By Chad Rischar
My first encounter with an invasive/exotic species in central Florida is still vivid in my mind. In 2000, a small group of friends and I were canvassing Osceola County after a typical late afternoon thunderstorm searching for herpetofauna (reptiles and amphibians). Herping was a common practice with this colleague group and the simple goal was to locate, observe, and learn about our local herpetofauna species. We somehow landed at the Kissimmee Post Office to regroup and were astounded by the cacophony of breeding calls throughout the parking lot. Frogs clung to the sculpted wall surfaces by the hundreds and chorused to a near deafening excitement. As amateur herpetologists and enthusiasts, one particular frog vocalization cut through like no other. That peculiar frog chirp of a non-native amidst the typical frog species cut through air, and even 20 years later, I remember the feeling that we had stumbled upon something genuinely perplexing and memorable.
A Cuban Treefrog (Osteopilus septentrionalis) in central Florida, courtesy of Chad Rischar
Florida, akin to many other states and abroad, has been infiltrated by an abundance of non-native, exotic, and invasive species. Florida’s subtropical and tropical climate allows invasive species from South America, the Carribean, Africa, and Asia to thrive. Anthropogenic mechanisms are largely responsible for the transmission of invasive species through shipping trades, the ornamental plant industry, captive fish and wildlife breeding facilities, and even hurricane damage to zoological facilities. Not only is Florida forced to reckon with reptiles, amphibians, and fish species, but a broad diversity of plants and trees continually invade and colonize our state. The diversity and density of non-native species is spiking, ultimately causing serious threats to native species and natural ecosystem functions. It also creates substantial land management issues, budgetary impacts, and puts native species’ life cycles at risk. The Florida Fish and Wildlife Conservation Commission created departments to research, manage, and allocate funding to protect native species, manage against non-native species, and protect the integrity of native ecological functions.
Reptiles and Amphibians
The Anuran (frog) species we collected in Kissimmee, Florida, was the Cuban Treefrog (Osteopilus septentrionalis). In 2000, the Cuban Treefrogs had marched through southern Florida and reproduced north well beyond the sub-tropical divide, withstanding winter frosts and infrequent hard freezes. With Cuba only 90 miles away from the Florida Keys, their presence doesn’t appear to be unrealistic in the depths of South Florida; however, the Kissimmee Post Office is located in Central Florida, only a few miles from Disney World and over 200 miles north of Miami.
The Cuban Treefrog now, unfortunately, resides in northeast Florida and beyond. Oddly enough, a population of Cuban Treefrogs has also been documented on the Hawaiian Island of Oahu. The Cuban Treefrog is a massive specimen (5 to 12.7 cm in size) with nuptial pads that allow it to scale glass windows, house siding and enclosed pool screens. Due to their immense size and appetite, they often outcompete our native tree frogs (Genus Hyladae) dominantly in suburban and urban environments. Tadpole Cuban Treefrogs even compete with native frog species through appetite vigor. Ample evidence exists that Cuban Tree Frogs prey on our native tree frogs, and I’ve personally witnessed a Squirrel Tree frog’s demise through our front storm door here in southern Clay County, Florida, through the toes and jaws of a Cuban Treefrog. At roughly a quarter of predator to prey size, the Squirrel Treefrog was an exploitable meal to capture and ingest.
Although the Cuban Treefrog has been etched into my memory, the Burmese python (Python bivittatus) is likely the most notable and publicized invasive species. A massive, Asian constrictor species that has systematically adapted to the South Florida lifestyle, the pythons have made national news and contributed to the demise in South Florida’s natural ecosystems, especially within Everglades National Park. Imagine an estimated hundreds of thousands of 8-18 foot-long pythons roaming and foraging throughout the vast expanses of South Florida marshes, grass prairies, and swamps. According to the U.S. Geological Survey in a 2012 study, populations of raccoons had dropped 99.3 percent, opossums 98.9 percent, and bobcats 87.5 percent since 1997. The Burmese python population is documented as the culprit of this mass decline of small mammals. Marsh rabbits, cottontail rabbits, and foxes effectively disappeared. The result over the last few decades has been an estimated decline of more than 90 percent of native small mammals, herpetofauna, birds, fishes, and even large mammals.
Burmese pythons are so abundant, 25 Wildlife Management Areas include language for its active harvest, year-long legal pursuit, and no bag limits. The South Florida Water Management District initiated The Program for Elimination of Pythons from District Lands as well. It financially incentivizes python removal agents to locate and remove them on District properties and rights-of-way in Miami-Dade, Broward, Collier and Palm Beach counties. This eradication program has been very successful; thousands of Burmese pythons are removed through this program every year. Although this program should be considered a resounding success, the overall population density of pythons throughout South Florida hasn’t curbed yet.
Ferns and Grasses
Another species introduced to South Florida is the Japanese climbing fern (Lygodium japonicum). It was originally introduced in the 1930’s via the ornamental plant industry and is abundant even on state and federal managed lands and throughout peninsular Florida. While waterfowling in South Georgia recently, I documented Japanese climbing fern present in spatial abundance along a narrow earthen berm in Lake Seminole Reservoir. I reported my waypoint to the Georgia Department of Natural Resources, but to my dismay, this species has been recorded in abundance for years. This climbing fern species is pervasive, tolerant of cooler climates, and genuinely destructive throughout the southeastern coastal plain ecology. As the name suggests, Japanese climbing fern can grow into a living wall, shading out ground cover and midstory vegetation. Without herbicidal and mechanical treatments, prolonged growth can consume the tree canopy and eventually decimate an entire plant community. Simply another example of an invasive species that requires judicious scientific survey, treatment and long-term management regimes.
Torpedograss (Panicum repens) is another prolific, invasive, and perennial species that quickly displaces and outcompetes native grasses in southeast coastal plain ecosystems. Lake Okeechobee is a prime example of how Torpedograss has drastically impacted vast sections of emergent habitat, through rhizome growth, tolerance to flooding and sustained drought, and fire tolerance. I’ve personally battled Torpedograss on several wetland restoration projects with moderate success, but remain amazed at the extent management tools and determination are required to stave off this species marching through marshes and prairie ecosystems.
The twenty-first century reality could be distilled down to saying that invasive and exotic species are perhaps a closed case in Florida, the southeast coastal plain, and the continental United States. Although this opinion is disturbing, the reality is that the management costs to hedge the invasion exceeds the budget of most state and federal agencies. The fierce challenge we face regarding our collective natural system functions is to properly evaluate them and prioritize funding to manage and eradicate non-native species in advance of significant ecosystem demise. Numerous studies exist showing a diminished population of native flora and fauna as a result of the impacts from invasive species, whether it was from vegetation, fishes, mollusks, snakes, frogs, and even mosquitoes.
How we as a society prioritize and allocate funding to counter the invasion, curb the continued introduction of invasive species, and allocate funding to manage and eradicate them will determine our near-future ecological destiny. Research and, most notably, active management are the forward-facing approaches that will restore our hurting natural systems, the integrity of our ecological communities, and the inherent values provided by native landscapes to civilization.
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