Natural History

Island Hoppers

Story & Photos By B. Naqqi Manco, Conservation Officers,
Turks & Caicos National Trust

Island ecology is a fascinating subject. Plant and animal species typically arrive on islands after leaving, or being taken from, larger continental homes. When introduced onto an island, a plant or animal species may find that the conditions are not suitable there, and die off. The species may find that the conditions are quite suitable to live comfortably on the island. Or, a species may find conditions partially suitable, and change over time to fit better into a niche on the island, becoming a separate subspecies or a new and unique species altogether.

How do plants and animals get to islands? If an island was at one time connected to a larger landmass, animals or plants may have ended up stuck on the island when it separated from the landmass. But what about islands that were never attached to any large landmass, or islands that have not been attached to landmasses for thousands of years — how do new plant and animal species become established on such islands?

Many plant species have seeds borne on parachutes of silky threads or papery wings that are able to fly long distances in the wind. Others are carried to islands by animals. Most insect and bird species are capable of flight, and many reach islands that way. Bats also are able to fly and often expand their range to islands. Birds and bats often carry fruit and seeds in their digestive track, which if released as droppings on an island can succeed in establishing a new plant species there.

A more recent addition to our bird life is the Cattle Egret, which is native to Africa. These birds crossed the Atlantic on their own and began spreading throughout the Caribbean and the Americas in the early part of the 20th century. They are now common in the Turks & Caicos Islands, but only 100 years ago they may never have been seen here.

Terrestrial mammals, reptiles, and amphibians have a more difficult time spreading their ranges to islands. Most make their way to islands by rafting. Rafting is not a deliberate attempt to colonize a new territory. It is typically accidental and usually happens several times over a long period of time to succeed in the established introduction of a species. Rafting is how our iguanas probably arrived in the Islands, from populations on other islands nearby.

Human introduction, deliberate or accidental, is typically the way that most terrestrial animals and plants reach islands today. Plants are not only introduced deliberately for agriculture and landscaping, but also accidentally as seeds stuck to shoes or clothing, used in livestock feeds, or found in imported potting soils. Animals such as snails, insects, spiders, lizards, snakes, and frogs may be introduced in potted plants, building materials, and large dry goods shipments.

frogletOne of the animals we have here in the Turks & Caicos Islands is a world-class “island hopper.” The Greenhouse Frog Eleutherodactylus planirostris is not only good at inhabiting new islands through introduction, but it is most perfectly adapted to do so. The Greenhouse Frogs of the Genus Eleutherodactylus all have this island-colonizing ability in common, and it is the result of an amazing and very unorthodox amphibian adaptation.

Greenhouse Frogs are small in size. The largest measure less than two inches in length and weigh just a few ounces. They are similar in appearance to tree frogs in that they have a compact body, sturdy limbs, and sticky toe-pads to adhere them to most surfaces. They are typically subtle shades of brown and tan for camouflage, and they move quickly in long, fast leaps.

Where Greenhouse Frogs are small in physical size, they make up for in family size. There are so many species in the Eleutherodactylus genus that they actually outnumber the species counts of any other genus of vertebrate animals — there are over 700 recognized species of Greenhouse Frogs!

In the Turks & Caicos Islands, we have the Cuban Greenhouse Frog Eleutherodactylus planirostris. This frog is tiny, typically under an inch long. They were first described from the Bahamas but later it was found that Cuba is their center of distribution. By rafting in vegetation, tree trunks, and bamboo stands washed out to sea in storms, these tiny frogs have sea-fared their way to almost all of the islands in the Bahamas. Whether they were introduced to the Turks & Caicos by human introduction (probably in potted plants) or if they made it here on their own is unknown. They were introduced into Florida from the Bahamas decades ago and have made their way northward into Georgia and other southern U.S.A. states.

Greenhouse Frogs are amphibians, like all frogs. The word “amphibian” comes from the meaning “double life” reflecting on the aquatic tadpole stage then the later terrestrial frog stage of most frog species’ lives. Most frogs require fresh water in which to lay their eggs so their tadpoles may grow.

Another frog species we have introduced here (also from Cuba) is the Cuban Tree Frog, which likely made its way here from Florida in building materials. Cuban Tree Frogs are large and are one of the few frog species able to breed in slightly brackish water, which is why they are able to survive in the Caicos Islands.

The Greenhouse Frog, unlike the Cuban Tree Frog, does not have to worry about finding water in which to lay their eggs. These frogs have a most amazing adaptation that allows them to colonize islands freely even if no standing water is available at all. When a female Greenhouse Frog is ready to lay eggs, she finds a shady, damp spot on the ground, often in a cave entrance, sinkhole, or well-vegetated area. She will lay her eggs, usually about 15 of them, right onto the ground in a small depression she digs with her hind legs. The eggs, about the size of a pinhead, are glassy and resemble pearls made of clear jelly.

The mother Greenhouse Frog will pay her eggs no further attention, and leave them in their moist, shady spot to develop. As the eggs develop, they grow. Through the glassy skin of most frog eggs, one can see a tadpole form from a simple dark spot. Usually, frog eggs then hatch and the tadpoles become free-swimming in water. The Greenhouse Frog, however, skips that step. The tadpoles remain inside the egg, and the egg simply grows with them. The egg grows until it is about the size of a dry pea, at which point the tadpole inside the egg grows legs, absorbs its tail, and turns into a tiny frog!

frog-babiesThe development of a tiny “froglet” inside the egg of a Greenhouse Frog takes from 13 to 15 days. In that time, the egg’s inhabitant goes through a complete metamorphosis from tadpole to frog. Finally, the froglet hatches and is ready to start its new life as a tiny frog. Barely able to cover a single typed letter on this page with their bodies, the froglets mostly hide at first, snapping up tiny ants, gnats, and other invertebrates in the moist soil where their eggs were laid. They eventually venture out of the moist nest to find a new hiding place, where they will continue to eat small insects and grow into their adult form.

While Greenhouse Frogs are native to the Caribbean Basin and South America, they have been introduced to other areas of the world where they are not regionally native. A Puerto Rican species, the Coqui Greenhouse Frog, as well as our own Cuban Greenhouse Frog have been introduced to Hawaii in the potted plant trade. There, they have caused great disturbance in the natural ecology of the wilderness by competing with native animals and possibly spreading plant parasites from nurseries into native plant communities. Also, the Coqui Greenhouse Frog’s amazingly loud voice has become a deterrent to the tourism industry as visitors have a hard time sleeping through the frogs’ continuous calls. Luckily, our Cuban Greenhouse Frog’s only calls are quiet chirps that are not disturbing at all.

This situation bears testimony to the dangers of introducing animals and plants into regions to where they are not native. It reminds us that we must take pride in our natural heritage and work to conserve and protect the species with which these islands are graced.

No doubt over time, there will be other “island hopping” species that end up in the Turks & Caicos, as it is the nature of islands to collect the occasional drop-in by some member of a species blown off its normal course. As we witness these natural introductions, it is important that we limit the deliberate and accidental species introductions caused by humans by making careful decisions and acting as stewards to care for our own unique species of island hoppers.

For more information, contact Bryan Naqqi Manco at 941-3536.



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On the Cover

Agile LeVin—photographer, explorer and chronicler of everything TCI on his website www.visittci.com—took this drone photo of the multi-textured wetlands of West Caicos. He was part of the expedition that investigated the site of the historic pirate attack in the area. For more information and photos, go to page 48.

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