When Invasive Species Prove Surprisingly Beneficial

There are plenty of horror stories about invasive species. Like wild hogs tearing up crops or zebra mussels damaging lakeshore infrastructure. But every once in a while, invasive species have actually been known to do some good. Invasive species, or alien taxa, are critters that thrive in places they didn't originate in. They can disrupt a habitat's natural balance by displacing or outcompeting native species. And in the United States alone, these disruptions cost roughly 21 billion dollars a year. So it might seem like these species are always pests that we'd like to eliminate. But as it turns out, some of them are more beneficial than we initially thought.

Like these seven invasive species that have actually kinda helped. [♪ INTRO] Green anoles are quick little lizards that you can find all over Florida. They're native there, but these days, you're more likely to spot their cousins, brown anoles. Brown anoles came from places like Cuba, the Bahamas, and the Cayman Islands, and they're invasive in Florida. While they aren't super destructive, they do compete with the green guys. Wherever brown anoles move in, the green anole population gets pushed out.

Despite this concern, brown anoles have been pretty helpful to us. Because it turns out that local mosquitoes have a taste for them. And when mosquitoes are busy feasting on lizards, that means they're not bugging residents, tourists, and other species affected by mosquito-borne viruses. As an Florida man myself, I definitely find this helpful. But lately, there's another bully on the playground that's been causing a ruckus. It's a burlier, more aggressive, and equally invasive lizard called the Peter's rock agama, and they're starting to outcompete brown anoles.

You might not immediately notice the difference if the Peter's rock agama replaced brown anoles. But mosquitoes don't bite the Peter's rock agama as often. So with fewer brown anoles to snack on, mosquitoes will have to move back to other victims. We don't yet know how this invasive lizard showdown will affect the spread of diseases like West Nile virus. The research is still ongoing, so we still can't quite determine whether brown anoles are a net positive to the overall Florida ecosystem. But this next invader does seem to be certifiably useful… In this case, it's a grass that had an unexpected benefit for the Botteri's sparrow, an unassuming little brown bird that has historically lived in southern Texas and Arizona.

But for a period in the late 1800s, the Botteri's sparrow was driven out of Arizona. The tall native grasses where the sparrows nest had been overgrazed by cattle. To replace the disappearing native grasses, lovegrasses were introduced as cattle feed. Unfortunately the cattle didn't love the lovegrasses, so they kept eating the small amounts of native grass that remained, allowing the lovegrasses to spread faster than expected. But, helpfully for the Botteri's sparrows, these non-native lovegrasses put up "vacancy" signs as they quickly swept across Arizona. When the sparrows finally returned to Arizona in the 1960s, they were spotted nesting in the invasive lovegrasses!

Researchers initially worried the alien grasses might be an "ecological trap". In other words, although the sparrow feels safe using the habitat, it might not offer as much cover from predators or facilitate healthy breeding. But they found that birds nesting in non-native grasses reproduced at the same rates as birds nesting in native ones. So even though the native habitat will always be the best home for the Botteri's sparrow, lovegrasses seem to be an acceptable alternative, given the state of the grass-housing market. While these grasses were a highly visible invader with big impact, tiny critters can pack a powerful punch, too.

Such as the microbial invaders in the Caribbean that are helping out corals. This probably isn't breaking news to you, but coral reefs are threatened by rising temperatures and changing ocean chemistry. Their life is a little complicated, because they rely on symbionts, tiny microbial partners. In the corals' case, they're algae that live in the coral and make food for it by photosynthesizing. Like a little live-in grocery store. One species of symbiont, Symbiodinium trenchii, has been spreading from the Indo-Pacific to the Caribbean.

S. trenchii isn't like other microbes. It's better at photosynthesizing under stressful conditions than the local Caribbean algae are, so it can tolerate higher temperatures. As a result, coral colonies infiltrated by S. trenchii also do better when things get toasty. It definitely sounds great that S. trenchii helps corals withstand higher temperatures, but there could be hidden costs tagging along. For example, in some colonies, this invasive symbiont seems to change how fast corals form their hard exoskeletons. So we'll keep an eye on that for a bit before declaring S. trenchii as a coral hero. And it turns out that corals and crocodiles have something in common,

because crocs also got a little help from an invader… But before we tell you who, we need a little help from this sponsor. This SciShow video is supported by DeleteMe, the hands-free subscription service that removes your personal information from hundreds of data brokers and people search sites. SciShow's executive producer, Nicole, signed up this year and already had 16 listings removed for her. They also made it really easy for her to remove additional listings herself with the click of a button.

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Australia's feral pigs are the descendents of 19th century domestic pigs that were convicted of crimes and then shipped off to Australia. Just kidding, the pigs weren't criminals, they were just brought to Australia as a food source for colonists. Today, there are about 23 million feral pigs in Australia. Feral pigs cause all kinds of environmental havoc, from disturbing vegetation to spreading weeds to wholescale habitat destruction. But not everyone has a beef with Australia's feral pigs.

Crocodiles find them quite useful! Until the 1970s, crocodile hunting was unregulated in this part of the world, and the croc population dwindled to just a few thousand animals. When the government realized how much danger they were in, crocodiles were given protected status. That surely helped. But researchers think they got an assist from those invasive pigs. In 2022, scientists compared samples of modern crocodile bones to those of animals killed between 1968 and 1986. They found that the older crocodile bones contained more specific isotopes of carbon and nitrogen than the bones of modern saltwater crocodiles.

Higher abundance of those carbon and nitrogen isotopes is associated with a fish-forward diet, because seafood like catfish and barramundi have more of those isotopes. Aquatic wildlife was the traditional fare of crocodiles in the past. But the decreased amounts of those carbon and nitrogen isotopes in the modern crocs suggests that, in the post-hunting era, crocs are relying more on terrestrial prey. The invasive pigs probably account for a big chunk of that land-based buffet, because they're pretty easy pickings: they're plentiful, nutritious, and often wallow in mud near croc territory.

This suggests the pigs have contributed to the crocs' resurgence Down Under! Speaking of Australia, our next invader is a native Aussie. The eucalyptus tree first arrived in California during the gold rush, and quickly became a local landscaping darling. Today, it's seen for what it is: invasive. Large eucalyptus groves can affect a microclimate's temperature, humidity, shading, and soil characteristics. But the eucalyptus tree is also offering a big helping hand to California's butterflies. In California, 34% of native butterflies use

non-native plants for food or as a place to lay eggs. Butterflies aren't doing so well lately because of widespread habitat loss. So any help they can get is welcome. One of California's most iconic butterflies, the Monarch butterfly, is also one of the most vulnerable. The population of monarchs that migrate up and down the west coast has declined by roughly 95 percent since the 1980s. Scientists put this population's chance of extinction before the year 2080 at roughly 99 percent. That is pretty bleak. One of the major reasons for that decline is loss of suitable habitat.

These western monarchs usually spend the winter on the coast of California. They migrate during the day, but roost in trees overnight. They specifically need trees with thick canopies that maintain a comfortable temperature. Many of the large, native trees that fit that bill have been removed by logging and development. So western monarch butterflies have shifted to roosting mostly in eucalyptus trees. They provide safety and nectar for the butterflies, giving them a better shot at survival. So I guess those silver-lined leaves have an ecological silver-lining, too.

And we have another example for you of invasive trees providing refuge for vulnerable species. This next tree may help protect a native snail from a dangerous predator. The common Norway rat is probably the one you're most familiar with. But the black rat is a different species, native to India. In most places, they've been largely out-competed by the Norway rat, but black rats are still found on most continents and are considered invasive. Japan in particular has a problem with black rats.

They wreak way more havoc than the typical ratty shenanigans you'd expect in attics and back alleys. Black rats also threaten native species, including one of its favorite snacks: the Japanese land snail. This is where our invasive tree steps in. The drooping sheoak is also native to Australia, just like eucalyptus. But now it's found on Anijima, an uninhabited island in Japan's Ogasawara Archipelago. These trees' destructive power is their ability to form a homogenous, nearly impenetrable forest. They grow fast, lay down a thick network of roots, and drop a lot of litter on the forest floor,

which basically makes it impossible for native plants to grow there. But that hostility to native plants also makes them an excellent hiding spot for those land snails. In fact, land snails dodge rats better in the sheoak forests than in native vegetation. Researchers think they might be hiding from the black rats in the litter that collects under these trees. Because when conservationists removed the trees, they also found that the snail population declined. So it seems like the sheoaks are giving our snail friends some much needed shelter. Although there are still a lot of reasons to remove the sheoaks, researchers advocate for

addressing the black rat population first, to give the land snails a better chance of surviving. And to wrap things up, we're headed back to Florida, you can't escape.This time we're talking about their huge problem with Burmese pythons. These constrictors are native to southeast Asia, but were imported to Florida by the pet trade. At some point, a few escaped captivity or were deliberately released, and they found that Florida's habitats suit them just fine. Today, officials say the Florida Everglades are likely home to "tens of thousands" of Burmese pythons. They are not friendly neighbors.

Burmese pythons have been feeding on native species. For some species, their population has declined as much as 95% since the pythons moved in. But the snakes have actually been helpful in one small way: they eat raccoons. Even though raccoons are native Floridians, it's kind of helpful to have fewer of them because raccoons eat the eggs of freshwater turtles. One research study found that python-infested areas also had much lower rates of predation on artificial turtle nests, compared to areas without pythons. And they're pretty sure that's because pythons had eaten many

of the animals that do the turtle nest predation. Even though the pythons are indirectly helping turtles and other egg-laying species, it doesn't negate the other serious problems they cause. As you might have guessed, when it comes to nature, there are no clear cut villains or heroes. And although in many cases invasive species have earned their bad reputation, we can't always assume that all invasives are all bad all of the time. In fact, some scientists are trying to quantify both the negative and positive impacts of alien taxa using hypothetical scenarios based on real data.

This would let them categorize alien taxa's potential benefits from minimal to massive, and allow conservationists to weigh the pros and cons of evicting any invasives. As is often the case, the full picture is complex. Scientists have learned that while eradicating invasive species is usually necessary to protect native species, it should be approached with caution, and only after considering all of the invasive species' helpful impacts, too. Because sometimes you can find a friend in the most unexpected places. [♪ OUTRO]