THE ISLANDS

GEOGRAPHY

The Caribbean islands fall into several groups. The four largest islands—Cuba, Jamaica, Hispaniola, and Puerto Rico—comprise the Greater Antilles; all are long and narrow and stretch from east to west. To the north of the Greater Antilles are the Bahamas, or Bahamas Bank, a cluster of more than seven hundred small, lowlying islands and cays, which includes the Turks and Caicos. To the east of Puerto Rico are the virgin Islands, followed by the southward-arching Lesser Antilles, stretching from Anguilla in the north to Grenada in the south.

CLIMATE

The islands of the Caribbean are characteristically warm, sunny, and humid year round. The average annual temperature is approximately 26°C (79°F), though it varies moderately with season. The northeast trade winds blow steadily at 16–32 km (10–20 mi.) per hour, providing a pleasant cooling effect.

Temperatures drop with increased elevation; thus high mountain areas often require a sweatshirt and rain gear. Rainfall is decidedly more variable than temperature, this especially being the case on mountainous islands. The mountains serve as barriers to clouds moving in from the northeast. They stack up over the eastern parts of the islands and deposit most of their moisture as rain and mist. Parts of the island of Dominica receive 900 cm (350 in.) of rain per year due to this phenomenon. The leeward sides of the mountains, contrarily, are dry, the southwest portions of each island generally being the driest. Such areas are semiarid and may receive but a few centimeters of rain per year. Flat islands tend to be semiarid. The second half of each year is wetter than the first, the hurricane season ranging from July through October.

BIOGEOGRAPHY

GEOGRAPHIC ISOLATION AND THE COLONIZATION OF ISLANDS

The Caribbean, with Barbados and the Bahamas being major exceptions, are of volcanic origin and originally erupted from the ocean floor. This being the case, organisms that colonized these islands had to arrive by crossing open ocean, sometimes for great distances. The sea is an effective barrier to dispersal, so relatively few continental organisms have succeeded in reaching this region and becoming established. Hardy fliers such as birds and bats were most successful. Also, plants with tiny wind-borne seeds or with seeds fed upon by birds and carried in their digestive tracts colonized relatively easily. On the other hand, terrestrial mammals, delicate butterflies, and freshwater fish were rarely able to reach the islands.

Another inhibitor to colonization is the limited number of ecological niches available on islands. An animal's niche refers to the specific set of environmental conditions that the species needs to survive. This includes the availability of food, habitat types, nest sites, and shelter. Island size, elevation, and distance from major landmasses from which organisms have to travel, all play significant roles in the potential of a colonizing species to reach and survive on the island. The vast majority of attempts fail. It is for this reason the Caribbean's fauna and flora are not represented by as large a number of species as adjacent continental areas.

UNIQUENESS OF ISLAND SPECIES

The selective process of island colonization explains the relative lack of species diversity. A second outcome, however, is that islands possess large numbers of endemic species—species that occur no place else in the world. Island species tend to become endemic due to their isolation. When genes are not shared between populations for many generations, those populations tend to become increasingly different from one another. Over millennia this leads to such substantive differences that were an island species to come into contact with members of its ancestral stock, they would be unable to breed with one another. Thus, the island form would have evolved into an endemic species.

A consequence of this phenomenon is that what the Caribbean lacks in species diversity, it more than makes up for in uniqueness. This inverse relationship between diversity and uniqueness is typical of oceanic islands such as those in the Caribbean. To take the matter one step further, the greater the distance an island is from a continent (assuming islands are of similar size and elevation), the fewer plant and animal species it will support but the greater the distinctiveness of those species. As an example, compare Trinidad and Tobago with Puerto Rico. Trinidad and Tobago are two sister islands lying off South America, to which they were once connected by a land bridge. Their combined land mass is little more than half that of Puerto Rico, but their native avifauna totals approximately four hundred species, nearly twice that of Puerto Rico's. However, all the bird species on Trinidad and Tobago, with the sole exception of an endemic guan, are found either on the South American mainland or elsewhere. Contrarily, Puerto Rico's native avifauna totals only two hundred and forty species but includes sixteen endemic species, which, except for two occurring in the nearby virgin Islands, are found nowhere else in the world.

Unfortunately, the isolation that permits evolution of many unique species also makes them highly vulnerable to environmental threats and ultimately to extinction. Oceanic island environments lack the diversity of predators and competitors present on continents. As a result, species that colonize successfully have an easy time, so to speak, since they do not have to be as wary. Over time, island species tend to lose many of the traits for discerning and avoiding predators that mainland species possess. Regrettably, recent colonization by humans has dramatically changed the dynamic of islands due to an array of human impacts, including the introduction of predatory species that were unable to reach such islands of their own accord. Island species, having lost their predator avoidance mechanisms, have suffered accordingly.

LOST FAUNAS

The Caribbean of today is quite different from the little-disturbed islands Christopher Columbus and his mariners encountered little more than five hundred years ago. Columbus described the island forests as being comprised of "trees that brushed the stars." Those original forests are gone. They were cut long ago for ship-building materials, to open lands for agriculture, for house construction, and for charcoal, among other uses. Wholesale deforestation was not the only early problem causing dramatic ecosystem change. Several exotic species were intentionally or accidentally introduced into the islands, where they outcompeted or preyed upon the local fauna. After hundreds of years of human impacts, the original delicate ecosystems of the Caribbean have been replaced by a complex of urban areas, degraded natural habitats, and a few preserved remnants of what once was. So much has been lost.

The casual visitor to these islands will be...