Lands of Giants, Lands of Dwarves

    The Caribbean islands form a very complex archipelago.

    The specific origin and development of the insular banks - groups of "sister" islands that lie on the same submerged insular platform and that comprise a single geological unit - vary widely among the Antilles. This means that although there are many similarities among all Caribbean islands as a whole - climatic, geologic, faunistic, biogeographic, etc. - every individual island is indeed unique, yet most similar to other islands in the same bank. In fact, when speaking about the distributions of West Indian plants and animals it is more appropriate to speak of groups of related organisms that inhabit "insular banks", better than merely naming those that inhabit individual islands as these appear to be above water.

    In any case, practically the entire terrestrial biota of the Antilles is no older than 65 million years, dating from the end of the Cretaceous and the beginning of the Paleocene geological periods. The Chicxulub crater, located off Mexico's Yucatan Peninsula, is the remaining evidence of what happened then: an asteroid or comet at least 10 kilometers in diameter crashed into that region, releasing a hundred gigatons of energy in seconds. The subsequent gigantic fireball, tsunamis, storms, debris shot into space and falling back on the surface, and earthquakes obliterated most living organisms of the West Indies and on much of this planet.

    Every Earthling alive today is a survivor of that instant.

    As happens everywhere else, topographic, climatic, and edaphic (soil) factors influence the distribution of plant and animal taxa in the Caribbean. Throughout the West Indies, hydric, mesic, and xeric areas have their own arrays of species. At least in the Greater Antilles, part of the existing terrestrial biota is very ancient in their origins. Some areas of what are today the Cuban, Puerto Rican, and Guadeloupean insular banks might have been continually above water since the lower Jurassic Period. This implies that a number of their terrestrial organisms have had a long and uninterrupted period of evolution and adaptation.

    In the Caribbean islands, as in other regions on Earth found between the tropics of Capricorn and Cancer, the warm and stable climate favors the evolution and coexistence - even in proportionally small areas - of creatures great and small: algae, plants, fungi, animals and, of course, microorganisms like bacteria and protozoans. A relatively small island like Puerto Rico has more than 500 native species of trees, about as many as the continental United States and Canada combined. The larger islands of Cuba, Hispaniola, and Jamaica have even richer florae. There are 186 families (with one endemic) and about 2500 genera (with 118 endemics) of seed plants in this region. Altogether, there is a total of about 13000 native Antillean vascular plants, of which 6550 are endemic to the Caribbean islands. Of these last, about half are endemic to the Cuban insular bank, and most of the rest are restricted to the other three Greater Antillean banks.

    The two main ways by which Antillean organisms reached their present distributions among the different islands are vicariance and dispersal. The first means that as islands split from their parent blocks, each carried an ancestral population of any given taxon. Upon the separation from their original population, each went its separate way, evolutionarily. Dispersal means that the parent population of the taxon reach their present location from overseas, either through their own means, as happened with flying insects, birds and mammals, or by fortuitous arrival from another land mass by means of ocean currents or wind, as in the case of reptiles, amphibians, and plant seeds. Dispersal and vicariance are not mutually exclusive in the long run, and any of several combination of events involving both means might have taken place in the case of many populations.

    The northern islands of the Greater Antilles and the Bahamas have been influenced from the north and west. Many of their birds are of North American origin, and most bats invaded the islands from Central America. In a manner similar to that in which southern biotic elements become scarcer the more northern and western the islands are, the North American and Mesoamerican character of the biota becomes increasingly less obvious as one moves from the Bahamas, Cuba, and Jamaica towards Grenada, just north of Venezuela.

    By far, the richest island in the Caribbean in terms of number of species is Cuba, followed in proper order by Hispaniola, Jamaica, and Puerto Rico. On regards to animals the species diversity varies unequally among the different taxa, both absolutely as well as proportionally. The patterns can be at times surprising. For example, although it might be the youngest of the Antilles, Jamaica (and not the far larger Cuba and Hispaniola) possesses the highest numbers of endemic birds. This may be due to its proximity to the Central American mainland, from which many of its avian species indeed derive. Cuba, with its proximity to North America, has a rather large number of birds identical to, or evolved from species in that continent. On the other hand, pine trees exist naturally in Cuba, Hispaniola and the Bahamas, but not elsewhere in the archipelago.

    On regards to reptiles, Cuba and Hispaniola have very large numbers of anoline lizards. The Hispaniolan and Puerto Rican insular banks have an unusually high number of amphisbaenians, and the group seems to have been already present in the combined northern Hispaniolan-Puerto Rican paleoisland, when it was closer to Mesoamerica.

    Some arthropod groups of primitive lineage are shared by Cuba and Puerto Rico, but not by the other islands. This seems to attest that these two islands are the most ancient in the Caribbean Basin, at least as far as parts of them being above water.

    From a biogeographic standpoint, it is very interesting to notice that there is a Lesser Antillean biogeographic divisive line located between the islands of Dominica and Martinique. This line partially divides the biotic communities in the island arc into a "northern" and a "southern" ones. What are today Guadeloupe and Dominica might have been much closer to the Puerto Rican insular bank several millions of years ago. This is inferred from the fact that these two islands, and those to the north of them, are inhabited by plants, insects, snakes, lizards, and even bats that seem to be derived from a Puerto Rican (and Greater Antillean) stock. South of Dominica, and beginning in Martinique, many of the Greater Antillean faunal and floral elements suddenly disappear, and are replaced by organisms with very obvious South American ancestries. As an example of this phenomenon, the anoles found from Dominica onwards to the north belong to the subgenus Ctenonotus, extending to Puerto Rico and Hispaniola. On the other hand, the anoles found from Martinique southwards belong to the South American subgenus Dactyloa.

    Among the Lesser Antilles, the Guadeloupan insular bank is a cradle of endemism unsurpassed by any of its sisters. Xenodontine snakes, anoles, bats, and several plant groups have speciated there like nowehere else in the volcanic arc. To the south of Dominica (itself south of Guadeloupe) Martinique already exhibits a stronger South American influence in its biota. This trend continues until we reach Grenada and its satellites the Grenadines, whose biota is largely northern South American in origin.

    This South American character becomes less evident as one moves to the north and west along the Antillean island chain but differently so, depending of the kind of organisms considered. While some groups originating in South America are spread through the entire Antillean region (for example, xenodontine snakes, most nonvolant mammals, and perhaps most anoline lizards) others are restricted to the southern islands. The pit vipers of the genus Bothrops and the dendrobatid frogs of the genus Allobates inhabit the West Indies only as far north as Martinique, and are not even found in every intervening island. Boa snakes presently reach Dominica while an extinct population is known from as far north as Antigua. By comparison, the also boid Corallus reach only as far north as Saint Vincent. The Cnemidophorus teiid lizard of Saint Lucia has its relatives in Venezuela. Aviculariine arboreal tarantulas like Avicularia and Tapinauchenius are found in the Lesser Antilles. Lesser Antillean parrots of the genus Amazona are all related to those of the continent to the south.

    There are in the West Indies several genera and some families with no living representatives anywhere else. Some are true relict groups whose ancestors, whether in North, South, or Mesoamerica disappeared and which Antillean descendants are all that remains of their kind. Among these are the todies, small birds distantly related to kingfishers and motmots. Others include the most massive lizards in the Western Hemisphere: the cyclurid iguanas of the Greater Antilles, the Cayman Islands and the Bahamas. Also among these is the the single xantusiid lizard in the region, Cuba's Cricosaura typica.

    Other peculiar endemic taxa in the region belong to larger groups still living in the American continents, but have evolved in situ from their ancestral populations, and have developed unique morphologies or behaviors, or fill ecologic niches occupied by very different organisms elsewhere. Examples of these are the Uromacer treesnakes of Hispaniola, the "crown giant" anoline lizards of the Greater Antilles, the Allenia, Cinclocerthia, and Margarops mimid birds of the Lesser Antilles, and the capromyid rodents and Calisto butterflies of the Bahamas and the Greater Antilles.

   The long geological history of the Antilles, still fraught with unsolved incognita, gave rise to biogeographic mysteries even among islands closely tied to one another. While, for easily understandable reasons, the closest relatives of many organisms in an island bank are frequently found in nearby banks, that is not always the case. Jamaica and Puerto Rico possess organisms - like some of their snakes and birds - most directly related to one another's than any of them are to Hispaniola's, which is situated between its two neighboring islands. This is possibly due to extinctions, further speciation, or both, that have occurred in the intervening islands. Other organisms, dispersed by sea currents, may have reached the shores of all islands nearby, but only survived where they were confronted by no pre-existing competitors. Such might have been the case of some typhlopid snakes and Anolis lizards which have flourished in some of the Bahamas after dispersing from distant Puerto Rico, but which might have been unable to colonize Hispaniola successfully.

    Given the prevalent east-to-west movement of the sea currents in the region, it is to be expected that plants and animals that disperse over water do so in that same direction. However, that does not always seem to be true. Antillean Diploglossus galliwasps are restricted to Cuba and Puerto Rico. However, one species is endemic to the Lesser Antillean island of Montserrat. The same happens with the Martinican Leiocephalus, whose congeners are all Greater Antillean, Bahamian, and Caymanian. Given the distances between these populations, it is highly improbable that vicariance was the means by which they reached the Lesser Antilles, yet dispersal by current ocean currents is also unlikely.

    Within a single island biogeographic patterns follow the climatic differences created, for example, by the presence of high mountain ranges. Particularly in the Greater Antilles, vast numbers of species are confined to such places, and sometimes their distributions extend to a single, isolated mountain or small highland massif. As an example, the Puerto Rican elfin frog, Eleutherodactylus unicolor, only lives in the cloud forests of the small Luquillo Range, near the eastern end of the island. Among reptiles, the Turquino twig anole, Anolis guazuma, is restricted to the highest reaches of Cuba's Sierra Maestra. Some exclusively montane Antillean birds are the Hispaniolan crossbill, Loxia megaplaga, of the alpine pine forests of Hispaniola, the Puerto Rican tanager, Nesospingus speculiferus, of the highland rain forests of that island, and the blue-headed hummingbird, Cyanophaia bicolor, of the mountains of Martinique and Dominica, in the Lesser Antilles.

    Similar habitat-specific populations occur within cavern systems, like those in Cuba, Puerto Rico, and Jamaica. The first has species of blind, cave-dwelling fish in some of its subterraneans systems, the second exhibits a similar situation with certain crustaceans, while the third has species of troglodyte velvet worms.

    In the rain shadow of the mountains there are xeric areas - some very extensive - which exhibit a huge variety of endemic organisms adapted to dry conditions. These cannot cross or invade more humid habitats, and are confined to specific regions if such are blocked by higher terrain. These arid ecosystems have given rise to plants like the West Indian Psychilis butterfly orchids. Because plants living in under such xeric situations cannot afford to easily loose their foliage to predators, several among them have developed toxins to deter grazers. Among these are the Hippomane trees, which sap makes them some of the deadliest plants on Earth.

    The wetlands of the West Indies are likewise centers of local endemism, where plants, snails, crustaceans, fish, and even birds have evolved in situ, adding to the immense menagerie found in the Caribbean. The best examples of the richness of Antillean wetlands are the Zapata Swamp, in Cuba, and the Enriquillo Lake and associated wetlands of Hispaniola.

    Islands across the world are laboratories of evolution and ongoing natural experiments on ecological relationships. Many strange, beautiful, and wonderful creatures inhabit the islands spread through the Earth's oceans, including the Antilles. Because of their isolation, the West Indies harbor unique plants and animals. Some are evolved there, while others comprise relict populations whose kin became extinct elsewhere (these taxa are called paleoendemics). Such last is the case with the todies, distant relatives of mot-mots and kingfishers which today survive only in the West Indies, after dying out in Central and North America.

    Due to special conditions and lack of groups common in continental land masses, extremes in size are found in several islands of the Caribbean. Here, instead of mammals, the largest predators are reptiles, like the Cuban and American crocodiles, the large Chilabothrus boas of the four Greater Antilles and the Bahamas, and the endemic Lesser Antillean species of the genus Boa. Likewise, the biggest extant grazers in the region are reptiles: the massive creatures belonging to the iguanid genera Cyclura and Iguana.

    Ecological niches that in continents seem to be filled by some insects and arachnids are here taken by tiny amphibians, reptiles, and birds. Specialization of this sort has provided the West Indies with minimalist world records among vertebrates. One of the smallest amphibians and the smallest bird in the World are found in Cuba, respectively the Mount Iberia frog, Eleutherodactylus iberia, and the bee hummingbird, Mellisuga helenae. The vervain hummingbird, Mellisuga minima, of Jamaica and Hispaniola is barely larger than its aforementioned congener. The tiniest lizards known, the Jaragua geckolet, Sphaerodactylus ariasae, and the Virgin Islands' dwarf geckolet, Sphaerodactylus parthenopion, live in the Caribbean. And the smallest snake on Earth is Tetracheilostoma carlae. It is thinner than a spaghetti noodle, and it is endemic to the Lesser Antillean island of Barbados.

    On regards to invertebrates - animals usually considered to be small - the Antilles exhibit some examples of insects that have grown huge, perhaps because of the absence of some specific predators. Some West Indian moths, walking-sticks, and katydids are immense, for their respective kinds. And the largest swallowtail butterfly in the Americas, Papilio homerus, flies in Jamaica. It is heavier than some of the local birds.

    The Antilles are inhabited by organisms which defy concepts held by many people used to see "normal" individuals of their kind. Here are found relatives of the roses and the magnolias that are 30 meters tall, orchids no larger than a human thumbnail, and mushrooms more than a meter in diameter; huge centipedes colored in blazing orange, and snails that are transparent green; giant anoles that run on water; enormous shrews and arboreal rodents the size of cats; birds which songs sound like electronic devices and frogs that sing like birds; bats that fish at sea and snakes that hunt for bats; spiders that resemble flowers and mantids that look like lichens; hermit crabs that feed high on trees, and owls that nest underground.

    These creatures often bear little resemblance to their counterparts in other latitudes.

    But all is not well in the West Indian Paradise.

    Due to the process of deforestation and other habitat degradations that ensued even in the pre-Columbian period, the abundance and distributions of the native West Indian flora and fauna has changed dramatically. Very little of the untouched primeval forests, mangrove swamps and savannas of the Caribbean remains. Biogeographic patterns have been altered, hundreds of exotic species have been introduced, the distributions of native species have contracted or expanded depending on how anthropogenic alterations to the environment have harmed some species and benefited others.

    Yet even after the numerous instances of human pride and carelessness, the Antilles still comprise one of the great biodiversity hotspots on Planet Earth. In spite of the recent wave of extinctions and local extirpations caused by man's mismanagement and destruction of their natural environments, an immense and bewildering variety of organisms still live in these lands.

    All together, these creatures contribute to give the islands of the Caribbean their unique appeal and mystique, and fill their mountains and valleys, rivers and caverns, pinewoods and grasslands, rain forests and deserts with mystery, and beauty, and splendor.

    They are prophecies of things yet to come.