All species become extinct. By most estimates, 99.9 percent of the species that have ever lived are now extinct.
While a sad truth to the human mind, the fact is, extinction is an integral and inextricable component of the evolutionary process. It is one side of the evolutionary coin that allows the other side – the development of new species – to occur. However, widespread extinction disrupts the balance of the biosphere, potentially endangering all living organisms.
Based on the fossil record, the rate at which species become extinct is on the order of one to five species per year. (Center for Biological Diversity, 2014) Because this “background extinction rate” is relatively low, new species continually evolve and fill new and existing niches. This yields relatively stable and consistent ecosystems, which may persist for millions of years.
However, the fossil record shows that things can change very rapidly and countless species can disappear more quickly than new species can replace them. Paleontologists call such period’s mass extinction events, and they have documented five over the history of life on Earth. Loosely defined as the loss of 75 percent of the living species in a short period of time, some mass extinction’s have been far more catastrophic. (Anthony D. Barnosky, 2011) For example, the Permian-Triassic extinction, which set the stage for the rise of the dinosaurs, was responsible for the extinction of 95 percent of the species that were alive at the time.
Earth Sixth Mass Extinction - The Anthropocene Extinction
Many ecologists believe that the Earth is currently experiencing its sixth mass extinction. Originally called the “Holocene Extinction,” many have adopted the term “Anthropocene Extinction,” in reference to the primary cause of the event. While the previous five extinction events are thought to have been caused by celestial impacts, volcanism or long-term climate change, the present mass extinction is being caused by the actions of a single – albeit highly influential – species: Homo sapiens.
Between 15,000 and 10,000 years ago, the great ice sheets covering many parts of the world began receding. Around the same time, anatomically and behaviorally modern humans began forsaking their nomadic lifestyle and establishing permanent residences. These naked apes would eventually colonize all corners of the globe and alter the habitats in which they live. Anthropologists call this crucial time the “Neolithic Revolution,” but it also marks the dawn of the Anthropocene Extinction.
The Scope of the Problem
Scientists suspect that species are currently disappearing 1,000 to 10,000 times more rapidly than the background extinction rate. (Center for Biological Diversity, 2014) In the last 500 years or so, 322 terrestrial vertebrates have gone extinct – even the survivors have seen their populations fall by 25 percent. (Rodolfo Dirzo, 2014) Over two-thirds of the invertebrate species surveyed since 1980 have experienced population declines of about 45 percent. (Rodolfo Dirzo, 2014)
The World Wildlife Fund contends that habitat destruction is likely the leading cause of most current species declines. Habitat destruction and fragmentation have led to declines in populations of Florida panthers (Puma concolor coryi), mountain gorillas (Gorilla beringei beringei), giant pandas (Ailuropoda melanoleuca) and polar bears (Ursus maritimus). While these charismatic mammals often receive the bulk of the attention, declines among small species – who often serve as pollinators, agents of seed dispersal and important components of the food chain – may trigger even greater ecological instability.
For example, humans destroy about 80,000 acres of rainforest habitat every single day –an area nearly 100 times larger than Central Park. (Scientific American, 2009) These ancient habitats have matured over thousands of years, and there is simply no quick fix for replacing these lost acres. Even more troubling is the fact that the rainforests are so poorly understood – millions of species may await discovery. As recently as 1980, scientists working in Panama discovered 960 previously undescribed beetle species. (World Wildlife Fund, 2014) Considering that each acre of rainforest holds between 20 and 86 tree species, the damage of deforestation is truly staggering. (Smithsonian Institution, 2014)
Climate change is another leading cause of species decline. In some cases, the shifting climate is untenable for a species’ biology, while in others, climate change effectively destroys the available habitat. Such is the case with polar bears, who are watching their habitat melt before their eyes. As the global temperature rises, the sea ice begins disappearing, thus robbing polar bears of their historic hunting grounds. Animals like turtles and crocodiles are especially vulnerable to climate change, as the gender of their offspring is often determined by the temperatures to which they are exposed while still inside their eggs. If global temperatures continue to climb, the sex ratios of these species may become highly skewed. (Refsnider, 2012) Plants and trees are also susceptible to climate change, as changing temperature cycles disrupt their historical rhythms. This can cause problems for animals that have adapted to these ancient patterns of blooming and fruiting.
Although a variety of problems, including overconsumption, pollution and poaching, are also significant factors in species decline, the final primary factor – on par with climate change and habitat destruction -- is the introduction of alien species. While non-native species have managed to colonize remote habitats throughout history, the rate at which this occurred was very low. A lizard species may raft on a log and colonize an island, or a flock of birds may begin expanding their range as their population grows. However, with ships, planes and trains crisscrossing the modern globe, many species manage to expand their range as stowaways. Unchecked by their natural habitats, many of these invaders thrive in their new lands, greatly altering the local ecosystems.
The brown tree snake (Boiga irregularis) is one of the most infamous alien species. Historically native to Australia and Indonesia, a handful of the snakes made it to the tiny island of Guam. Once on the island, these adaptable serpents found life very easy. Without any similar serpentine predators on the island, the native birds had not evolved defense mechanisms to protect themselves. Over the course of only a few years, the snakes eradicated 9 of the islands 12 indigenous forest birds. (Bruce A. Colvin, 2005) Courtesy of an ample prey base and few predators, the island contains approximately 12,000 to 15,000 snakes per square mile. (Patrick, 2001)
As you can see, the causes of the Anthropocene Extinction are varied, interconnected and often exacerbate each other. Accordingly, it will take a comprehensive effort to reverse these trends. Many of the problems require solutions at the federal or global level, leaving few ways for everyday environmentalists to contribute. However, a few simple steps can help you reduce your individual contribution to the problem, while policy makers attempt to affect broad changes.
- Reduce your carbon footprint as much as practical to reduce your contribution to climate change. Turn down the heat and put on a sweater, opt for a fuel-efficient car, switch to high-efficiency appliances and telecommute, rather than travel, whenever possible.
- Purchase products made from sustainable materials rather than materials derived from species under environmental stress. For example, avoid purchasing products made from rainforest hardwoods to help reduce your contribution to habitat destruction.
- Avoid introducing more invasive species in your area by planting native trees, grasses and shrubs, rather than exotic ornamentals with a high potential for becoming invasive. You can also purchase firewood locally, which helps to prevent the spread of alien tree pests.
- Landfills take up considerable space, and their construction destroys local habitats. Accordingly, recycling and reusing items is preferable to discarding them. Additionally, try to purchase recycled items whenever possible.
- Vote and advocate for representatives who care about the Anthropocene Extinction, and are prepared to take concrete steps to rectify the problem.
- Vote with your dollar by purchasing from retailers that have made significant strides in reducing their carbon footprints, protecting natural habitats or battling the current biodiversity crisis in other ways.
Anthony D. Barnosky, e. a. (2011). Has the Earth’s sixth mass extinction already arrived? Nature.
Bruce A. Colvin, e. a. (2005). REVIEW OF BROWN TREESNAKE PROBLEMS . USDA National Wildlife Research Center - Staff Publications.
Center for Biological Diversity. (2014). The Extinction Crisis. Retrieved from Center for Biological Diversity: http://www.biologicaldiversity.org/programs/biodiversity/elements_of_biodiversity/extinction_crisis/
Patrick, L. (2001). Brown Tree Snake (Boiga irregularis). Retrieved from Introduced Species Summary Project: http://www.columbia.edu/itc/cerc/danoff-burg/invasion_bio/inv_spp_summ/boiga_irregularis.html
Refsnider, J. M. (2012). Effects of climate change on reptiles with temperature-dependent sex determination and potential adaptation via maternal nest-site choice. Iowa State University.
Rodolfo Dirzo, e. a. (2014). Defaunation in the Anthropocene. Science.
Scientific American. (2009). Measuring the Daily Destruction of the World's Rainforests. Retrieved from Scientific American: http://www.scientificamerican.com/article/earth-talks-daily-destruction/
Smithsonian Institution. (2014). Diversity and Survival. Retrieved from Smithsonian Tropical Research Institute: http://www.stri.si.edu/sites/rainforest/diversity_and_survival.html
World Wildlife Fund. (2014). How many species are we losing? Retrieved from World Wildlife Fund: http://wwf.panda.org/about_our_earth/biodiversity/biodiversity/
Ben Team writes about all things nature. Ben is an ISA-certified arborist and environmental educator of over 16 years. Ben maintains FootstepsInTheForest.com, a source for information, observation and narration about the natural world and the creatures living in it.