Chapter 47: The Biosphere
Earth is different from all other planets. Out of all the other planets that we know of, Earth is the only planet that has life on it. These living things constantly interact with each other and with their
environment.
47-1 Earth: A Living Planet
It is only during the past few years that people have finally begun to understand that our planet, Earth, is home to other life forms besides people. In order to properly care for our planet, we must study ecology, or the study of how organisms interact with each
other and their environment. (Scientists who study ecology are called ecologists.)
From space, it is very easy to that Earth is a single living system. Scientists have named this the biosphere, or the part of Earth where life exists. The biosphere includes all the areas of land, air, and water on the entire planet, as well as which type of organism populates each area. The biosphere not only includes the surface of our planet, but extends also about 8 kilometers into our atmosphere, as well as 8 kilometers below the ocean surface. While the biosphere is very large, the number of organisms that live there are not equally distributed —for example, very few organisms live in arctic circle, whereas many live in tropical rain forests.
Ecologists have divided the biosphere into a variety of smaller unites called ecosystems. Ecosystems consist of all bioticA and all abioticB factors that surround an organism. For example, a pond ecosystem would be composed of:
• the pond itself (the water)
• the plants that live inside the pond
• animals that live inside the pond
• protists that live and use the pond
• bacteria that live in the water
Important: Although it may appear as if ecosystems may be isolate from one another, that is not true. For example, if a stream passes through a forest and dumps into a pond (these are two different ecosystems), then, for example, a frog that lives near the pond would eat insects that live in the trees of the forest. Also remember that each organism changes the
ecosystem that it lives in — for example, leaves from said forest decay and drop into the stream, which carries them to the pond, thereby introducing new nutrients to the pond and helping organisms grow. Because so many organisms alter their surroundings, all environments are changing in the process called ecological succession. In ecological succession, an existing communityC is gradually replaced by
A Definition: living B Definition: non-living
C Definition: a group of organisms living in a common environment and interact with one another.
Biotic factors include all living organisms, such as tree or grass.
another community. Sometimes, ecological succession occurs in a place where there was no existing community. Ecological succession often leads to a stable community with a collection of plants and animals called a climax community. In reality, a climax community is described by its major forms of plant life. (The reason that ecologists do this is because animals that inhabit this environment either directly or indirectly depend on the plants.) Ecologists often depict different parts of the community by their common climax community. Although a climax community is described as “relatively stable,” that does not mean that a climax community is static and does not change over time. Natural disasters such as fires, floods, or droughts can disturb a climax community. In any case, a natural disaster can greatly disturb or completely wipe out a community, causing ecological succession to begin.
47-2 Land Biomes
Areas that are similar in climate and other physical factors develop similar climax communities. A biome is an environment that has a characteristic climax community. Earth is made up of two main biomes: land biomes and aquatic biomes.
Most land biomes are named for their climax community. The major land biomes are:
• taiga
• tundra
• temperate deciduous forest
• grassland
• tropical rain forest
• desert
North America, Asia, and Europe are covered by biomes called tundra. The tundra is also the northernmost land biome and is nearly treeless, being covered mostly by mosses, lichens, and grasses. Many animals migrate north to the tundra to feed off of the various plants that grow there. This includes many species of birds, who then also fly south for the winter (where the weather is warmer). The most characteristic feature of the tundra is
permafrost, or a permanently frozen layer of subsoil. During the summer, the
ground thaws and becomes wet and soggy, and during the winter, this layer hardens again — through this cycle, plant roots and formed and then broken, which causes the plants that grow in the tundra to be very small.
South of the tundra, you can find biomes that are dominated vastly by
coniferous, or cone bearing trees, such as pine. These biomes are called taiga. The taiga stretches across much North America and Asia, and a small part of Norway and Sweden. Although winters in the taiga are cold, summers are mild and long enough to give many plants and animals sufficient time to reproduce, and many small birds and animals live in the taiga during the summer and
migrate to warmer climates during the winter. Other inhabitants of the taiga include:
• black / grizzly bears
The tundra biome
• wolves
• moose
Covering the eastern coast of the United States and the souther border of Canada and most of Europe are biomes that are characterized by changing seasons and a leaf fallD. These biomes are called temperate deciduous
forests. A temperate deciduous forest gets its name because it has forests from forests of oak or birch trees, which are deciduous and shed their leaves in the autumn when the weather turns cold. Although rainfall is sufficient year-round, frigid winters stunt plant growth for several months out of the year. In addition, because trees shed their leaves every fall, the changes in seasons are very dramatic. In the spring, plants grow very quickly,so that
smaller plants have a chance to flower before they are shaded by the leaves of bigger plants, such as trees. Although a great number of animals once inhabited these forests, they have been hunted down to near extinction, although new laws that prohibit hunting of certain animals have caused said animals to begin reappearing. In this biome, an abundance of organic matterE and nutrients are stored in a layer of decomposing leaves and twigs called humus. These biomes have suffered a lot of devastation due to settlements, but has since recovered. Some of the animals that live in this biome include:
• chipmunks
• opossums
• squirrels
Found in the interior of many continents, grasslands are biomes that are very large and are covered with grass and small leafy plants. Although this biome gets a significant amount of rainwater — anywhere between 25 cm and 75 cm a year — it mostly comes during one season of the year only. The grasslands cover the prairies of North America, Russia, South Africa, and Argentina. In the United States, the grasslands are characterized by hot summers and cooler winters — there is very little change in temperature from season to season, instead, the seasons change from wet to dry.
Tropical grasslands that have groves of trees, such as in Africa, are called savannas. Due to the climate of grasslands, wheat and other grains are grown. Some animals that live in the grasslands are:
• gazelles
• impala
• elephants
In the tropical rain forest, the weather stays consistently warm and rain falls year-round. (On average, a tropical rain forests will get anywhere between 200 cm and 400 cm of rain each year.) Temperatures stay pretty warm all year. This biome covers:
• most of South America
• southern Asia
• Africa
D Definition: the season of autumn, where the leaves turn color and fall off the trees. (This occurrence does not happen in every biome.)
E Definition: anything that contains Carbon in its chemical sturcture.
The temperate deciduous forest biome
The grassland biome
• Central America
The tropical rain forest biome is home to more species of plants and animals than any other biome in the world combined. Trees grow very high, and the tops of the trees form a dense covering called a canopy. Trees also provide the necessary support needed to have other plants grow atop the trees. (One such example is a plant called a Liana.) Animal life in the rain forests are varied, and many plants and animals that live in this biome produce chemicals that are very useful in fighting certain diseases. The rain forests, however, are being rapidly destroyed by the growing human population, causing the extinction of many plants and animals that call this biome home. Some animals that live in this biome are:
• the sloth
• the squirrel monkey
Deserts are biomes that are found in areas where there is very little rain — usually less than 25 centimeters. There are many types of deserts in the world. For example, the Sahara Desert gets almost no rain, and the wind is very hot and dry, which means that almost nothing can grow there. Deserts also house various species of lizards and insects. In seasonal deserts, unlike the Sahara, there is some rainfall, and plants absorb this water to bear fruit and flowers, and then become dormant until the next rainfall. Yet another type of desert is found on high mountain tops, and the high altitudes cause
a dramatic decrease in temperature, and as a result, these are called cold deserts. Cold deserts have brief rainy seasons that allows small plants to consistently grow. (Today, scientists have created irrigation systems that make deserts suitable for farming. Desert soil is very rich in nutrients, and get lots of sunlight, making it idea for plant growing, and the water systems make it possible.)
47-3 Aquatic Biomes
In addition to ecosystems that survive on land, there are also water ecosystems, or aquatic biomes. These biomes include:
• the freshwater biome
• the marine biome
• estuaries
Some of the abiotic factors that affect which organisms live there are:
✔ light intensity: how much light the biome can get through the water
✔ oxygen (O2) and carbon dioxide (CO2) availability: how much oxygen and carbon dioxide are
available in the water. These two elements are vital.
✔ OrganicF and inorganicG product availability: How much organic / inorganic nutrients are available in the water. For example, a plant which requires a lot of
organic matter will not be able to survive in a very highly-inorganic environment.
Unlike land biomes, aquatic biomes do not vary in temperature from biome to biome.
F Definition: matter that has carbon in its chemical structure
G Definition: matter that does not have carbon in its chemical structure
The desert biome
Rivers, streams, and lakes are called the freshwater biomes of the Earth. These biomes not only provide fresh drinking water for us, but it also provides a vital source of food. Small plants and animals are eaten by larger organisms, such as fish and other amphibians. Large species in the Amazon of South America (which is a tropical rain forest biome) live in the large freshwater that pass through the rain forests. People around the world, however, are using freshwater biomes and places to dump waste, which causes water pollution.
The marine biomes encompass the ocean habitats, which cover most of the surface of the Earth. Since the oceans are very deep, sunlight can only go a short distance into the water
before it is absorbed — as a result, photosynthesis can only take place near the ocean surface. The region where photosynthesis takes place is called the photic zone. The photic zone ranges from 30 meters to 200 meters, and it is in this layer of the ocean that various phytoplanktonH and algae grow. Oceanographers have divided have divided the marine biomes into “zones” that are classified by their depth and how far
they are from the shore. Each zone has organisms that are adept to living there:
➔ Intertidal Zone: The intertidal zone is the most difficult zone in a marine biome for an organism to live in. The organisms must be able to tolerate very radical changes in their environment on a day-to-day basis: once or twice a day, the intertidal zone is completely submerged, and the other times of the day, it is not and is exposed to air and sunlight. Through evolution, organisms that live in this zone of the biome have been able to adapt to the constant waves. One organism that lives in the intertidal zone is the clam, which survives by burrowing itself in the sand to prevent being washed out to sea by the waves. Other animals that live in this zone include:
▪ sea urchins
▪ starfish
➔ Neritic Zone: The neritic zone is part of the marine biome that extends from the low-tide line to the “open sea.” Plants such as seaweed are in abundance here because this zone is inside the photic zone, where sunlight can still penetrate through the water. Some of the animals that live in this zone are:
▪ turtles
▪ fish
▪ other invertebrates
➔ Open-Sea Zone: In the open-sea zone, phytoplankton make up anywhere between 80% and 90% of photosynthetic activity. These phytoplankton are then eaten by larger animals as part of the food chain. Also living in the open-sea zone are fish and amphibians of all shapes and sizes, as well as various sea birds. Nutrients are very scarce in this zone, and as a result, the growth of phytoplankton is relatively slow, which ultimately restricts the number of organisms that can live in the open-sea zone at one time. In contrast, the zones closer to the shore have an abundance of nutrients, and as such, many fish swim there for food.
➔ Deep-Sea Zone: The deep-sea zone is an area of very high pressure, cold temperature, and almost total darkness. Very few organisms live in this zone of the marine biome, and some of these are the strangest creatures that biologists have encountered. Here, zooplanktonI wait for night to swim up to the surface and feed off of phytoplankton. Since this is where the ocean floor is, many of the animals that live in the deep-sea zone crawl along the ocean floor.
H Definition: small, photosynthetic plants that are free-floating in ocean water I Definition: free-floating microscopic animals.
The biome that is to be the boundary between the other two aquatic biomes — freshwater and marine — are called estuaries. Examples of estuaries include:
• salt marshes
• lagoons
• river mouths
Estuaries contain a mixture of both salt and fresh water. They support many life forms, and because they are usually shallow, sunlight is able to penetrate
through the water. Photosynthesis can occur in all level of an estuary, yielding many aquatic plants. Many fish and invertebrates lay their eggs in estuaries, as do several species of birds.
47-4 Energy and Nutrients: Building the Web of Life
One of the most important factors of any ecosystem — land or aquatic — is how energy flows through the ecosystem. Out of all of the energy that the sun gives off, only about .1%J is used on a daily basis. However small this amount is, this amount of energy is solely responsible for producing several thousand grams of organic matter per square meter of forest per year. Approximately half the the sunlight that plants obtain is used immediately, and the rest is stored in energy-storing compounds called carbohydrates. Animals that eat plants obtain the energy that was stored in carbohydrates, and they store an even smaller amount than what they consumed, and since energy cannot be used twice, it is called a “flow,” not a “cycle.” While energy is not reused, however, nutrients are. Once nutrients are used by one organism, they decompose and are eventually used by another organism.
The sun is the ultimate source of energy for all living things. During the process of photosynthesis, green plants and certain bacteria trap sunlight and use it to fuse carbon dioxide (CO2) and water (H2O) into carbohydrates, which are polysaccherides. Because organisms that are able to perform
photosynthesis are able to make their own food out of inorganic substances, they are called producers. Animals, however, cannot get their energy from photosynthesis, and must get their energy either directly or indirectly from producers. As such, animals are consumers:
• consumers that get food directly from producers are called primary consumers. Primary consumers are animals that are herbivores (animals that have a plant-based diet).
• consumers that eat primary consumers are are called secondary consumers. Secondary consumers are, by and large, carnivores (animals that have a meat-based diet).
• Tertiary consumers feed off of secondary consumers, and
• Quaternary consumers eat tertiary consumers.
When plants and animals die, however, their remains do not build up due to the presence of decomposers, which are organisms that get their nutrients from non-living matter. Decomposers include:
• fungi
• bacteria
Sun → producers → consumers → decomposers
Each step of organisms eating other organisms is called a trophic level. There is no limit to the number of trophic levels in an ecosystem. However, the higher the trophic level, the less energy is saved from
J 1/1,000, or one-thousandth of the sun's energy
level to level. While most of the energy used by herbivores is used to fuel metabolism, a small amount is saved and created into animal biomass, which is the total mass of all of the organisms in a trophic level.
As a rule, approximately 10% of energy used in one trophic level is left over for the next level. In order to represent energy relationships between trophic levels, ecologists use diagrams called ecological pyramids. There are three types of ecological pyramids:
A pyramid of energy is used to show the net amount of energy that can be used by each successive tier.
A pyramid of biomass is used to show the total mass of tissue at each level. For example, it can show how much algae is used to feed a fish throughout the course of its life, and how many fish are needed to feed a polar bear throughout the course of its life. A pyramid of biomass only, however, shows the amount of organic material at one time
A pyramid of numbers is used to show how many organisms live on each tier.
Although energy moves one way only — forward — nutrients are recycled. Animals require many complex compounds, such as proteins and amino acids, as well as vitamins and other organic material in oder to survive. As members of each trophic level eat those who are in the trophic level below them, they obtain certain complex molecules in addition to energy, and although nutrients and energy move from one trophic level to the next together, they move through the biosphere differently. Nutrients move through the biosphere through a series of physical and chemical processes called biogeochemical cycles:
➔ The Water Cycle: This cycle is the movement of water through the atmosphere. Water starts out is some body of water, such as a lake or stream. The water then evaporates into the atmosphere, where it condenses into clouds. The water then comes back down to the surface in some form of precipitation, such as water or snow. Most of the water runs into a stream or river, which carries it to a bigger body of water. Some water, however, is absorbed by the ground, and is called ground water.
➔ The Nitrogen Cycle: All organisms, no matter what photic level they are on, need nitrogen to build proteins. This nitrogen, however, is not readily available — it must be converted into other forms. The process of nitrogen fixation is when bacteria in certain plants capture nitrogen in the air and convert it into nitrogenous compounds, such as nitrateK. The nitrogen is then absorbed by animals. When the animals die, the nitrogen returns to the ground, where bacteria break down the nitrogenous compounds back into nitrogen in a process called denitrification. Nitrogen is then returned to the atmosphere.
➔ The Carbon Cycle: This is the process by which carbon moves through the atmosphere. During the process of photosynthesis, plants use carbon to form glucose during cellular respiration, where carbon dioxide is made. Carbon is subsequently released into the atmosphere.
➔ The Oxygen Cycle: This is the process by which oxygen moves through the environment. During the process of photosynthesis, oxygen molecules are split, and are used for respiration. Water is created; then released. The water is absorbed by plants, and the process repeats. The rate at which producers (plants) can capture energy and use it to produce tissue is controlled by many factors, namely the availability of the nutrient needed. If a nutrient is in limited supply, then is called a limiting factor. For example, coastal ocean water contains sufficient nutrients to support much more plant growth than is normally present in that biome. These producers, however, lack sufficient
nitrogen, making growth slow.
