Caribbean islands are ecological treasure troves, harboring many species unique on Earth. Yet in our increasingly globalized economy, they’ve been invaded by foreign plants and animals, brought there either intentionally or by accident. On many islands, the invaders threaten to oust native species entirely.
Cuba is an outlier: Its trade and tourism dialed down more than half a century ago after Fidel Castro came into power, and has only been dialing back up in the last few decades. While many Cubans suffered under Castro’s regime, the economic isolation also protected the island from invasive species, according to a new study.
Surveying 45 islands across the Caribbean, a team of American and Cuban scientists found that Cuba had relatively few invasive plant species than other, far smaller islands.
The findings are “strong evidence that Cuba is a really special, spectacular place,” says lead author Meghan Brown, an ecologist specializing in invasive species at Hobart and William Smith Colleges in Geneva, New York. The study was published recently in Frontiers in Ecology and the Environment.
Brown and her colleagues first compiled a list of 738 non-native plant species known to be ecological problem-causers or fast spreaders in the Caribbean. For instance, the fast-spreading Madagascar rubbervine, Cryptostegia madagascariensis, is known for displacing native species and sometimes enveloping trees, and has invaded coastal forests in Puerto Rico and the U.S. Virgin Islands.
Looking at the distribution of such ecological misfits across 45 islands, the team found that in general, the larger the island, the more invaders it tended to have.
But Cuba was an outlier: Its intruder counts were on par with Puerto Rico’s, a tenth of Cuba’s size. It’s unlikely that those species were simply overlooked in Cuba, Brown says: her co-author, Cuban botanist Ramona Oviedo Prieto, organized extensive surveys across the island.
The Madagascar rubbervine hasn’t been spotted in Cuba, and neither has a small herb known as the lark daisy, Centratherum punctatum, which can quickly take over large areas and starve native plants of light and nutrients. It too is an invader in Puerto Rico and the U.S. Virgin Islands, Brown adds.
Only 13 percent of Cuba’s plant species are not native. By contrast, around 30 percent of plant species in Puerto Rico and Grand Cayman, and nearly 20 percent of those in Jamaica and on the island of Hispaniola, aren’t native there.
Although a number of factors probably contribute to Cuba’s “invasion deficit”—maybe ecosystems there are more resilient to invasions, for example—the country’s post-revolution economy definitely plays a strong role, Brown says.
In the aftermath of the 1959 revolution, when Castro took power, the country’s connections with the outside world receded, in part because of a U.S. trade embargo. In 1991, the breakup of the Soviet Union, Cuba’s closest trading partner, temporarily aggravated the isolation.
Invasive species are a cost of open economies, and Cuba’s unusual isolation has probably helped shelter its native ecosystems, says study co-author Rafael Borroto-Páez, an invasive species biologist at Cuba’s Tropical Geography Institute in Havana. His previous research has revealed similarly low numbers of invasive reptiles and amphibians.
The team also identified dozens of invasive or potentially invasive plant species, mostly from Asia, Africa, and the Americas, that Cuba does have, but weren’t found on other Caribbean islands—a pattern that probably reflects the country’s trading partners. That includes, for instance, the parlor palm Chamaedorea elegans, a popular houseplant in the U.S. that is native to Central America, and the cactus-like African milk weed Euphorbia trigona, another attractive pot plant that can grow into dense thickets in the wild.
Politics and plants
Although plants have helped sculpt societies, politics, and trade, the reverse is also true, Brown says: “Politics has influenced our modern ecology.”
But definitively proving cause and effect is always tricky with complex data, notes James Ackermann, a plant ecologist at the University of Puerto Rico who wasn’t involved in the study. Some data suggest that in Puerto Rico, for instance, most invasions occurred before the 1960s, when the island had already become a major stop for international trading ships. If Cuba’s invasion trajectory was similar, then it’s possible not many invaders would have arrived since the Cuban Revolution anyway, irrespective of the island’s isolation. Ideally, if Cuba’s plant intrusions could be mapped over time, it could rule out that possibility, he adds.
The new research by Brown and her colleagues points to tourism as a powerful driver of invasive plant introductions. In general, across 20 islands for which both trade and tourism data were available, invasion numbers tended to correlate more closely with the number of tourists than with trade data.
“Islands [with] heavy tourism traffic, like Grand Cayman or Saint Thomas, have hundreds more [invasive] species than we’d expect for their area,” Brown says.
Cuba has a limited tourism industry by Caribbean standards. In particular it doesn’t host many cruise ships, which often set sail from South Florida, a likely crossroads of invasive plants that can hitch a ride.
Some ecological intruders could be brought by tourists themselves—unknowingly stepping off planes or cruise ships with seeds stuck to their shoes, or even intentionally bringing seeds to Caribbean relatives, Brown says. But many could be a byproduct of tourism: exotic ornamental flowers brought there deliberately to landscape hotels and vacation homes and create a pleasing tropical atmosphere. In fact, the Madagascar rubbervine is popular in the landscaping industry due to its large pink flowers.
“It’s a huge industry,” remarks plant ecologist Julissa Rojas-Sandoval of the University of Connecticut, whose own research suggests that nearly 40 percent of invasive plants on Caribbean islands are ornamental species. The tourism industry is a major consumer of them.
To Rojas-Sandoval, the new study (which she didn’t participate in) underscores an urgent need to control the arrival of destructive foreign species into Caribbean ecosystems, many of which are already damaged by habitat loss. Invasive species add “an additional level of vulnerability threatening…unique Caribbean wildlife even more.”
Some islands, like New Zealand, have minimized the risk of invasion in part by regulating the species the country imports and inspecting imported goods—while still maintaining open borders, Brown notes.
Cuba’s tourism and trade are expected to grow in the coming years, and Borroto-Páez says he hopes its policymakers will scale up actions to protect the island from invasives, and help “preserve the exceptional biodiversity of the West Indies.”