds and authorizes emergency action within states that are not taking adequate measure to eradicate the plant pest or noxious weed. Under the Act, the USDA has broad authority to declare quarantine and take remedial action to prevent the introduction of new, or not widely distributed, plant pests or noxious weeds. In contrast to the Lacey Act, the Plant Protection Act preempts state laws that are in conflict with or are more stringent than the federal law except where a state can demonstrate a special need for additional restrictions.
The Florida Division of Plant Industry (DPI) in the Department of Agricultural and Consumer Affairs (DACS) does maintain its own list of noxious weeds, which includes species on the federal list, as well as additional species that are invasive in Florida but are not on the federal list. Similar to the Plant Protection Act, Florida law prohibits the introduction, possession, and movement of noxious weed unless permitted by DPI for limited purposes, such as research. Most of the invasive plants in the Everglades, including Brazilian pepper, air potato, Australian pine, Old World climbing fern, cogongrass, water lettuce, skunk vine, and downy rose myrtle, are on the Florida list (Florida Administrative Code Annotated, Rule 5B-57.007). As with the federal noxious weed list, DPI typically lists species only after they have become a problem.
Early Detection and Rapid Response
Eradication is far more likely and less costly early in the sigmoid invasion curve (Figure 6-14), but this requires early detection associated with a rapid response mechanism. Thus, investments in early monitoring can yield great economic benefits by finding invasions while relatively inexpensive eradication or containment efforts are still feasible. Of course, monitoring has costs, so the likely benefit of finding and acting early on invasions needs to be weighed against the cost of a given degree of monitoring. Estimating these costs and benefits involves many unknowns, but the principle is clear (Epanchin-Niell et al., 2012).
In the Everglades, wild red rice (Oryza rufipogon) was detected and eradicated before it could spread (Westbrooks and Eplee, 2011). Another success of early detection and rapid response (EDRR) is the sacred ibis (Threskiornis
aethiopicus), a large African bird first discovered breeding in the Everglades in 2005 after many escapes from captivity (Herring and Gawlik, 2008). This species, which is known to prey on eggs and young of several bird species in aquatic habitats (Lefeuvre, 2013), appears to have been eliminated from the Everglades before it could disperse widely (Rodgers et al., 2013). The quick effort to eradicate exotic black mangrove (Lumnitzera racemosa) before it could spread from a site near Fairchild Tropical Botanical Garden also appears to be nearing success (Rodgers et al., 2013). These examples show that, if an invader is detected before it is widespread and if action is quick, eradication is sometimes possible.
The Everglades Cooperative Invasive Species Management Area (ECISMA; discussed later in this chapter), which coordinates nonnative species management in South Florida, has developed an EDRR system for the Everglades (ECISMA, 2009). Such systems have proven to be possible and cost-effective elsewhere (Westbrooks and Eplee, 2011). Several detection programs have been established in the Everglades—largely through ECISMA—including a public hotline and website (1-888-IVE-GOT-1; www.ivegot1.org) operated by FWC for reporting nonnative animals (no analog exists yet for plants). The hotline was used successfully to alert ECISMA agencies to Argentine black and white tegus in residential areas of Dade County in time to remove them through targeted trapping. Also, more than 30 tegus that had been abandoned in an outdoor breeding facility in Panama City were discovered and removed after a hotline report (J. Ketterlin-Eckles, FWC, personal communication, 2013).
Another ongoing ECISMA EDRR effort is the Everglades Invasive Reptile and Amphibian Monitoring Program (EIRAMP), implemented by a team from the University of Florida with support from FWC and the SFWMD. Under this program, regular monthly monitoring is conducted on 20 routes (Rodgers et al., 2014a). However, the degree of monitoring is insufficient, and the system does not assign specific responsibilities for monitoring for many sorts of species. EIRAMP’s routine monitoring routes are located along just a few roads and trails (see Figure 6-15), a minuscule percentage of available area, and not all reptiles and amphibians would be likely to occupy such habitats. Members of the EIRAMP team are also contracted for a certain number of follow-up visits to address hotline and website reports of reptiles and amphibians.
FWC has also mounted a Python Patrol program, started by the Nature Conservancy and now operated by FWC, to limit the spread of pythons into new areas. The program trains land managers to capture and remove large constrictors and also provides outreach to people who frequent natural areas, such as hunters, local law enforcement agents, and state agency workers. These persons are trained to identify and report pythons, as well as other nonnative animals. Python Patrol trainees may also respond to hotline and website reports. This program has resulted in the removal of the first Burmese python in Picayune
FIGURE 6-15 Everglades Invasive Reptile and Amphibian Monitoring Program (EIRAMP) routes.
SOURCE: RECOVER (2014a).
Strand after it was reported on the hotline, and responders trained under the Python Patrol Program were able to find and remove the snake. So far, over 400 persons have received capture training and over 1,400 have received training on detecting invasive animals.
ECISMA relies heavily on the Early Detection and Distribution Mapping System (EDDMapS), a web-based mapping system and clearinghouse founded in 2005 by the Center for Invasive Species and Ecosystem Health at the University of Georgia. EDDMapS accepts reports of nonnative species from the public at large and forwards the information to South Florida invasive species managers to determine the accuracy of the species determination. Panther chameleons (Furcifer pardalis) were located and possibly eradicated from a Broward county property after a report of the chameleons on EDDMapS. After surveys, FWC and the University of Florida were able to remove more individuals from the surrounding community, and continuing surveys have detected no panther chameleons recently (J. Ketterlin-Eckles, FWC, personal communication, 2013).
It is unclear for certain types of species who decides what, if any, response to a verified hotline, website, or EDDMapS report is required and what entity should implement the response. In general, a rapid response requires quick access to resources, which was generated by FWC for exotic black mangrove. Other invasive species that were detected early and for which adequate resources were mobilized quickly were the sacred ibis (now thought to be eradicated in the Everglades) and the northern African rock python (currently contained to a limited area). However, efforts to eradicate incipient invasions in the Everglades have more often been stymied by the inability to obtain funds from federal, state, or local sources. For example, the Argentine black and white tegu was confined to a very small area when first discovered in Dade County in 2009. A plea for quick action (Pernas et al., 2012), which would have yielded a high probability of successful eradication, went unheeded because none of the agencies queried could provide the necessary resources. This lizard is now almost surely too widespread for eradication with currently available technologies.
Time is of the essence for eradicating invasive species. Although eradication was once viewed as impossible or unlikely in most cases (Simberloff, 2003), technologies have improved greatly over the last few decades, particularly for terrestrial vertebrates (Genovesi, 2011). In general, aquatic species, insects, and plants have proven more difficult to eradicate than terrestrial species, especially vertebrates. Nevertheless, there have been successful eradications of all classes of organisms, especially in instances where the invasion was detected early enough that the nonnative species had not spread widely. As noted in the pre-
vious section, several spatially restricted invaders have been eradicated in the Everglades region, including plants. No widespread invader in the Everglades has been targeted for eradication. However, invasions frequently pass through a stage in which there are several spatially separated populations of a nonnative species. In such a circumstance, it is often strategically desirable to eradicate small, discrete populations in the hope of containing the invasion in a smaller area and perhaps ultimately eradicating it (Moody and Mack, 1988). Nationally, this strategy has been used successfully in a high-profile massive attempt to stem the spread of the Asian long-horned beetle (Anaplophora glabripennis). In the Everglades area, the strategy has been pursued with isolated populations of the Argentine black and white tegu in residential areas.
Several invasions that became very widespread have nevertheless been eradicated, such as a pasture weed (Kochia scoparia) in western Australia. In the United States, a 50-year campaign to eradicate the parasitic plant witchweed (Striga asiatica) from 400,000 acres of North and South Carolina is nearing success (Simberloff, 2013a). However, in both instances, the locations of the invasive individuals were well known and the invaders were agricultural pests, so the high cost of the effort (particularly for witchweed) could be borne as an agricultural expense. In the Everglades, some locations of many widespread invaders are poorly known, and the cost of an invasion campaign against widespread invaders would likely be prohibitive, at least with current technology.
As described previously in this section (see Prevention), a number of federal and state laws are designed to reduce the introduction of potentially invasive nonnative species into the United States. Once an invasive species is established, however, federal statutes are of limited utility. Because large areas of the Everglades are owned or managed by federal, state, or tribal governments, however, these public land owners and managers typically have specific legal authority to address invasive species concerns on their land. For example, the National Park Service Management Policies (NPS, 2006) authorizes the destruction of species detrimental to Park Service resources on Park Service lands. In addition, Presidential Executive Order 13112 directs federal agencies to take actions to control invasive species, and the U.S. Army Corps of Engineers (USACE) is currently working to develop a strategy to comply with this mandate.
When invasive species management depends on removing plants or animals that may be on private land and may have the ability to spread to public lands, it may be necessary to access private lands to remove invasive plants or animals. In some circumstances, private landowners are willing to provide access and permission to remove the invasive species. When private landowners are not willing to provide access and permission, however, there is limited legal authority for government officials to control invasive species on private property. In certain extreme circumstances, state or federal agencies may be able to
access private property to remove invasive species that pose significant risks. For example, the State of Florida has destroyed citrus trees on private land when citrus canker threatened a major economic interest in the state. However, in that case, specific legislation authorized the state action and the state paid compensation to private landowners whose trees were destroyed. It is not clear under what circumstances and to what extent statutes such as the Plant Protection Act would allow similar actions to be taken to private land to protect the natural resources of the Everglades without running afoul of constitutional protections against illegal search and seizure and taking of property without just compensation. The Gambian pouched rat on Grassy Key persists only because it is on six private properties whose owners do not permit access to federal or state officials (Witmer et al., 2010a). As long as this rat is present, there is the possibility that it will spread to other areas of South Florida.
If eradication fails or is not attempted, several technologies can be used to maintain invasive populations at low levels. Traditional approaches to such maintenance management are
1. Physical control, such as pulling invasive weeds or catching snakes by hand;
2. Mechanical control, entailing the use of machines;
3. Chemical control, using pesticides and herbicides; and
4, Biological control, importing natural enemies, such as predators and parasites, from the native region of the targeted pest.
Each of these approaches has been successful in some cases, and each has failed in other cases (Simberloff, 2009, 2014). The important point is that technologies have evolved in all of these methods (e.g., Clout and Williams, 2009; DiTomaso, 2011; Van Driesche et al., 2008). All have been used in the Everglades. For instance, several invasive plants, such as melaleuca and Australian pine, have been targeted by specially adapted land-clearing machines (Anonymous, 2005). Herbicides, both aerially dispersed and delivered by hand sprayers, have been also been used (Laroche and McKim, 2004). The USDA’s Invasive Plant Research Laboratory in Davie, Florida, seeks and tests biological agents, mostly insects, to attack major invasive plants in the Everglades, and in 2013 the USDA completed construction of a mass rearing facility as an annex to the laboratory as part of the CERP (see Chapter 4). Melaleuca is one of several key invasive plants in the Everglades that have been substantially reduced by biocontrol agents (Figures 6-2 and 6-16). Other methods of maintenance management are used less frequently
FIGURE 6-16 Melaeuca treatment via mechanical and chemical methods (left) and biological control by means of the melaleuca snout beetle (Oxyops vitiosa).
SOURCE: Photograph courtesy of Tony Pernas, National Park Service, and Stephen Ausmus, Department of Agriculture.
but have provided significant control of particular invaders. In the Everglades, for example, prescribed fire applied to stands of melaleuca seedlings has contributed to developing a successful maintenance management program.
New approaches to maintenance management have occasionally provided control of previously refractory invaders, including the use of pheromones and genetic manipulation (Simberloff, 2014). Invasive species whose control seems hopeless today, as that of melaleuca did 20 years ago, may someday be managed well by methods resulting from ongoing research. The melaleuca management program, which evolved over 20 years and includes biological, chemical, and mechanical control (Figure 6-16) as well as prescribed burns, is an example of a program that developed gradually from several lines of research and is now showing substantial success (Figure 6-3).
COORDINATION AND ORGANIZATION
The management of nonnative species in South Florida is distributed across many federal, state, and local agencies and programs. Federal agencies that have at least some jurisdiction over nonnative species include the FWS, the National Marine Fisheries Service, the NPS, the USDA Animal and Plant Health Inspection Service and Agricultural Research Service, the U.S. Forest Service, the USACE, and the U.S. Customs and Border Patrol. State agencies include the FWC, the SFWMD, the Florida Department of Agriculture and Consumer Services, and the Florida Department of Transportation. Miami-Dade County and the Miccosukee
and Seminole Indian tribes also have strong interests and management roles, as do a variety of nongovernmental and academic organizations.
Although official communication channels exist among many of these organizations and many individuals associated with them communicate as well, they do not all share the same legislative and regulatory mandates, they have differing budgetary and other constraints, and they have differing degrees of technical expertise. Two notable attempts have been or are being made to coordinate efforts and resources for managing nonnative species.
Everglades Cooperative Invasive Species Management Area
Federal, state, and local governments have been collaborating to address Everglades nonnative species issues since the Everglades Forever Act was passed in 1993, and the establishment of the ECISMA in 2008 formalized the collaboration and expanded the partners involved. Like other CISMAs, ECISMA is a formal partnership composed of federal, state, and local government agencies, tribes, individuals, and various interested groups that manage invasive species in the Everglades region (see Box 6-1).
ECISMA has fostered an increasing amount of coordination at the operational level. Among ECISMA’s stated goals are to
• Formalize areas of coordination and cooperation among agencies;
• Define specific geographic areas and prioritize species for Everglades restoration; and
• Integrate coordination, control, and management of invasive species at regional, multijurisdictional levels.
ECISMA has improved coordination of the implementation of invasive species management. Its website provides access to a great deal of pertinent information, such as distribution maps (EDDMapS) of invasive plants and animals. ECISMA has also had some notable successes with EDRR, as discussed previously in this chapter. However, ECISMA does not coordinate and cross-calibrate sampling methods.
However, there does not appear to be a formal process to determine systemwide priorities—which nonnative species are managed to what extent, what monitoring is performed, and what monitoring or other observations trigger a management response. Currently, nonnative species management appears largely driven by the objectives of individual agencies, with limited leveraging of funding across agencies to address the needs of multiple agencies. How systemwide prioritization for management, coordination of management activities, and funding sources are determined remains obscure. This committee could not iden-
The Everglades Cooperative Invasive Species Management Area (ECISMA) coordinates nonnative species management in South Florida through a formal agreement under the Florida Invasive Species Partnership. The ECISMA partners include
- Florida Fish and Wildlife Conservation Commission
- South Florida Water Management District
- U.S. Army Corps of Engineers
- U.S. Fish and Wildlife Service
- U.S. National Park Service
- Miami-Dade County
- Auburn University
- Broward County
- Friends of Everglades CISMA, Inc.
- The Everglades Foundation
- Fairchild Tropical Botanic Garden
- Florida Department of Agriculture and Consumer Affairs
- Florida Department of Transportation
- Florida Power and Light
- Miccosukee Tribe of Indians of Florida
- National Oceanic and Atmospheric Administration
- Seminole Tribe of Florida
- The Nature Conservancy
- University of Florida
- University of Georgia—Center for Invasive Species and Ecosystem Health
- USDA Agricultural Research Service
- USDA Wildlife Services
- U.S. Geological Survey
tify an algorithm or formal process by which nonnative species are prioritized for management action or particular resources are allocated to nonnative species management activities. Nor could the committee identify how a specific agency comes to bear responsibility for dealing with particular nonnative species.
For instance, ECISMA lists 14 plant species and 16 animal species as the highest priority for management. What process led to these designations? What process led to specification of management activities targeting these species and entities charged with carrying them out? For plants, there is no doubt that several of the targeted species have great impacts, although it is not obvious that other
species do not have equally great impacts. Two of the 14 priority plant species are not yet widespread and are perceived as eradicable. Nonnative animals have been a management focus for a much shorter period than nonnative plants (Rodgers et al., 2013), and it is even less clear how the 16 priority animal species were chosen. Some priority species are already believed to have a substantial impact, although others with suspected major impacts (e.g., feral housecat) are unlisted. Other priority species are not currently having major effects and are still geographically restricted and believed to be feasible targets for eradication, even though possible management methods tend to be poorly developed or unknown (Table 6-3).
Comprehensive Invasive Species Strategic Framework
The second coordinative effort recognizes and responds to a problem with policy and management of biological invasions to date: namely, the absence of sufficient coordination, particularly at the strategic level. DOI’s Office of Everglades Restoration Initiatives, in coordination with the Task Force, is currently supporting development of a Comprehensive Invasive Species Strategic Action Framework that includes greatly enhanced high-level coordination and a crosscut budget.5 In December 2012, the Task Force established a working group to conduct a comprehensive review of the coordination and nature of efforts to combat invasive species in the Everglades. As of December 2013 a strategic planning exercise was under way by the working group to fashion the Strategic Action Framework. Efforts to devise a governance structure to address the current gap in strategic and funding coordination could be particularly useful. This activity is in its early stages, but it appears to be directed at a concern expressed to this committee by many individuals—the lack of high-level coordination in developing priorities for budgets and actions across agencies to address invasive species.
INVASIVE NONNATIVE SPECIES IN THE CONTEXT OF RESTORATION GOALS
The catchphrase “get the water right” governing planning for Everglades restoration assumes that restoring a semblance of the pre-development water flow to the region will lead to restoration of ecosystems and species. This dictum has dominated aquatic and wetland restoration since its inception and has been termed the “field of dreams” hypothesis (Palmer et al., 1997). As discussed in this chapter, many empirical examples of nonnative species invasions show that this is not necessarily the case (Palmer et al., 2014). It is possible that getting
the water right will, for certain nonnative species, at least help to lower their populations and impacts, but for others, attempts to get the water right may actually exacerbate impacts and even foster further invasions (Ogden et al., 2005; RECOVER, 2014a).
Recently, the USACE and SFWMD issued guidance to incorporate invasive species management into CERP project planning and implementation. CERP Guidance Memorandum 062.00 (USACE and SFWMD, 2012d) required invasive species management to be incorporated into all phases of CERP projects and an invasive and nuisance species management plan to be developed as part of the project implementation report (PIR) process. To date, plans have been developed for C-111 Spreader Canal, Biscayne Bay Coastal Wetlands, and the Central Everglades Planning Project (USACE and SFWMD, 2011, 2012a, 2013a), although only the Central Everglades Planning Project addresses both plants and animals (RECOVER, 2014a). Several projects that were developed prior to the guidance memorandum have now developed vegetation management plans. At a national level, a December 2013 draft Program Management Plan for the Invasive Species Leadership Team (USACE, 2013f) provides a detailed vision for management of invasives at all stages of project planning and implementation, including considerations of design features to reduce the likelihood of enhancing the spread of invasives. The document provides a strategic plan for educating USACE staff and implementing new regulations, including Executive Order 13112 (1999), which directed federal agencies “to prevent the introduction of invasive species and provide for their control and to minimize the economic, ecological, and human health impacts that invasive species cause,” as well as the 2009 USACE Invasive Species Policy Memorandum (Temple, 2009). If fully implemented, these documents could help address major concerns of invasive species management associated with CERP project planning and implementation, and the committee looks forward to evaluating their results.
Despite the enormous impacts of some nonnative species, invasive species management has so far not been a major focus of the CERP, beyond treating invasive plants that spread during construction. Communities composed of mixtures of nonnative species with varying remains of native assemblages are commonplace in the Everglades landscape. There is great urgency to detect and eliminate new arrivals and manage those that have spread beyond the point where eradication is still feasible. However, funding and manpower are limiting and effective control techniques (e.g., biocontrol agents) for many nonnatives are still in the development stage (see Tables 6-2 and 6-3). Prioritization decisions leave some areas unmanaged and some nonnative species uncontrolled because the particular system is not ecologically or economically feasible to restore or because some nonnative species have not been shown to have substantial harmful ecological impacts or possess seemingly desirable characteristics. Thus,
many parts of the greater Everglades landscape, particularly remote areas with poor access, remain invaded by multiple nonnative species and will remain so for the foreseeable future.
Thus, although restoration to a semblance of the way the Everglades looked and functioned a century ago may, with sufficient effort, be possible for certain areas, such a goal is impractical for other sites. The spatial extent of the problem highlights the importance of understanding the effects on ecological functions as well as potential ecosystem services of these altered assemblages to the overall ecosystem. Although it is highly likely that the functioning is different and services are reduced compared with uninvaded, native communities, some research in this system has shown that certain nonnative species can provide benefits (e.g., exotic apple snails as a potentially important food for native snail kites [NPS, 2013]), even if they are simultaneously detrimental in other respects.
The need to prioritize management resources and decipher how vast sections of the “invaded” Everglades are functioning, however, should not obscure the ideal goal of a functioning Everglades with its full complement of native species. CERP partners will have to decide on the restoration goals for specific areas of the Everglades, recognizing that hydrological restoration alone will not necessarily achieve ecological restoration goals (Clewell and Aronson, 2013). Discussions on this issue will need to consider that areas left unmanaged for invasive species because full restoration is not a goal can serve as sources of seeds, spores, and other propagules and thereby threaten other areas being managed for more ambitious restoration goals.
In addition, as described earlier in the chapter, interactions between nonnative and native species and between different nonnative species often are complicated, and one invasion may exacerbate the spread of another (as exemplified by the case of the invasive figs and their fig wasp pollinators).
CLIMATE CHANGE AND INVASIVE SPECIES
With global warming, sea-level rise, and the water management activities associated with them, distributions and abundances of nonnative species are expected to shift across the landscape. New species will likely invade, while distributions of some existing species will contract and others expand (Hellmann et al., 2008). These changes will be driven in part by shifting climatic envelopes, but also by changes in species interactions (Simberloff, 2012).
As discussed in Chapter 5, global climate change models developed at coarse scales for the Everglades vary with respect to projected temperature and precipitation regime changes, as well as rate of sea-level rise (Obeysekera et al., 2011a). Responses of nonnative species to these scenarios, as well as the anticipated changes in hydrologic regimes with restoration activities, present
an area of great uncertainty that has received relatively little attention. Given the ever-growing number of nonnative species in the system, a multitude of species-specific response patterns and interactions with native flora and fauna is likely as the effects of these environmental changes unfold (Junk et al., 2006).
One possible climate change scenario includes increased temperatures and potential evapotranspiration, along with reduced precipitation, resulting in reduced water supplies to the entire system. Human-caused changes to the Everglades ecosystem have already shortened hydroperiods, in some cases favoring the spread of many nonnative plant and animal species (Jones and Doren, 1997; Olmstead and Loope, 1984). Further shortening of hydroperiods under some climate change scenarios may promote their continued expansion (Davis et al., 2005b). In addition, many of the species introduced into the Everglades are native to tropical habitats and are thus likely to expand with warmer conditions at the expense of resident native flora and fauna that are better adapted to temperate and subtropical climates. For instance, Trexler et al. (2000) suggest that the densities and range of several nonnative fish species in the Everglades currently are limited by occasional low temperatures or severity of droughts. A changed climate could relax some of those limiting constraints.
Biological control agents have been introduced to counter many invasive nonnative species in the Everglades. These species themselves are generally nonnative as they have been selected and introduced from the home range of the target species. As with other nonnative species, there is great uncertainty with respect to effects of climate change on these agents. As temperature and rainfall patterns change, geographic distributions of the agents and their targets are likely to change as well. Such changes could promote increased contact between agents and nontarget species. Further, the effectiveness of these agents could be affected by changing environmental conditions and shifts in timing of the plants’ or animals’ life-cycle events (Parmesan, 2006; Simberloff, 2012). Agents that are currently effective may become less useful and potentially problematic if they become spatially or temporally decoupled from their targets.
CONCLUSIONS AND RECOMMENDATIONS
Despite excellent progress in developing coordination of the management of invasive species at the operational level, most notably through ECISMA, there is a lack of coordination at a strategic level that includes a comprehensive view of all nonnative species in all parts of the Greater Everglades. Currently, plants and animals tend to be considered separately. Management and restoration activities need to take account of the entire biotic community and not be partitioned into different taxa. This indeed is consistent with the vision for Everglades restoration. However, it can be difficult to take such a view at a project level. Further,
for many invasive species, different agencies take on management activities in different areas, yet individuals of such species move between areas, so that management in one area can impact other areas. These factors argue for the creation of a high-level coordinative entity to oversee policy, management, and budgets related to nonnative species. Prioritization of research needs and control efforts across areas, species, habitats, and agencies would be a major responsibility of this entity. The committee is optimistic that the Comprehensive Invasive Species Strategic Action Framework being developed by the Task Force will be a major step toward achieving these goals of high-level coordination.
A strategic early detection and rapid response (EDRR) system that addresses all areas, habitats, and species is needed. EDRR is an essential strategy if new invasions of nonnative species in the Everglades are to be eradicated (or at least contained) while it is still feasible and relatively inexpensive to do so. Currently several EDRR efforts are under way, but the current level of monitoring is insufficient to address the geographic extent and range of nonnative species threats in the Everglades. In general, a rapid response requires quick access to resources, but efforts to eradicate incipient invasions in the Everglades have more often been limited by the inability to obtain funds from federal, state, or local sources. The costs of additional monitoring and response should be weighed against the likely benefits of finding and acting on early invasions. Additional funding would allow for greater public outreach, expanded operation of the reporting hotline, increased early detection monitoring, and improved capacity for rapid response to facilitate eradication. The committee recognizes that the goal of this recommendation—addressing all areas, habitats, and species—likely is beyond any reasonable expectation of resources, but keeping this goal in mind emphasizes the value of prevention and clarifies the magnitude of the challenge.
There is no systemwide mechanism for prioritizing research on and management of invasive species. Many agencies participating in the Everglades restoration already undertake research activities on certain nonnative species and also undertake management activities, but these efforts are limited by insufficient resources and are typically driven by specific agency needs rather than systemwide priorities. Effective prioritization requires a comprehensive understanding of all nonnative species present in the Everglades, their impacts and threats, as well as those of impending or likely new arrivals.
Research is lacking on nonnative species and their impacts to inform prioritization efforts adequately. Tables 6-2 and 6-3 highlight some of the many gaps in knowledge about species considered to be priorities for management. Given the spatial extent of the problem and the threats of future invasions, substantial research is needed to assess the various impacts of nonnative species on ecosystem functioning and native species and to develop or improve control mechanisms. This does not mean comprehensive research of all details of the biology
and effects of every nonnative species. Rather, enough basic information should be gathered systematically to determine which species could reasonably be predicted to have considerable ecological impacts. Such knowledge is important in guiding decisions on detailed research on possible impacts and management of particular threats and would help inform priorities for management actions.
If eradication proves impossible, maintenance management and long-term control at acceptable levels should be explicitly recognized as a goal in some cases. Indeed, current practice seems implicitly to recognize this goal. Maintenance management at low densities is sometimes possible by various combinations of biological, chemical, mechanical, and physical controls. In the Everglades, a striking example is the current management of melaleuca, once thought too widespread and dense to be manageable. As a result of sustained intensive research, this species is currently under substantial control in most regions through a combination of mechanical, chemical, and biological control as well as prescribed burns. Maintenance management requires continued, diligent monitoring and flexible, but reliable funding that can be devoted strategically to achieve and maintain long-term control.
At every step of the CERP planning process, full consideration is needed of the implications of restoration activities for introduced species and their impacts. Until very recently, invasive species have not been considered in CERP project planning and implementation beyond simply removing any invasive species encountered at construction sites. Ideally, hydrologic restoration should favor the reestablishment and expansion of many native wetland species that are better adapted to longer hydroperiods. However, aquatic and flood-tolerant nonnative species may also benefit and replace native species. Removing levees and filling in canals may, in certain circumstances, facilitate the spread of nonnative species by increasing their potential for dispersal. For each CERP project, the potential to increase the spread of invasive species should be examined and the effects on ecosystem functioning assessed. Based on this analysis, strategies and technologies to lessen these impacts should be appropriately considered. Recent CERP guidance and plans to implement national USACE invasive species policy indicate that these considerations are increasingly being incorporated into project planning and implementation, although it is too soon to evaluate this new approach.
Long-term monitoring and research are needed to understand the potential impacts of climate change on Everglades nonnative species management. Climate change has the potential to significantly impact the distributions and abundances of nonnative species in the Everglades and their impacts on the ecosystem as a whole. Thus, research and monitoring to understand long-term changes in nonnative species distribution and behavior and the effectiveness of maintenance control strategies in the context of climate change are needed.