DIVERSITY & ENDEMISM
The biodiversity of Mesoamerica represents the confluence of flora and fauna from two biogeographic regions, the Nearctic of North America and the Neotropical of South and Central America and the Caribbean. North and South America were once two separate landmasses, with independently evolved plant and animal species. Then, about 3 million years ago, sections of Central America rose above sea level, forming a land bridge between north and south. Species began to flow in both directions between the continents, and their interaction in this transition zone helped produce Mesoamerica's unique and diverse array of life forms.
Additionally, the highlands and mountain chains that run along the hotspot's main north-south axis have facilitated isolation and speciation throughout Mesoamerica. Because the mountains have often posed an impassable barrier, there are considerable differences in species composition between the Pacific and Caribbean coasts. On the other hand, the valleys and lowlands running parallel to the mountains have long served as natural corridors for animal and human migrations.
Mesoamerica has a total of about 17,000 species of vascular plants, nearly 3,000 of which are endemic (17 percent). In addition, 65 of 2,523 genera are endemic, 50 of which are represented by a single species. The number of species and genera endemic to this hotspot is lower than might be expected, because a large number of genera spill over into the neighboring Mexican states of Oaxaca, Veracruz and Tamaulipas.
The plants of Mesoamerica provide a window into the unique role of this region as a land bridge between the flora and fauna of North and South America. Many Nearctic and Neotropical plants reach their southerly and northerly range limits, respectively, in this hotspot. The highlands of Guatemala are the northernmost reaches for the páramo vegetation of the northern Andes, including the families, Umbelliferae and Compositae. The coniferous forests of Mexico, Guatemala, El Salvador, Honduras, and Nicaragua represent the southernmost extension of several genera of trees, including Pinus, Abies, Juniperus, Cupressus, and Taxus.
Commercially valuable timber species are found within the hotspot and, as in the case of big-leaf mahogany (Swietenia macrophylla
, VU), have historically driven the exploitation of the region's forest resources. Other valuable timber species include Pacific mahogany (Swietenia humilisi
, VU), extirpated from much of its natural range, Spanish cedar (Cedrela odorata
, VU), and rosewood (Dalbergia stevensonii
). The hotspot also contains more than 300 cacti species, of which about 60 percent are endemic, or nearly so, to the hotspot (and 85 percent of these are found exclusively within the Mexican portion of the hotspot).
Plant endemism is highest within Mesoamerica in the diverse topography of the region's mountains, especially the high mountains of Guatemala and southern Mexico. Three plant families are endemic to the hotspot, each represented by a single species: Haptanthaceae (Haptanthus hazlettii), Lacandoniaceae (Lacandonia schismatica), and Ticodendraceae (Ticodendron incognitum). Lacandonia is particularly unique among flowering plants for having "inside-out" flowers, i.e., the central androecium (stamens) surrounded by the gynoecium (separate pistils).
The forests of Mesoamerica are home to nearly 1,120 birds species, including more than 200 species restricted to the region. About 20 bird genera are endemic to the hotspot, and BirdLife International has identified 17 Endemic Bird Areas in Mexico and Central America, covering nearly the entire extent of the hotspot. The best known species from this region and conservation symbols for their cloud forest habitats are the resplendent quetzal (Pharomachrus mocinno), whose brilliant green and crimson plumage is the national emblem of Guatemala, and the horned guan (Oreophasis derbianus, EN), a large bird – sole representative of its genus – with a distinctive red horn protruding from the top of its head. Both of these endemic species are threatened by habitat destruction.
Of the more than 40 species of threatened birds found in this hotspot, endemics include the Honduran emerald (Amazilia luciae, CR), the Cozumel thrasher (Toxostoma guttatum, CR) and the Socorro mockingbird (Mimodes graysoni, CR). The forests of Mesoamerica, the third largest in any of the hotspots, also provide critical winter habitat and stop-over points for about 225 species of migratory birds. Three of the four major trans-regional migratory bird routes in the Western hemisphere converge here.
Mesoamerica holds roughly 440 species, and more than 65 (15 percent) of these are endemic. A number of these endemics are confined to offshore islands, including two threatened species on Cozumel: the Cozumel harvest mouse (Reithrodontomys spectabilis, EN) and Cozumel raccoon (Procyon pygmaeus, EN).
Some of the most visible symbols of mammal diversity in Mesoamerica are its monkeys, including the Central American spider monkey (Ateles geoffroyi) and Mexican black howler monkey (Alouatta pigra, EN), which produce impressive roars that can be heard for miles, and Central American squirrel monkey (Saimiri oerstedii, EN). Two other large mammals, the Baird's tapir (Tapirus bairdii, EN) and the jaguar (Panthera onca) are both important flagships for the regions forests.
However, much of the mammal endemism in Mesoamerica is attributable to the diversity of small mammals. Some 20 species of shrews and more than 180 species of rodents (including nearly 20 species of pocket gophers, and around 20 species of squirrels) are found in Mesoamerica; many of these are endemic. Three endemic species, Van Gelder's bat (Bauerus dubiaquercus), the Yucatán vesper rat (Otonyctomys hatti), and Bang's mountain squirrel (Syntheosciurus brochus), are all representatives of endemic genera.
Mesoamerica has very high reptile and amphibian diversity and endemism. The area is the most diverse hotspot for reptiles, with more than 690 species found here, and nearly 240 (35 percent) endemic. Many genera are endemic, as is one monotypic turtle family, the Dermatemydidae, represented by the Central American river turtle (Dermatemys mawii, EN) from the rivers of southern Mexico and adjacent Guatemala and Belize, and one of the most highly threatened freshwater turtles in the world. Another endemic reptile found in many of the same rivers is Morelet's crocodile (Crocodylus moreletii).
There are also many important nesting beaches for marine turtles, including Tortuguero, Costa Rica — one of the most important nesting beaches for green turtles (Chelonia mydas, EN) 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 and endemism also reach exceptional levels in Mesoamerica, with more than 550 species, over 350 of which are endemic. Over 20 percent of the 52 amphibian genera in the hotspot are endemic. Guatemala and the adjacent Mexican state of Chiapas are especially rich in salamanders, and are considered a center of origin and dispersal for tropical salamander species. In total, the hotspot has approximately 160 species of the order Caudata (the newts and salamanders), and some 120 are endemic; all endemics belong to the family Plethodontidae (lungless salamanders).
One of the most poignant symbols of conservation in Mesoamerica and worldwide is the golden toad (Bufo periglenes, EX). A beautiful, bright orange toad found only in Costa Rica's Monteverde Cloud Forest, the golden toad hasn't been seen since 1989, when it disappeared virtually overnight. The plight of the toad, which is presumed to be extinct, is an oft-cited example of the worldwide phenomenon of declining amphibian populations. In total, more than 230 species of the amphibians present in this hotspot (just less than half) are threatened with extinction, particularly the salamanders in the genus Bolitoglossa and the frogs in the speciose genus Eleutherodactylus.
Freshwater fishes are an important component of Mesoamerica's vertebrate diversity. The hotspot is home to more than 500 species, nearly 350 of which are endemic; there are also 25 endemic genera. More than 200 of the hotspot's fish species belong to two families: the cichlids (with 12 endemic genera) and the live-bearing Poeciliidae. Nearly a quarter of Mesoamerica’s fishes have distributions restricted to single bodies of water or small tributaries in larger watersheds.