Fauna of the Caribbean

The Caribbean Sea is bordered to the west and south by Central and South America, respectively, to the east by the Lesser Antillean Island arc, and to the north by the Greater Antilles. When used in a biogeographic context, however, the Caribbean Region is usually defined as the islands that have been called the West Indies since the days of Christopher Columbus. These islands vary greatly in size and age. The oldest islands sit on the Caribbean Plate, which first emerged in what is now the eastern Pacific Ocean, drifted between ancient North and South America before the Isthmus of Panama had formed, and eventually collided with the Bahama Platform and the Atlantic Plate. Throughout this passage, rising and falling sea levels repeatedly inundated entire low-lying islands and at least the lower elevations of the higher ones. Additionally, to the east, a subduction zone creates a band of intense and often explosive volcanic activity, which has been responsible for the creation of many Lesser Antillean islands that constitute the newest additions to the archipelago. Islands vary in size from barely emergent rocks to Cuba (over 110,000 square kilometers or 42,800 square miles) and Hispaniola (over 75,000 square kilometers or almost 30,000 square miles), but sizes have varied as rising sea levels during interglacial periods have fragmented island banks and inundated smaller landmasses.

The island fauna has, like that of any region, been defined by a combination of historical events and current realities. Although transient contact with Central America may have occurred at one time, most of these islands have never been connected to a continent. Because seas are generally effective barriers to dispersal, relatively few terrestrial animals successfully reached the islands, and even fewer became established. Another factor limiting the number of species is the small number of ecological niches available on relatively small islands. Larger islands with greater elevations are more ecologically complex and contain more niches than smaller islands with less topographical relief, but even the largest islands pale in comparison with the ecological diversity of continents. However, when the region is considered as a whole, the fragmentation and isolation of the islands result in a phenomenally high species richness (of at least some animals) and a very high degree of endemism.

A Fauna Dominated by Reptiles and Amphibians

Studies of West Indian invertebrates are largely limited to those of specific sites or groups, and an overview would be cursory at best. As for terrestrial vertebrates, the quantity of mammalian fauna is relatively impoverished, and most birds are migratory; consequently, amphibians and reptiles dominate the fauna in terms of both diversity and numbers. On islands with limited resources, the greater energetic needs of birds and mammals limit population sizes. In contrast, amphibians and reptiles do not require large amounts of energy to sustain stable body temperatures, and, as a result, phenomenally high population densities are possible.

Over fifty species of bats and over one hundred species of other non-marine mammals are known from the region. However, at least twenty-three endemic mammals are extinct, victims of habitat destruction, competition with introduced exotics, or exploitation by humans. Another 25 percent are considered globally threatened. Consequently, the mammalian fauna is dominated by bats and introduced species. While thirty-six bird genera are endemic to the region, most of the over 565 West Indian species of birds are migrants, and another large number are sea birds with broad distributions throughout the world. Of the endemic groups, as many as a dozen appear to be relics of genera that were formerly widespread on adjacent continents. Consequently, the avifauna merely mirrors the greater mainland diversity.

In contrast, almost seven hundred frogs (but no salamanders or caecilians), turtles, crocodilians, and squamate reptiles (lizards and snakes) are known from the region, and around 82 percent are endemic. Population densities include one of the highest reported for any vertebrate anywhere in the world (approaching 70,000 per hectare for at least two species of dwarf geckos).

Evolutionary and Ecological Studies

The diversity and population densities of amphibians and reptiles have provided biologists with many opportunities to investigate evolutionary, ecological, and biogeographic questions. In particular, the most diverse groups have demonstrated repeatedly the remarkable abilities of animals to speciate by adapting to varying local conditions on isolated islands or disjunct habitats created by topographic relief on larger islands. West Indian lizards in the genus Anolis have provided the best insights into the principle of ecomorphology. Structurally and behaviorally, similar species on different islands are more closely related to very different species on the same islands than to their ecological counterparts elsewhere. This phenomenon provides evidence for evolutionary adaptations to local conditions and divergence from relatives that adapted to other available habitats. Many fundamental biogeographic principles have also been developed or supported by studies on West Indian animals. Over-water dispersal of large terrestrial vertebrates, long a staple of biogeographic hypotheses, was first demonstrated in 1995 when green iguanas were transported over hundreds of kilometers of open ocean from Guadeloupe to Anguilla on a floating mass of debris. Other important biogeographic concepts emerging from West Indian studies include positive relationships between biodiversity and area, habitat heterogeneity, and proximity to the nearest large body of land—and between habitat fragmentation and extirpation or extinction.

Conservation Concerns

Studies of habitat fragmentation, unfortunately, also provide many examples of the negative impact humans have had on the survival of the other species on the planet. Although Indigenous people began the process and may have been responsible for the extinction of the few large land mammals known to have lived in the islands, the most harm has resulted from humans of European and African descent, to whom the islands have been subjected longer than any other area in the Western Hemisphere. In addition, human population growth has been rapid, and island areas are limited.

Furthermore, economic development, often related to tourism, is accelerating to accommodate the growing needs of humans living in a region with few natural resources. Efforts in the early 2020s aimed to limit the extinction of wildlife in the Caribbean. The UN Environmental Protection Programme, for example, developed a comprehensive plan addressing the well-being of migratory species, including marine mammals and sea turtles, as well as a support plan providing insight for the control and management of invasive species, including sargassum, an invasive seaweed that can suffocate the oxygen levels in oceans harming fish and coral reef populations.

Many West Indian animals have small ranges and are extremely vulnerable to habitat alteration and the impact of introduced exotic flora and fauna. A large percentage of frogs and some lizards are restricted to forests that are disappearing rapidly. Other species, notably the critically endangered iguanas of the genus Cyclura, the most endangered reptiles in the world, and hutias, large endemic rodents, have suffered from exploitation by humans for food. Many species in both groups are extinct, and most populations are threatened or endangered. Predators, notably feral cats and the mongoose, were introduced to control rats in sugar cane fields and eliminate populations of ground-dwelling snakes and lizards on many islands. Goats denude vegetation on which native species depend. The outlook is grim for many species, but hard lessons learned in the West Indies might lead to more enlightened policies elsewhere.

Another factor that has impacted the region is extreme weather patterns and storms, such as hurricanes, floods, droughts, and rising sea temperatures and levels. These various weather incidents combine and put pressure on vulnerable species throughout the region.

Principal Terms

Ecological Niche: The sum of environmental conditions necessary for the survival of a population of any species, including food, shelter, habitat, and all other essential resources

Ecomorph: Species of different phyletic origins (at most distantly related) with similar structural and behavioral adaptations to similar niches

Endemism: The condition of a species that has evolved in a given area, adapted to local conditions, and is found nowhere else in the world

Speciation: An increase in the number of species, usually resulting from descendants of a common ancestor adapting to different environmental conditions in different geographic areas

West Indies: A body of islands including the Greater Antilles (Cuba, Jamaica, Hispaniola, Puerto Rico), the Lesser Antilles (an island arc extending from east of the Virgin Islands to the north of Trinidad and Tobago), associated smaller island banks, the Bahamas, and sometimes the islands of the western Caribbean east of Nicaragua, but not the continental islands of Central and South America

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