Page 304 - Environment: The Science Behind the Stories

100 Overharvesting For most species, hunting or harvest-
90 ing by people will not in itself pose a threat of extinction,
but for some species it can. Large mammals of the African
80
Percent of habitat lost 60 Large in size, long-lived, and raising few young in their
savannas, such as elephants and rhinoceroses, are examples.
70
50
lifetimes—classic K-selected species (p. 87)—elephants
and rhinoceroses are just the type of animal to be vulnerable
40
to hunting. People have long killed elephants to extract their
30
20
nations enacted a global ban on the commercial trade of
10 tusks for ivory (Figure 11.13). Because of this, the world’s
0 Desert Tundra ivory. Since imposition of the ban in 1989, elephant num-
Temperate grassland Chaparral Tropical dry forest Savanna Tropical rainforest Boreal forest illegally each year, and ivory trade continues on the black
Temperate rainforest
Temperate deciduous forest
bers have recovered, but thousands still are slaughtered
market. Similarly, rhinoceroses are killed for their horns,
which are sold illegally to Asian nations for traditional med-
icine and to some Middle Eastern countries for ornamental
use as dagger handles.
Over the past century, hunting has led to steep declines
Figure 11.12 Human impact has caused habitat loss in all in the populations of many K-selected animals. In central
the world’s biomes. Shown are percentages of original area that Africa, gorillas and other primates are killed for their meat
were fully and directly converted for human use through 1990. and may face extinction soon. Across Asia, the tiger is
Adapted from Millennium Ecosystem Assessment, 2005. Ecosystems and human threatened by habitat loss and poaching; body parts from one
well-being: Biodiversity synthesis.World Resources Institute, Washington, D.C.
tiger can fetch a poacher $15,000 on the black market, where
they are sold as aphrodisiacs in Asian countries. Today half
Pollution Pollution can harm organisms in many ways. the world’s subspecies of tiger are extinct, and most of the
Air pollution (Chapter 17) degrades forest ecosystems. Water remaining animals are crowded onto just 1% of the land they
pollution (Chapter 15) impairs fish and amphibians. Agricul- originally occupied. In the oceans, decades of whaling drove
tural runoff containing fertilizers, pesticides, and sediments the Atlantic gray whale extinct and have left several other
(Chapters 5, 9, and 10) harms many terrestrial and aquatic whales threatened or endangered. Thousands of sharks are
species. Heavy metals, polychlorinated biphenyls (PCBs), killed each year simply for their fins, which are used in soup.
endocrine-disrupting compounds, and other toxic chemi- Today the oceans contain only 10% of the large animals they
cals poison people and wildlife (Chapter 14). Plastic garbage once did (p. 459).
in the ocean can strangle, drown, or choke marine creatures To combat overharvesting, governments have passed
(p. 450–454). The effects of oil spills on wildlife (pp. 454–455, laws, signed treaties, and strengthened anti-poaching
556–559) are dramatic and well known. efforts. Scientists have begun using genetic analyses to
Although pollution is a substantial threat, it tends to be expose illegal hunting and wildlife trade. For instance,
less significant than public perception holds it to be. The dam- DNA testing can reveal the geographic origins of elephant
age to wildlife and ecosystems caused by pollution can be ivory and whether whale meat sold in markets is from an
severe, but this tends to be surpassed by the harm caused by animal caught illegally (see THe SCieNCe beHiND THe STOrY,
habitat alteration or invasive species. pp. 318–319). CHAPTER 11 • Bi odiv ER si T y A nd Cons ER vAT i on Bi ology

Figure 11.13 Poachers kill
elephants to sell their tusks
for ivory. Despite the long-standing
ban on ivory trade, 2009–2013 saw the
most poaching and ivory confiscation yet.
Here, Kenyan officials prepare to set fire to
thousands of confiscated tusks at Masai
Mara National Park in an effort to dampen
the trade. 303

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