Biological Diversity of Mexico:  Origins and Distribution.  T. P. Ramamoorthy, R. Bye, A. Lot, and J. Fa eds.  Oxford University Press, New York.  1993.

 

Our knowledge of biodiversity of our environment is incomplete.  Mass extinctions of taxa, particularly in the tropics, where biodiversity is the highest, are proceeding at a fast rate.

 

Although Mexico is the 14^th largest country in the world, it ranks third in the greatest biodiversity behind Brazil and Colombia.  No complete treatments of the fauna or flora exist for large parts of the country.

 

Large portions of Mexico that are species-rich (the tropical south) or centers of endemism (the morphotectonic province of the Trans-Mexican Volcanic Belt and the Sierra Madre del Sur) remain only partially explored.

 

The taxonomy of many Mexican biotic groups is obscure and poorly understood.

 

Although many things have been published on the Mexican biota, the publications are in many cases not available in either Mexico or abroad.

 

Mexico has approximately 30,000 species of plants.  More than 21,600 in about 2,500 genera are flowering plants.  More than 300 genera and 50-60% of the species are endemic to Mexico.

 

About 150 species of coniferous trees are widely distributed in the country.

 

There are more mammalian species (449) in Mexico than in Brazil.  More than twice as many are endemic to Mexico.

 

Many crop plants originated in Mexico.  There are 35 species of Phaseolus (beans) in Mexico; four major species of cultivated beans were domesticated there.  Gene flow between these and their wild progenitors has been documented.  Zea mays was domesticated there and spread to other areas of the Americas.  This plant was the mainstay of American civilizations.

 

The biological consequences of extinctions are only poorly understood.  Our understanding of the role of various species in ecosystems is only now emerging.  For many crop plants, disease-resisting progenitors may be of incalculable value as sources of genes.  For example, Zea diploperrenis, a relative of cultivated corn, contains genes resistant to at least 7 major diseases that affect corn.

 

More than 105 economically important plants were manipulated by people before the arrival of the Spanish.  More than 50% of the plants arose from natural communities.  Most weeds are indigenous.

 

The raw materials for genetic engineering are largely contained in the natural resources of the biological world.

 

Centers of endemism in Mexico.  Trans-Mexican Volcanic Belt and the Sierra Madre del Sur are two of the major centers of endemism in Mexico.  Other areas of endemism are scattered throughout the country.  Many are highly disjuncted.

 

Species richness:  Endemism in the grass family is especially important in the Chihuahuan-Coahuilan Plateaus and Ranges Morphotectonic Province in northern Mexico.

 

The regional diversity of Mexico is a product of the dynamics of the lithosphere.  The plates that have had a major influence are the North American, South American, Cocos, Farollan, and Caribbean.  Laurasian elements in the flora may be older than the Neotropical elements.  Mexico has been an active theater of speciation for taxa that have originated elsewhere.  The complex geological history of Mexico has been a major evolutionary force.  Mexico can be divided into 11 morphotectonic provinces.  One of these, the Sierra Madrea del Sur can be divided in turn into 14 subprovinces.  This geological complexity is complemented by the high biodiversity.

 

Conservation policies in Mexico are complicated by the complex patterns of endemism and the overall level of poverty, population, and growing unemployment.  This is complicated because many of the endemic taxa are widely scattered around the country.  The greatest threat to biodiversity in Mexico comes from loss of habitats.  Many of these problems are linked to grazing, erosion of soil, availability of water, and proper management of municipal and industrial wastes.  We’ll come back to some of these issues when we deal more directly with conservation biology.

 

 

I. Ferrusquía-Villagfranca.  Geology of Mexico:  A Synopsis. Chapter 1 in Biological Diversity of Mexico:  Origins and Distribution.  T. P. Ramamoorthy, R. Bye, A. Lot, and J. Fa eds.  Oxford University Press, New York.  1993.

 

In order to understand the biodiversity of Mexico, and the complex patterns of peoples and cultures, it is necessary to have some feeling for the geological origin of the country, the soils, and the climate.

 

Mexico can be divided into 11 morphotectonic provinces.  These are:  Baja California Peninsula, Northwestern Plains and Sierras, Sierra Madre Occidental, Chihuahua-Coahuila Plateaus and Ranges, Sierra Madre Oriental, Gulf Coast Plain, Central Plateau, Trans-Mexican Volcanic Belt, Sierra Madre del Sur, Sierra Madre de Chiapas, and the Yucatan Platform.

 

Two-thirds of Mexico is 800 m above sea level or higher.  The relief, dominated by mountains, is rugged.  The climate is highly varied.  In general, the portion north of the Trans-Mexican Volcanic Belt and the Yucatan Platform are quite dry.

 

The geological composition is varied as well:  Rock types range from sedimentary to volcanic, to intrusive, to metamorphic.  They vary greatly in composition.  Many folds and faults are distributed throughout the country.  Few countries have such a complex makeup.