Mesoamerica

Russell A. Mittermeier¹, Jan Schipper⁹⁷, Gerrit Davidse²⁶, Patricia Koleff²⁴, Jorge Soberón²⁴, Manuel Ramírez⁹⁹, Barbara Goettsch⁹⁸ and Cristina G. Mittermeier¹

The Mesoamerica Hotspot includes all tropical and subtropical natural plant formations from eastern Panama west and north through Costa Rica, Nicaragua, Honduras, El Salvador, Guatemala, and Belize, as well as in portions of southern and coastal Mexico. Within Mexico, the hotspot extends as far north as northern Sinaloa (Río Fuerte) on the Pacific Coast and as far as the middle of the Sierra Madre Oriental (west of Tampico) on the coast of the Gulf of Mexico. It includes all of the tropical and subtropical moist, seasonal, and dry forest formations, as well as small portions of paramo montane grasslands, mangroves, semidesert and thornscrub, and is usually considered to be part of the northern Neotropical region. However, the hotspot does not encompass the true desert and desert scrub formations of the Baja California Peninsula, Sonora, Chihuahua, and Coahuila in northwestern and central Mexico, or the subtropical pine-oak forests in the higher elevations of the Sierra Madre Occidental and Oriental mountains (here included in the Madrean Pine-Oak Woodlands Hotspot).

The Mesoamerica Hotspot covers all of political Central America, with the exception of easternmost Panama (which is included in the Tumbes-Chocó-Magdalena Hotspot). Within Mexico, the region includes the entire area of the Mexican states of Chiapas, Yucatán, Quintana Roo, Tabasco, Campeche, Veracruz, and portions of the states of Oaxaca, Guerrero, Puebla, México, Michoacán, Morelos, Querétaro, Jalisco, Nayarit, Colima, Guanajuato, San Luis Potosí, Zacatecas, Sinaloa, Durango, Sonora, Chihuahua, and Tamaulipas. Also included in this hotspot are numerous nearshore and offshore islands in both the Caribbean Sea and Pacific Ocean, which are important biologically due to the presence of endemic species and as nesting areas for seabirds. These islands include the Revillagigedos (2 965 km²; Mexico), Tres Marías Islands (400 km²; Mexico), Cozumel (539 km²; Mexico), Islas de la Bahía (373 km²; Honduras), Cocos (24 km²; Costa Rica), Providencia (17 km²; Colombia), San Andrés (44 km²; Colombia), and Coiba (50 km²; Panama), as well as Clipperton Island (7 km²; France). In all, this hotspot covers some 1 130 019 km².

Although the Mesoamerica Hotspot does not have quite the breadth or the great heights of the Tropical Andes Hotspot, it does have a series of impressive highlands and mountain chains stretching along its main axis. These include ancient, worn-down crystalline uplands; younger, upthrust, metamorphic mountain ranges; and strings of frequently active volcanoes. Peaks in several of the latter two types of highlands reach and sometimes exceed 4 000 m in total height —the highest being the Pico de Orizaba or Citlaltépetl located in the State of Veracruz, a part of the neovolcanic chain and Mexico's highest peak at 5 610 m.

The main axes of these mountains, locally called “sierras” or “cordilleras,” have always acted as barriers to species dispersal, resulting in considerable biological differences between the Pacific and Caribbean lowlands to either side, and form the continental divide throughout much of Central America. Additionally, many of the mountain chains and volcanoes are isolated from each other, the result of which is high beta-diversity between landscapes. The valleys and lowlands running parallel to the mountains, on the other hand, have long served as natural corridors for animal and human migrations and dispersal. The species which today inhabit the Mesoamerica Hotspot are relicts of the convergence between the flora and fauna of North and South America in the late Pliocene (approximately 3 million years ago), when the land bridge between these two continents was finally complete at what is today the Isthmus of Panama—giving rise to one of the greatest species interchanges in the history of the Americas. The result is a complex mosaic of plant and animal communities that have converged, adapted and, in many cases, evolved into new species. Thus, the unique geological and evolutionary history of Mesoamerica has resulted in some of the highest levels of diversity and endemism on Earth.

In terms of plants, the latest estimate for total diversity of this hotspot is some 17 000 species with 2 941 endemics. This estimate is based upon what is known from the Flora Mesoamericana Project, which covers the seven Central American countries as well as the five southernmost Mexican states of Campeche, Chiapas, Tabasco, Quintana Roo, and Yucatán. In addition, of 2 523 genera, 65 are endemic (of which 50 are represented by single species), a number that is perhaps lower than expected, but which probably reflects a relatively recent (on the geological time scale) mass movement of plants from both the north and the south into the isthmus. Both the number of species and genera present and endemic would be considerably higher for the Mesoamerica Hotspot because a significant number of genera (such as Plocosperma) just spill over into Oaxaca, Veracruz, and Tamaulipas. Finally, there are three endemic families, each with a single species: Haptanthaceae (Haptanthus hazlettii), Lacandoniaceae (Lacandonia schismatica), and Ticodendraceae (Ticodendron incognitum). Lacandonia, which has a close affinity with the family Triuridaceae, is particularly unique among flowering plants for having “inside-out” flowers, i.e., the central androecium (stamens) surrounded by the gynoecium (separate pistils). Within the Mesoamerica Hotspot there are approximately 312 cacti species, of which 60% are endemic, or nearly so, to the hotspot (and, of these, 85% are found exclusively within the Mexican portion of the hotspot) (B. Goettsch, unpubl.).

Vertebrate diversity is even more impressive. There are 440 species of mammals recorded within the hotspot, of which 66 are endemic. Three endemic species, Van Gelder's bat (Bauerus dubiaquercus), the Yucatán vesper rat (Otonyctomys hatti), and Bangs' mountain squirrel (Syntheosciurus brochus), are all representatives of endemic genera. A number of endemics are confined to offshore islands in the hotspot, including three species on Cozumel (Reithrodontomys spectabilis, EN;Procyon pygmaeus, EN; and Nasua nelsoni, EN). The primates of the Mesoamerican forests, particularly the spider monkeys (Ateles spp.), the howler monkeys (Alouatta spp.), and the squirrel monkeys (Saimiri spp.), are often among the most conspicuous elements of the local fauna, play important ecological roles as seed dispersers, and have great value as ecotourism attractions. The two largest Neotropical land mammals, Baird's tapir (Tapirus bairdii, EN) and the jaguar (Panthera onca), are rarely seen in the wild, but are among the most well-known flagship species for Mesoamerica's tropical forests.

In terms of bird diversity, there are 1 124 species known to occur regularly in the hotspot, and of these, 213 are endemic. This region is also a top priority for BirdLife International, which recognizes no less than 17 Endemic Bird Areas (EBAs) within this hotspot (Stattersfield et al. 1998) covering almost its entire extent. Among the bird species endemic to this hotspot, perhaps none is more impressive than the resplendent quetzal (Pharomachrus mocinno), the most important flagship for conservation of Mesoamerica's precious cloud forest, a habitat upon which it depends for survival and which also retains the headwaters of critical watersheds for much of the region. Less well known, but at least as spectacular, is the horned guan (Oreophasis derbianus, EN), a monotypic genus endemic to this hotspot and found only in high-altitude cloud forests in southern Mexico and Guatemala. Besides the guan, a further 19 genera are endemic. In addition to the endemics, this region is also a critical trans-regional “flyway” for at least 225 migratory species, as three of the hemisphere's four migratory bird routes converge in Mesoamerica.

Reptile diversity is again extremely high, with a total of 686 species recorded from the hotspot, of which fully 239 are endemic. Included among these are an endemic family, the Dermatemydiidae, with a single species, the Central American river turtle (Dermatemys mawii), and 10 endemic genera, seven of which are represented by single species (for example, Coloptychon rhombifer, Scolecophis atrocinctus, and Exiliboa placata). Along with the Dermatemys, another important reptile flagship is Morelet's crocodile (Crocodylus moreletii), also endemic to the hotspot and occupying much the same range in rivers of southern Mexico and adjacent parts of Guatemala and Belize. The hotspot also hosts many important nesting beaches for marine turtles, including Tortuguero, Costa Rica —one of the most important nesting beaches for green turtles (Chelonia mydas) in the Western Hemisphere. Other beaches on both the Caribbean and Pacific coasts also provide important nesting areas for hawksbill (Eretmochelys imbricata, CR), olive ridley (Lepidochelys olivacea, EN), and leatherback (Dermochelys coriacea, CR) sea turtles.

Amphibian diversity is comparably impressive, with a total of 580 species, 353 of which are endemic. Furthermore, 14 of the 60 amphibian genera found in the Mesoamerica Hotspot are also endemic. Guatemala and the adjacent Mexican State of Chiapas are particularly rich in salamanders, and are considered a center of origin and dispersal for tropical salamander species. In total, the hotspot has 164 species of the order Caudata (the newts and salamanders), and 121 are endemic; all endemics belong to the family Plethodontidae (lungless salamanders), for which a total of 156 species occur. Among the amphibians endemic to this region are several important flagship species, including the golden toad (Bufo periglenes) —an Extinct species that serves as a flagship for the worldwide decline in amphibian populations. Additionally, the hotspot is home to the golden harlequin frog (Atelopus zeteki, CR) of Panama, and a number of magnificently colored members of the poison dart frog family, Dendrobatidae.

Freshwater fishes form a striking component of the vertebrate diversity of this hotspot, with a total of 509 species, of which 340 are endemic. In addition, 25 genera are endemic, including several genera of livebearing fishes in the family Poeciliidae and 12 endemic genera of cichlid fishes. With more than 200 species between them, these two families are numerically the most significant elements of the fish fauna. Both families have undergone striking radiations inside the hotspot associated with a complex history of hydrographic changes. Nearly a quarter of the region's fishes have distributions restricted to single bodies of water or to small tributaries in larger watersheds.

Unfortunately, Mesoamerica exhibits some of the highest deforestation rates in the world, and a large part of Mesoamerica's Western Pacific lowland forests was cleared prior to the twentieth century for export crops and subsistence agriculture. Deforestation during the past 100 years has been most severe in the remaining Caribbean lowland forests, which are converted for banana production (the Banana Republic), and at higher elevations on both slopes for coffee production —predominantly export crops. In many cases, abandoned plantations make way for cattle production, a boom and bust industry throughout Central America. In areas of steep terrain, erosion and eventually landslides add to the impact of large-scale agriculture —with severe effects to both the terrestrial and freshwater environment, as well as human health.

As a result of all these impacts on the forests and other ecosystems of Mesoamerica, a major portion of the region's natural vegetation has already been lost, such that estimates for remaining natural vegetation in the Mesoamerica Hotspot range from 31.5% to 47%. For example, a detailed analysis for Costa Rica estimates the remaining forest cover of the country at 40.29% (CCT/CIEDES 1998). However, these figures include secondary forest formations and plantations of many different kinds, and greatly overestimate the remaining natural vegetation types. The percentages remaining in primary forest in Nicaragua, Honduras, Guatemala, Panama, and Belize are likely similar to those for Costa Rica. Those for Neotropical Mexico are probably somewhat lower, and for El Salvador likely much greater. Consequently, we estimate that roughly 20% of the original vegetation remains intact in this hotspot.

Currently, a total of 12.6% of the Mesoamerica Hotspot is included in protected areas (nearly 11% in protected areas in IUCN categories I to VI), although this figure is less than half when one considers only those in categories I to IV (5.7%). In terms of the percentage of national land area protected, Belize and Costa Rica top the list with 36.6% and 31% of their land area covered by protected areas in categories I to VI, respectively. Although the Mexican portion of the hotspot accounts for the largest relative area of land under protection (41 835 km²), this represents only 6.7% of the total 625 700 km² of the area of the hotspot in Mexico.

Conservation action to counter the ongoing threats to the Mesoamerica Hotspot concentrates on the creation and maintenance of the Mesoamerican Biological Corridor, as well as numerous other initiatives to integrate sustainable development with biodiversity conservation. Adopted by a host of donors, the region's governments, and four major international conservation groups —Conservation International, the World Wildlife Fund, The Nature Conservancy, and the Wildlife Conservation Society— during the 1980s, the Mesoamerican Biological Corridor has three objectives: to maintain the integrity of the protected areas that already exist in the Mesoamerica Hotspot; to determine where new protected areas need to be created in order to extend the corridor concept; and to connect these new and existing protected areas through the establishment of high conservation value forestry plantations and agroforestry systems that run between the corridor's existing parks, refuges, and biosphere reserves. This large-scale corridor strategy has gained wide support because it presents a simple, yet elegant structure on which to promote a wide range of conservation activities, such as biodiversity protection, buffer zone management, regional planning, and sustainable private enterprises based on regional development goals. This region is particularly important strategically for food security, since it is home to wild relatives of important crops such as maize, cacao, beans, and others.

A regional perspective such as the Mesoamerican Biological Corridor, among others, offers a much broader perspective concerning the natural range of variability seldom captured by national policy and within political borders. Planning should seek to combine local policy with the specific objectives of habitat connectivity for area-sensitive species, such as the jaguar; habitat-specialists, such as the resplendent quetzal; and narrow-ranging species, such as some Atelopus toad species. Equally important is the representation of the full range of the wide variety of ecosystems within protected areas. There is great potential to develop a regional network of transboundary protected areas, such as exists between Costa Rica and Panama (La Amistad International Park), a concept which is emerging elsewhere as well. The Critical Ecosystem Partnership Fund (CEPF) is facilitating a regional approach to promote conservation by supporting bi- and tri-national initiatives that rely on cooperation of governments and NGOs. The fact that there are eight countries in this hotspot, each with disparate political agendas and motivations, makes this a great challenge.

The Mesoamerica Hotspot also has within it a globally recognized model for the value of ecotourism as a foreign exchange earner and as an alternative to harmful extractive industries. For a variety of reasons, Costa Rica recognized early on the great potential for ecotourism and structured itself to take advantage of this source of income. As a result, Costa Rica earned $1.25 billion in tourism-related industries in 2000, and it is estimated that 70.7% of tourists visit natural protected areas —an enormous figure for a small country with a population of only 3.9 million people. On the other hand, there remains a very delicate balance between tourism potential and agriculture-based revenue generation.

In conclusion, although the problems in this region are many and the commitment to conservation varies from country to country, there exists in Mesoamerica a variety of mechanisms for regional-level government dialogue on the environment which are far better than in many other hotspots that spread over several sovereign nations. Other positive indicators include the shared vision of the Mesoamerican Biological Corridor; the high percentages of national territory already in parks and reserves in four of the eight nations (Costa Rica, Guatemala, Panama, Belize); the strong and growing local capacity that exists within the region; the proven value of alternatives like ecotourism and non-timber forest products; the development of several national-level institutions for biodiversity research and conservation; the promotion of sustainable use initiatives; and the continuing interest and involvement of a variety of donor agencies and international conservation organizations.

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