July 2017

Extinction and the Future of Biodiversity
Monthly Feature, July, 2017.
By Frederick S. Rogers

PART I: BACKGROUND TO THE CURRENT BIODIVERSITY CRISIS

What is Extinction?

To those of us living in the modern world, especially those of us concerned with the many pressing issues of environmental concern, extinction is an unfortunately all-to-familiar word, the meaning of which is clearly understood: it is the complete disappearance of a taxon (for example, a species) of organism. Perhaps surprisingly, however, the concept of extinction is a very recent one in human history. It was the great French stratigrapher, paleontologist, and comparative anatomist Georges Cuvier, who, around the beginning of the 19th century, demonstrated to the scientific community and to the world at large the reality of extinction. We now know that the vast majority (>90%) of the organisms that have lived on Earth are forever gone - extinct!

Today, we differentiate between background extinction and mass extinction. Background extinction refers to the normal course of events, the normal rate of 0.1 to 1.0 species per million species per year suffering extinction. Indeed, it is the normal course of evolution that species originate (evolve from ancestral species), persist for a time (about 12 million years, or so, for invertebrate species; about 2 million years, or so, for vertebrate species), then become extinct. This fact that species have a point of origination, and a subsequent point of extinction, gives them their time value in reading the geologic record: the physical stratigraphic range of a species in the rock record also delineates a finite span of time from the evolutionary origin of a species to its demise, or extinction. This, in turn, allows us to tell time in the rock record, and to correlate, in a time sense, rock units in even widely separated localities. This relative time scale based on fossils (established by the middle of the 19th century) coupled with the absolute time scale based on radiometric dating of igneous rocks - such as ancient lava flows interbedded with fossiliferous sedimentary rocks - (established by the middle of the 20th century) gives us our modern geologic time scale.

Diversity of life over 600 million yrs.
with mass extinctions indicated.

On the other hand, mass extinction refers to those periods of time when the rate of extinction is accelerated, dramatically so, perhaps as much as 1000 to 10,000 times the background extinction rate. It is these mass extinction events that are of particular interest to us. As is dramatically apparent in the rock record, mass extinction events literally reset the evolutionary clock. Across a stratigraphic boundary marking a mass extinction event, the post-extinction biota of the planet is markedly different from the pre-extinction biota. Whether in the marine realm or in the terrestrial realm, once-dominant groups of organisms are drastically reduced in diversity, or become extinct altogether, and once-subsidiary groups of organisms now become the dominant organisms.

(Click here to expand this section about mass extinctions)

The Pleistocene (“Ice Age”) and Holocene (“Recent”) Extinctions

The period of time from 2.6 million years ago to 11,700 years ago is known as the Pleistocene, or, more popularly, the “Ice Age.” The last 11,700 years up to the present is known as the Holocene, or “Recent.” The period of time from the beginning of the recession of the last continental ice sheets to the present, that is, the last 20,000 years (Late Pleistocene through Holocene), has been notable for its extinctions, most famously the extinctions of the mammoths, mastodons, wooly rhinoceroses, long-horn bison, giant ground sloths, cave bears, saber-toothed cats, dire wolves, etc. – the list goes on. Collectively, these spectacular, but now extinct, animals dominated the ecosystems of the northern hemisphere continents during the Ice Age, and are known as the “Pleistocene Megafauna.” However, the extinctions did not stop, about 11,000 years ago, with the demise of the megafauna, but rather have continued into the present day. The totality of these individual extinction events is popularly referred to as the “Sixth Extinction,” alluding to the “The Big Five,” and suggesting that our present time is the time of the Phanerozoic Eon’s sixth major mass extinction event. How does this on-going extinction event compare to its predecessors?

Although it is tempting to attribute these extinctions to the dramatic shifts in climate and floral distributions of the last 20,000 years – in other words, to attribute these extinctions to natural causes – natural causes are only part of the story. The other part of the story is entirely related to human activities – the impacts caused by hunting pressure, reduction of habitat area, appropriation of resources and energy, pollution, and climate change, beginning with the rise of agriculture about 11,000 years ago, and accelerating in the 200 years since the start of the Industrial Revolution. In short, this ongoing extinction event is not like “The Big Five” extinction events of the geologic past, for two reasons. The first reason is that, although it is a popular perception that we are in the midst of the sixth major mass extinction event of the Phanerozoic Eon, and although we do seem to be rapidly heading toward that horrific “goal,” we really are not quite there yet. Although there are many alarming estimates of present rates of species extinction, and these estimates probably are largely accurate for oceanic islands – the bellwethers of the biodiversity crisis – we really do not have direct empirical evidence that current global rates of extinction are yet at the rates estimated for “The Big Five.” This in no way means that there is no serious issue before us – emphatically, there is a serious issue before us. The second reason is that this largely is a human-induced extinction event, and, therefore, is an extinction event whose effects, with appropriate will and action on the part of humankind, can be ameliorated.

PART II: THE CURRENT STATE OF AFFAIRS

The Condition of Modern Ecosystems

Fred Rogers on the Block Island
ferry contemplating the current
state of coastal ecosystems.

So what is the actual state of affairs that we now find ourselves in? I think our current situation is well – and alarmingly – illustrated in what are two important publications in the areas of ecology and conservation biology, Jackson et al. (2001) and Yeakel and Dunne (2015). The research presented, and the conclusions reached, in each of these studies is based on excellent paleontological, archeological, and historical data sets. Jackson and colleagues focus on estuarine, coastal, and continental shelf marine ecosystems around the globe, while Yeakel and Dunne review a variety of marine and terrestrial ecosystems spanning the Phanerozoic Eon, from the half billion-year-old, Middle Cambrian-age Burgess Shale to the modern Egyptian terrestrial ecosystem and the modern Adriatic Sea marine ecosystem. In each study, the authors make a convincing case that modern marine and terrestrial ecosystems, by and large, and with few exceptions, are mere shadows of their former selves. What is alarming about our modern ecosystems is not so much the extinction of species per se – although that certainly already has occurred in some instances – but that for most of the species in these ecosystems the number of individuals typically is very low in comparison to the often fantastically large number of individuals prior to the modern era, especially prior to the Industrial Revolution. These small populations matter because they make a species susceptible to extinction, and, when a species is critical to maintaining the structure and function of the ecosystem (more likely for species high in the food web), its extinction can cause the ecosystem as a whole to collapse. This appears to have happened in a number of marine ecosystems studied by Jackson and colleagues and in the terrestrial ecosystems of Egypt studied by Yeakel and Dunne. It is my opinion that a thorough review of the technical ecology and conservation biology literature will reveal dozens of similar, depressing examples. We may not yet be at the level of a “Sixth Extinction,” but because we are “insulting” and overexploiting our already reduced and fragile ecosystems, we may be nearing a tipping point for many of them, and thus may be poised to fall in that direction very soon. To directly quote Yeakel and Dunne (2015, p. 195), “From a perspective of self-preservation, biological diversity is the raw material from which agriculture, medicine, and all natural resources – including the air we breathe – derive! Maintaining intact communities of interacting species harbors that diversity, and is thus a requirement for the survival of human societies.”

Koyaanisqatsi: Life Out of Balance

Some readers of this essay, those of my “vintage,” may remember the visionary environmental film “Koyaanisqatsi,” the title being the Hopi word for “life out of balance,” a title perhaps now even more appropriate than it was then, given the acceleration we now are experiencing with human population growth, habitat loss, hunting and fishing pressure, climate change, ecosystem disruption, and outright extinction. As mentioned above, we may not yet be in the midst of the “Sixth Extinction,” but we certainly have in place all the prerequisites for falling into it in the near future! The question of how to proceed in the face of this comes to mind.

In my lifetime, I have actually heard some people express the opinion that we should not be worrying about extinction because, as “The Big Five” mass extinction events show us, extinction is an entirely natural process – even if 95% of all species go extinct, as in the end Permian event, life will go on, and it will rebuild back to the level of biodiversity that was there before the mass extinction event, and then go on to exceed that previous level of biodiversity. In the meantime, so goes this argument, humanity will find ingenious solutions to living on the post-mass extinction Earth. To this argument I would say that no, the present extinctions are occurring against a radically different background than those earlier events occurred against. First of all, our current situation is not “natural,” it is the result of the activities of human beings, and so we do have the power to change the direction of events. Second, if we do not change that direction, we may end up having altered the Earth’s surface to such a degree that life cannot rebound to its previous level of biodiversity even in the usual several tens of millions of years – for all practical purposes, extinction really is forever! Third, in the meantime, an Earth largely populated by plants we normally consider to be “weeds” and resilient animals like cockroaches and rats, along with the loss of the services that intact ecosystems provide, may not be as pleasant an Earth to live on as the people who make this argument think it will be!

I have also heard people express the opinion that we now have the possibility, in the near future, of escaping the confines of a dying Earth, if necessary. We will terraform and colonize Mars and other bodies in our Solar System, even travel on to planets orbiting other stars. In short, we will be able to escape whatever ecological catastrophe that may befall us by moving on just as earlier, less technologically-advanced civilizations here on Earth – civilizations that overshot their natural resource bases – moved on to new lands, even to new continents. So to this argument I also would say no – no, I do not believe that terraforming Mars and other bodies in our Solar System will ever meaningfully replicate Earth, and no, for some very good reasons, we cannot just move out into the galaxy, either.

(Click here to expand this section about extra-solar planets)

PART III: A WAY FORWARD

Hope for 2100

We have this one Earth, and we all will be on this one Earth together for some time into the foreseeable future, and our children and grandchildren will all be on it together after we are gone. We owe it to ourselves and to those future generations to change this current course that we are on, and to become stewards of the Earth. Earlier essays in this series have illustrated humanity’s deep spiritual connections to nature, the philosophical and ethical foundations for stewardship of nature, and examples of, and reasons for, hope for the future. There really are many individual instances of species averting extinction that give hope for the future, the comeback of bald eagles, peregrine falcons, and, more recently, nenes (Hawaiian geese), come to mind – but now, more than ever, we need to build on these and other individual conservation successes with comprehensive, ecosystem-scale initiatives, indeed, global-scale initiatives, in order to permanently avert a human-caused “Sixth Extinction,” to rebuild our fragile ecosystems before they reach that tipping point and their species slide into extinction. Even if ultimately unrealistic, we need to strive to realize E. O. Wilson’s vision of saving 50% of the Earth entirely for nature. Planning for both the rural and urban environments, at the local, regional, national, and international levels, should be “biodiversity-based planning,” always with the goal of maximizing habitat for nature, maximizing species connectivity, the coherence of ecosystems, and ecosystem services. We need a new “Green Revolution,” as it were, not only in agriculture, but in economics, industry, transportation, housing, recreation, and energy that not only protects the biodiversity of the Earth, but that also meaningfully employs the Earth’s human population in ways that help support that biodiversity!

I will close with a verse from a song by a seminal rock band of the 1960s, a verse written before that first Earth Day on April 22, 1970, but still as current as it was then:

Falling into your passing hands
Please don’t destroy these lands
Don’t make them desert sands

- The Yardbirds, "Shapes of Things"

Frederick Rogers is a Professor of Geology and Environmental Science in the Division of Natural Sciences at Franklin Pierce University in Rindge, New Hampshire, USA. He is a paleontologist specializing in micropaleontology and biostratigraphy, and with a strong interest in the history and diversity of life and in the effects of mass extinctions on the trajectory of the evolution of life.

REFERENCES

Jackson, J. B. C.,M. X. Kirby, W. H. Berger, K. A. Bjorndal, L. W. Botsford, B. J. Bourque, R. H. Bradbury, R. Cooke, J. Erlandson, J. A. Estes, T. P. Hughes, S. Kidwell, C. B. Lange, H. S. Lenihan, J. M. Pandolfi, C. H. Peterson, R. S. Steneck, M. J. Tegner, and R. R. Warner. (2001) Historical Overfishing and the Recent Collapse of Coastal Ecosystems. Science, volume 293, issue 5530, pages 629 – 637.

Ward, P. D., and D. Brownlee. (2000) Rare Earth: Why Complex Life Is Uncommon in the Universe. Copernicus Springer–Verlag, New York, 333 pages.

Yeakel, J. D., and J. A. Dunne. (2015) Modern Lessons from Ancient Food Webs. American Scientist, volume 103, number 3, pages 188 – 195.

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