Understanding the Etiology of the Biodiversity Crisis

Chief Seattle’s words are emblematic of the historic sentiments of people who were directly involved with the land for their sustenance and shelter. Early civilizations revolved around small communal hunter–gatherer societies. These societies had an integral dependence on interaction with nature. They were in constant contact with natural resources and depended on a basic respect for the rhythms of nature to maintain societal sustainability. Native American Indians of the Eastern Cherokee Nation developed these ideals into a harmony ethic of noncompetitive and reciprocal symbiotic relations with nature and their fellow man.¹¹

Successful hunter–gatherer societies gradually increased in population. Additional demand for food resources coincided with discovery of plant cultivation technology, leading to agrarian civilizations and additional needs pertaining to land ownership and permanent settlements. Agrarian culture and resultant success of permanent settlements eventually led to development of cities, states, and empires. The industrial revolution took hold as a result of advances in scientific discovery and the need for greater productivity to meet the demands of a burgeoning populace. Civilization’s advances gradually moved individuals further and further away from the necessity of physical contact with the natural world. Intermediaries with nature, such as farmers, fishers, and merchants, satisfied the sustenance needs of city dwellers. It is not coincidental that environmental degradation and biodiversity loss secondary to the byproducts of industrialization occurred without apparent knowledge in a society so seemingly independent of nature. It became easy to ignore an unknown and intangible threat, namely, biodiversity loss. Robert Ornstein and Paul Ehrlich²³ hypothesize that humans are affected by a lack of natural selection for response to slowly developing threats such as biodiversity loss. They explain this factor as follows:

The insidious processes of planetary degradation have reached a crisis phase. The miracle of the combustion engine and invention of plastics have become the potential bane of our existence, as the consequences of injudicious burning of fossil fuels and the discovery of toxic byproducts such as dioxin and bisphenol A have shown. However, loss of biodiversity represents a unique challenge that demands an agenda for action. It is difficult enough to effectively communicate the risks associated with known technological hazards such as lead, mercury, and greenhouse gases. Convincing the public of the adverse consequences of the extinction of the Dusky Seaside Sparrow (Figure 110-2, online) or the Montverde golden toad (Figure 110-3) represents an even greater challenge. Loss of these flagship species is a story that must be told, for the sparrow’s demise is a tale of the health-related dangers of dichlorodiphenyltrichloroethane (DDT) and mismanagement of marshland in the United States. In this regard, extinction of a seemingly inconsequential avian species serves as an indicator of the ecological dangers associated with pesticide exposure and loss of the water filtration and hazard protection services that marshlands provide to protect human health in coastal areas. The Monteverde golden toad succumbed to a multitude of pressures associated with invasive species introduced by tourists and aquatic chytrid fungal infections that are theorized to be associated with El-Niño–induced climate change in the toad’s former home range of Costa Rica. Loss of this particular species is indicative of the threat that amphibians face worldwide. A recent study revealed that 32% of the 6000 species of amphibians under analysis were threatened and 43% were in decline.²⁴ The potential medicinal value of chemical compounds that have been extracted from amphibians is evident in the 200 psychoactive alkaloids that have been extracted from the skin of frogs and toads.¹ Some of these compounds have been subsequently used in medical research pertaining to nerve and muscle disorders. The alkaloid known as epibatidine, which is synthesized from skin of the Phantasmal poison frog, is being tested as a nonaddictive and nonsedating analgesic that exhibits 200 times the potency of morphine.¹ Bufogenin and bufotoxin, substances that have been extracted from parotid glands of toads from the same Bufo genus as the extinct Monteverde golden toad, exhibit adrenal and cardiovascular effects in humans.¹ Further investigation of the adverse sequelae of biodiversity loss as evidenced by ecosystem degradation, species decline, and loss of genetic diversity provides additional validation of the corollary threat to human health.

FIGURE 110-3 Monteverde golden toad.

(Courtesy U.S. Fish and Wildlife Service. Public domain.)

FIGURE 110-2 Dusky seaside sparrow.

(Courtesy U.S. Fish and Wildlife Service. Public domain.)

Threatened Ecosystems

Ecosystems represent abiotic and biotic components of an environment. Variation in ecosystems, from arid desert of the South American Atacama to Siberian subarctic taiga forests, is determined by climatic and geologic characteristics of the respective regions. Mineral components of soil and nitrogen-fixing capacities of soil microbes; salinity, turbidity, and other hydrologic aspects of the respective environment; and the variety of flora and fauna that inhabit a region create a syncretic balance that is sustainable in a healthy ecosystem. Speciation within these respective biomes and ecosystems has developed over millions of years, as chronicled by successes and failures of living organisms that did (or did not) establish sustainable niches in a vast array of seemingly hospitable and inhospitable locales.

Ecosystems provide a multitude of features that are essential to human well-being. Food resources, fresh water, sediment retention, nutrient cycling, disease regulation, erosion control, air quality, and climate change depend on healthy ecosystems.¹⁸ Human activities, ranging from land-use patterns associated with increased urbanization to clear-cutting of rain forest for agricultural purpose, have degraded the quality of ecosystems worldwide. The British ecologist, Norman Myers, developed the concept of biodiversity hotspots to identify areas of the planet with a high number of endemic species under extreme threats to their ecosystems as evidenced by loss of at least 70% of the natural vegetation.⁶ Conservation International states that “over 50 percent of the world’s plant species and 42 percent of all terrestrial vertebrate species are endemic to the 34 biodiversity hotspots” (Figure 110-4).

FIGURE 110-4 Biodiversity hotspot map.

(With permission from Conservation International.)

Tropical rain forests exemplify the human health risks associated with ecosystem compromise. These biomes provide habitats for more than one-half of all plant and animal species in the world. Prior studies have counted 100 to 300 species in a 1-hectare area in South America. Approximately 25% of all pharmaceutical agents are estimated to contain compounds that are found in tropical rain forest plants.² The United Nations estimates that 13 million hectares of tropical forest are destroyed each year for logging and agricultural land clearing.¹⁰ In South America, Mexico, and Guyana, rain forests have been cleared for cattle grazing, soybean farming, logging, and gold mining (Figure 110-5, online). Less than 1% of all tropical rain forest species have been evaluated for pharmacologic benefit. Degradation of this essential ecosystem has human health consequences that range from loss of potential life-saving medicines to alterations in climate associated with carbon sequestration by forest trees and burning of forest land.

FIGURE 110-5 Tropical rain forest destruction Mexico.

(Courtesy Azari Nicks. Public domain.)

Mangrove estuaries and wetland sloughs represent another class of threatened ecosystems. Land development, agriculture, and aquaculture pursuits have led to loss of at least 35% of this ecosystem worldwide.³² Considered to be one of the planet’s most productive ecosystems, wetlands are referred to as “nature’s kidneys,” because they filter sediments and pollutants and regulate water flow. Mangroves act as a natural buffer to prevent coastal erosion and provide essential habitat for crustaceans, fish, and several other species. Runoff from excessive amounts of nitrogen- and phosphorous-based fertilizers used in monoculture farming has led to eutrophication of coastal forests and increased mortality of mangrove species as a result of root damage (Figure 110-6, online).

FIGURE 110-6 Everglades National Park mangrove tidal estuary.

(Courtesy Moni2. Public domain.)

Coral reefs support more than 4000 species of fish, and are home to approximately 25% of all marine species. In addition, reefs provide important breakwater protection for coastal areas during tropical storms. Scientists estimate more than 50% of the world’s coral reefs face potential destruction by the year 2030. Global warming is a major threat to this important ecosystem, as a sea temperature change of 1° to 2° C (1.8° to 3.6° F) has been associated with physiologic stress and immune compromise to corals, which leave them with subsequent increased susceptibility to bacterial and fungal pathogens³ (Figure 110-7, online).

FIGURE 110-7 Florida Keys critically endangered elkhorn coral.

(Courtesy the National Oceanic and Atmospheric Administration. Public domain.)

Species Decline

Species decline is another form of biodiversity loss. Variety of species in an ecosystem is critical to sustainability of the respective habitat. Excluding bacteria and viruses, approximately 1.5 million species have been taxonomically identified, and approximately 10 million species are believed to exist on Earth.⁵ The 2008 Living Planet report indicates that, between 1970 and 2005, the earth’s wildlife populations declined by a third.³⁷ The International Union for Conservation of Nature has estimated that in 2010, 22% of all vertebrates, 34% of all invertebrates, 70% of all plants, and 50% of all fungi and protists were listed as critically endangered, endangered, or vulnerable species. Species that are considered threatened worldwide include 30% of all amphibians, 21% of mammals, and 86% of mosses.¹⁶ Species are disappearing at the alarming rate of 1000 to 10,000 times the natural background rate of 1 to 10 species per year. E.O. Wilson, “the father of biodiversity,” estimates the current extinction rate is 137 species per day in tropical rain forests alone³⁶ (Figure 110-8).

FIGURE 110-8 Extinction rate per millennium.

Invertebrate species, which represent approximately 76% of all life forms, are suffering from a significant rate of extinction. Dam construction, water pollution, and deforestation have challenged the capacity of several invertebrate species to retain a foothold in ecosystems worldwide. A keystone species in the Antarctic ecosystem, the Antarctic krill (Figure 110-9) is indicative of the threats that face invertebrate species. Krill are an important food source for whales, seals, squid, penguins, and fish. In addition, these small crustaceans act as an essential component of the ocean’s capacity to sequester carbon. Recession of the Antarctic ice pack and acidification of ocean waters associated with carbon dioxide emissions and global warming are challenges to vitality of the Antarctic krill.

FIGURE 110-9 Antarctic krill.

(Courtesy Uwe Kils, Creative Commons, Share Alike 3.0.)

Loss of Genetic Diversity

Some analysts believe that the greatest threat to human welfare comes from losses of genetic diversity within species.³⁵ Farmers and pastoralists have used selective planting and breeding techniques for centuries to increase crop yield and product output. With the advent of techniques to genetically engineer crops for resistance to variations in climate and susceptibility to disease and pests, biodiversity of the gene pool has been drastically altered. In 1970, the United States lost 15% of its Midwest corn crop as a result of a fungus that the genetically modified crop was unable to resist. By 2007, an estimated 73% of the U.S. corn crop was genetically modified or engineered. Uniformity of plant crops has led to pesticide-tolerant species. There is continuous need for further engineering of crops to resist pests and climatic influences, the latter which was previously tolerable as a result of the capacity for a diverse gene pool to provide protection from adverse influences through the processes of natural selection. Although man has dramatically increased crop yields, this has occurred at the risk of increased susceptibility to unanticipated pathogens and environmental extremes as a result of the loss of indigenous strains that were well adapted to local ecosystems.³⁵

Fragmentation of habitats caused by urbanization and deforestation has prevented species from interbreeding by loss of historic migration corridors, leading to genetic bottlenecks. Species ranging from the grizzly bear in the Central Canadian Rockies to the Florida panther in the Everglades face the dangers associated with increased susceptibility to disease and genetic mutation caused by inbreeding of small populations. Loss of vitality in these species affects predator–prey relationships and ultimately contributes to spread of human pathogens (e.g., Borrelia burgdorferi, the causative agent of Lyme disease).

Genetic uniformity among honeybees has resulted in problems with reproduction and disease. A condition known as colony collapse disorder has led to an alarming die-off among honeybee colonies. This is a significant concern to beekeepers, who have witnessed a decline of 30% to 90% of their hives in some parts of the United States. The disorder has been associated with a lack of genetic diversity in managed beehives. The potential effect on apple, peach, soybean, and other honeybee-dependent crops could be devastating if these keystone pollinators continue to decline in number.