Human Impact on Earth: Extinction, Conservation, and Hope

1. Chapter 25: Extinction and Conservation Robert E. Ricklefs The Economy of Nature, Fifth Edition

2. Take note • Be sure to check the readings on the website • They will be on the exam

3. Human Impact on Earth • The human impact on the earth is substantial: • in the year 2000, human population was 6 billion: • we are still growing at the robust rate of 2% per year • humans control or indirectly affect much of the earth’s surface: • 35% of land area is used for crops or permanent pastures • countless additional hectares are grazed by livestock • tropical forests are being felled at 17 million hectares per year • 2% of remaining forest is cut per year • desertification is a widespread problem, especially in Africa • air and water pollution are also widespread

5. Human impacts on the planet can be reduced. • Negative consequences of human impacts on natural systems are enormous: • deterioration of the environment: • will lead to a declining quality of life for all humans • already affects the other life forms on the planet • But there is cause for hope: • humans can live in a clean and sustaining world, but only by placing support for our own population into balance with preservation of other species and the ecological processes that nurture us

6. Three Lessons from Ecology 1 • The science of ecology has much to tell us about living sustainably in a healthy world. • Environmental problems cannot be solved until the human population is brought under control: • density-dependent control of the human population will mean untold suffering • we must learn to value individual human experience over numbers of progeny

7. Three Lessons from Ecology 2 • Individual consumption of energy, resources, and food produced at higher trophic levels must be reduced: • we have already exceeded the capacity of earth to support the current human population at a level enjoyed by the most affluent societies • we can make contributions to sustainability by: • investing in and utilizing energy- and resource- efficient technologies • eating lower on the food chain

8. Three Lessons from Ecology 3 • Ecosystems should be maintained in as close to their natural state as possible to keep natural processes intact: • areas unsuitable for grazing or agriculture should not be converted to such uses: • these areas are best set aside for conservation and recreation • living with nature is always preferable to, and less costly than, going against it

9. Biological diversity is incompletely described. • There may be as many as 10 to 30 million species of plants, animals, and microbes worldwide: • only 1,500,000 species have been catalogued • although lists are important, they represent only one approach to the documentation of biological diversity or biodiversity, the many unique attributes of living things

10. Proportions of named species…

11. Components of Biodiversity 1 • Ecological diversity: • each species has unique attributes and adaptations that define its place in the ecosystem: • plants, for example, vary in: • tolerances of environmental conditions • defenses against herbivores • growth form • strategies for pollination and seed dispersal

12. Components of Biodiversity 2 • Genetic diversity: • crucial to evolutionary responses of organisms to changing environments • has both within- and between-species components • Geographic diversity: • each region has different species composition and diversity • endemic species are restricted to small geographic areas • regions with many endemics possess high endemism

13. Endemism • Oceanic islands are well known for harboring endemic forms: • nearly all native birds, plants, and insects of isolated islands live nowhere else • loss of such island species caused by habitat destruction, hunting, or alien species means worldwide extinction • humans have caused many extinctions of island endemics

14. Be sure to … • Spend some time here: http://biodiversity.moe.gov.lb/

15. Value of Biodiversity • Current loss of species is at an all-time high in earth’s history: • some estimates place this rate in excess of one species per day • Why should we be concerned about loss of species? • many species are gone already • extinction is a natural process

16. Moral Responsibility • Extinction raises important moral issues: • some feel that because humankind affects all of nature, it is our moral responsibility to protect nature • if morality is intrinsic to life itself: • rights of nonhuman individuals and species are as legitimate as the rights of individuals in human society • Environmental ethics

17. “What is a man without the beasts? If all the beasts were gone, men would die from great loneliness of spirit, for whatever happens to the beasts also happens to man.”—Chief Seattle

18. Economic Benefits • Individual species have direct economic and recreation values for humankind: • food resources • game species • sources of forest and other natural products • drugs and other organic chemicals • about 25% of prescriptions filled in the United States / more than 100 important medicinal drugs / are extracted directly from flowering plants • Assigning economic value to one species – does not address conserving biodiversity in a general sense. Why not?

19. Economic values of species can cause environmental harm. • Policies favoring certain species may harm others: • cultivated species displace other species viewed as having lesser value • predators, such as wolves, are eliminated because of conflicts with livestock operations • overexploitation of resources (such as fisheries) may lead to their demise

20. Ecotourism • Some species have high value because they attract tourists, in a practice known as ecotourism: • many countries have benefited from the willingness of tourists to visit game parks and preserves; ecotourism: • often brings much-needed foreign currencies into developing countries • is responsible for development of parks and preserves • is expanding, but its potential is finite: • people have limited resources to devote to such activities • many species and ecosystems are not attractive to ecotourists

21. Giving monetary value … • Chief Seattle: How can you buy or sell the sky, the warmth of the land? The idea is strange to us. • If we do not own the freshness of the air and the sparkle of the water, how can you buy them? • Only after the last tree has been cut down, Only after the last river has been poisoned, Only after the last fish has been caught, Only then will you find money cannot be eaten. • ~ Cree Prophecy

22. Indication of Environmental Quality • Individual species may have value as indicators of environmental change: • birds of prey declined during the 1950s and 1960s in the United States: • this decline was traced to pollution of aquatic habitats by breakdown products of DDT, which: • entered aquatic food chains and were concentrated at each step in the chain • interfered with physiology and reproduction in birds • identification of the problem led to banning of DDT and subsequent recovery of many species

23. Broken eggshells in the nest of a brown pelican

24. Maintenance of Ecosystem Function • Diversity may help stabilize ecological systems: • the research of Tilman and Downing has shown that biomass production was less affected by drought on high-diversity plots: • with many species present, some can assume key roles when environmental conditions change • such switching is less likely in less diverse systems

25. Decrease in plant biomass after event – related to plants species richness before event

26. Plant biomass increases w/ number of plant guilds

27. Extinction is natural, but its present rate is not. • Extinction is of concern because evolutionary lineages are lost forever. • The relatively low rate of natural extinction is called background extinction: • life span of most species in the fossil record is 1 to 10 million years • analysis of the fossil record indicates a background extinction rate of 1 species per year

28. Other Types of Extinction • Mass extinctions are caused by natural catastrophes, such as meteor impacts: • such bolide impacts are thought to occur at intervals of 10 to 100 million years: • may have been responsible for mass extinctions at the end of the Paleozoic and Mesozoic eras • Anthropogenic extinctions are caused by humans: • such preventable extinctions have brought the modern extinction rate to far in excess of natural levels

30. Humans cause extinctions by several mechanisms. • Populations disappear because deaths exceed births over a prolonged period: • extinction may be viewed as a failure to adapt to changing conditions • a recent survey has revealed the principal causes of population decline for endangered U.S. species: • habitat reduction and modification (67% of cases) • small population size • introduction of exotic species • overexploitation

31. Habitat Reduction and Fragmentation • Habitat reduction and fragmentation threaten many species: • some habitats are reduced or eliminated altogether • fragmentation creates a suite of additional problems: • small areas may not be able to support viable populations of larger species, such as mammals • small populations are subject to stochastic local extinction • fragmentation increases edges, exposing forest interior species to increased parasitism and predation • species of fragmented habitats may be unable to migrate with changing climate induced by global warming

33. Atlantic coastal forests of Brazil – reduced to a small fraction

34. Fragmented habitats… • …support smaller populations • Becomes a biological ‘island’

35. Small Population Size • Stochastic extinction is a risk that increases dramatically for the smallest populations. • Reduced genetic variation in small populations may further increase the probability of extinction: • founder effects, inbreeding, genetic drift, and population bottlenecks all pose problems • some species, notably the northern elephant seal, have survived severe population bottlenecks successfully

36. Introductions of Exotic Species • Decreases in habitat quality are frequently the consequence of introduced predators, competitors, or disease organisms: • many species arrive accidentally and others are introduced intentionally • islands seem to be most vulnerable to introduced species (Hawaiian Islands have suffered greatly from introduced species) • aquatic systems are also vulnerable to effects of exotics • continental areas are not immune to effects of exotics

42. Overexploitation • Many species have succumbed to effects of direct exploitation by humans: • efficient hunting and fishing may drive species to extinction • humans have a long history of overexploitation: • arrival of humans in North America was accompanied by rapid extinction of 56 species in 27 genera of large mammals

43. Overexploitation: changes the species composition of a community

46. Vulnerability to extinction is poorly understood. • Why some species are more vulnerable to extinction than others is hard to determine. • Some attributes that predispose species to extinction include: • species attractive for exploitation • species that have evolved in the absence of hunting • species that have evolved in the absence of diverse disease organisms • species with limited geographic range, restricted habitat distribution, and small local population size