Location and General Description
Caribbean islands are often portrayed as lush tropical paradises, but Aruba, Bonaire and Curaçao are better described as desert scrub. The three islands, known locally as the ABC’s, are located 40-80 km off the coast of Venezuela just 12 N of the equator. Due to their leeward location, the islands receive only 350-550 mm of rain per year (half of which falls in Oct-Dec) and have very low humidity (Debrot and deFreitas 1993). Constant tradewinds and warm year-round temperatures contribute to evapotranspiration and water loss from the islands. All three islands are a mix of limestone and quartz diorite. Curaçao is the largest of the three islands at 65 km long and up to 11 km wide. From Mount Christoffel, the highest point of Curaçao (375 m), you can see Bonaire 40 km to the east and Aruba, 75 km to the west.
Most of the natural areas on Aruba, Curaçao and Bonaire are sparsely vegetated with cactus scrub. Columnar cacti are common, and can grow up to six meters tall. The dominant cacti species are: Stenocereus griseus, Subpilocereus repandus, and Pilosocereus lanuginosus (Petit and Pors 1996). These species flower and fruit profusely during the dry season, and provide critical resources for a variety of bats, birds and other animals. Also characteristic of the area is the wind-swept divi divi tree, the branches of which grow at a 90 degree angle to the trunk; Croton flavens and Cordia cylindrostachya are also common (Stoffers 1956). The cactus scrub gives way to a cactus-woodland mix on the western sides of the island where there is slightly higher rainfall. Common species in this area include: Prosopis juliflora, Acacia tortuosa, Haematoxyln brasiletto, Capparis indica, Celtis iguanaea, Malphigia punicifolia, Bourreria succulenta and Casearia tremula. This woodland is only 3-4 meters tall, and the thorny trees are interspersed with cacti (Cephalocereus lanuginosus, Melocactus sp., Opuntia, wentiana; Debrot and deFreitas 1993). The Acacia and Opuntia are most common in grazed areas of the island.
There are very few endemic plant species on the islands: only 1 on Bonaire, 5 on Curaçao, and 2 on Aruba. Nevertheless, the floral community has a distinct character. The xerophytic community of the ABC’s may not have the diversity of a tropical rainforest, but it does boast a unique fauna, with its own radiation’s. The most important components of this community are the cacti- they dominate the landscape and provide critical food resources for nectarivores and frugivores. Bats in particular rely upon the cacti for food resources, and the cacti in turn rely upon the bats for pollination services and for some seed dispersal. There are 7 species of bats on Curaçao, the most abundant being Glossophaga longirostris elongata, with a population of almost 2000 individuals. The other six species include L. curasoe, a subspecies of Leaf-chinned bats (Mormoops megalophylla intermedia), a species of Funnel-eared bats (Natalis tumidirostris), of Little Brown bats (Myotis nesopolus), of Leaf-lipped bats (Pteronotus davyi), Bulldog bats (Noctilio leporinus) are all rare, and Petit (1996) has argues that they should all be classified as endangered on Curaçao. The loss of cactus-scrub is an important factor in the decline of these bat species.
Lizards are also an abundant and diverse component of the cactus scrub community. Iguanas are especially abundant, despite the fact that they are often hunted and used in soups and stews. There are endemic lizards on all three islands, as well as species with more widespread distributions. Aruba also has two snakes: the cascabel (Crotalus thurissus unicolor), an endangered subspecies of rattlesnake, which does not use its rattle; and the Aruba cat-eyed snake (Leptodira bakeri). There are approximately 200 resident bird species on the three islands, many of which are rare. Species of particular concern include the endangered Bonaire Lora (Amazonia barbadensis) and Aruban burrowing owl (Athene cunicularia arubensis), the Aruban parakeet (Aratinga pertinax arubensis), Bonaire Green parrot, and flamingos. The flamingo breeding grounds on Bonaire are protected by a special sanctuary. The islands are also a favored stop-over and wintering ground for North American migrants.
There are still large tracts of cactus scrub on Aruba, Bonaire and Curaçao. Tourism is now the primary industry, and the local governments are working hard to preserve the natural heritage of the islands. All three islands have reserves dedicated to preserving the unique cactus scrub communities and the native fauna. Most notably, the Washington Slagbaai National Park covers almost one third of Bonaire, and the Arikok National Park covers 17% of Aruba, also on Aruba, a Coastal Protection Zone extending 1 km inland has been designated to preserve the entire northern and eastern sides of the island. On Aruba, the serious decline of at least 11 of the 48 native tree species has led to efforts to restore natural areas through out-planting and goat control. Private organizations such as the Save the Lora Association are also working to protect endangered species on the islands.
Types and Severity of Threats
Despite recent conservation initiatives, destruction of native vegetation through unregulated real estate development is a continuing problem. The columnar cacti are considered "fever-giving weeds" and are deliberately removed from all new developments (Petit and Pors 1996). This loss of cacti reduces the nectarivore carrying capacity of the island and is likely to result in a permanent decrease in bat populations. The bats are also negatively affected by human disturbance of caves and other roost sites (Petit and Pors 1996). Habitat changes and the loss of native vegetation have also led to a shift in the butterfly fauna, and possibly a shift in other groups as well (Debrot et al. 1999). Feral goats and sheep abound on the islands, and graze heavily on the native vegetation. Studies have shown that the presence of introduced ungulates can shift the balance of species found on the islands; areas rife with ungulates tend to be dominated by grazer-resistant species such as Opuntia, while other areas have a higher proportion of grazer-sensitive species (Debrot and deFreitas).
Justification of Ecoregion Delineation
The cactus scrub classification of the ABC islands was determined by consolidation of the following terrestrial life zones according to CCA Preliminary Data Atlas (1980) for each individual island: cactus scrub, dry woodlands, littoral vegetation, and secondary vegetation. Because of the proximity of these island and similar flora and fauna these three were lumped together and habitat was distinguished only between cactus scrub and mangroves.
Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: Bonaire, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.
Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: Curaçao, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.
Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: Aruba, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.
Debrot, A. O. and J. A. deFreitas. 1993. A comparison of ungrazed and livestock-grazed rock vegetations in Curaçao. Biotropica 25(3): 270-280.
Debrot, A. O. et al. 1999. The butterfly fauna of Curaçao, West Indies: 1996 status and long-term species turnover. Caribbean Journal of Science 35: 184-194.
Petit, S. 1996. The status of bats on Curaçao. Biological Conservation 77(1): 27-31.
Petit, S. and L. Pors. 1996. Survey of columnar cacti and carrying capacity for nectar-feeding bats on Curaçao. Conservation Biology 10(3): 769-775.
Stoffers, A.L. 1956. Studies on the flora of Curaçao and other Caribbean islands. Vol. 1: The vegetation of the Netherlands Antilles. Utrecht: Kemink & Zn.
Prepared by: Winnie Roberts
Reviewed by: In process