12.E: Diversity of Life (Exercises) - Biology

12.E: Diversity of Life (Exercises) - Biology

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12.E: Diversity of Life (Exercises)

The Diversity of Life

This represents an outstanding overview of the worldwide threat to biodiversity, an accessible presentation of relevant principles of ecology, and an outline of promising lines of action to save ourselves from our suicidal path. For a scientist, Wilson is surprisingly eloquent and skillful in conveying a lot of information and issues without coming off like a textbook. By coincidence, the Pope just this week presented an Encyclical which exhorted politicians and individuals everywhere to do ever This represents an outstanding overview of the worldwide threat to biodiversity, an accessible presentation of relevant principles of ecology, and an outline of promising lines of action to save ourselves from our suicidal path. For a scientist, Wilson is surprisingly eloquent and skillful in conveying a lot of information and issues without coming off like a textbook. By coincidence, the Pope just this week presented an Encyclical which exhorted politicians and individuals everywhere to do everything possible to preserve biodiversity.

If you are like me, it’s easy to get struck dumb with hopeless, depressing feelings over facts continually dumped on our heads about species loss linked to the progressive destruction of natural habitats. But, as with a health threat, a clear diagnosis, prognosis, and comprehensive preventative and treatment plans do wonders in helping one face dark truths. For me, Wilson’s book makes a great complement to a recent read of Kolbert’s The Sixth Extinction, which balances a journalistic and history of science approach to the same issues relating to the recent age as one comparable to five other mass extinctions in geological time (now termed the Antropocene). They cover some of the same ground in highlighting how the current ecological catastrophe in modern times is just an extension of human impact on species loss by hunting and habitat destruction everywhere he expanded out from Africa and Eurasia. For example, the Paleo-Indian invasion of America across the Bering Strait land bridge about 12,000 years ago is linked to the loss of many prominent large mammals (“If this were a trial, the Paleo-Indians could be convicted on circumstantial evidence alone, since the coincidence in time is so exact”). I like his portrayal of a virtual American Serengeti awaiting humans:
From one spot, say on the edge of a riverine forest looking across open terrain, you could have seen herds of horses (the extinct, pre-Spanish kind), long-horned bison, camels, antelopes of several species, and mammoths. There would be glimpses of sabertooth cats, possibly working together in lionfish prides, giant dire wolves, and tapirs. Around a dead horse might be gathered the representatives of a full adaptive radiation of scavenging birds: condors, huge condor-like teratorns, carrion storks, eagles, haks, and vultures, dodging and threatening one another …

Although Wilson’s book was published in 1992, it is great for expanding my knowledge of the basic science through clear examples. What is a species, what contributes to their formation and extinctions, what is an ecosystem, and what is known about dependencies between species? I especially appreciated his emphasis of how little we know. We may know about a good fraction of vertebrates on our planet, but the vast majority of invertebrates and plants are as yet unidentified. We may know something of less than 2 million species, but we can only guess if there are 10 million or 100 million more out there (not counting even vaster numbers of unknown microorganisms). The riot of life in the tropical rain forests has long been largely inaccessible because of their remoteness and concentration of species high off the ground. When scientists fogged single trees with insecticides, they found each one had hundreds of unknown species of bugs. Thousands of orchids and other parasitic plants called epiphytes reside out of sight in the canopy, each one of which can provide niches for unique fungi, mosses, insects, and snails.

One thing I never thought much about before is how the loss of an individual species usually involves extinction of others which depend on them, including an array of specialized microparasites. Beyond the squeamish recognition of critters in my eyelashes and skin and of gut bacteria, think of comparable niches on the bodies of every mammal and bird. Even insects have their fellow travelers. Wilson describes a special mite (a blood sucking arthropod) that forms a boot on the foot of a particular ant. Such interdependency between species and complexities in food webs are areas we only begin to scratch the surface. For example, the discovery that all vascular plants depend on a symbiosis with fungi in their root systems is relatively recent. We don’t know how many species can be lost from an ecosystem before the whole thing collapses. When one species gets attention as endangered (e.g. panda, tiger, songbird), Wilson educates us to think of them as a sentinel or stand-in for the larger set associated with their particular habitat and ecosystem.

If a species is lost in the forest and no one is aware of it, did it happen? An insidious aspect of our ignorance is the silent disappearance of species we know nothing about. Some volunteer biologists mapped an incredible array of new species on a ridge containing a dry tropical forest on a ridge in the foothills of the Ecuadoran Andes, a habitat isolated by valleys and elevation. Returning later, the ridge had been clear-cut. What would have been an invisible loss of species was accidentally documented:

Around the world such anonymous extinctions—call them “centinalan extinctions”—are occurring, not open wounds for all to see and rush to staunch but unfelt internal events, leakages from vital tissue out of sight. Any number of rare local species are disappearing just beyond the edge of our attention. They enter oblivion like the dead of Gray’s Elegy, leaving at most a name, a fading echo in a far corner of the world, their genius unused.

In other cases, the smoking gun of human blunder is obvious to discern. In the Great Lakes of East Africa resides an amazing adaptive radiation of hundreds of cichlid fish species reminiscent of the Galapagos finch diversity that inspired Darwin. The introduction of an aggressive Nile perch species into Lake Victoria as a game fish in the 1920s led so far to disappearance of half the cichlid species. The contribution of alien species to accelerated extinction rates is an old story for human impact. In addition to predation by pets like dogs and cats, the human spread of critters like rats and inadvertent spread of disease organisms has contributed to doom of many a species.

Wilson is quite engaging in introducing the reader to the new specialized fields within ecology of biodiversity science and conservation biology. The relationship of species survival and sustained diversity to population size and geographical space is a basic challenge. Biogeographical studies of islands reveal some principles, such as how a tenfold increase in area is typically linked to sustaining about twice as many species. Studies by Jared Diamond and associates of islands formed by rising seas after the last ice age confirmed the inverse relationship for species loss after restriction in habitat area. From such a mathematical relationship, Wilson presented an estimate for species loss of 10-20% over 30 years associated with rates of worldwide rain forest destruction. At the end of the 80’s, the rate of rainforest loss approached 2% of the total per year, which he translated to an area the size of the 48 continental states of the U.S. sustaining annual losses of an area the size of Florida. Fortunately, the rate of tropical deforestation has dropped since then (a recent estimate I saw was about .5% per year for the two decades up to 2010).

The last quarter of the book deals with arguing for the value of biodiversity and a range of promising practices and strategies to preserve it. If the reader doesn’t need or want all the biological foundations for the problem of biodiversity, they could profit in understanding and hope by reading this section by itself. An obvious problem to addressing the threat to biodiversity is that the richest ecosystems and most species are in tropical areas and in the hands of the poorest nations. Much deforestation is due not to corporate level forestry and cattle ranching, but to individual poor families clearing land to survive:

The raging monster upon the land is population growth. In its presence, sustainability is but a fragile theoretical construct. To say, as many do, that the difficulties of nations are not due to people but to poor ideology or land-use management is sophistic.

Big solutions are needed to preserve ecosystems, starting with priority hot spots. The wealthy nations and international corporations may have been villains of exploitation in the past, but now they must work together and invest in solutions. Major goals for concerted teamwork between science, business, and government include: 1) survey the world’s fauna and flora 2) create biological wealth 3) promote sustainable development, 4) save what remains, 5) restore the wildlands. Some of his ideas for exploiting new food sources or alternative sources for fibers are of interest to individuals wanting to make a difference. His support of aquaculture as a major solution has come under serious criticism for inefficiency and practices that cause much pollution. Since the book was written, the effect of ocean acidification on coral reefs has turned out to be a huge problem seeming beyond the scope of the solutions he proposes for land ecosystems.

The concept that zoos, botanical gardens, seed banks, and tissue banks will have a major impact for conservation he sees as a pipe dream. He is quite eloquent in quashing certain forms of complacency:

It is also possible for some to dream that people can go on living comfortably in a biologically impoverished world. They suppose that a prosthetic environment is within the power of technology, that human life can still flourish in a completely humanized world, where medicines would all be synthesized from chemicals off the shelf, food grown from a few dozen domestic crop species, the atmosphere and climate regulated by computer-driven fusion technology, and the earth made over until it becomes a literal spaceship rather than a metaphorical one, with people reading displays and touching buttons on the bridge. Such is the terminus of the philosophy of exemptionalism: do not weep for the past, humanity is the new order of life, let species die if they block progress, scientific and technological genius will find another way. Look up and see the stars awaiting us.

His final argument for action speaks to the spiritual value humanity gives to wildness in nature and the importance of not short changing all future generations by our inaction:

We do not know what we are and cannot agree on where we want to be …
Humanity is part of nature, a species that evolved among other species. The more closely we identify ourselves with the rest of life, the more quickly we will be able to discover the sources of human sensibility and acquire the knowledge on which an enduring ethic, a sense of preferred direction, can be built.

I doubt this review will sway many of you to read this book. That’s okay. I often like to read book reviews as a substitute for reading book, which is why I waxed long on details. Even a schematic level of knowledge is enough sometimes to inspire an individual to take constructive actions at different levels. There are plenty of organizations that can keep non-biologist people tuned into work on solutions. If you want to explore graphical portrayals of the interacting factors at play and state of progress, I recommend a recent Internet initiative called the Biodiversity Indicators Dashboard:

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