WHAT IS AN ECOSYSTEM?

Energy Pyramid

A triangular diagram that shows an ecosystem's loss of energy, which results as energy passes through the ecosystem's food chain, is called an energy pyramid. An energy pyramid is shown in Figure 8. Each layer in the energy pyramid represents one trophic level. Producers form the pyramid's base, which is the lowest trophic level. The lowest level has the most energy in the pyramid. Herbivores have less energy and make up the second level. Carnivores that feed on herbivores make up the higher level. The energy stored by the organisms at each trophic level is about one-tenth the energy stored by the organisms in the level below. So, the diagram takes the shape of a pyramid. Big predators, such as lions, are rare compared to herbivores. Big predators are rare because a lot more energy is required to support a single predator than a single herbivore. Many ecosystems do not have enough energy to support a large population of predators.

Tropical Biomes

Because they are located at low latitudes near the equator, all tropical biomes are warm. However, each tropical biome receives a different amount of rain. Tropical rain forests receive large amounts of rain and are warm all year. They have the greatest biodiversity of any land biome. At least half of Earth's species of land organisms live in tropical rain forests. Savannas are tropical grasslands. They get less rain than tropical rain forests do. Savannas also have long dry seasons and shorter wet seasons.

High-Latitude Biomes

Biomes at high latitudes have cold temperatures. Coniferous forests in cold, wet climates are called taiga. Winters are long and cold. Most of the precipitation falls in the summer. Moose, wolves, and bears live in the taiga. The tundra gets very little rain, so plants are short. Much of the water in the soil is not available because the water is frozen for most of the year.

Freshwater and Wetlands

Freshwater ecosystems are located in bodies of fresh water, such as lakes, ponds, and rivers. These ecosystems have a variety of plants, fish, arthropods, mollusks, and other invertebrates. Wetlands provide a link between the land and fully aquatic habitats. Water-loving plants dominate wetlands. This ecosystem supports many species of birds, fishes, and plants, as shown in Figure 4. Wetlands are important because they moderate flooding and clean the water that flows through them.

Food Web

In most ecosystems, energy does not follow a simple food chain. Energy flow is much more complicated. Ecosystems almost always have many more species than a single food chain has. In addition, most organisms eat more than one kind of food. For example, hawks eat fish, small birds, and rabbits. Rabbits are food not only for hawks but also for wolves, mountain lions, and many other carnivores. This complicated, interconnected group of food chains, such as the group in Figure 6, is called a food web.

Equilibrium

f a major disruption strikes a community, many of the organisms may be wiped out. But the ecosystem reacts to the change. An ecosystem responds to change in such a way that the ecosystem is restored to equilibrium.

Aquatic Ecosystems

he diverse regions in the world's bodies of water are not usually called biomes. They are often called aquatic ecosystems. Aquatic ecosystems are organized into freshwater ecosystems, wetlands, estuaries, and marine ecosystems.

Change in an Ecosystem

he first organisms to appear in a newly made habitat are called pioneer species. Pioneer species are often small, fast-growing plants that reproduce quickly. They change the habitat in such a way that other species can live in the ecosystem.

A Community of Organisms

A community of organisms is a web of relationships. One relationship is that of a predator eating its prey.Some species help each other. Relationships between organisms are examples of biotic factors that affect an ecosystem. Biotic describes living factors in an ecosystem. Biotic factors also include once-living things, such as dead organisms and the waste of organisms.

Ecosystems

A group of various species that live in the same place and interact with one another is called a community. The group, along with the living and nonliving environment, make up an ecosystem. An ecosystem includes a community of organisms and their physical environment.

estuaries and marine ecosystems

An estuary is an area where fresh water from a river mixes with salt water from an ocean. Estuaries are productive ecosystems because they constantly receive fresh nutrients from the river and the ocean. Marine ecosystems are found in the salty waters of the oceans. Kelp forests, seagrass communities, and coral reefs are found near land. The open ocean, far from land, has plankton and large predators, such as dolphins, whales, and sharks.

Temperate Biomes

Biomes at mid-latitudes have a wide range of temperatures throughout the year. Temperate grasslands have moderate precipitation and cooler temperatures than savannas do. Temperate grasslands are often highly productive when used for agriculture. Herds of grazing animals, like bison, used to live on the temperate grasslands of North America. Temperate forests grow in mild climates that receive plenty of rain. Trees of the temperate deciduous forests shed their leaves in the fall because of the cold winters. Trees of temperate evergreen forests do not lose their leaves or needles during the winter.

Terrestrial Biomes

Earth's major terrestrial biomes can be grouped by latitude into tropical, temperate, and high-latitude biomes. High-latitude biomes are at latitudes 60º and higher. Latitude affects the amount of solar energy that a biome receives and thus affects a biome's temperature range.

Loss of Energy

Energy is stored at each link in a food web. But some energy that is used dissipates as heat into the environment and is not recycled.

Major Biological Communities

The kinds of species that live in a particular place are determined partly by climate. Climate is the average weather conditions in an area over a long period of time.A biome is a large region characterized by a specific kind of climate and certain kinds of plant and animal communities. Two key factors of climate that determine biomes are temperature and precipitation. Most organisms are adapted to live within a particular range of temperatures and cannot survive at temperatures too far above or below that range. Precipitation also determines the kinds of species that are found in a biome.

Physical Factors

The physical or nonliving factors of an environment are called abiotic factors. E These physical factors shape organisms. Water supply also affects the number of individuals and variety of species that an ecosystem can support. A crop of corn will have a higher yield in a wetter habitat than in a drier habitat. A habitat is the place where an organism lives.

Trophic Levels

The primary source of energy for an ecosystem is the sun. Photosynthetic organisms, such as plants and algae, change light energy from the sun into energy that they can use to grow. These photosynthetic organisms are PRODUCERS, the basic food source for an ecosystem. CONSUMERS - are organisms that eat other organisms instead of producing their own food. DECOMPOSERS -, such as bacteria and fungi, are organisms that break down the remains of animals. In an ecosystem, energy flows from the sun to producers to consumers to decomposers. Each step in the transfer of energy through an ecosystem is called a TROPHIC LEVEL

Biodiversity

The variety of organisms in a given area is called biodiversity.Physical factors can have a big influence on biodiversity. In places that have very high or very low temperatures, biodiversity is often lower. Limited water and food also cause lower biodiversity. The biodiversity of habitats and ecosystems varies greatly. The vast expanse of the open ocean has very low biodiversity. In contrast, rain forests and coral reefs have very high biodiversity. When ecosystems have high biodiversity, they are often more able to resist damage. Damage to ecosystems can be caused by severe weather events or human activities. Systems with low biodiversity can be severely damaged easily. When biodiversity decreases in any ecosystem, that ecosystem is not as healthy as it could be.

The Ten Percent Rule

When a zebra eats grass, some of the energy in the grass is stored in the zebra. The energy may be stored as fat or as tissue. However, most of the energy does not stay in the zebra. As the zebra uses energy from the grass to run and grow, the energy is changed into heat energy. Then, the heat energy is dispersed into the environment. Thus, the zebra does not keep 90% of the energy that it gets from the grass. Only about 10% of the energy in the grass becomes part of the zebra's body. This amount of stored energy is all that is available to organisms at the next trophic level that consume the zebra. For example, a 100 kg lion needs 1,000 kg of zebras. And combined, the zebras need 10,000 kg of plants! By understanding energy flow between trophic levels, we can learn how to feed more people. If people eat big fish that are in the third trophic level, it takes 1,000 kg of producers t

Succesion

When we observe an ecosystem, it may look like an unchanging feature of the landscape. However, all ecosystems change. As an ecosystem changes, the kinds of species that the ecosystem supports change. The replacement of one community by another at a single place over a period of time is called succession.

Food Chains

n ecosystems, energy flows from one trophic level to the next, forming a food chain. The first trophic level of ecosystems is made up of producers. Plants, algae, and some bacteria use the energy in sunlight to build energy-rich carbohydrates. The second trophic level of a food chain is made up of herbivores, which eat producers. Cows are an example of an herbivore. The third trophic level includes animals that eat herbivores. Any animal that eats another animal is a carnivore. Some carnivores are on the third trophic level because they eat herbivores. For example, small birds eat caterpillars, which feed on plant leaves. Other carnivores are on the fourth trophic level or an even higher trophic level because they eat other carnivores. For example, hawks eat small birds. Omnivores, such as bears, are animals that are both herbivores and carnivores.