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Honors Biology Section 2
May 7, 2010
Chapter 21 Ecosystems
Terrestrial Biomes
The Major Biomes
- Biomes are distinguished by the presence of characteristic plants and animals
- Most ecologists recognize 8 major biomes (tundra, topical forest, temperate forest, taiga,
temperate grassland, savanna, chaparral and desert) and several minor biomes
- Because abiotic factors change over a landscape, biomes seldom have distinct boundaries
Tundra
- Tundra: a cold and largely treeless biome that forms a continuous belt across northern North
America, Europe and Asia
o It is the largest and northernmost biome, covering about 1/5 of the world’s land
surface
- Permafrost: a permanently frozen layer of soil under the surface, characterizes the tundra
- Trees do not usually grow in the tundra because the winters are long and extremely cold and
permafrost prevents their roots from penetrating far into the soil
- Receives little precipitation
- Has a very short growing season (2 months)
- Cold temperatures
- Slow decay = few nutrients
- Grasses, sedges and mosses
- Caribou, musk oxen, snowy owls, arctic foxes, lemmings and snowshoe hares
Forests
- 3 main types: tropical, temperate and boreal (taiga)
Tropical Forests
o Near the equator, in the region between 23.5°N and 23.5°S, known as the tropics
o Region includes parts of Asia, Africa, South America and Central America
o Stable temperature
o Abundant rainfall
o Most productive biome type
o 2 seasons: wet and dry
 Wet: tall trees and plants
 Dry: trees lose their leaves
o Competition for light is intense
o Canopy: a continuous layer formed by treetops
o Much of the forest floor is free of vegetation because so little sunlight reaches the
ground
o Jungle: dense growth found along riverbanks and in disrupted areas where sunlight
can reach the forest floor
o Epiphytes: small plants that live on branches of tall trees (mosses, orchids, and
bromeliads)
o Have the highest species richness of all biomes
o Monkeys, snakes, lizards and colorful birds (parrots)
Temperate Forests
o Occur in eastern North America, western and central Europe and northeastern Asia
o Distinct seasons
o Moderate climate
o Coniferous trees: bear seeds in cones and tend to be evergreen
o Deciduous trees: shed their leaves each year
Temperate Deciduous Forests
o Temperate deciduous forests: characterized by trees that lose all of their leaves in the
fall and re grow them each spring
o Stretch across eastern North America, much of Europe and parts of Asia and the
Southern Hemisphere
o Bears, wolves, white-tailed deer, foxes, raccoons and squirrels
o In United States, Europe and Asia, large amounts have been cut for timber or cleared
to make way for farms, towns and cities
Taiga
o Taiga (boreal): a forest biome dominated by coniferous trees
o Stretches across large areas of northern Europe, Asia and North America between
50°N and 60°N
o During the long winter, snow covers and insulates the ground, protecting tree roots
against freezing
o Long cold winters
o Short summers
o Nutrient poor soil
o Moose, bears, wolves, lynxes and hares
Grasslands
Temperate Grasslands
o Dry
o North America, Asia, Europe, Australia and South America
o Rich, fertile soil
Savanna
o Savanna: tropical or temperate grasslands that have scattered deciduous trees and
shrubs
o Africa, South America and Australia
o Alternating wet and dry seasons
o Zebras, wildebeests, giraffes, gazelles, lions, leopards and cheetahs
o Most of the rain falls during wet seasons
Chaparral
o Chaparral: a biome that is dominated by dense, spiny shrubs and has scattered clumps
of coniferous trees
o Mild, rainy winters
o Hot, dry summers
o Periodic fires
o Middle latitudes about 30°N and 30°S of the equator
o Found in coastal regions
Deserts
- Deserts: areas that receive an average of less than 25 cm of rainfall per year
- Large parts of North Africa, central Australia, southwestern North America and eastern Asia
-
Hot in summer
Cold in winter
At night temperatures may fall by as much as 30°C because the dry air is a poor insulator,
allowing the heat the builds up during the day to escape
Sparse vegetation
Some leaves have a waxy coating that reduces evaporation
Cactus have an expandable body that can store water and leaves that have evolved into sharp
spines that protect the plant from herbivores
Many animals avoid the heat of the day by hiding in small spots of shade or by burrowing
into the ground
Active only at night
Aquatic Ecosystems
Ocean Zones
- Aphotic zone: sunlight cannot penetrate an photosynthesis cannot occur
- Photic zone: the part of the ocean that receives sunlight
- Intertidal zone: the area of shoreline that is twice daily covered by water during high tide and
exposed to air during low tide
- Neritic zone: extends from the intertidal zone over the continental shelf and to relatively
shallow water depths of about 180 m
- Oceanic zone: the deep water of the open sea
- Pelagic zone: open ocean
- Benthic zone: ocean bottom
The Intertidal Zone
o Organisms in the intertidal zone are adapted to periodic exposure to air during low
tide
o Organisms must be able to withstand the force of crashing waves
The Neritic Zone
o The most productive zone in the ocean
o Water is shallow enough for photosynthesis
o Upwellings (strong currents) mix nutrients
o Plankton: communities of small organisms that drift with the ocean currents
o Coral reefs
The Oceanic Zone
o The deepest parts of the ocean
o Organisms living deep in the ocean must cope with near-freezing temperatures and
crushing pressure
o Organisms have slow metabolic rates and reduced skeletal systems
o Fishes have large jaws and teeth and expandable stomachs that can accommodate the
rare prey that they can catch
o Volcanic vents
Estuaries
o Estuary: occurs where freshwater rivers and streams flow into the sea
o Bys, mud flats, mangrove swamp forests and salt marshes
o Great variation in temperature and salinity
o Inhabitants are adapted for frequent change
Freshwater Zones
- Lakes, ponds, freshwater wetlands, clear mountain streams and slow sediment-rich rivers
Lakes and Ponds
o Eutrophic lakes: rich in organic matter and vegetation, so waters are relatively murky
o As the number of plants and algae in a lake grows, the number of bacteria feeding on
decaying organisms also grows. These bacteria use the oxygen dissolved in the lake’s
waters. Eventually, the reduced amount of oxygen kills organisms that need oxygen
to survive. Lakes naturally become eutrophic over a long period of time.
o Oligotrophic lakes: contain little organic matter
o The water is much clearer, and the bottom is usually sandy or rocky
Rivers and Streams
o A body of freshwater that flows down a gradient, or slope, toward its mouth
o Powerful currents
o Slow-moving rivers and their backwaters are richer in nutrients
Freshwater Wetlands
o Freshwater wetlands: areas of land that are covered with fresh water for at least part
of each year
o Two main types: marshes and swamps
o Marshes contain non woody plants
o Swamps contain woody plants
o Bog: dominated by sphagnum mosses
o Freshwater wetlands are the most productive freshwater ecosystem