Eye on the Invaders

It is a sad and common story in island ecology: humans bring new species that eat or outcompete native species. Usually we bring them by accident. Hitchhiking animals are the unintended consequence of global trade.

While their arrival may be accidental, there are a number of factors that contribute to the success of these invaders. Animals and plants from large islands or continents are adapted to more complex, more competitive ecosystems. Arriving on a small island they find it easy to excel—imagine Rihanna showing up to karaoke night at your neighborhood bar.

House Sparrows make a home in some of the least natural places on earth.

Often, successful invaders are also well-adapted to life in degraded habitats. House Sparrows are a good example. We find them living in airports, train stations and other places that would be unthinkable for most species. It’s no surprise many invaders can live in landscapes that have been changed by humans. Living around humans makes them more likely to be transported and more likely to find success in a new home.

A devastating hurricane is a big opportunity for species skilled at living in marginal spaces. Post-hurricane conditions have a lot in common with human-altered landscapes. Vegetation is cleared and new growth may be at least temporarily dominated by a handful of fast-growing species. That’s a lot like land cleared for development or agriculture—a forest replaced with a handful of plants.

On St. Martin, a couple of introduced species have been living on the edge for years. These two tree lizards have established populations, but each has been stuck in a little corner of the island. The Puerto Rican Crested Anole has lived at Port de Plaisance, and the Cuban Brown Anole has lived at the cruise ship terminal.

The Puerto Rican Crested Anole is still here.

Each of these lizards has found limited success in a very unnatural habitat. Neither has made it into wild scrub or forest areas. In those areas, our two native tree lizards—the Anguilla Bank Anole and Bearded Anole—still rule the roost. All four species occupy very similar spaces in the local ecosystem, which may be on reason the introduced species have had trouble spreading.

Hurricane Irma posed a challenge to our invaders: either small colony could have been wiped out. It also may have opened an opportunity. Widespread destruction may have given them a chance to spread.

The Cuban Brown Anole, living on the edge in St. Martin.

Like so many other things, the status of these invaders on post-Irma St. Martin deserves some attention. Do natural disasters and human activity work together to speed the invasion of non-native species? For now, we know that the colony of Puerto Rican Crested Anoles has survived. To see if it spreads, we will have to keep an eye on these invaders.

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