CK-12 Biology I - Honors

by CK-12 Foundation

  Why is Biodiversity Important? What are We Losing?

  Why should humans care if biodiversity declines? Does it matter that we have 170 fewer amphibians, or that we are losing thousands of species each year, when the Earth holds millions of other species, and life has been through extinction before? The answer is a definitive yes! It matters to us even if we consider only the economic and spiritual benefits to humans. It matters to us because we do not even understand the myraid of indirect benefits – now recognized as ecosystem services- that we reap from other species. And, of course, it matters to other species as well.

  Direct Economic Benefits of Biodiversity

  Food Supply: Monocultures (large-scale cultivation of single varieties of single species) are extremely vulnerable to disease. A water mold caused the infamous Irish potato famine where potatoes had been bred from a single Incan variety. As recently as 1970, blight swept the corn belt where 80% of maize grown in the U.S. was a single type. According to the Food and Agricultural Organization of the United Nations, humans currently cultivate only 150 plant species, and just four provide over half of the food we eat. Just 15 animal species make up over 90% of our livestock.

  Potential for hybridization requires a diverse “bank” of wild, native species. Contemporary breeders increase genetic diversity by hybridizing crop species with wild species adapted to local climate and disease (Figure below).

  Figure 18.8

  Wild varieties of domesticated crops, such as this unusually shaped Latin American maize, hold the potential to enhance productivity, nutritional value, adaptation to local climates, and resistance to local diseases through hybridization. Loss of biodiversity limits our ability to increase the genetic diversity of crops.

  Clothing, Shelter, and Other Products: As many as 40,000 species of plants, animals, and fungi provide us with many varied types of clothing, shelter and other products. These include timber, skins and furs, fibers, fragrances, papers, silks, dyes, poisons, adhesives, rubber, resins, rubber, and more.

  Energy: In addition to these raw materials for industry, we use animals for energy and transportation, and biomass for heat and other fuels. Moreover, hydroelectric power depends on ecosystem structure: Chinese scientists calculated that the economic benefits of maintaining forest vegetation in the Yangtze River watershed “produced” more than twice the economic value of timber (had it been harvested) in annual power output.

  Medicine and Medical Models: Since the first microorganisms competed for food, evolution has been producing chemicals for “warfare” and “defense” in bacteria, fungi, plants, and animals; Figure below shows several used by humans. According the American Museum of Natural History Center for Biodiversity Conservation (AMNH-CBC), 57% of the most important prescription drugs come from nature, yet only a fraction of species with medicinal potential have been studied.

  Figure 18.9

  A pharmacopoeia of the living world: The Rosy Periwinkle (A) is the source of two chemotherapy drugs effective against leukemias. The mold (B) produces the antibiotic penicillin to defend its territory (in this case, a mandarin orange) from competing microorganisms. Aspirin originates in the bark of the White Willow (C). And several species of tropical frogs in the genus (D) produce poisons used by South American tribes for hunting with darts.

  Unique features of certain species have opened windows into how life works. For example, the Atlantic squid’s giant axon revealed the basics of neurophysiology, and the horseshoe crab’s (Figure D below) optic nerve and photoreceptors taught us how vision works. Other animals serve as disease models; as far as we know, other than humans, only armadillos suffer from leprosy, and only sea squirts form kidney stones.

  Efficient Designs: Inspiration for Technology: Biomimicry, also known as biomimetics or bionics, uses organisms for engineering inspiration and human innovation. Rattlesnake heat-sensing pits, for example, suggested infrared sensors. Zimbabwe’s Eastgate Centre Figure below incorporates air-conditioning principles from termite mounds. The 2006 Mercedes-Benz Bionic employs the body shape of the yellow box fish to combine high internal volume and efficient aerodynamics. Biomimetics professor Julian Vincent estimates that only 10% of current technology employs the highly efficient biological designs crafted by evolution and natural selection. Loss of biodiversity can be viewed as the loss of millions of years of evolutionary wisdom.

  Figure 18.10

  Bionics, or biomimicry, engineers structures based on biological designs made efficient by millions of years of evolution and natural selection. Above: The air-conditioning efficiency of a termite mound (left) inspired the design of the Eastgate Centre in Zimbabwe (right), which requires just 10% of the energy needed for conventional building of the same size. Below: The rigid exoskeleton and low-drag body shape of the tropical yellow box-fish (left) inspired the 2006 Mercedes-Benz (right), which combines large internal volume with optimal aerodynamics.

  Warnings of Toxins and Other Ecosystem Disruptions: If you know how miners use canaries to detect poisonous gases underground, you will understand how widespread extirpation of peregrine falcons (Figure E below) warned us about the dangers of the pesticide DDT and food chain concentration of toxins.

  Indirect Benefits of Biodiversity: Ecosystem Services

  Increasing Ecosystem Productivity: Ecologist David Tilman compared grassland plots to show that increasing species diversity increased overall productivity (yield). Different plants utilize different resources, so a variety of plants may more completely use resources within an area. As noted above, diversity also reduces system vulnerability to pests and disease.

  Increasing Ecosystem Stability: Tilman observed his grassland plots through several cycles of drought and documented a similar relationship between biodiversity and stability. Plots which were more diverse were more resistant to drought and later recovered more completely. Reducing ecosystem vulnerability to pests and disease may also be a factor in the relationship between diversity and stability. As you have learned before, diversity among individuals within a species increases the chance that at least some will survive environmental change; similarly, diversity among species within an ecosystem increases the chance that at least some species will survive environmental change.

  Maintaining the Atmosphere: As you learned in the chapters on photosynthesis and respiration, plants and algae produce the O2 which makes up 20% of the atmosphere essential to aerobic organisms, and remove CO2 produced by respiration and burning fossil fuels. As Joseph Priestley expressed this service, plants “restore the air” which has been “injured by the burning of candles” or “infested with animal respiration.” O2 is also critical to life because it helps to maintain the ozone shield, protecting life from dangerous Ultra-Violet radiation.

  Maintaining Soils: Soil microorganisms maintain nutrients in complex but critical chemical pathways. Vegetation and litter prevent erosion of soils which require thousands of years to form. Estimates suggest that erosion destroys as many as 3 million hectares of cropland annually, and that as much as one-fifth of the world’s cropland is “desertified” through salination, acidification, or compacting.

  Maintaining Water Quality: Water treatment plants rely in large part on microorganisms for water purification, and natural systems do the same. In nature, wetland, waterway, and watershed root systems combine with soil adsorption and filtration to accomplish water purification. When New York City decided to restore the Catskill watershed, their $1-1.5 billion investment in “natural capital” contrasted favorably with the $6-8 billion initial cost and $300 million annual operating cost of a new treatment plant.

  “Fixing” Nitrogen: One of the most amazing aspects of biological systems on earth is their absolute need for nitrogen – to build the proteins and nucleic acids upon which life depends – and their nearly universal dependence on microorganisms to “fix” atmospheric N2 gas and recycle the nitrogen of waste and death. Only after the bacterial “service” of processing nitrogen is it available in usable chemical for
m to plants, and through them, to animals (Figure A below).

  Figure 18.11

  Ecosystem services which depend on biodiversity include nitrogen fixation (A), pest control (B), pollination (C), medical models such as the horseshoe crab optic nerve and photoreceptors (D), and early warning about toxins, e.g. the peregrine falcons extirpation by the pesticide DDT (E).

  Nutrient Recycling and Waste Disposal: Bacteria and nitrogen are not the only contributors to the waste management services of ecosystems. Fungi, protists, and scavengers help to decompose waste and dead organisms so that new life can reuse the available nutrients.

  Pollination: The list of biotic pollinators, essential for sexual reproduction in many plants, is long including not only insects such as wasps, bees, ants, beetles, moths, butterflies, and flies, but also fruit bats and birds such as hummingbirds, sunbirds, spiderhunters, and honeyeaters. Although U.S. crops have relied on commercial honeybees (which are “migrated” to keep pace with maturing crops!), native pollinators in nearby forests or wild grasslands have been shown to improve the productivity of apples or almonds by 20%. The American Institute of Biological Sciences estimates that native insect pollination is worth $3.1 billion annually. Current alarm over honeybee colony collapse highlights the importance of biodiversity to the ecosystem service of pollination.

  Pest and Disease Control: According to the AMNH-CBC, farmers spend $25 billion annually on pesticides, while predators in natural ecosystems (Figure B above) contribute 5 to 10 times that value in pest control. Costs associated with the use of chemical pesticides (such as water pollution) add to the value of natural pest control. Natural enemies are adapted to local environments and local pests, and do not threaten each other’s survival (or ours!) as do broad-spectrum chemical pesticides. Preservation of natural enemies is associated with preservation of plant diversity, as well. Disrupted ecosystems can lead to increasing problems with disease. In Africa, deforestation has led to erosion and flooding, with consequent increases in mosquitoes and malaria.

  Aesthetic Benefits of Biodiversity

  Cultural, Intellectual, and Spiritual Inspiration: Music, art, poetry, dance, mythology, and cuisine all reflect and depend on the living species with whom we share the Earth. Our cultures reflect local and regional variations, and as such, biodiversity underlies our very identities. The beauty and tranquility of living ecosystems have inspired environmentalists (Rachel Carson, Aldo Leopold), spiritualists (Thomas Berry), and writers such as (Barry Lopez) throughout history. Recently, the increasing distance of human society from the natural world has raised concerns about our psychological and emotional health; E.O. Wilson has proposed that biophilia (love of the living world) is an increasingly ignored part of our human psyche, and Richard Louv believes that too many of our children suffer from “nature deficit disorder” caused by our increasing alienation from nature.

  Recreational Experiences: Many people choose to use vacation and recreation time to explore natural ecosystems. Outdoor recreational activities – many of which are increasing in popularity - include hunting, fishing, hiking, camping, bird-, butterfly- and whale- watching, gardening, diving, and photography. Indoor hobbies such as aquariums also celebrate biodiversity. For Costa Rica, Ecuador, Nepal, Kenya, Madagascar, and Antarctica, ecotourism makes up a significant percentage of the gross national product. Ideally, ecotourism involves minimal environmental impact, conservation of bio- and cultural diversity, and employment of indigenous peoples.

  Political and Social Benefits of Biodiversity

  Some analysts relate biodiversity to political and social stability. Unequal access to food, clothing, water, and shelter provided by diverse ecosystems threatens social equity and stability. Land ownership and land use practices which threaten biodiversity often marginalize poorer people, forcing them into more ecologically sensitive areas and occupations. Poverty, famine, displacement, and migrations are problems related to loss of biodiversity which have already led to billions of dollars in relief costs and significant local armed conflict.

  Intrinsic Value of Biodiversity

  Many people value biodiversity for its inherent worth, believing that the existence of such a variety of genes, species, and ecosystems is reason enough for our respect. Intrinsic value goes beyond economic, aesthetic, environmental, and political benefits. For many people, intrinsic value alone imposes great responsibility on us to monitor our actions in order to avoid destroying the diversity of life.

  Why is biodiversity important? It supplies us with essential resources, raw materials, and designs which have direct economic value. It enhances the stability and productivity of ecosystems which in turn provide essential, under-appreciated services. These services, too, have great economic value, although we are only beginning to recognize their importance as we experience their loss. Biodiversity is critical for cultural identity, spiritual and intellectual inspiration, and our own re-creation. Biodiversity goes hand-in-hand with social and political stability. And for many people, biodiversity has inherent worth apart from its many benefits for us and our environment.

  Biodiversity is critically important for us and for the Earth, and it is declining at an unprecedented rate. What is causing current extinctions? What can we – what can YOU – do to help?

  Causes of the Sixth Extinction: Human Actions and the Environment

  What are the causes of the Sixth Extinction? There is nearly universal agreement that most result from human activities (Table below and Figure below). Although our activities have changed, we remain the single species most able to alter the Earth’s genetic, species, and ecosystem biodiversity.

  Continent/Island Human Settlement (Years Before Present) Extinctions Which Followed

  Africa, Eurasia Humans evolve here relatively few extinctions

  Indonesia 50,000 50% of large mammal species

  Australia 40,000 55 species large mammals, reptiles, and birds

  North and South America 10,000 - 12,500 70-80% of large mammals (at least 135 species) within 1000 years

  Mediterranean Islands 10,000 large mammals and reptiles

  West Indies 7,000 Mammals, birds, reptiles all 5 endemic mammals of Puerto Rico

  Madagascar 2,000 virtually all large endemic land mammals, reptiles, and birds within 1500 years

  Hawaiian Islands 1,500 (Polynesians) 250 (Europeans)

  2/3 of native vertebrate species, 90% of bird species after European arrival, 20 more bird species

  New Zealand 1,300 No mammals originally Frogs, lizards, and over 1/3 (40 species) of birds

  Figure 18.12

  Large animal extinctions followed the arrival of humans in many regions of the world, suggesting that human activities caused the extinctions.

  Convincing evidence for human responsibility for Ice Age extinctions is outlined in Figure above. Comparing Ice Age to pre-human extinctions provides more evidence:

  Ice Age extinctions affected large animals disproportionately; pre-human extinctions affected all body sizes.

  Ice Age extinctions occurred at different times in different regions; pre-human extinctions were global and simultaneous.

  Recent extinctions follow human migration with regularity.

  The “syncopated” pattern does not fit climate change, and earlier interglacial periods did not see similar extinctions.

  Although the data above has led to considerable agreement about human responsibility for the early Holocene extinctions, scientists still debate exactly how human activities caused extinctions. Hypotheses include:

  Overkill: Animals outside Africa and Eurasia evolved in the absence of humans. Many did not fear humans and would have been easily killed, explaining the disproportionate numbers of large species affected.

  Cascade effects: Extinctions of very large animals could have had major effects on ecosystems, including secondary extinctions. Loss of predators could have led to overpopulation and starvation of prey species. Loss of large herbivores would have affected their predators. Rem
oval of even a single keystone species could have destabilized complex ecosystem interactions, leading to multiple extinctions.

  Disease: Humans often brought along rats, birds, and other animals as they migrated to new regions. Animals in those new regions, however, would not have evolved resistance to the diseases they carried. Avian malaria, for example, is still spreading through Hawaii, having already caused the extinctions of many bird species.

  Predation by exotic animals: The rats, birds, and other animals accompanying humans brought not only disease but also new appetites to regions where animals had evolved without predators. Like humans, these animals found the “naïve” prey easy to capture.

  Habitat destruction: Deforestation and agriculture accompanied humans, and the loss of habitat inevitably resulted in loss of species.

  These effects of early human habitation foreshadow today’s even greater threats to biodiversity. Overpopulation, industrialization, technology, cultural differences, and socioeconomic disparities compound the six major causes of today’s Biodiversity Crisis. Most experts agree on the primary cause of extinction today: