Physical Geography

Unit 3 – Ecosystems

LIFE SYSTEMS (p. 92)• Complex life forms, like those that exist on Earth, have needs that must be

met for their existence. What are these needs?Food Water Oxygen Energy

• Of these needs, energy is the most important ingredient for life. Organisms usually get energy from their food sources.

• All energy received through food on Earth ultimately comes from the Sun. The conversion of solar energy to food energy (carbohydrates) occurs through the process of photosynthesis:

Components Process Result

• Energy from the Sun• Carbon dioxide from the

atmosphere• Water from atmosphere

and soil• plants

1. Plants take in carbon dioxide and solar energy through their leaves. Plants take in water through their leaves and roots.

2. Chlorophyll, a pigment in green plants, “fixes” the three ingredients to produce carbohydrates.

1. Carbohydrates provide food (energy) for plants themselves and for the life forms that eat the plants.

2. When carbohydrates are produced, oxygen is released into the atmosphere.

THE WEB OF LIFE (p. 92)• As we have just seen, plants are the only organisms that can convert solar

energy into a usable form (through photosynthesis) for life on Earth. For this reasons they are called producers.

• Organisms that must eat plants or other animals to obtain the energy they need are called consumers:– herbivores: animals that eat only plants.– carnivores: animals that eat only other animals.– omnivores: animals that eat plants and animals.

• Decomposers are simple organisms (e.g.: bacteria, fungi, and moulds) that live in soil or water and break down the wastes of other consumers and the decaying tissues of dead organisms into basic chemical compounds and nutrients.

• These decomposed substances are returned to the environment to be reused by plants for growth and food production.

• The network of relationships between plants, animals, and non-living parts of an environment forms an ecosystem. Ecosystems can be placed in particular geographic areas.

FOOD RELATIONSHIPS IN ECOSYSTEMS (p. 93)• Herbivores, as animals that eat only plants, are considered first-level or

primary consumers.• Carnivores can be divided into two categories:

– second-level or secondary consumers, who feed on herbivores.– third-level or tertiary consumers, who feed on animals that eat

herbivores.• These food relationships are often illustrated through a linear sequence that

represents the nutrition of various species from the simplest plant to the top carnivore. This linear sequence is called a food chain:

• In most ecosystems, there are many different, overlapping food chains. This is because some organisms obtain from several sources.

• These organisms become a part in the food chains of each separate plant or animal they consume.

• Multiple food chains in a single ecosystem include a wide range of relationships between food sources and consumers, and are represented by a food web.

• Arrows in food chains and food webs indicate the direction of nutrient flow.

ENERGY LEVELS IN FOOD CHAINS (p. 94)• As we have seen, solar energy flows through food chains and food webs.• The majority (85-90%) of the Sun’s energy does not pass to a higher stage

in a food chain:– Some energy is lost as heat– Most of the energy is used up to maintain an organism’s life processes– A small amount of energy (the remaining 10-15%) is stored as food energy

• It is this 10-15% of solar energy that passes to the next link in a food chain as the organism is consumed by a higher level consumer.

*Complete #s 1-9 on pp. 92-95*

FOOD PYRAMIDS AND TROPHIC LEVELS (p. 95)• A diagram called a food pyramid, is used to represent the energy flow in

ecosystems:– Producers appear at the base of the pyramid– Primary consumers appear at the second level– Secondary consumers appear at the third level– Tertiary consumers appear at the top of the pyramid

• The pyramid shape represents the decrease in both numbers of organisms and energy at each level.

• As we move up the pyramid, the amount of energy available to consumers decreases, and therefore each consumer must feed on a greater number of plants/animals in order to obtain the energy it needs to survive.

• Each level of a food pyramid is referred to as a trophic level (the amount of energy resulting after an energy transfer).

Magnification of toxin levels in food chains:• Biological Amplification refers to the fact that higher trophic levels receive

a higher dose of food chain toxins.• There are two factors involved in biological amplification:

1. Many toxic chemicals are fat soluble and stay in an animal's fat, rather than being flushed out as waste products.

2. The higher up a food chain, the greater the number of animals (and therefore toxins) consumed by carnivores.

• An animal at a low trophic level may only consume a small amount of toxin, but animals at high trophic levels must consume many organisms, thus increasing the concentration of toxin in their bodies.

• The most common and publicized case was that of DDT (a pesticide) which was first used to control insect populations in the 1950s.– The accumulation of toxins in ecosystems went unnoticed until carnivores at

top levels showed signs of decline (many died, others showed serious reproductive problems.

– For example, the shells of birds such as pelicans and peregrine falcons became so thin the eggs would break before they could hatch.

– DDT was banned in 1970s when high levels were found in human breast milk.

• Rachel Carson, a marine biologist and environmentalist, published Silent Spring in 1962. This book highlighted the negative effects of DDT on bird populations in ecosystems and was important in raising awareness of the issue.

• Her efforts in this area and others spearheaded the modern environmental movement, which strives to protect the natural world and less the destructive impacts of human activity.

*Complete #s 11, 12, 14, and 16 on pp. 97-100*

ECOSYSTEMS THROUGHOUT THE WORLD (p. 101)• Several patterns emerge when we consider the diverse kinds of life on

Earth:– certain organisms must live in the tropics– others must live in colder regions– some live on land– others live in swamps or oceans

• All life on Earth is suited to specific set of physical characteristics (climate, geology, and topography). These characteristics have been used by biologists to divide the biosphere into world ecosystems.

• One essential feature that helps identify a world ecosystem is climax vegetation: the chief type of plant life that has developed in a region over a long period of time, given a particular climate.

• It takes a long time for vegetation to achieve dominance in a region, due to the constant changing nature of ecosystems:– plants grow and are eaten by herbivores– animals are killed and eaten by others– organisms die and decay

• Because all organisms in an ecosystem are linked by nutrient and energy relationships, a change in one affects all others. Once this ever-changing ecosystem reaches a state of stability or equilibrium, a climax vegetation results.

• E.g.: Coniferous forests in N. America, Russia, and N. Europe:• Trees have needle-leaves, thick bark,

and conical shape.• Trees have grown together in dense

stands, which prevents sunlight from reaching forest floor and preventing undergrowth.

• Only trees hardy enough to endure cold continental climates.

CLIMATE AND ECOSYSTEMS (p. 103)• Regions that are located in

different parts of the world, but have similar climates tend to be classified as the same ecosystem.

• Climate zones and ecosystems are virtually interchangeable, because the same factors that determine climate also determine vegetation:– solar radiation– average annual temperature– annual precipitation

• Sunshine is the most important of these factors. Average temperatures and precipitation are the easiest to measure, however, and are often used to define ecosystems.

*Complete #s 17-21, 23-26 on pp. 102-107*

CHARACTERISTICS OF WORLD ECOSYSTEMS

Climate, Vegetation, and Adaption

TUNDRA

Climate • Polar – sub arctic climate• Short summers• Avg. monthly temp. always

below 10oC• Very cold long winter• Light precipitation

Vegetation• Grasses, shrubs and low plants • Found only in the northern

hemisphere, north of the Boreal forest

• Shrubs and bushes are well adapted to the extreme winter months: – shallow roots are needed

because of permafrost• The fast flowering and

reproduction cycle is needed due to 1-2 month growing season

BOREAL (CONIFEROUS) FOREST

Climate

• Temperate cold winter climate

• Warm summers• Moderate precipitation

Vegetation• Evergreen trees• Found only in the northern

hemisphere and is located in a broad band across Northern North America and Northern Eurasia

• Coniferous trees are well adapted to lack of water in winter (it is all frozen): – needle leaves reduce surface

area for transpiration – drooping branches and conical

shape allow heavy snow to fall off relieving pressure

• Thick bark reduces water loss

TEMPERATE (DECIDUOUS) FOREST

Climate

• Temperate Mild winter climate

• Warm – hot summers• Moderate - heavy

precipitation

Vegetation• Deciduous trees (oak, birch and

maple)• Found mostly in North America

and South America, but also Australia and Europe and Asia

• Deciduous trees are well adapted to lack of water in winter

• Losing their leaves in winter helps them reduce water loss through leaves (transpiration)

TEMPERATE GRASSLANDS

Climate

• Semi-arid climate or temperate cold winter

• Light precipitation, most of which occurs in summer

• Warm to hot summer

• Cold winters

Vegetation• Grass: – shallow roots– a small water requirement

• Found in North America, South America, Australia and Eurasia

• Grasses are well adapted to lack of water (small size)

SAVANNA

Climate

• Tropical wet & dry to semi-arid climate

• High temperatures most of the year

• Light to moderate precipitation usually all in one season

Vegetation• Grass: – shallow roots– small water requirement

• Found in South America, Australia, Africa and Southeast Asia

• Grasses: small size means that it requires less water

DESERT

Climate

• Arid climate• High temperatures year

round• Little precipitation

Vegetation• Cacti and fleshy plants: – long roots– water storage capability– leaves modified as needles

• Found in North America, South America, Australia, Africa and Asia (10-30° N or S)

• Cacti are well adapted to lack of water. They are often referred to as Xerophytes (often remain dormant during dry spells, germinating only after periods of rain

• Long roots help them obtain water

TROPICAL RAIN FOREST

Climate

• Tropical Wet climate• High temperatures year

round• High precipitation year

round

Vegetation• Tall evergreen broadleaf trees: – Buttress roots

• Found in South America, Africa, Australia and South east Asia

• The tall trees are well adapted to the thin soil with buttress roots to help support their height

• Some plants are epiphytes: they reach the sun by lying in the canopy, while their roots hang in the air and absorb moisture

THREATS TO ECOSYSTEMS

Soil and Desertification

EARTH’S SOIL RESOURCE (p. 135)• Soil is vitally important, both for the natural world and our human

needs.• Soil has three primary parts to its composition:• Organic Content: a soil's fertility is determined as a ratio of the

organic content to the content of ground bed rock.• Mineral content: varies with precipitation because heavy rains tend

to leach soils removing minerals from the root region of soil. • Soil Texture: the mixture of fine particles (sand), very fine particles

(silt) and extra fine particles (clay) found in soil. The best texture for agriculture is an even mixture of each.

• A soil profile is a cross section that shows the different layers (called horizons) that make up soil.

• If a great amount of rain is common, two process affect soil:– Leaching refers to nutrients being

washed downward in soil (dissolving).

– Eluviation refers to other minute organic particles from the surface that are washed downward through soil.

• In dry hot areas minerals dissolved in soil can be drawn upwards towards the surface. This is called capillary action.

• A thick humus layer (decomposed organic matter high in nutrients) produces better conditions for plant growth.

Types of Soil (p. 136)

1. Podzol: poor for agriculture (acidic due to decomposition of needle-leaves) and is found in the boreal forest.

2. Chernozem: the best for agriculture. Found in grasslands which are semi-arid resulting in a low amount of leaching and eluviation. Soils maintain a high nutrient and mineral content.

3. Latosol: very infertile due to the high amount of leaching. Found in tropical rain forests with high amounts of rain for much of the year.

podzol chernozem latosol

ENVIRONMENTAL FACTORS AFFECTING SOIL• Temperature:– affects the development of humus. Too cold and the decay of

organic matter is slowed considerably, therefore less humus.

• Precipitation:– affects the mineral content of soil. Too much rain and minerals

will be leached (dissolved in rainwater) beyond the reach of plant roots.

– Too much rain also results in eluviation which moves mineral content down through the soil and away from plant roots.

– Dry conditions will result in capillary action (high levels of heat draw water and minerals up through soil to the surface).

*Complete #s 11-13 on p. 136*

Soil Texture (p. 138)• This refers to the size of particles in soil:

– Stones are roughly baseball-sized– Gravel is small stones– Sand is fine particles– Silt is very fine particles– Clay is extremely fine particles.

• Soil is predominantly composed of a combination of sand, silt, and clay.

• The texture of soil is determined by the combination of these three.

• An even mix of all three particle sizes produce loam, which is the best soil texture for agricultural crops. Loam allows space for easy movement of roots and nutrients. The roots can find plenty of air, water, nutrients, drainage and moisture retention.

•Sandy soils have particles that are too loose and coarse to retain sufficient water.•Clay soils have particles packed too close together, resulting in a “sponge” effect, soaking up too much water.•Silty soils combine qualities of the other two.

• Soil texture is shown in a triangular graph

• Each side represents a type of particle.

• % of clay is shown from left to right

• % of silt is shown from upper right to lower left

• % of sand is shown from lower right to upper left

• Loam can have subtypes depending on the predominant particle (e.g.: silty loam, clay loam).

*Complete #18-21, p. 140*

THREATS TO SOIL PRODUCTIVITY (p. 140)

THREAT DESCRIPTION

Soil Availability Though soil covers the earth’s surface, highly productive soils are limited to grassland regions.

Soil Management Even grassland soil fertility will decrease globally if proper soil management (crop rotation, natural fertilizers, etc.) is not practiced.

Soil Erosion Agricultural land on slopes/mountains are more susceptible to water erosion.

Urban Expansion People traditionally settle near good farmland, but as cities grow that land is used for housing, businesses, etc.

Overgrazing Livestock overgrazing in semi-arid regions can remove plants that contribute to soil’s organic content.

Deforestation Cutting down of large forests removes trees that have root systems which help prevent soil erosion.

Desertification: The process by which semi-arid grasslands good for farming are degraded and become unproductive and unable to support vegetation.

CASE STUDIES• Read the following case studies that deal with threats to

ecosystems and soil and complete the questions that accompany each:– “Ranching in Brazil”, p. 119 – Do #8– “Desertification in the Sahel”, p. 123 – Do #11