According the The Center for Biological Diversity, we’re in the midst of the Earth’s sixth mass extinction crisis. Harvard biologist E. O. Wilson estimates that 30,000 species per year (or three species per hour) are being driven to extinction. Compare this to the natural background rate of one extinction per million species per year, and you can see why scientists refer to it as a crisis unparalleled in human history.
So where does wildlife stand today in relation to 7 billion people? Worldwide, 12 percent of mammals, 12 percent of birds, 31 percent of reptiles, 30 percent of amphibians, and 37 percent of fish are threatened with extinction. Not enough plants and invertebrates have been assessed to determine their global threat level, but it is severe.
Extinction is the most serious, utterly irreversible effect of unsustainable human population. But unfortunately, many analyses of what a sustainable human population level would look like presume that the goal is simply to keep the human race at a level where it has enough food and clean water to survive. Our notion of sustainability and ecological footprint — indeed, our notion of world worth living in — presumes that humans will allow for, and themselves enjoy, enough room and resources for all species to live.
Lange's metalmark butterfly from Amy Harwood.
Florida panther: The Florida panther once ranged throughout the southeastern United States, but now survives in a tiny area of South Florida representing just 5 percent of its former range. It was listed as an endangered species in 1967 because of habitat destruction and fragmentation through urban sprawl. Large numbers of panthers died as the expanding network of roads connecting Florida’s rapidly growing human population spread throughout its range. As of 2011, there are only 100 to 120 panthers left.
As Florida’s panther numbers plummeted, the state’s human population nearly doubled over the past 30 years. Recent development patterns pose extreme threats to panthers. As the Florida coasts approach full buildout and have become unaffordable to most people, development has moved inland to the same places panthers retreated to as safe havens decades ago.
Atlantic bluefin tuna
Atlantic bluefin tuna: Marine fish provide 15 percent of all animal protein consumed by human beings. Fisheries management, however, has been outpaced by our population growth, causing global fisheries to collapse under the unsustainable pressure. A 2009 assessment found that 80 percent of global fish stocks are either overly and fully exploited or have collapsed. Though a catch reduction of 20-50 percent is needed to make global fisheries sustainable, the demand for fish is expected to increase by 35 million tons by 2030.
Of greatest concern is the western Atlantic bluefin tuna that spawns in the Gulf of Mexico and has declined by more than 80 percent since 1970 due to overharvesting. Prized as a sushi fish around the world, it has become more valuable as it has become rare. One fish in 2011 sold for $396,000. The large, warm-blooded bluefin tuna is a common, upscale sushi menu item and has been severely overfished. The Atlantic bluefin, like so many other ocean species, is threatened by humans’ ravenous appetites: Demand far exceeds sustainable fishing levels.
Loggerhead sea turtle
Loggerhead sea turtle: More than half the world’s 7 billion people live within 150 miles of the coast, putting tremendous pressure on species trying to find space to live and reproduce among the crowds. Among them is the loggerhead sea turtle, which was listed as a federally threatened species in 1978 owing to destruction of its beach nesting habitat, harassment while nesting, overharvesting of its eggs, and bycatch death via commercial fishing gear.
Ninety-five percent of the U.S. breeding population of loggerheads nests in Florida, whose human population has doubled in the past 30 years. Thanks to careful management, the species’ population increased 24 percent from 1989 to 1998, but under intense pressure from development and recreational beach use, it declined dramatically thereafter, raising concerns it should be uplisted to “endangered” status. The population has increased in recent years, but is still highly vulnerable to nesting habitat destruction and disruption. Just 42,000 nesting attempts were made on Florida beaches in 2011.
Sandplain gerardia: As the human population has increased, it has consumed remote landscapes with houses and other structures. The natural disturbances caused by fire, flood, drought and storm patterns, are suppressed despite playing essential roles in ecosystem health. In conflict with the permanence of human development, these disturbances create an ever-changing blend of meadow and forest, young and mature vegetation patterns. By controlling, limiting and often stopping these essential natural processes, we have changed ecosystems across America, eliminating habitat for rare and endangered species that depend on open habitats.
In New England and the Atlantic coast, brush fires once thinned out dense pine forests and created a constantly moving mosaic of grasslands and prairies. The fires have been suppressed to protect human structures, causing open habitats to be permanently replaced by forest and brush. This nearly caused the extinction of the sandplain gerardia, a coastal plant in the snapdragon family.
Lange’s metalmark butterfly
Lange’s metalmark butterfly: Many endangered species are endemics, meaning they naturally have very small ranges and populations sizes, and usually require very particular soil, vegetation or climate conditions to survive. These species are especially vulnerable to human encroachment. Among them is Lange’s metalmark butterfly, protected as endangered in 1976.
Lange’s metalmark lives only in the Antioch Dunes at the southern end of San Francisco Bay. This unique ecosystem harbored many unique species, and many species have gone extinct as its dunes were hauled away in massive increments. After the 1906 fires, the city of San Francisco was rebuilt using brick-building material removed from the dunes.
Lange’s metalmark is one of the most endangered species in the United States. It declined from some 250,000 in historic times to just 154 in 1986. It improved a bit, but then declined to just 45 butterflies in 2006. Today the species is still on the knife edge of extinction, with about 150 individuals remaining.
Mississippi gopher frog
Mississippi gopher frog: The Mississippi gopher frog lives in stump holes and burrows dug by other animals, laying its eggs in ponds so shallow they dry up for several months of the year, keeping them free of fish that would eat frog eggs. It was placed on the endangered species list in 2001.
The U.S. Fish and Wildlife Service proposed to designate 7,015 acres as protected critical habitat for the Mississippi gopher frog in Mississippi and Louisiana in 2011.
Reduced to approximately 100 individuals in the wild, the Mississippi gopher frog exists in just three small ponds just outside the proposed “town” of Tradition, Mississippi. Planned development would have a devastating effect on this rare frog.
White River spinedace
White River spinedace: The human population of Nevada grew by 35 percent between 2000 and 2010, nearly four times faster than the national average. Las Vegas was one of the fastest-growing areas of the state. But the city is in the middle of a desert, so accommodating that explosive growth requires securing more water from nonlocal supplies.
The Southern Nevada Water Authority has proposed a massive project to pump billions of gallons of groundwater a year from eastern Nevada and western Utah through a 300-mile pipeline to supply rapidly growing urban areas like Las Vegas. The project will have a disastrous effect on dozens of imperiled species, including the White River spinedace, which was protected as an endangered species in 1985. One population of this rare fish was extirpated in 1991 because of irrigation diversion, and fewer than 50 fish remained in a single population in northeast Nevada.
Polar bear: A polar bear is fit to swim 100 miles for food, in search of mates or, more recently, just some ice to stand on. With five inches of blubber keeping this enormous bear prepared for subzero temperatures, the largest member of the bear family has adapted to remarkable Arctic conditions. The fat stored in a polar bear carcass becomes essential food for other Arctic species, like the Arctic fox. However, the extreme impacts that human-caused climate change has had on the Arctic is pushing the polar bear closer to extinction.
The rapid growth of the global human population — which has doubled since 1970 — has fed a massive push for more and more polluting fossil fuels and dramatically altered the planet’s atmosphere. A 2009 study on the relationship between population growth and global warming found that the “carbon legacy” of just one person can produce 20 times more greenhouse gases than one person saves by carbon-reducing steps such as driving high-mileage, using energy-efficient applicants and light bulbs. Few animals are bearing more of the brunt of the global climate crisis than the polar bear.
Gulf sturgeon: Lake Lanier, a manmade reservoir in Georgia, feeds several important river systems in the southeastern United States and has been the site of a longstanding conflict between Georgia, Florida and Alabama over water-use rights.
The gulf sturgeon, an anadromous fish, was placed on the threatened species list in 1991. Its most imperiled populations occur in the Apalachicola River, fed by rivers from Lake Lanier. Gulf sturgeon lay eggs on the waterlines along the banks of rivers, and maintaining the right level of water is critical to their breeding success.
Population growth has strained the capacity of Lake Lanier to supply water to Atlanta and other urban areas. A 2009 study explicitly identified explosive population growth as the cause of the ensuing water war between Georgia, Alabama and Florida following a regionwide drought: “…Nineteenth-century droughts, which are perhaps better thought of as a single multi-decadal dry period, are well within the range of historical records and could potentially have had an agricultural effect but probably would not have had an effect on water availability for people given the generally wet climate of the Southwest and the much smaller population then as opposed to now.”
San Joaquin kit fox
San Joaquin kit fox: The San Joaquin kit fox was relatively common until the 1930s, when people began to convert grasslands to farms, orchards and cities. By 1958, 50 percent of its habitat in California’s Central Valley had been lost, due to extensive land conversions for agriculture, intensive land uses and pesticides. By 1979, less than 7 percent of the San Joaquin Valley's original wildlands south of Stanislaus County remained untilled and undeveloped.
The kit fox was listed as endangered in 1967. Today there are fewer than 7,000 scattered among fragmented populations. The four counties with known San Joaquin kit foxes have grown by 60 percent — by another 1.5 million people — since 1983.
Besides habitat loss, the San Joaquin kit fox is threatened by pesticides and rodenticides associated with intensive agricultural use, industrial activities and residential areas in the Central Valley. Kit foxes’ small-mammal prey base has been significantly reduced by rodenticides, which not only kill life-sustaining prey but can also kill kit foxes when they build up in the foxes’ bodies. Kit foxes have adapted to get their water from the prey they eat making them even more dependent on their food source. They also often burrow in other animals’ dens, leaving them vulnerable to other human activities such as fumigants used to kill coyotes.