Biology 10, Las Positas College
The Biosphere
Chapter 42

II-Abiotic Factors of the Biosphere
III-Terrestrial Biomes
IV-Aquatic Biomes


A. Ecosystem = communities of organisms living within a defined area and the nonliving environmental factors with which they interact.

B. Biomes = ecosystems of plants and animals that occur over wide areas of land within specific climatic regions and are easily recognized by their overall appearance.

C. Biosphere = all parts of the Earth where life exists: extends from the tops of the mountains to the depths of the seas. Often spoken of as the environment = land, air, water & every living thing on Earth.

II-Abiotic Factors of the Biosphere

Temperature and rainfall patterns -> the abundance of 4 basic requirements for life: nutrients, water, energy, temp. compatible with life

A. Sunlight
The angle of a beam of solar energy striking the Earth at the equator is perpendicular to the surface of the Earth.

B. Seasons
Seasons occur in northern and southern hemispheres because the Earth is tilted on its axis.

C. Air Circulation & Rain

Near the equator, warm air rises and flows toward the poles, cools, and falls back to earth at 30 degree latitudes.
Air rises again, at 60 degree latitudes. Air falls at poles. Air mass cooler and dryer with every cycle. ->deserts near 30 degrees north or south latitude.
Wettest areas of world at equator & 60 degrees N & S.
Driest areas at 30 degrees N & S & poles.

D. Wind & Ocean Currents

Land contours and distance from oceans also determine rainfall. Some deserts are on the other side of the mountain or in the interiors of the large continents.
Ocean currents also influence warmth of land masses.

III-Terrestrial Biomes

The characteristics of biomes are a direct result of their temperature. and rainfall patterns.
These patterns result from the interaction of the features of the Earth itself with two physical factors:

1. The amounts of heat from the sun that reach different parts of the Earth and the seasonal variations in that heat.
2. Global atmospheric circulation and the resulting patterns of oceanic circulation. -> local climate, including the amounts and distribution of precipitation.

In general the biomes are arranged by distance from equator but elevation also greatly affects placements.

Biomes in order from equator or elevation are: tropical rain forests, savannas, deserts, temperate grasslands, temperate deciduous forests, coniferous forests, tundra.

1. Tropical rain forests-Central America, parts of South America, Central and Western Africa, SE Asia. High temperatures and rainfall, generally little seasonal difference. Very tall trees, vines grow up them to get light. Only 2% of sun shining on forest canopy reaches its floor. Plants that do grow there have large, dark leaves adapted to conducting photosynthesis at low light levels. Many diverse animals. Poor soils.

2. Savannas-open grasslands with scattered shrubs and trees. Much of central and Southern Africa, northern Australia, large areas of northern and east-central South America. Between tropical forests and deserts. Heat, periodic dryness, poor soils. Vegetation supports large grazing herbivores such as buffalo, wildebeests, and zebra. Predators (lions). Lots of insects (homes mainly in ground). Plant eaters.
Trees rare because of lightening fires & grazing.

3. Deserts-very little rain. Vegetation sparse. Deserts radiate heat rapidly at night. ->substantial daily changes in temp, sometimes more than 55oF between day and night. Summer daytime temps very hot.
Plants have developed a wide variety of adaptations to survive. Some skip dry season as seeds. Succulents store water in their tissues. Trees and shrubs often have deep roots to reach water far below the surface. May lose their leaves during the hot, dry seasons. Some have hard, reduced leaves.
Desert animals - adaptations too. Some 'hibernate' in holes beneath surface (cool, moist) during hot, dry weather. Some only come out at night. Some seek better weather during hot, dry season.

4. Temperate grasslands -Various names: prairies of North America, steppes of Russia, veld of South Africa and pampas of South America. 10-30 in. of rainfall annually, less than savannas but more than deserts. Large quantities of perennial grasses, rainfall insufficient to support forests or shrublands. Populated by burrowing rodents, such as prairie dogs and herds of grazing mammals, such as the North American bison. Predators. Grazing prevents woody vegetation. Make good farms-many rich agricultural lands in US and southern Canada were originally occupied by prairies.
Seasonal drought, lightening fires, grazing -> open grassland.

5. Temperate Deciduous forests-Northern hemisphere, such as eastern US and Canada and an extensive region in Eurasia. Trees lose their leaves and are dormant during the winter. 30-60 in. precipitation well distributed during year but water generally unavailable during winter because it is frozen. Vegetation grows closer to earth than tropical forest and forest floor has ferns, herbs, mosses. Often a layer of shrubs. Animal life on floor abundant.

6. Coniferous forests. (in northern hemisphere) Long, cold winters with little precipitation. Most of the precipitation falls in summer. Days are long in summer and short in winter (high latitude). Light, warmth, and rainfall of summer allows plants to grow rapidly, and crops often attain large size in a surprisingly short time. The trees of the taiga occur in dense stands of one or a few species of cone-bearing trees. Many large mammals can also be found there, such as elk, moose, deer. Stalked by carnivores, such as wolves, bear, lynx.

7. Tundra-Fartherest north in Eurasia, North America -between the coniferous forests and the permanent ice-is the open, often boggy community known as the tundra. Circles the top of the world, covering 1/5 of the Earth's land surface. (No well-developed tundra in Antarctica because there is no land at the right latitude.) Scattered patches of grasses, heather, lichens. Few small trees at margins of streams and lakes. Low annual precipitation, unavailable most of the year because frozen. During brief Arctic summer, some of the ice melts. The permafrost, or permanent ice, about a meter down from surface never melts. When surface ice melts in summer, it forms puddles. The alpine tundra found at high elevations in temperate or tropical regions does not have this layer of permafrost. Tundra teems with life during its short summer. Herbs and grasses grow, large grazing mammals (musk oxen, caribou, and reindeer) migrate from the taiga. Many species of birds and water fowl nest in the tundra in summer and then migrate to warmer climate.

IV-Aquatic Biomes

A. Life in Fresh Water-Ecosystems lie near and are intertwined with terrestrial ecosystems. From them, organic and inorganic material continuously enters freshwater ecosystems.

Shore-plants, frogs, snails, dragonflies, tiny invertebrates.
Open-water zone-light penetrates -> algae, plantlike organisms (phytoplankton), protozoans feed on phytoplankton, small fish eat protozoans, etc.
Deep zone-light does not penetrate, no producers. Inhabited by decomposers and scavengers such as shrimp and clams.
Streams & rivers-movement -> fewer plants, more O2 than ponds & lakes.

B. Estuaries-Fresh water joins salt water. Nutrients are abundant in estuaries because estuaries are close to terrestrial ecosystems. and derive much of their nutrients from them like rivers and streams. Sometimes polluted from industry or shipping. Teaming with plants, oysters, crabs, lobsters, shrimp, fish. All must adapt to moving water and changing salinity.

C. Life in the Oceans-Oceans cover 3/4 of Earth's surface.

Three major life zones: 1. Intertidal zone-area between the highest and lowest tides. 2. Neritic zone-shallow waters along the coasts of the continents, which extends from the low tide mark to waters down to depth of 200 meters (about 600 feet). 3. Open-sea zone, composing the remainder of the ocean.

1. Intertidal zone-conditions change as tide rolls in and out-wet to dry, sun protected to sun parched, wave battered to calm. Rocks contain lichens and algae, lower- barnacles, lower-oyster, blue mussels, limpets, lower- brown algae and red algae. Kelp in areas only exposed for short periods.

Sandy shores-Organisms burrow in sand during low tide. Near low tide mark, sea anemones, sea urchins and sea stars. Plentiful light-home to variety of producers.

2. Photic Zone - shallow water-continental shelf-from intertidal zone to about 650 ft. deep water. Abundant producers and therefore, animal life.

Ex: coral reef. Built by corals that secrete calcium carbonate to build complex ecosystem. Provide habitats for a variety of invertebrates and fishes. One of most highly productive ecosystems in term of biomass.

3. Open-sea Zone-beyond continental shelf, called pelagic or open ocean zone. Upper layer receives light ->phytoplankton which serves as base for oceanic food webs. Zooplankton eat them. Fishes eat them. Air-breathing mammals such as whales, porpoises, dolphins seals and sea lions eat them.

Little light penetrates below 650 - 3250 feet. No photosynthesis.

Benthic zone - Pressure increases with depth. Some weird animals like bioluminescent fish, swordfish some sharks and whales, octopi and squid. At more than 3250 feet below surface-high concentration. of salt, immense water pressure, very cold. Scavengers crawl around eating detritus. Sea urchins, sea cucumber, clams, worms, bacteria-also found in other ocean zones but are different species.