5

Principles of Ecology: Biomes and Aquatic Life Zones

Chapter Outline

Weather and Climate: An Introduction

What factors influence weather and climate?

The Coriolis Effect

Ocean Currents

The Biomes

Tundra

Taiga

Temperate Deciduous Forest

Grassland

Desert

Tropical Rain Forest

Altitudinal Biomes

Aquatic Life Zones

Freshwater Lakes

Rivers and Streams

Protecting Freshwater Ecosystems

Saltwater Life Zones

Key Terms

weather polar easterlies grassland

climate Gulf Stream short-grass prairie

trade winds biomes tall grass prairie

tropics tundra dust bowl

temperate zone taiga lateritic soils

polar regions temperate deciduous forest altitudinal biomes

Coriolis Effect desert alpine tundra

westerlies tropical rain forest aquatic life zones

phytoplankton zooplankton freshwater lakes

littoral zone limnetic zone profundal zone

benthic zone epilimnion thermocline

hypolimnion fall overturn spring overturn

watershed estuary coastal wetlands

coral reef continental shelf continental slope

abyssal plain neritic zone euphotic zone

abyssal zone bathyal zone

Objectives

1. Discuss the major factors that determine weather and climate.

2. Explain the Coriolis Effect and the resulting global air circulation and wind patterns.

3. List the earth’s major biomes and their characteristics.

4. Discuss the major freshwater aquatic life zones.

5. Describe the major saltwater life zones.

6. Discuss the four life zones of the marine ecosystem.

7. Explain why the world’s richest biome grows on some of the world’s poorest soils.

8. Explain why there is a yearly cycle of “turnover” in many freshwater lakes.

9. Summarize some adaptations of organisms to different biomes/aquatic life zones.

10. Discuss the phenomenon called “El Niño”.

Lecture Outline

Weather and Climate: An Introduction

A. Weather refers to the daily conditions in our surroundings, including temperature and rainfall. Climate is the average weather over a along period, approximately 30 years. The climate of a region determines what plants can live there.

B. Major Factors That Determine Weather and Climate

1. The earth is unequally heated creating three major climatic zones:

a. Tropical - between 30° north and 30° south latitudes.

b. Temperate - between 30° and 60° of both hemispheres.

c. Polar - above 60° in both hemispheres.

2. The temperature and rainfall patterns in the above zones are also influenced by the flow of moist air and heat from the equator.

3. When air is heated it expands and becomes less dense. It rises and moves toward the poles. Cold air from the poles moves toward the temperate zones in each hemisphere.

C. The Coriolis Effect - The deflection of wind currents by the spin of the earth on its axis.

1. The following wind patterns are formed in the major climatic zones listed above:

a. Trade winds - These winds are found in the tropics and are easterlies.

b. Westerlies - These winds are found in temperate regions.

c. Polar Easterlies - These winds are found in polar regions.

D. Ocean Currents - Warm water from the equator flows toward the poles, warming land masses near which it passes.

1. Gulf Stream - a current that flows from the equator northward carrying warmer water.

2. Humboldt current - a current that flows from the southern polar regions toward the equator along the western side of South America. This current is a deep current that emerges at the surface in regions called upwellings. Every 10 years or so, the Humboldt current turns warm causing the phenomenon called El Niño. This weather pattern creates heavy rain and rough seas and can have a devastating effect on coastal communities.

The Biomes - Biomes are regions with a distinct climate and a unique assemblage of plants and animals.

A. The Tundra - Tundra is the biome characterized by the harshest climate.

1. It is found in the northernmost portions of North America, Europe, and Asia.

2. Tundra covers about 10% of the earth.

3. Tundra is a treeless area characterized by grasses, shrubs, and mat-like vegetation (mosses and lichens).

4. Tundra receives less that 25 centimeters or 10 inches of precipitation per year.

5. The deeper layers of the soil remain frozen throughout the year and are called the permafrost.

6. Summer on the tundra is a time of great activity. Many birds nest in the tundra and take advantage of the swarms of insects for food to feed their young. Ptarmigan, musk oxen, arctic hares, arctic foxes, wolves, and polar bears are all adapted to survive on the tundra.

B. The Taiga - The taiga is a band of coniferous forest spreading across the northern continents just below the tundra.

1. Sometimes called the northern coniferous biome, this land of pine, fir, and spruce trees extends across Canada, part of Europe, and Asia.

2. The taiga receives more precipitation than the Tundra and is able to support deep-rooted plants such as trees (38-100cm/15-40in)

3. The forests and other habitats of the taiga support a variety of species such as bear, moose, deer, and many smaller mammals.

4. The forests of the taiga are being harvested for their timber at a high rate. There is much concern for the old-growth forests of the taiga since few remain undisturbed.

C. The Temperate Deciduous Forest Biome - This biome occurs in regions with abundant rainfall and long growing seasons (75-150cm/30-60in).

1. The temperate forest biome is located in the eastern United States, Europe, and northeast China. In the U.S. this biome is home to about half of the human population.

2. The dominant plants of the temperate deciduous forest are deciduous trees, the broad-leaved trees that shed their leaves each fall. Maple, oak, black cherry, and beech tress are examples of some deciduous trees.

3. The temperate forest has a deep, rich soil that supports numerous crops.

4. The fertile soil and abundant plant life of the forest support a rich and varied population of insects, microorganisms, birds, reptiles, amphibians, and mammals.

5. This biome has been greatly altered by human activities and little of the original forest area remains. East of the Mississippi river, only 10% of the land is still forested and only 0.1% of the original forest remains. Most of the forests are second, third, or fourth growth stands.

D. The Grassland Biome - The grassland biome occurs in regions of intermediate precipitation, enough to support grasses but not enough to support trees (25-75cm/10-30in).

1. Grasslands exist in temperate and tropical regions. Grasslands are found in North America, South America, Africa, Europe, Asia, and Australia.

2. All grasslands bear a similar topography; most are on flat or slightly rolling terrain.

3. The soils found in grasslands are among the richest in the world. As a result, grasslands have been exploited for growing crops.

4. Grasslands in North America once supported an enormous population of bison, elk, and even grizzly bears.

5. Poor agricultural practices on farms and ranches throughout the world have resulted in widespread soil erosion and desertification in the grassland biome. The most dramatic and well know example of abuse came in the 1930s on the Great Plains. Millions of tons of topsoil were lost from farms in the U.S. during the dust bowl.

E. The Desert Biome - The desert biome is characterized by dry, hot conditions but often abounds with plants and animals adapted to the heat and lack of rainfall.

1. Deserts exist throughout the world. The Sahara stretches across northern Africa and is about the size of the United States. Deserts in North America exist primarily on the downwind side of the mountain ranges.

2. Precipitation in deserts is low (under 25cm/10in).

3. Plants living in desert conditions are adapted to low soil moisture and can survive extreme temperature changes. Water is stored by many desert plants in succulent, water-retaining tissues, giving the plant an ample supply during the rainless months.

4. Many insects and other animals make the desert their home. The thick scales of snakes and lizards are an adaptation to reduce water loss.

5. Large cities have sprung up in many of the world’s deserts. This can create serious water problems as a result of depletion of ground and surface waters.

6. Each year, millions of acres of new desert form on semiarid grasslands. Deserts are expanding primarily because of human actions. Livestock overgrazing destroys grasses and can remove enough vegetation to reduce rainfall. This process of expanding deserts is called desertification.

F. The Tropical Rain Forest Biome - This biome is the richest and most diverse biologically.

1. Tropical rain forests receive abundant rainfall (150-400cm/60-160in) and have a warm climate.

2. Tropical rain forests exist near the equator in South and Central America, Africa, and Asia.

3. This is the most diverse of all biomes and supports an incredible variety of life.

4. The tropics actually contain a variety of different ecosystems of which the rain forest is the largest and best known.

5. Tropical forest soils are poor in nutrients. The biomass that reaches the ground is quickly used by forest organisms and is not accumulating as it does in the temperate deciduous forest. Nutrients released into the soil by decomposers are quickly absorbed by the roots of trees. The nutrients are very quickly cycled back into the plants and animals of the forest.

6. Many rainforest soils are useless for long-term farming and ranching since they are high in iron content (laterite or lateritic soils; meaning “brick”). When cleared and exposed to sunlight, lateritic soils bake as hard as bricks making it difficult to cultivate.

7. Tropical trees are the lungs of the planet. They absorb carbon dioxide and release oxygen during daytime hours. The absorption of carbon dioxide reduces global warming.

8. Rainforests may be the most threatened biome on earth. A recent United Nations study suggested that about 17 million hectares (42 million acres) were being cleared each year. This is an area about the size of the state of Washington. Widespread destruction of tropical forests could upset global rainfall patterns and could affect global climate by reducing the amount of carbon dioxide removed from the atmosphere each year.

G. Altitudinal Biomes - Because climate varies with altitude, the distribution and abundance of life also changes.

1. Altitudinal biomes mirror the latitudinal biomes discussed earlier. These result from differences in precipitation and temperature associated with altitude.

III. Aquatic Life Zones - The aquatic equivalent of biomes on land; these regions of life are influenced by available energy and nutrients.

A. Freshwater Lakes

1. Lakes are divided into four habitats:

a. Littoral zone - The littoral zone consists of shallow waters at the margins of a lake. Aquatic vegetation is often growing in this area.

b. Limnetic zone - This area extends from the edge of the littoral zone to the point of depth were light no longer penetrates. This is the main photosynthetic zone of the lake and supports abundant phytoplankton, the primary producers of the lake ecosystem.

c. Profundal zone - This region lies beneath the limnetic zone in deeper lakes and extends to the bottom. Little or no light enters this area and conditions are not favorable for plant and algal growth. Fishes can survive in this region but rely on food produced in the limnetic and littoral zones.

d. Benthic zone - The bottom of the lake is the benthic zone. Organisms such as snails, clams, crayfish, aquatic worms, and insect larvae live in bottom sediments.

2. Temperature layers - Deeper lakes often contain three distinct temperature layers during the summer months. Twice a year the lake waters will turn over, mixing the surface and deep water (spring and fall overturn). The summer layers of the lake are listed below:

a. Epilimnion - This is the uppermost layer of the lake containing warm water.

b. Thermocline - This is a layer of water where the temperature gradient is greater than in the epilimnion or hypolimnion.

c. Hypolimnion - This is the layer of water below the thermocline and is the coldest layer.

B. Rivers and Streams - Rivers and streams are complex ecosystems that rely more on agitation for oxygenation of their water than lakes do.

1. Watershed - A watershed is the region drained by a stream.

2. Streams may receive much of their nutrients from the surrounding terrestrial ecosystems. Leaves, animal feces, seeds, stems, and other biomass may wash or fall into streams.

3. Many primary consumers in streams are detritivores.

4. Primary productivity varies in streams and depends on the amount of light reaching the water. Producers like algae and mosses and rooted vegetation are found in stream ecosystems.

C. Protecting Freshwater Ecosystems - Lakes are repositories for pollutants and are highly vulnerable to them. Streams generally fare better than lakes because of their flow, which tends to whisk pollutants away.

1. Protecting lakes, rivers, and streams requires measures to control or eliminate pollution.

2. Waste reduction is a more sustainable strategy. Companies are learning that if they can eliminate the use of toxic substances this is often cheaper than end-of-pipe controls.

D. Saltwater Life Zones - The oceans of the world consist of distinct life zones differing in biotic and abiotic conditions.

1. Coastal life zones - Coastlines are highly productive waters characterized by abundant sunlight and a rich supply of nutrients, which contribute to an abundance of life forms.

a. Estuaries and Coastal Wetlands - Estuaries are areas where freshwater mixes with salt water. Estuaries are rich in life because streams and rivers transport nutrients from the land and incoming tides carry nutrients into estuaries from the sea. Coastal wetlands (salt marshes, mangrove swamps, and mud flats) are located near estuaries. Human activities that disrupt rivers, like dams, can have a devastating effect on these ecosystems.

b. The Shoreline - Shorelines are rocky or sandy regions that are home to a surprising variety of organisms adapted to the tide and to the turbulence created by wave action

c. Coral Reefs - Coral reefs are wonderful areas of high diversity, the equivalent of the tropical rainforest in water! Coral reefs are found in relatively warm and shallow waters in the tropics or subtropics.

2. The Marine Ecosystem - The marine ecosystem consists of four ecologically distinct life zones:

a. Neritic zone - The neritic zone is similar to the littoral zone of lakes. This zone lies above the continental shelf and contains relatively shallow water and receives abundant light. Most commercial fishing is done in the neritic zone.

b. Euphotic zone - This zone is similar to the limnetic zone of lakes. It is the open-water region that extends to the lower limits of sunlight (about 200 meters; 650 feet). This region supports numerous species of phytoplankton.

c. Bathyal zone - This zone is a region of semidarkness and is too dark to support photosynthesis. The bathyal zone is home to a variety of animals that feed on material sinking in the water column.

d. Abyssal zone - This zone is a region of complete darkness. It has no photosynthetic organisms and is low in oxygen. Animals that live in this zone are adapted to cold water, high pressure, low oxygen, and complete darkness. Sediment in the abyssal zone is often rich in nutrients.

Suggestions for Presenting the Chapter

· Nothing is better for students than seeing biomes in person. Fieldtrips to local biomes is an excellent way to introduce the concepts in this chapter.

· If fieldtrips are not practical in your setting, there are many excellent environmental videos that examine biomes and ecosystems.

· Classes can be involved in monitoring local weather conditions, perhaps in conjunction with local TV meteorologists or meteorology classes on campus.

· Worksheets can be prepared to examine local climatic conditions, such as mean annual temperature, monthly, seasonal, and yearly precipitation, and even the effects of El Niño.