Phillip's Natural World: Invasion of the Bullfrogs

The consequences of climate change for animals can seem very direct, as with polar bears in a warming Arctic. Others involve leaps, like the case of an invasive bullfrog: by 2080, it could splash into some of South America’s most ecologically rich protected areas, disrupting unique hotbeds of biodiversity. At least, that is the prediction of a study in the journal PLoS One.

Worldwide, researchers have increasingly been focusing on how a changing climate has altered or is likely to alter migration patterns and the habitats that different species may find hospitable.

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A Green Frog sitting atop an American Bullfrog

For example, one recent study suggests that more than a million giant king crabs have ventured into the warming waters of Palmer Deep in the Antarctic shelf in recent decades, destroying native sea life. (Colder waters may have kept these “skeleton-crushing predators” at bay for more than 14 million years, the report said.)

Another, a meta-analysis published in the journal Science, found that a host of animal and plant species were moving away from the equator at a striking speed (an average of eight inches an hour). They have moved farthest in regions where the most warming has occurred, the report said.

American Bullfrogs

And then there is Lithobates catesbeianus (or Rana catesbeianus), commonly known as the American bullfrog.

The authors of this latest study, working out of universities in Argentina, Brazil and Colombia, have mapped species distribution models against climate models, information about biological preserves and sites where the species currently lives.

The result is a prediction of what places are more likely to be invaded by 2080. If the climate changes as anticipated, it appears that a bullfrog invasion will subside in portions of central western Brazil, Argentina, Paraguay and Bolivia. But it will increase in parts of northern Brazil, southeastern Colombia, eastern Peru and southern Venezuela, the researchers project.

The American bullfrog is a particularly vexing trespasser. Bullfrogs are superfrogs, very adaptable and seemingly immune to most of the causes of amphibian decline. They live in a wide variety of habitats, colonize new ones readily, and eat everything that fits into their mouths.

If that seems like an overstatement, consider the United States Geological Survey’s summary of the species’ diet, which includes birds, rodents, frogs, snakes, turtles, lizards and bats. In short, they are voracious eaters who will also prey on their own young, the survey says.

The American bullfrog gets so big that people around the world have embraced it for culinary purposes (frog legs).

Endemic to the eastern United States and Canada, the species has been introduced in more than 40 countries and four continents, including more than 75 percent of South America.

The American bullfrog has a record that even Cortés might envy. But beyond its history, there are additional reasons that the species seems likely to colonize new territory.

Amphibians rely on external temperatures, moisture levels, rainfall to regulate their own conditions. They have semipermeable skin, so even slight changes in rainfall can really affect them. Given their reliance on external temperatures and climate, as the climate changes, they are going to move.

For native species, the arrival of the American bullfrog often means new competition, predation and the rapid spread of deadly disease among amphibians. The bullfrog is a carrier of amphibian chytrid fungus, perhaps the most devastating disease to affect an entire class of animals, certainly vertebrates.

According to the International Union for Conservation of Nature, based near Geneva, nearly half of all amphibians are now at risk of extinction for many reasons, climate change among them.

What to Do

When Wild Animals Attack

Run or fight? That is the question prompted by a series of recent animal attacks on humans, including an alligator that dragged a 2-year-old to his death in an Orlando lake earlier this month. Last weekend, CNN reported that a mountain lion in Colorado attacked a 5-year-old boy, who was saved when his mother pried away the child from the animal.

While both of those incidents were rare events, travelers seeking to watch wildlife or spend time in national parks and preserves should maintain a safe distance from any animals encountered, say experts.

“You’re safer in a national park than you are in any city if you use respect and allow the animal a comfort zone,” said Jack Hanna, the director emeritus of the Columbus Zoo and Aquarium who has hosted several television series devoted to wildlife.

Safe distances depend on the animal. A rattlesnake, he said, can spring a body-length or more from its coil, and should be given at least a six-foot berth. Give an alligator 50 to 60 feet and a bear not less than 30 yards and up to 50 if they have babies.

How to respond to an encounter with a wild animal depends on which animal it is, as outlined in these species-specific responses to North American wildlife.

ALLIGATORS

Alligators are found from North Carolina to Texas but are especially prevalent in Florida where, according to the Florida Fish and Wildlife Conservation Commission, they number 1.3 million and populate all 67 counties.

“They prefer fresh water lakes and slow-moving rivers and their associated wetlands, but they also can be found in brackish water habitats,” wrote Tammy Sapp, spokeswoman for the commission, in an email.

The agency reports that alligator incidents are rare. From 1948 through April 2016, 383 people have been bitten. Of those, 23 died.

It advises not swimming between dusk and dawn when the animals are more active. If an alligator does attack, fight back by hitting, kicking or poking it in the eyes. The commission recommends getting immediate medical attention, as alligator bites can result in severe infection.

BEARS

Bears are usually only a threat when surprised or when they are protecting their cubs, both of which can happen when hiking in remote areas. Rangers at Yellowstone National Park recommend hiking with bear spray, a pepper spray that inhibits the bear’s ability to see, smell or breathe.

To deter surprise encounters, the park recommends avoiding hiking at dawn, dusk or night, and making noise while walking along, such as periodically yelling out “Hey, bear!” especially when encountering blind corners or heading through brush. It also encourages visitors to hike in groups of three or more. Ninety-one percent of people injured by bears in Yellowstone since 1970 were hiking alone or with just one companion.

If you do encounter a bear at a distance, slowly back away. If you surprise one, do not run as it may trigger a chase response from the animal. Slowly retreat, drawing your bear spray. If the bear charges, stand your ground and begin spraying it when it is 30 to 60 feet away. Only when it makes contact should you play dead to show that you are not a threat.

Fighting back during an attack only makes it worse. According to park statistics dating to 1970, those who fought back sustained very severe injuries 80 percent of the time. Those who remained passive received only minor injuries 75 percent of the time.

The advice holds for black and brown bear. “Black bear are more carnivorous than a grizzly,” Mr. Hanna said.

He survived his own encounter with a mother grizzly and two cubs on a hiking trail in Montana six years ago. By backing away, he and a group of hikers successfully escaped two bears. One cub, however, charged, forcing Mr. Hanna to use his bear spray, after which the animal fled. “As a human being you want to run like hell, but if you run you won’t make it,” he said.

MOUNTAIN LION

According to the nonprofit Mountain Lion Foundation, which is devoted to protecting the cats and their habitats, mountain lions are generally found in 14

Western states. Because they are solitary and hard to spot, population estimates are difficult, though the foundation believes there are less than 30,000 in the country.

“I’ve seen one three times in 40 years of being in the mountains,” said Mr. Hanna, who has a home in Montana. “The mountain lion is one of the most elusive cats in the wild.”

He said attacks are extremely rare, “and when they do hurt people it’s when they’re injured or older. That’s like a needle in a haystack.”

Avoid hiking alone, or take bear or pepper spray along. If you are attacked, according to the Mountain Lion Foundation, do not run, but stand tall and open your coat or raise your arms to look big. Maintain eye contact, slowly wave your arms, speak firmly and throw items at the mountain lion if necessary. Normally, the cat will move on.

SHARKS

Shark attacks are on the rise, according to the International Shark Attack File at the University of Florida, which tracks incidents worldwide. There were 98 shark attacks in 2015, beating the prior record of 88 set in 2000. Of those, the largest share, at 59, took place in the United States.

To prevent a shark attack, the university research center recommends not swimming at dawn, dusk or night; not swimming where people are fishing, where fish are schooling or where seabirds are feeding; and not wearing shiny jewelry in the water.

If you are attacked by a shark, pound it on the nose and scratch at its eyes and gills.

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