Page 642 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

606 part IV Soils, ecosystems, and Biomes
The diversity of organisms on the living Earth is one of our planet’s most impressive features. This diversity is a response to the interaction of the at- mosphere, hydrosphere, and lithosphere, which produces a variety of conditions within which the biosphere exists. The diversity of life also results from the intri- cate interplay of living organisms themselves. Each species uses strat- egies that maintain bio- diversity and species coexistence.
The biosphere, the
sphere of life and organic
activity, extends from
the ocean floor to an al-
titude of about 8 km into
the atmosphere. The biosphere includes myriad ecosys- tems, from simple to complex, each operating within gen- eral spatial boundaries. An ecosystem is a self-sustaining association of living plants and animals and their non- living physical environment. Earth’s biosphere itself is a collection of ecosystems within the natural boundary of the atmosphere and Earth’s crust. Natural ecosystems are open systems with regard to both solar energy and matter, with almost all ecosystem boundaries functioning as tran- sition zones rather than as sharp demarcations. Ecosys- tems vary in size from small-scale, such as the ecosystem of a city park or pond, to mid-scale, as a mountaintop or beach, to large-scale, as a forest or desert. Internally, every ecosystem is a complex of many interconnected variables, all functioning independently yet in concert, with compli- cated flows of energy and matter.
Ecology is the study of the relationships between or- ganisms and their environment and among the various ecosystems in the biosphere. The word ecology, developed by German naturalist Ernst Haeckel in 1869, is derived from the Greek oikos (“household” or “place to live”) and logos (“study of”). Biogeography is the study of the distri- bution of plants and animals, the diverse spatial patterns they create, and the physical and biological processes, past and present, that produce Earth’s species richness.
Earth’s most influential biotic agents are humans. This is not arrogance; it is fact—humans powerfully af- fect every ecosystem on Earth. From the time humans first developed agriculture, tended livestock, and used fire, the influence of humans over Earth’s physical systems has been increasing. For example, the U.S. Gulf Coast wet- lands and associated coastal habitat, shown in Figure 19.1, bore the brunt of the 2010 British Petroleum (BP) oil spill;
(b) A Little Blue Heron in coastal wetland habitat near Sanibel Island, Florida Gulf Coast.
(a) The Barataria Preserve Wetland is a swamp in the Mississippi delta with bald cypress trees.
▲Figure 19.1 Gulf Coast wetland ecosystem. [Bobbé Christopherson.]
restoration of coastal marshes is ongoing. The degree to which modern society understands Earth’s biogeography and conserves Earth’s living legacy will determine the ex- tent of our success as a species and the long-term survival of a habitable Earth.
In this chapter: We explore the methods by which plants use photosynthesis and respiration to translate solar energy into usable forms to energize life. We then examine relevant nonliving systems and important bio- geochemical cycles, and look at the organization of living ecosystems into complex food chains and webs. We also examine communities and species interactions. Next we consider how the biodiversity of living organisms results from biological evolution over the past 3.6+ billion years. We conclude with a discussion of ecosystem stability and resilience, and how living landscapes change over space and time through the process of succession, now influ- enced by the effects of global climate change.
Energy Flows
and Nutrient Cycles
By definition, an ecosystem includes both biotic and abi- otic components. Chief among the abiotic components is the direct input of solar energy, on which nearly all eco- systems depend; the few limited ecosystems that exist in dark caves, in wells, or on the ocean floor depend on chemical reactions (chemosynthesis) for energy.
Ecosystems are divided into subsystems. The biotic tasks are performed by primary producers (plants, cyano- bacteria, and some other unicellular organisms), consumers (animals), and detritus feeders and decomposers (worms,