Chapter 4 Ecosystems and Communities
Section 4 Biomes
Be Able To
•Explain what abiotic and biotic factors characterize biomes
•Explain what areas of our planet are not easily classified into a major biome.
Key Terms: canopy, understory, deciduous, coniferous, humus, taiga, and permafrost.
The Major Biomes
• Biomes are a group of
ecosystems that share similar climate characteristics and typical organisms.
• Each biome may contain several different types of ecosystems.
• The climate of an area determines which plant
communities will be present which in turn determines which animals will be present.
• Variations in abiotic and biotic factors in a biome are due to
differences in elevation, local soil conditions, exposure, or human activity.
The Major Biomes
• Climate of a biome is
determined by its average
temperature and precipitation.
• The climatic patterns within a biome can be summarized in a climate diagram, climatogram.
• Generally the higher the
temperature and precipitation are the taller and denser the vegetation is.
• Organisms within each biome can be characterized by
adaptations the enable them to live and reproduce successfully there.
Other Land Areas
• Some land areas do not fit neatly into a major biome due to high altitude or high latitude.
• Latitude - polar regions lie on the border of the tundra and do not have much if at all vegetation.
• Altitude - the height above sea level of mountain ranges limits both vegetation and animal life.
• Climate gets colder as latitude and altitude increase.
What is a biome?
Tropical Rain Forests
• Exist between 300 N and 300S of the equator.
• Warm and wet (250 cm of rain/year)
• Growing season is year round.
• Harbor the most biodiverse terrestrial communities.
• Soil is unusually nutrient poor.
• Because of extensive vertical stratification (pg. 148 figure 7) the ground receives little sunlight.
• Many animals of the rain forests are specialists.
• Camouflage and bright colors are common characteristics of rain forest animals.
Threats to Tropical Rain Forests
• Extensive lumbering
and clearing of the land for cattle grazing are
the major threats to tropical rain forests.
• 142,000 km2 are lost a year (football field per second).
• At current rates of
deforestation half of the remaining rain forest
will be gone in 20 years.
• How many species are lost a year?
Temperate Rain Forests
• Occur in N. America, S.
America, Australia, and New Zealand.
• Seasonal temp. variation and wet (150-500 cm of rain/year)
• Growing season limited to warm months.
• Temperate rain forests of the Pacific Northwest are
dominated by coniferous
trees with a lush ground layer of ferns and mosses.
• Soil is rich in nutrients due to decaying plant matter.
• Most animals live on ground level.
• The greatest threat is the lumbering industry.
Temperate Deciduous Forests
• Occur in between 300 and 500 N of the equator.
• Seasonal temp. variation and precipitation (75-100 cm of rain/year)
• Growing season lasts 4 to 6 months
• Soils are nutrient rich due to decaying leaf and animal material.
• Deciduous forests are also
vertically stratified, yet the forest floor gets more sunlight than rain forests
• Forest plants lose their leaves in fall and their roots become
dormant in winter.
• Many birds are migratory and most mammals become fairly inactive in winter.
Threats to Temperate Deciduous Forests
• Logging and clear-cutting for agriculture and urban
development are major threats.
• Acid rain has damaged even the most remote forests in N.
America.
• Introduction of exotic species threatens the survival of
native species.
Savannas
• Savannas are found in the
tropics, between 300 N and 300 S of the equator.
• Precipitation comes primarily during the wet season.
• Savannas are dominated by grasses.
• Savanna trees and grasses have an extensive root system as an adaptation to frequent fires and water conservation.
• Large grazing herbivores migrate to greener areas.
• The number of different species is small, but the
number of individuals is large.
• Poaching has been a major threat to animals of the
savanna.
Temperate Grasslands
• The pampas of Argentina, the
steppes of Russia, and the prairies of N. America are all temperate
grasslands.
• Temperate grasslands receive seasonal precipitation and have moderate temperature ranges.
• Precipitation in the prairies ranges from 25 cm to 90 cm a year.
• Fires are a necessary abiotic factor for the dominant plant species, tall grasses.
• Grassland soil is nutrient rich, which means that it is fertile for agriculture.
• Root depth and grass height is dependent on precipitation.
• Large herds of wild grazing animals have been replaced by domesticated grazing animals.
• 99.9% of the tall grass prairies have been replaced by monoculture.
Chaparral
• Chaparrals occur in mid
latitudes approximately 300 N and 300 S of the equator in Mediterranean climates.
• Characterized by hot dry
summers and mild wet winters.
• Dense spiny evergreen shrubs dominate chaparral biomes.
• Plants are adapted to fires and some will produce seeds that germinate only after fires.
• Roots resprout quickly after fires.
• A common animal adaptation is camouflage.
• Major threat to chaparrals is human development, e.g.
Hollywood.
Deserts
• Deserts receive less than 25 cm of rain/year.
• Often are found in the shadows of mountains.
• Daily temperatures can reach 600 C during the day and near freezing at night.
• Desert plants have fleshy stems and leaves to store water.
• Spines prevent desert animals from eating plants.
• Roots of desert plants spread out widely in search of water.
• Thick scaly skin of reptiles and some amphibians prevents water loss.
• An adaptive behavior is nocturnal activity.
• Major threats to deserts include all aspects of human development.
Tundra
• Tundra covers roughly 20% of the area above the Arctic circle.
• Summers are short and winters are long.
• Only a a few cm of the soil thaws during the summer months.
• Cold temperatures, high winds, and permafrost prevent tree growth on the tundra.
• Water accumulates in depressions that form shallow ponds across the landscape in the summer.
• Mosses and lichens cover rocks and the thin soil supports small plants with shallow roots.
• Migratory birds breed in the tundra in the summer and feed on insects and fruits of plants.
• Caribou and reindeer migrate to the tundra during the summer and are followed by carnivores such as wolves.
• Year round residents use camouflage as protection.
• Tundra is a fragile ecosystem and is
threatened by oil companies that want to mine the land.
Taiga or Boreal Forest
• Exist just below the Arctic Circle forming a broad band across N.
America and northern Eurasia.
• Cold and snowy (50 cm of precipitation/year)
• Growing season lasts 2 months.
• Dominated by coniferous forests.
• Conical shape protects limbs from heavy snow accumulation.
• Forest floor is somewhat bare due to acidic soil conditions.
• Many lakes and ponds attract migratory animals in summer and those that stay adapt to cold winters.
• Major threats to these areas comes from logging industry
