Chapter 44: The Biosphere

          Does a Cactus Grow in Brooklyn?

          A.   Unrelated species in distant regions often show striking similarities.

           B.   The distribution of species is related to climate, topography, and species interactions.

           C.   The biosphere is the sum total of all the earth regions where organisms live.

                  1.   Hydrosphere = all water on or near the earth’s surface.

                  2.   Lithosphere = the earth's outer, rocky layer.

                  3.   Atmosphere = gases, particles, and water vapor enveloping the earth.

           D.   Climate includes temperature, humidity, wind velocity, cloud cover, and rainfall; it is shaped by four factors:

                  1.   variations in the amount of incoming radiation,

                  2.   the earth’s daily rotation and annual revolution,

                  3.   the world distribution of continents and oceans,

                  4.   the elevation of land masses.


   I.     Air Circulation Patterns and Regional Climates

           A.   The atmosphere has mediating effects on the earth's climate.

                  1.   Ultraviolet radiation is absorbed by ozone and oxygen in the upper atmosphere.

                  2.   Clouds, dust, and water vapor in the atmosphere absorb and reflect solar radiation.

                  3.   Radiation warms the earth’s surface and generates heat that drives the earth’s weather systems.

           B.   Air currents are the result of heating from the sun.

                  1.   The sun differentially heats equatorial and polar regions creating the world's major temperature zones.

                  2.   Warm equatorial air rises, cools, releases its moisture, and spreads northward and southward where it descends at 30o latitudes as very dry air (results in deserts).

                  3.   The air is warmed again and ascends at 60o latitudes; as it moves toward the poles, regional areas receive varying amounts of rainfall that in turn influence ecosystems.

           C.   The amount of solar radiation reaching the earth’s surface changes in the Northern and Southern hemispheres; this results in seasonal changes in climate.


II.     The Ocean, LandForms, and Regional Climates

           A.   Ocean Currents and Their Effects

                  1.   Ocean water covers 71 percent of the earth's surface.

                  2.   Latitudinal and seasonal variations in solar heating cause ocean water to warm and cool on a vast scale.

                          a.   Surface waters tend to move from the equator to the poles, warming the air above.

                          b.   Currents form because of the earth’s rotation, winds, variations in temperature, and distribution of land masses.

                  3.   Immense circular water movements in the Atlantic and Pacific Oceans influence the distribution of ecosystems.

           B.   Regarding Rain Shadows and Monsoons

                  1.   Topography refers to physical features of a region, such as elevation.

                  2.   Mountains, valleys, and other features influence regional climates.

                          a.   Monsoon rains occur when warm winds pick up ocean moisture and release it over the cooler land masses of Asia and Africa.

                          b.   The mountains of the western United States cause the winds from the ocean to rise, cool, and lose their moisture.

                          c.   As the winds descend on the leeward (eastern) slopes, they gain moisture from the earth and its vegetation causing a rain shadow effect.


III.     Realms of Biodiversity

           A.   Plants and animals show a great diversity from one global region to another.

                  1.   Climatic factors determine patterns of vegetation and why unrelated species may have similar adaptations.

                  2.   Biogeography is the study of the global distribution of species.

           B.   The Earth's surface has been divided into regions for easier study.

                  1.   Biogeographic realms are very broad land regions with characteristic types of plants and animals; there are six of these.

                  2.   Biomes are large vegetational subdivisions including all animals and other organisms.

                          a.   Biome distribution corresponds with climate, topography, and soil type.

                          b.   The form of the dominant plants tells us something of the weather conditions.

                    c. Ecoregions are large areas representative fo the globally important biomes and water provinces vulnerable to extinction.


IV.     Soils of Major Biomes

           A.   Soil is a mixture of rock, mineral ions, and organic matter.

                  1.   The size of the rock can range from gravel, to sand, silt, and clay.

                  2.   The organic matter, in variable stages of decomposition, is called humus.

           B.   Soil profiles are defined by the composition of soil from the surface downward.

                  1.   Topsoil has the most humus and is the most vulnerable to weathering.

                  2.   Loam topsoils have the best mix of sand, silt, and clay for agriculture.


V.     Deserts

           A.   Deserts are areas where evaporation exceeds rainfall (30o north and south latitudes).

                  1.   Vegetation is scarce but there is some diversity.

                  2.   Day/night temperatures fluctuate widely.

           B.   More than a third of the world’s total land area is arid or semiarid due to drought and overgrazing, which can lead to desertification.


VI.     Dry Shrublands, Dry Woodlands, and Grasslands

           A.   Dry shrublands and dry woodlands occur in western or southern coastal regions of the continents between 30o and 40o north and south latitudes.

                  1.   The climate is semiarid; rains occur during mild winter months.

                  2.   Summers are long, hot, and dry; domi­nant plants have tough, evergreen leaves.

           B.   Dry shrublands prevail when rainfall is less than 25–60 cm (example: the highly flammable California chaparral).

           C.   Dry woodlands occur when rainfall is about 40–100 cm; there are trees but not in dense forests.

           D.   Grasslands extend across the interior of continents in the zones between deserts and temperate forests.

                  1.   Characteristics include: flat or rolling land, high rates of evaporation, limited rainfall, grazing and burrowing animals, and few forests.

                  2.   There are several types around the world:

                          a.   Shortgrass prairie of the American Midwest is typified by short, drought-resistant grasses that have been replaced by grains that require irrigation.

                          b.   Tallgrass prairie was originally found in the American West where water was more plentiful.

                          c.   Savannas such as the African savanna  are hot, dry and bear small bushes among the grass.

                         d.   The monsoon grasslands of southern Asia experience seasons of torrential rain alternating with near drought.


VII.   Tropical Rain Forests and Other Broadleaf Forests

           A.   Evergreen broadleaf forests occur between 20o N and S latitude.

                  1.   Most typical is the tropical rain forest where temperatures, rainfall, and humidity are all high.

                  2.   Plant growth is luxuriant, with competing vines; there is incredible animal diversity.

           B.   Deciduous broadleaf forests are common at temperate latitudes.

                  1.   In the tropical deciduous forest, many trees drop some or all of their leaves during the pronounced dry season.

                  2.   The monsoon forests  of Southeast Asia also have such trees.

                  3.   In the temperate deciduous forests of North America, conditions of temperature and rainfall do not favor rapid decomposition; thus, nutrients are conserved to provide fertile soil.


VIII.  Coniferous Forests

           A.   The typical “tree” in these forests is some variety of evergreen cone-bearer with needlelike leaves.

           B.   These forests are found in widely divergent geographic areas:

                  1.   Boreal forests (or taiga) are found in the cool to cold northern regions of North America, Europe, and Asia; spruce and balsam fir are dominant.

                  2.   Montane coniferous forests  extend southward through the great mountain ranges; fir and pine dominate.

                  3.   Temperate rain forest parallels the west coast of North America and features sequoias and redwoods.

                  4.   Southern pine forests  grow in the sandy soil of south Atlantic and Gulf states.


IX.     Arctic and Alpine Tundra

           A.   Arctic tundra  lies to the north of the boreal forests; it is a vast treeless plain, very cold, with low moisture; it is characterized by permafrost, which prevents growth of large trees.

           B.   Alpine tundra  occurs at high elevations in mountains throughout the world.


X.     Freshwater Provinces

           A.   The earth's water provinces, which include lakes, rivers, ponds, estuaries, wet­lands, shores, coral reefs, and open oceans, are more extensive than the biomes.

           B.   Lake Ecosystems

                  1.   A lake is body of freshwater with three zones:

                          a.   The littoral zone  extends from the shore to where rooted plants stop growing.

                          b.   The limnetic zone includes open, sunlit waters beyond the littoral to a depth where photosynthesis is no longer significant; plankton life is abundant.

                          c.   The profundal zone is the deep, open water below the depth of light penetration; detri­tus sinks from the limnetic and is acted upon by decomposers.

                  2.   In temperate regions, lakes undergo changes in density and temperature.

                          a.   In winter, ice (less dense) forms on the surface over water that is warmer, much of it at 4o C (greatest density), and heavier.

                          b.   During the spring overturn, warming and winds cause oxygen to be carried down­ward and nutrients to the surface.

                          c.   By midsummer a thermocline between the upper warmer layers and lower cooler layers prevents vertical warming.

                         d.   During autumn, the upper layers cool and sink causing a fall overturn.

                  3.   Interactions of soils, basin shape, and climate produce a continuum of trophic struc­ture.

                          a.   Oligotrophic lakes are deep, nutrient-poor, and low in primary productivity.

                          b.   Eutrophic lakes are shallow and nutrient-rich often due to agricultural and urban runoff wastes.

           C.   Stream Ecosystems

                  1.   Streams start out as freshwater springs or seeps.

                  2.   Three kinds of habitats form along a continuum from head waters to river’s end:

                          a.   Riffles  are shallow, turbulent stretches where water flows swiftly over sand and rock.

                          b.   In pools, deep water flows slowly over a smooth, sandy or muddy bottom.

                          c.   Runs  are fast-flowing waters with a smooth surface and a bottom of bedrock or rock and sand.

                  3.   Several factors affect streams:

                          a.   Average flow and temperature are influenced by geography, altitude, and forest shade.

                          b.   Volume and temperature vary with rainfall, snow melt, drought, and the seasons.

                          c.   Chemistry and pollution of the water depend on materials leached into, or added to, the stream.

                         d.   Streams erode their valleys and participate in cycles of erosion and redeposition of sedi­ments and nutrients.


XI.     The Ocean Provinces

           A.   The open ocean consist of two vast provinces:

                  1.   The benthic province includes all the sediments and rocky formations of the ocean bottom.

                  2.   The pelagic province  includes the entire volume of ocean water and is subdivided into two zones:

                          a.   The neritic zone  constitutes the relatively shallow water overlying the continental shelves.

                          b.   The oceanic zone is the water over the ocean basins; photosynthetic activity is restricted to the surface.

           B.   Primary Productivity in the Oceans

                  1.   Phytoplankton are the beginning of ocean food webs; organic remains and wastes enter the detrital webs.

                  2.   As much as seventy percent of the productivity may be from microscopic ultraplankton.

           C.   Hydrothermal Vents

                  1.   In the fissures between the earth's crustal plates, water becomes heated and laden with minerals as it escapes.

                  2.   Elaborate food webs are supported at this sites.


XII.   Life Along the Coasts

           A.   Mangrove Wetlands and Estuaries

                  1.   Mangroves are forests in sheltered regions along tropical coasts.

                          a.   Ocean waves do not reach these saltwater ecosystems, so anaerobic sediments and mud accumulate.

                          b.   Salt-tolerant plants with prop roots dominate.

                  2.   Estuaries are partially enclosed regions where fresh and salt water meet.

                          a.   Estuaries are incredibly productive feeding and breeding grounds for many animals.

                          b.   Many marine estuaries are under assault from raw sewage, agricultural runoff, industrial wastes, and too much freshwater.

           B.   Rocky and Sandy Coastlines

                  1.   The intertidal-zone inhabitants are alternately exposed and submerged; existence is difficult.

                  2.   Rocky shores have three vertically arranged zones:

                          a.   The upper littoral is submerged only during the highest possible lunar tide; it is sparsely populated.

                          b.   The mid-littoral is submerged during the regular tide and exposed at the lowest tide of the day.

                          c.   The lower littoral is exposed only during the lowest lunar tide.

                  3.   Sandy and muddy shores are rather unstable stretches of loose sediments; detrital food webs occur; invertebrates are plentiful.

           C.   Upwelling Along Coasts

                  1.   Upwelling is the upward movement of deep, nutrient-rich water along the margins of continents.

                          a.   Under the influence of northern winds and the earth's rotation, water along the western coasts of the Northern Hemisphere move westward where cold, deep water moves in vertically to replace it.

                          b.   At places where currents stir the ocean water and circulate nutrients, primary pro­ductivity increases.

                  2.   Every three to seven years, the warm surface waters of the western equatorial Pacific move eastward to the coasts of South and Central America to cause "downwelling"—a phenomenon known as El Niño,.


XIII.        Focus On Science  Rita in the Time of Cholera