MEXICAN SPIDERS

INTRODUCTION

Mexico is considered one of the megadiverse countries, occupying the third place world-wide. The reasons for this huge biological variety are, among others, its geographic situation within two biogeographic regions, the Neoartic and the Neotropic and the confluence of both; as well as its huge physiogeographic, climatic and ecological heterogeneity. Its great richness can be confirmed observing the variety of organisms living here (Llorente et al. 1996).

When talking about the variety of Mexico, the Mexican vertebrates are emphasised, but the invertebrates are nearly not considered, as in the case of the arthropods. The Phylum Arthropoda constitutes 85% of the entire global fauna and represents 65% of all the known variety of species, estimated at about 1.7 million species; for Mexico an estimation does not exist, as the arthropods have been studied little and they are even species which have not been studied apart from their taxonomic classification (Llorente et al. 1996).

Within this Phylum, subordinated to the five big insect groups (Coleoptera, Hymenoptera, Lepidoptera, Diptera und Hemiptera), the class of the arachnids, the spiders, make up one of the most diverse invertebrate group world-wide, occupying the seventh place (Coddington and Levi, 1991 and Hoffman, 1995). In the whole world, about 150 families, 3,000 genus and 34,000 species are known and it is estimated that the number of species which still have to be described amounts to 170,000 (Coddington and Levi, 1991). In Mexico, 62 families, 413 genus and 2,506 species have been found (Jiménez, 1996); it is estimated that these estimates are considerably lower than the actual numbers. In this country, a lot of information has to be gathered and a lot of reasearch has still to be done regarding the arachnologic fauna (Coddington and Levi, 1991; Hoffman, 1995 and Jiménez, 1996).

These invertebrates owe their diversity to their high adaptation capacity to the environment, as they can live not only in the highest mountains but also in the deepest caves, the dry and hot deserts, very cold zones, dunes, zones influenced by the tides and some species even have invaded the sweet and salt-water environment. In summary, it can be affirmed that they can be found everywhere, except in the air or the open sea (Foelix, 1996). Furthermore, in places where any kind of terrestrial life exists, it is possible to find spiders related to it (Turnbull, 1973), because in spite of the fact that spiders are carnivores, it does not endanger their survival, as they can subsist on almost every kind of arthropod and some vertebrates (fish, frogs and small birds), which is a very good reason to consider them as indispensable to almost every ecosystem (Rod and Ken, 1994).

Brief description of the realised studies of Mexican spiders

The Mexican spiders have been studied a lot, but not totally, in the sense that there are collections of thousands of specimen, but they do not represent all the arachnologic fauna of the country. Furthermore, regrettably all the most complete collections of Mexican spiders are located in the United States of Northamerica, England and France (Jiménez, 1996). Mexico disposes only of small collections in some national institutions in the states of Baja California Sur, Chiapas, Veracruz, Nuevo León and Distrito Federal (Jiménez, 1996). For this reason, the purpose of this page is to make known this richness of our country.

Cited literature

Coddington, J.A. and H.W. Levi, 1991. Sytematics and evolution of spiders (Araneae).
Annu. Reav. Ecol. Syst., 22:565-92

Foelix, R.F., 1996. Biology of spiders. Second edition. Oxford University Press. New York. 330 pages.

Hoffman, A., 1995. El Maravilloso Mundo de los Arácnidos. La ciencia desde México. No. 116. Mexico 1997, 166 pages.

Jiménez, María-Luisa, 1996. Araneae, en Biodiversidad, Taxonomía y Biogeografía de Artrópodos de México, Chapter 11, Instituto de Biología, UNAM, Mexico, Pages 83-101.

Llorente, J.B., González, E.S., García, A.N.A. and Codero, C., 1996. Breve Panorama de la Taxonomía de Artrópodos en México en Biodiversidad, Taxonomía y Biogeografía de Artrópodos de México, Chapter I, Instituto de Biología, UNAM, Mexico, Pages 2-14.

Rod and Ken Preston Mafham, 1994. "Spiders of the world". Facts On File. An Infobase Holdings. Hong Kong, 187 Pages.

Tumbull, A.L., 1973. Ecology of true spiders (Araneomorphae). Annual Review of Entomology, 18:305-348.