by David B Richman, USA
I sifted through the samples from the Pawnee National Grassland with mounting amazement. I never thought a grassland could contain such a diversity of spiders. The samples had been sent to me for identification by researchers at Colorado State University. I was their spider "expert" and now I found myself struggling with a much larger variety than I had bargained for. The ground spiders in the family Gnaphosidae were especially diverse. This diversity was not isolated, however. Other spider samples sent to me by researchers at the University of New Mexico from various places around the state also showed a mind-boggling variety of spiders! In at least some cases the spiders were undescribed or represented new state records. These areas were all in the temperate part of North America, not in the Amazonian rain forest, and it was obvious that at least some groups are numerous in species even in the Temperate Zone.
El Yunqe, Puerto Rico, rain forest
These days the word 'biodiversity" seems to be everywhere in the scientific literature of biology. It is a common buzzword among conservationists and a target of right-wing political leaders and would-be leaders. However, this constant bombardment from both sides of the issue brings up the question of what does biodiversity really mean? In the popular parlance of TV documentaries it is usually applied to distant and endangered tropical rain forests and oceanic reefs and islands. Indeed, these are the main centers of diversity for a huge number of biotic entities. If Terry Erwin, a tropical biologist from the Smithsonian Institution in Washington, D.C., is right, there may be more than 30 (or perhaps even 80) million species of organisms on this planet, of which a major portion is found in these tropical Edens, now so endangered by stupid mindless development. Even based on more recent estimates from researchers sampling in the Old World tropics, the number seems to be in the neighborhood of 4.5-6 million species, most of which are less than 10 mm in body length (and thus of interest to the microscopist)! This is still much more than the 1 million species of known organisms currently described from the planet. Without a doubt the loss of this cornucopia of living things would be and is a great tragedy of our age. On the other hand we have to appreciate the biodiversity in our own back yard before we can tell others to save theirs. Actually, "saving" biodiversity may be giving us poor mortals too much credit. Conversely, I really doubt that we can truly destroy life on this planet, although we can certainly put it into a bottleneck much as an asteroid strike apparently did at the end of the Cretaceous, thus changing it in ways that would almost certainly be hostile to us.
Falls in rain forest of the central
mountain range of Puerto Rico
We should do our best to protect biodiversity, but I believe that there are some limitations on what we can do in either direction, especially under the current political climate. We also need, I think, a more sophisticated concept of biodiversity than that often promulgated by the popular media. As noted, in the popular mind this usually seems to involve only rain forests and tropical reefs. Despite the huge diversity of the tropics (which we should really try to avoid destroying), certain taxonomic groups may not even be found in such places. For example penguins are found in the tropical zones only where cold water is carried north by ocean currents. Certain other groups may be represented by one or a few species in the tropics, but have their highest diversity in north or south temperate zones. Rattlesnakes, for example, are most diverse in Mexico and the Southwest, while having only one common species in tropical South America. By contrast the pit vipers in the current genera formally placed in Bothrops are extremely diverse in the tropics, with hardly any temperate species. When you get into microorganisms, we have no real idea of the biodiversity on most of the planet. It all depends on which groups you examine, although the tropics are certainly endowed with a large number of species, including 500 species of native trees on Puerto Rico and the Virgin Islands alone and 350 on the islands of Trinidad and Tobago.
One example of a family with high diversity in pantemperate regions is the grasses, family Poaceae. Grasses are important for a number of reasons. One of the main ones, from our perspective, is that they contain most of the major grains used to maintain civilization. Many of these, including wheat, oats, barley, and rye, are productions of the Northern Hemisphere. Rice, maize, millet, and some minor grains are originally more subtropical-tropical crops, but still the majority of important grain species come from temperate regions, or at least are easily grown there. Part of the reason for this imbalance in grass crops may be the political dominance of European civilization over the last five hundred years, but still it also points up the need to respect the biodiversity of all biotic communities, not just those in the tropics. Several of the non-bamboo grass subfamilies are much more highly diverse in the grasslands of North America than in the Amazonian forest.
This said; the biodiversity of the tropics is staggering. For many years evolutionists have debated how such large numbers of species could have evolved nearly side by side. It is generally thought that most speciation is allopatric; that is, it takes place in populations isolated from the parent species. Work with tepheritid ("fruit" or picture wing) flies over the last thirty or so years has produced another possible mechanism in plant feeding insects—host switching leading to host isolation and speciation. This is a sort of sympatric speciation, but some biologists point out that a barrier need not be large if the organism is small and unable to cross it. Thus allopatric speciation can occur within a very small area. Whatever the cause, numerous organisms have evolved in the rain forests of Africa, Southeast Asia and especially tropical America. "God" sure seems to love weevils, ants, orchids, and weird parasites!
Undoubtedly speciation and macroevolution may proceed in a variety of ways, perhaps even by the movement of gene sequences from one organism to another via viruses, or from chromosome to chromosome via "jumping" genes. In other words "Mother Nature" (or "God"—take your pick) may have been in the business of "biotechnology' before we yard apes ever thought of such a thing! Lynn Margulis has suggested that macroevolution proceeded primarily by the symbiotic fusing of microorganisms into more complex creatures, in the process inserting whole new genetic sequences into the system. The mechanisms of macroevolution are far from understood, but the evidence for the inter-relatedness of living beings is so pervasive that it is sheer folly to deny it. Whether God, gods or extraterrestrials directed such evolution is a matter of belief and cannot be addressed by science. However the idea that a literal interpretation of Genesis, or any other ancient written account, can adequately describe the development of life on this planet is almost certainly wrong. Thus "Creation Science" (or in its modern guise of "Intelligent Design") is true neither to the best of religion or science, but is instead a narrow-minded attempt to ram a "pure" and simple religious ideology down everybody's throat.
What do we make of biodiversity? Is it a result of the creative energies of extraterrestrial or supernatural beings? Is it a result of blind chance or of an automatic process based on the very nature of matter? When we get into this area we enter a world of weirdness because no matter what explanation at which we arrive, it does not seem totally plausible on reflection. Questions seem to multiply, not just about the origin of the diversity of life, but of life itself as well. Did life begin in the sea? Did life begin in fresh water or clay? What caused the formation of bacterial cells apparently several billion years ago? How did life with external or internal skeletons develop? Lynn Margulis has perhaps the most reasonable explanation, but even this boggles the mind. However, it is easier for me to understand the development of composite life from bacteria than to imagine some god or gods making each individual species. Especially when one considers that these include parasitoids of butterflies, plague bacteria, malarial parasites, vampire bats, land leeches, stink horn fungi, diatoms, Euglena, Volvox, rotifers, water bears and multitudes of species of weevils. Such a god would be odd indeed. Perhaps, as some early writers suggested, the devil made such things; but no, this will not do. We soon find ourselves sliding into the slippery slope of medieval superstitious fear. Under this line of thought we will soon be reciting "From ghoulies and ghosties and long-leggedy beasties, and things that go bump in the night, Lord, God deliver us!" This way lies madness indeed. Either the universe makes sense or it does not, and I, for one, would prefer it to make sense. I can live with a god of the deists, but not one of the fundamentalists.
If biodiversity is to make sense it has to follow from common descent. Despite the huge differences between organisms, we all share a portion of our genetic makeup and we all have similar life processes. It would be unlikely that such apparent inter-relatedness was an accident. I much prefer a god, if there is one, who sets things in motion and then steps back to watch the world develop on its own. I would not like to imagine one who spends time separately fashioning more powerful killing machines (such as the great white shark or the dysentery amoeba) and odd beetles, while throwing us off the track by using the same or similar chemical building blocks that imply descent!
However produced, whether a product of an initiator god, extraterrestrials, the nature of matter or blind chance, we still depend on biodiversity for our existence. We would be unwise indeed to remove rivets, as the ecologist Paul Ehrlich put it, from our airplane before we ascertain which rivets are vital to its function. Thus biodiversity is no mere buzzword, but an important and basic concept, at least to us humans, if we are to both survive and have a life that is worth living. Our crops, future, past and present, our domestic animals and the ambience of our lives depend on the variety of living things we find around us. I am inclined to believe that our health, physical and spiritual, is also dependent on the multitudinous organisms found on this planet. Our very cells are probably derived from microorganisms, whose diversity made our existence possible. Thus, in the face of our current extinction crisis there is only one motto that adequately expresses my sentiments as a biologist and human being. Viva biodiversity!
All comments to the author David Richman are welcomed.
(All images by the author. Title background image: view of grassland sweeping out to mountains, Socorro County east of San Antonio, New Mexico.)
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