Sustainable Future: Human Impact on Ecology

1. Chapter 26: Economic Development and Global Ecology Robert E. Ricklefs The Economy of Nature, Fifth Edition

2. Looking to the Future • As the human population continues to grow and humans dominate ecological systems worldwide, the question of how we can create a sustainable future for both humans and other species becomes increasingly important: • there is considerable room for pessimistic conclusions • positive steps have been taken in the United States: • Clean Air Act (1970) • Clean Water Act (1972) • Endangered Species Act (1973) • But… • In Lebanon?

3. Positive Steps Toward Sustainability • Laws regarding endangered species, clean air, and clean water have been implemented worldwide. • Straightforward ecological and engineering solutions exist for environmental problems. • People worldwide share a concern for the environment.

4. What can Ecologists Contribute? • The challenge to ecologists is to provide the scientific information needed to develop social consensus, build political commitment, and inform decision making on issues concerning the environment.

5. Ecological processes hold the key to environmental policy. • Conserving ecological processes is the key to maintaining a sustainable biosphere: • the fundamental processes of energy use and recycling of materials have built-in mechanisms to restore imbalances when these occur: • when consumers increase to high numbers, declining birth rates and increasing death rates restore a sustainable relationship between consumer and resource • if natural processes are disrupted, ecosystems may not be able to maintain themselves

6. Human activities threaten local ecological processes. • All human activities have consequences for the environment: • emphasis on short-term returns can lead to collapse of a resource: • one after another of the commercial whale species were hunted to near-extinction, forcing the industry to turn progressively to less profitable species • many profitable fisheries have collapsed because of overfishing

7. Human activities threaten local ecological processes. • Some consequences of human activities have indirect effects: • clearing of watershed land for agriculture or timber leads to undesirable consequences downstream: • alteration of riverine habitats • siltation of dams • damage to reef habitats

8. Overexploitation • Fishing, hunting, grazing, and logging are classic consumer-resource interactions: • in natural systems, such interactions come into equilibrium: • efficiency of exploitation by consumers and resistance to exploitation by resources have evolved over long periods • humans have used technology to escalate beyond all natural limits their ability to overexploit natural resources, with undesirable consequences: • when resources are exhausted, human populations suffer

9. Sustainable and Unsustainable Practices • Consider the lowland tropics: • soils contain few nutrients, with natural fertility maintained by recycling of nutrients between detritus and living plants: • clearcutting, especially when followed by grazing, breaks this cycle, resulting in a badly degraded system • humans have learned to live sustainably in such ecosystems through the practice of shifting agriculture • by clearing 1-2% of the land per year and cultivating for 2 or 3 years, farmers allow sufficient time in fallow for nutrient stocks to recover from agriculture

10. Introduction of Exotic Species • Humans have taken other species with them everywhere they have traveled; for example: • 50,000 nonindigenous species have been introduced to the United States • New Zealand has a predominantly alien flora and fauna: • most of the area is occupied by introduced plants and animals: • native forests were cut and replaced by eucalyptus • native moas were killed by Maori natives, replaced by European transplants

11. Why did aliens prosper in New Zealand? • Of the total New Zealand flora of 2,500 species, 500 are introduced: • introduced species account for most of the vegetation • why were these species so successful? • most natural habitats had been disturbed • because of low diversity and simple structure, island ecosystems are generally more easily invaded

12. Can effects of aliens be predicted? • Alien species may displace natives, but do not necessarily disrupt ecosystems: • introduced species may simply assume the ecological roles of natives • effects of introduced species are hard to predict: • aliens may also be disruptive, altering ecosystem function and community structure: • Nile perch in Lake Victoria eliminated an entire trophic level of planktivorous fish

13. Habitat Conversion • Altering habitats can upset natural processes: • cutting of tropical forests: • breaks the tight cycle of nutrient regeneration • results in increased erosion • plowing of prairies set the stage for the “dust bowl” conditions of the 1920s and 1930s in the United States • disruption of mangroves in tropical coastal areas have left the land vulnerable to hurricane-driven floodwaters • damming rivers increases silt transport, blocks fish migrations, alters downstream ecosystems

14. Irrigation • Benefits of irrigation are often offset by substantial environmental problems: • environmental costs associated with infrastructure (dams, canals, etc.) • lowered water tables where wells are used • reduction of groundwater quality (through introduction of pesticides and fertilizers) • accumulation of salt in irrigated lands • transmission of diseases by aquatic organisms

15. Fertilization and Eutrophication 1 • Inorganic fertilizers (e.g., nitrates, phosphates) inevitably make their way into aquatic systems: • fertilization of aquatic systems (eutrophication) leads to overproduction: • waters are no longer attractive for recreational use • decaying organic matter can lead to deoxygenation of water and fish kills

16. Fertilization and Eutrophication 2 • Addition of organic wastes poses a serious problem for water quality: • organic matter increases biological oxygen demand, decreasing oxygen levels: • killing fish and other obligate aerobes • cutting migration routes for other species • Problems associated with eutrophication can be avoided by: • cutting off or diverting sources of nutrients • improving treatment of organic wastes

17. Toxins • Toxins are poisons: • these chemicals kill animals and plants by interfering with normal physiological functions • many toxins occur naturally, but humans have increased their accumulation in the environment • various classes of toxins exist, including: • acids • heavy metals • organic compounds • radiation

18. Acids • Two principal sources of acidity are associated with human activities: • acid mine drainage: • oxidation of sulfur and thiol in mine wastes by bacteria creates sulfates, which become sulfuric acid in mine drainage • mine drainage may be sufficiently acidic as to sterilize aquatic environments downstream • acid rain, the result of combusting fossil fuels

19. Acid Rain • Burning of coal and oil releases nitrogen oxides and sulfur dioxide into the atmosphere: • these gases dissolve in raindrops, creating acids: • pH of rain may drop to as low as 3-4 • consequences of acid rain have been especially severe in industrialized areas: • direct impacts of acidity on aquatic systems • depletion of fertility in terrestrial systems • Reducing emissions of sulfur and nitrogen oxides, reductions in energy use are solutions to acid rain.

20. Heavy Metals • Mercury, arsenic, lead, copper, nickel, zinc, and other heavy metals are toxic even in low concentrations: • these enter the environment as byproducts of mining, manufacturing, fungicides, fuels • emissions of heavy metals from smelting operations have been especially troublesome: • emissions adversely affect mosses, lichens, fungi, other soil organisms, vascular plants, and higher animals • adverse effects may extend many km downwind of smelters

21. Organic Compounds 1 • Organic compounds have been introduced to many ecosystems in the form of pesticides: • classes include: • organomercurials (methylmercury) • chlorinated hydrocarbons (DDT) • organophosphorus compounds (parathion) • carbamate insecticides • triazine herbicides • these compounds may accumulate in ecosystems with adverse effects on unintended targets

22. Organic Compounds 2 • Can the adverse effects of pesticides be reduced? • modern pesticides and efficient delivery systems can reduce unintended impacts • alternatives to chemical warfare against other organisms can be explored • bioremediation (using biological agents to restore habitats) can be explored • Another anthropogenic impact caused by organic compounds is oil spills (3-6 x 106 tons annually): • oil kills by coating organisms, disrupting membranes

23. Radiation • Of special concern are extremely energetic (short wavelength) forms of radiation and subatomic particles emitted by disintegration of atomic nuclei: • low levels occur naturally as background • extreme radiation hazards are posed by nuclear power plants, nuclear wastes of various kinds, and nuclear war • even peaceful uses of nuclear materials are limited by problems associated with disposal of long-lived wastes

24. Atmospheric Pollution • Pollution of the oceans and atmosphere are of particular concern: • circulation leads to widespread distribution of pollutants far beyond their sources • of greatest concern are two anthropogenic effects on the atmosphere: • destruction of the ozone layer • increase in carbon dioxide, other greenhouse gases

25. The Ozone Layer and Ultraviolet Radiation • Ozone (O3) is molecular oxygen in a highly reactive form: • ozone readily oxidizes organic molecules • anthropogenic ozone near the earth’s surface is a byproduct of combustion of fossil fuels: • nitrous oxide (NO2) combines with oxygen to form ozone in the presence of sunlight • high levels of ozone are damaging to human health, crops, and natural vegetation

26. Ozone in the Upper Atmosphere • Naturally occurring ozone in the upper atmosphere absorbs ultraviolet radiation: • ozone thus shields earth’s surface from damaging effects of UV radiation • reaction of chlorine with ozone in the upper atmosphere breaks down ozone: • chlorine has increased as result of emissions of CFCs (chlorofluorocarbons) • depletion of stratospheric ozone at high latitudes has been referred to as ozone holes

27. Damaging Effects of Ozone Depletion • Depletion of stratospheric ozone leads to increased UV radiation at the earth’s surface: • Consequences include • damage to DNA and resultant cancers • reduced photosynthetic production by plants • Ozone depletion is now addressed by conventions phasing out use of CFCs: • Vienna Convention for Protection of the Ozone Layer (1985) • Montreal Protocol (1987)

28. Carbon Dioxide and the Greenhouse Effect 1 • Carbon dioxide (CO2) is a naturally occurring atmospheric component, at about 280 ppm in the preindustrial atmosphere. • CO2 and several other atmospheric gases form an insulative layer, passing visible light, but absorbing longwave radiation emitted by the earth: • referred to as the greenhouse effect

29. Carbon Dioxide and the Greenhouse Effect 2 • CO2 levels have varied considerably during earth’s history: • at times in the past when CO2 levels were high, earth was much warmer • CO2 levels are now creeping upward as a result of combustion of fossil fuels and forest clearing: • CO2 level is now 350 ppm and increasing • we are now faced with increasing global temperatures and related effects (such as rising sea levels)

30. Carbon Dioxide and the Greenhouse Effect 3 • Humans now add carbon to the atmosphere at a rate of about 7 billion tons annually: • the oceans absorb about 2.4 billion tons: • this is insufficient to balance anthropogenic additions, so atmospheric levels will continue to rise • Most effects of increased atmospheric CO2 and global warming will be negative: • increasing drought stress in arid environments • inundation of coastal areas by rising sea level

31. Human ecology is the ultimate challenge. • If we are to leave a habitable world for future generations, our top priority must be to achieve a sustainable relationship with the rest of the biosphere. This will require: • putting an end to population growth • developing sustainable energy sources • providing for regeneration of nutrients and other materials • restoring deteriorated habitats

32. Increase in Oil and Energy Prices Over Demand for Fish Population Growth Arable Land Over Demand Droughts Unsustainable Fishing Practices Food Production Biofuel and Food Competition Sea Food Supply Self Sufficiency Rate Increase in Speculative Trading Fisherman Income Food Deficit Rise in Food Prices Market Policies Food Security Poverty Direct Compensating Variation (DCV) Use of Cultivable Lands Desert Areas Salination Rise in Extreme Poverty Water Shortage Urban Expansion Migration to Urban Areas Overgrazing Climate Change Over Demand Farmer’s Low Income Desertification Population Growth

33. Future Scenarios • Potential consequences of unrestrained population growth and human impacts are devastating: • energy and material shortages • many living in poverty and disease • a badly polluted environment • escalating social and political strife • The future need not be like this…

34. Positive Alternatives • Humankind has the choice of adopting a new attitude toward its relationship with nature. We are a part of nature, not apart from nature. • To the extent that our intelligence, culture, and technology have given us the power to dominate nature, we must also use these abilities to impose self-regulation and self-restraint. • We have succeeded famously in becoming the technological species. Our survival now depends on our becoming the ecological species and taking our appropriate place in the economy of nature.

35. Summary 1 • The key to human survival is the development of sustainable interactions with the biosphere. • Local threats to integrity of natural systems are overexploitation of resources, introductions of exotic species, habitat conversion, irrigation, eutrophication, and production of toxic materials.

36. Summary 2 • Global threats to integrity of natural systems include depletion of stratospheric ozone and global warming caused by increasing atmospheric carbon dioxide. • Solutions to the environmental crisis will require new attitudes promoting sustainability and self-restraint.