Biodiversity. This is a term much in vogue these days, but what, precisely, does it mean? In its most common usage, biodiversity is the number of different species found in a specific region. The organisms can encompass all of life – from bacterium to vertebrates and everything in between – or narrowly focus in on one taxonomic group reptiles for instance. The region may be as large as the earth itself or, more often, profile a specific area.
Here we will apply a biodiversity magnifying lens to our Sky Island region – one which stretches between the northern terminus of the Sierra Madre Occidental in Mexico and the
White Mountains of Arizona. This region is further bookended by the Chihuahuan Desert to the east and the Sonoran Desert to the west.
Within this large region loom approximately 43 tall, isolated, and wooded mountains that harbor Madrean evergreen or oak-pine-juniper woodland. These “islands” of forested habitat are isolated from each other by intervening “seas” of desert and grassland, making a rich, unique and biodiverse archipelago that links the tropical and the temperate realms. Add two rainy seasons – winter and the monsoon – as well as great topographical relief, and our subtropical latitudes and the result is an area rich in a myriad of species.
Latitudinally speaking, we share our 32-degree zone with such far-flung places as northern India, Saudi Arabia, North Africa, southern South Africa, and Sydney, Australia. Each of these places also contain an extraordinary wealth of species. 32 degrees may be the freezing point in terms of temperatures, but for biodiversity it is definitely hot!
The U.S. portion of the Sky Islands region contains about 2,000 plant species. They are an eclectic mix of tropical, temperate, and desert species. Here, Douglas firs meet western coral beans and saguaros. Lichen and fungi diversity is also high. These high levels
of floral and fungal biodiversity in turn support a truly astounding number of wildlife species – many found nowhere else in the U.S.
The number of invertebrate species found in the Sky Islands truly boggles the mind with new species no doubt still awaiting discovery. We have the most bee species on the planet – likely over a 1,000 species! Our dual precipitation pattern combined with its associated flowering seasons may largely account for this.
Ants, as you may well have noticed, are legion here. The Chiricahua Mountains alone contain about 187 species, representing nearly 25% of the combined ant biodiversity of the U.S. and Canada. Here we have slave-making ants, harvester ants, leaf-cutter ants, army ants and so much more.
Add to the bees and ants high levels of biodiversity in many other invertebrate groups – spiders, centipedes, scorpions, beetles…. We are literally crawling in such species.
While fish (around 33 species for the state) and amphibian (18 species locally) diversities are certainly not high in our area, each taxonomic group contains endemic species – ones found only in our region. Take the Sonoran chub, which in the U.S. lives only within the narrow confines of Sycamore Canyon in the Atascosa Mountains. This same area provides the only U.S. habitat for Tarahumara frogs. Thus, even where we are depauperate, we are also rich.
Reptile numbers are impressive here. Our region has the most reptiles (80), the lizards (33), the most snakes (42), and the most venomous snakes (10) of any comparable region in the
Our reptiles run the gamut from the terrestrial desert box turtle to the arboreal and venomous brown vine snake to the highly nocturnal western banded gecko. Every habitat here has its entourage of reptiles, highly adapted to its local environments.
Our bird biodiversity is renowned and in part drives our thriving ecotourism economy. Where else in the U.S. can you find such an eclectic and electric mix of avian species? In the same day at Patagonia Lake I have, for example, seen green kingfisher, elegant trogon, hooded merganser, and white-crowned sparrow. These are geographically far-flung species that all come together here in the Sky Islands at certain times of the year.
We finish with mammals, as well as with a cautionary note. As you may guess by now – yes, we have the most mammal species in the U.S. Approximately 108 species call our Sky Islands home. 29 bat species have been recorded in Arizona in addition to 46 rodent species, the highest numbers worldwide for these two mammal orders. We have the most feline species as well – mountain lion, bobcat, ocelot, and jaguar.
But we have already lost significant parts of our biodiversity. Call it ecological erosion if you like, for we are slowly, inexorably unraveling. We have already lost such incredible species or subspecies as Mexican grizzly bear, Mexican wolf, black-footed ferret,
Colorado pike minnow, and thick-billed parrot. No less than the renowned biologist E.O. Wilson has called our area one of the “best places in the biosphere”. Given the current onslaught of mining, continued overgrazing, housing developments, and water abuse how much longer will we be able to lay claim to the title of most biodiverse area in the U.S.?
Vincent Pinto and his wife, Claudia, run RAVENS-WAY WILD JOURNEYS, their Nature Adventure & Conservation organization devoted to protecting the unique biodiversity of the Sky Islands region. Visit: www.ravensnatureschool.org