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May
07
    
Posted (crates) in biology, Ecology, Evolution, nature on May-7-2012

    Central America is the site of contending crustal plates–notably the Cocos Plate in the Pacific Ocean which is being subducted beneath the Caribbean Plate right off the western coast of central america at a rate of 72-81 mm/yr.  It’s this area where the Central America Volcanic Arc exists which forms the volcanoes of Guatemala, El Salvador, Nicaragua, and Costa Rica.  To the north there is the North America Plate which is moving to the west at about 20 mm per year resultng in further seismic turmoil.  Then to the east the North American plates dives beneath the Caribbean plate as does the South American plate to the south.

     Once the link between North and South America was established there was a great influx of North American fauna into South America and vice versa to  a lesser extent.  The great marsupial fauna of South America died off mostly as did other less successful groups.  Some of the South American biota moved into North America.  Central America remains today one of the most biologically diverse areas in the world.

    Costa Rica and the rest of the isthmus has acted as a filter bridge in this great migratory process that really picked up steam only three million years ago when the connection was complete between North and South America.  The diverse topography of Costa Rica has resulted in refugia where species could still live after dying out in other areas.  This combined with the species from the north and from the south has resulted in a tremendous amount of biotic diversity in this small area.

    It is estimated that in this small country there are 500,000 to 1,000,000 species of plants and animals with most remaining unknown.  Insects by themselves make up about half of this diversity, whereas 850 species of birds can be found–about ten percent of all known species of birds.  North America has about half that number.  Others estimate about 160 species of amphibians, 220 species of reptiles and about 10% of all known butterflies.

   And all this in the second smallest Central American Nation (El Salvador is the smallest).  Only 119 km across at the narrowest point in the south and 280 km wide at its broadest point, it is quite easy to drive across the country in about five hours.  Solely in the tropical latitudes it still exhibits a broad range of distinct climate zones (12). 

The eastern Caribbean side is the wetest whereas the western pacific slopes are the driest.  Most areas have a rainy season, or “green season,”  (May-November) and a dry season (December-April) with the rainfall almost everywhere following a predictable schedule.  Usually the highland ridges are wet with the windward sides being the wettest.

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