Page 667 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 19 ecosystem essentials 631
that over half of Earth’s present species could be extinct within the next 100 years. The Human Denominator, Figure HD 19, offers examples of some human causes of biodiversity decline.
Five categories of human impact represent the great- est threat to biodiversity:
• Habitat loss, degradation, and fragmentation as nat- ural areas are converted for agriculture and urban development
• Pollution of air, water, and soils
• Resource exploitation and harvesting of plants and
animals at unsustainable levels
• Human-induced climate change, discussed in this
chapter’s Geosystems Now and in Chapter 11
• Introduction of non-native plants and animals, dis-
cussed in Chapter 20
The World Conservation Monitoring Centre and its International Union for Conservation of Nature (IUCN) maintain a global “Red List” of endangered species at www.iucnredlist.org/. See also the Committee on the Status of Endangered Wildlife in Canada, www.cosewic.gc.ca, and the endangered species home page of the Fish and Wild- life Service at www.fws.gov/endangered/. Let us now look at some specific examples of species in decline.
Threatened species—Examples Research indicates that amphibians are vulnerable to changes in both terres- trial and aquatic ecosystems, such as habitat destruction, pollution, invasive species, and changing climate—this puts them at higher risk than mammals, fish, and birds. Although amphibian declines can also be attributed to natural causes such as competition, predation, and dis- ease, the bottom line is that these species are not evolving fast enough to keep up with the rate of change.
In the Arctic region, the polar bear (Ursus mariti- mus) faces melting sea-ice habitat associated with cli- mate change. The IUCN in 2006 listed the species as “vulnerable” to extinction, and it was designated as “threatened” under the U.S. Endangered Species Act (ESA) in 2008. Research released by the U.S. Geologi- cal Survey in September 2007 predicted that with the loss of Alaskan, Canadian, and Russian sea-ice habitat, some two-thirds of the world’s 23000 polar bears will die off by 2050 or earlier. The remaining 7500 bears will be struggling.
In Africa, black rhinos (Diceros bicornis) and white rhinos (Ceratotherium simum) exemplify species in jeopardy from declining habitat and overharvesting. Rhinos once grazed over much of the savannas and woodlands. Today, they survive only in protected dis- tricts in heavily guarded sanctuaries (Figure 19.24). Consider these statistics:
• Black rhinos: The population of 70 000 in 1960 dropped to 2599 in 1998—a decline of 96%. South Af- rica guards about 50% of the herd. Slow recovery is under way; numbers rose to 4880 in 2010. The western
▲Figure 19.24 The rhinoceros in Africa. White rhinoceros (Ceratotherium simum) with young, from the southern population, lake nakuru national Park, kenya. [Chris Minihane/getty images.]
black rhino, a subspecies, has not been seen since 2006
and is considered extinct.
• White rhinos: The 11 northern white rhinos surviving
in 1984 increased to over 25 by 1998 but then dropped as political unrest in the Congo slowed protection ef- forts. In 2014, only 6 were left in the Ol Pejeta Conser- vancy in Kenya. The southern white rhinos are on the increase; their population topped 20000 in 2014.
Rhinoceros horn sells for $29000 per kilogram as an aphrodisiac (but in reality has no medicinal effect). These large land mammals are nearing extinction and will survive only as a dwindling zoo population. The limited genetic pool that remains complicates further reproduction.
Relating systems analysis to species Extinction
Scientists are using systems analysis (as discussed in Chapter 1) to understand extinctions of harlequin frog (Atelopus varius) and golden toad (Bufo periglenes) spe- cies in the Monteverde Cloud Forest Reserve, Costa Rica, and elsewhere in Central and South America. Specifically, they are analyzing how climate change is altering the frogs’ exposure to diseases and pathogens. One infectious agent, the chytrid fungus (Batrachochy- trium dendrobatidis), has spread into mid-elevation re- gions (1000 m to 2400 m) of the mountain cloud forest, where optimum temperature conditions for the fungus now exist. As a result, this non-native fungus today co- exists in habitats of the harlequin frog.
To understand the amphibian die-offs, scientists analyzed ocean and air temperature records and used a systems perspective to make connections. They pro- pose that human-forced climate change has increased the temperature of the ocean and atmosphere, which causes higher evaporation rates, which in turn affects
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