Chapter 8. CASE 8: BIODIVERSITY HOTSPOTS: RAIN FORESTS AND CORAL REEFS

CASE 8: BIODIVERSITY HOTSPOTS: RAIN FORESTS AND CORAL REEFS

When we think about mass extinctions, the demise of the dinosaurs is often the first example to spring to mind. But many conservationists believe we are in the midst of a great mass extinction at this very moment. The International Union for the Conservation of Nature has estimated that 800 plant and animal species have died out in the last 500 years, and more than 16,000 are currently at risk of extinction.

The cause of this mass die-off isn’t an asteroid impact or a cataclysmic volcanic event. Instead, human activity is dramatically altering the planet and its biological diversity.

Despite our role in the extinctions, it’s clearly not possible to save every single species threatened with extinction. Conservationists must make difficult choices, prioritizing which species to protect. To get the most bang for every conservation buck, ecologists have identified 25 priority areas, or biodiversity hotspots.

These hotspots are areas with disproportionately large concentrations of native species. Scientists estimate that as many as 44% of all vascular plants and 35% of vertebrate species, for example, are confined to these 25 hotspots. Those figures are impressive, considering that the identified hotspots make up just 1.4% of Earth’s land surfaces.

The islands of the Caribbean—the West Indies— constitute one such biodiversity hotspot. The Caribbean Sea contains more than 7000 islands rich in biological diversity, including an estimated 6550 native plant species. All the Caribbean islands are flush with flora and fauna, but one island in particular epitomizes the concept of a biodiversity hotspot. Hispaniola—the second largest of the Caribbean islands—was the site of the first New World colonies, founded by Columbus. Today, Hispaniola is shared by two countries, Haiti to the west and the Dominican Republic to the east.

Hispaniola is only about the size of Ireland, yet it contains a striking assortment of habitats including desert, savanna, rain forests, dry forests, pine forests, coastal estuaries, and interior mountains. With such a rich abundance of habitats, Hispaniola is, in some ways, a microcosm of the planet’s many ecosystems. And like the Earth’s other natural places, Hispaniola faces many of the same challenges.

Of all the habitats on Hispaniola, the forests have the greatest variety of plants, animals, and other organisms. Ferns, orchids, and bromeliads—spiky relatives of the -pineapple—grow in the treetops far above the forest floor. These plants, known as epiphytes, absorb water from dew, rainwater, and even the air. Their roots never reach the soil.

The forest is alive with activity. Ants march silently. Crickets and cicadas buzz and whine in the treetops. Vertebrate vocalists such as frogs and birds fill the air with chirps and whistles, making themselves known both to potential mates and rivals. Bats swoop through the darkened skies, using ultrasonic calls to locate insect prey. About 30,000 species of multicellular organisms are found on Hispaniola, and a third of those are endemic—they are found nowhere else in the world. One example is the Hispaniolan solenodon, a long-nosed mammal that resembles an overgrown shrew and secretes toxic saliva. Listed as endangered, the solenodon has flirted with extinction for decades.

How did all these species come to live on the island? Over tens of millions of years, organisms traveled to Hispaniola by air and by sea. Geographically separated from their ancestors on the mainland, many of these organisms evolved to become distinct species. As they adapted to fill vacant niches on the island, animals such as Anolis lizards, frogs, and crickets evolved an impressive diversity of forms.

In some cases, scientists have been able to explore Hispaniola’s evolutionary history directly. They have found remains of insects and other species entombed in fossilized tree resin, or amber, 30–23 million years ago. Many of these preserved specimens resemble species still living on Hispaniola. Others are unlike any creatures found on the island today.

The stunning diversity of Hispaniola doesn’t just exist on land. Conservationists consider the warm, shallow reefs of the Caribbean one of the world’s marine biodiversity hotspots. Coral reefs in general are among the world’s most biologically diverse ecosystems. Species from all recognized phyla of animals are found on reefs.

Around the world, reefs support hundreds of thousands of species, including snails, corals, lobsters, and fish. Many, but not all, of these creatures spend their entire life in this habitat. Reefs also act as vital nursery grounds for animals that live in other parts of the ocean, from sea turtles to sharks. Reef biodiversity is critical to maintaining fisheries that provide food and income for millions of people.

Hispaniola’s rain forests and reefs—and indeed all the biodiversity hotspots identified by conservationists—aren’t just notable for their biological richness. They have also been given priority status because they are facing serious threats.

Reefs around the world are being damaged by human activities. Overfishing and pollution take their toll on reef ecosystems. Climate change is increasing seawater temperature and altering ocean chemistry. Those changes are threatening the coral organisms that form the backbone of the reefs.

Ecosystems on land, too, face significant challenges. The Caribbean islands retain only about 11% of their original primary vegetation. Humans have cleared great swaths of land for agriculture and chopped trees to use as fuel. Humans have also introduced non-native, or invasive, species to the islands, both intentionally and accidentally. On Hispaniola, Europeans introduced the Javanese mongoose to control rats in sugarcane fields. The mongoose has devastated local populations of reptiles, amphibians, and birds.

If Hispaniola serves as a microcosm of the planet’s ecosystems, it also serves as a cautionary tale. Two divergent paths have emerged on the single island. Haiti has historically suffered greater poverty than the Dominican Republic, and has much greater population density. Those factors put more pressure on the environment in Haiti, and have contributed to much greater deforestation on the western half of the island.

The case of Hispaniola illustrates the complex challenges facing conservationists. Solutions to environmental challenges must take into consideration the effects of poverty, culture, and other social pressures. Balancing the needs of humans with the needs of natural ecosystems is no easy task. But as a relatively small island, Hispaniola may in fact be in a better position to turn things around than larger, more politically complex countries. The world’s biodiversity hotspots might yet lead the charge in finding ways for humans and the rest of the planet’s inhabitants to peacefully coexist.