Varanus glauerti, Mertens, 1957

Pianka, Eric R., 2012, Can humans share spaceship earth?, Amphibian & Reptile Conservation 6 (1), pp. 1-24 : 6-7

Varanus glauerti (above) and V. keithornei (below). Photos by Stephen Zozaya (above) and Jeff Lemm (below).

People sometimes ask me why I study lizards. Or worse, some say “what good are lizards?” to which I respond with “what good are YOU?” Those who would think, let alone ask, such a narrow-minded question seem to me to be hopelessly anthropocentric. Lizards are spectacular and beautiful fellow Earthlings that deserve our full respect and care. They were here long before us and deserve to exist on this spaceship, too.

When my co-author Laurie Vitt and I received the advance copy of our coffee-table book “Lizards: Windows to the Evolution of Diversity,” we sat side-by-side thumbing through its pages. Laurie said “if there’s a copy of this 50 years from now, people will be looking at these photos and saying ‘were these things really here?’” For us, and for many others, a world without lizards would not be a world worth living on. That said, let us explore future prospects for all lizards including monitors. Gibbons et al. (2000) reviewed the global decline of all reptiles, comparing it to the loss of amphibians, especially frogs. They identified many threats, including habitat loss and degradation, introduced invasive species, pollution, disease, unsustainable land use, and of course global climate change.

Minimum Viable Populations and Extinction Vortices

Conservation biologists have formulated concepts of “minimum viable population size” and “extinction vortices.” Together, these can capture an endangered species and inexorably drive its population to extinction (Gilpin and Soulé 1986; Pianka 2006; Traill et al. 2007), as follows. Habitat destruction, degradation, and fragmentation lead to reduced population density or even rarity, at which stage a species’ survival becomes precarious. Small populations lose genetic variation, which limits their ability to adapt to changing environments. They also experience elevated demographic stochasticity, which can lead to extinction by a random walk process if deaths exceed births. When exposed to added insults of climate change, pollution, disease, and competition and predation by invasive species, a threatened target species can become doomed to extinction.

Because they are aquatic and long-lived, pollution and disease are important threats to crocodilians and turtles, but these two agents are less likely to impact most lizards. However, studies of pollutant contamination of aquatic African nile monitors living near abandoned chemical stockpiles in West Africa showed that pesticide and heavy metal contamination levels in tissues differ between the sexes, but are not high enough to have noticeable detrimental effects ( Ciliberti et al. 2011, 2012). Nevertheless, Campbell and Campbell (2005) suggest that lizards could be useful as sentinel species to detect and monitor low levels of pollution through bioaccumulation.

For many lizard species, habitat loss and climate change are the two major factors that have had strong negative impacts and both will almost certainly continue to increase well into the foreseeable future.

Habitat destruction and species loss: Modern day fossils

When I first began studying desert lizards just half a century ago, North American deserts were largely unfenced and pristine. Permits were not required to conduct field research, and lizards were very abundant at a dozen study areas I worked from southern Idaho to Sonora. I have since returned to several of these former study sites only to find that they no longer support any lizards: one is now part of the city of Mojave, California, another at Twentynine Palms has been developed, and a third outside Casa Grande, Arizona, is now a trailer park. Two sites in northern Mexico have succumbed to agriculture (Google Earth). Specimens collected a mere 50 years ago, safely ensconced in major museums, now represent fossil records of what was once there before humans usurped the habitat ( Pianka 1994). Human populations have more than doubled during the past half century—we already use over half of the planet’s land surface and more than half of its freshwater. Our voracious appetite for land and other resources continually encroaches on the habitats of all our fellow Earthlings, including lizards.

Many people embrace the anthropocentric attitude that Earth and all its resources exist solely for human benefit and consumption. Organized religions teach mastery of nature and by setting people above all else, they have led to many of the worst ecological abuses. For example, the Bible says “be fruitful, and multiply, and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth” (Genesis I, 28), but it also says “and replenish the earth.” Our numbers have increased vastly, and we have overfished the world’s oceans and decimated many birds, but we have not abided by the latter command. Instead we have raped and pillaged the planet for anything and everything it can offer. Millions of other denizens of spaceship Earth evolved here just as we did and are integral functional components of natural ecosystems. All life on Earth requires space to live—other organisms have as much right to exist on this planet as people do. We need to embrace bioethics and we must learn to share.