Page 671 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

THEhumanDENOMINATOR 19 Ecosystems and Biodiversity
ECOSYSTEM PROCESSES HUMANS
•All life, including humans, depends on healthy, functioning ecosystems, which provide the food and all other natural resources that humans use.
19a Beaver are large, semi-aquatic rodents known for building dams that modify
HUMANS ECOSYSTEM PROCESSES
Human activities cause declining biodiversity. For example,
• Habitat loss occurs as natural lands are converted for agriculture and urban development.
• Pesticides and other pollutants poison organisms and food webs.
• Overharvesting of plants and animals leads to extinction.
• Climate change affects plant and animal distributions and overall ecosystem function.
• Fertilizer use and industrial activities alter biogeochemical cycles,
as when dead zones disrupt the nitrogen cycle.
19b
Scientists outfitted the first satellite tracking tags for baby loggerhead sea turtles in 2012. Past efforts at developing such devices were limited by the animal’s small size and rapid growth. The tags will allow experts to follow migration routes throughout all life stages, providing critical information for sea turtle conservation. (See GeoReport 19.2.) [Jim Abernathy, NOAA.]
Scientists are attributing increased foliage cover since 1982 throughout parts of Australia to the “CO2 fertilization effect”—the increase in photosynthesis caused by rising atmospheric CO2 levels. In Australia’s warm, dry climates, leaf cover is more responsive to increased CO2 than in other regions; as leaves draw in extra CO2, they lose less water so that the plant puts out more leaves, producing a “greening” that shows in satellite images. Other warm, arid regions of the world show the same trend. (See the world map of foliar cover change at www.csiro.au/ Portals/Media/Deserts-greening-from-rising-CO2.aspx.) [© Copyright CSIRO, 2013. Used by permission.]
landscapes and create wetland habitat for many plants and other animals. Hunted to near-extinction by the early 1900s, the Eurasian beaver (Castor fiber) was successfully reintroduced throughout most of its former range. The North American beaver (Castor canadensis) also declined, although populations have today recovered in most regions. [Danita Delimont/Getty Images.]
19d
Orcas (Orcinus orca), also known as killer whales, are threatened by high levels of polychlorinated biphenyls (PCBs), as well as other contaminants, in Puget Sound, Washington. Persistent organic pollutants are stored in the whale’s tissues and may be a primary cause for declining resident populations of these marine mammals. [Danita Delimont/Getty Images.]
19c
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Change in foliage cover
ISSUES FOR THE 21ST CENTURY
• Species and ecosystem conservation and restoration will be essential for saving species from extinction.
• Fire ecology will become increasingly important as climate change leads to prolonged drought in some areas and as human populations spread further into wildlands.
• Addressing and mitigating climate change may become essential to preserv- ing a future for all species, including humans.
• Human health will be affected by climate change, as disease-carrying hosts expand their ranges.
geosystemsconnection
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Earth’s biosphere is a remarkable functioning entity of abiotic and biotic components, all interacting and interrelated through some 13.6 million species. Plants harvest sunlight through photosynthesis and thus begin vast food webs of energy and nutrition. Life on Earth evolved into this biologically diverse structure of organisms, communities, and ecosystems that gain strength and resilience through their biodiversity. We next move to a discussion of biomes and to a synthesis of the subjects from Chapters 2 through 19, as we bring all the book’s topics together to form a portrait
of our planet.