Ecosystems

An ecosystem is all the living and nonliving things and all their interactions in an area. Living things have basic needs that must be met in order for them to survive and thrive. Matter and energy in their environment (such as light, gases, water, and nutrients) provide necessary resources for living things. Resources are taken in by organisms and recycled back into the environment as organisms live, grow, and die. Matter in an organism’s environment is cycled among living and nonliving things. This cycling ensures that an environment’s occupants obtain what they need from the environment while contributing to its health and sustainability.

Every organism needs energy in order to survive. Organisms use energy to carry out functions such as respiration, metabolism, movement, and temperature maintenance. All organisms get resources and energy from their environments and use and store them internally. Producers are organisms capable of acquiring their energy directly from nonorganic resources available in their environment. In turn, they release gas, energy, and other matter into their environments. Producers are typically immobile and may provide protection in the form of shelter to other members of an environment. Producers use the energy from sunlight to perform photosynthesis, a process that converts carbon dioxide and water into oxygen, water, and carbohydrates. Note that the amount of water used in the process of photosynthesis is greater than the amount available after photosynthesis is completed. The products of photosynthesis (oxygen and glucose) are used by other producers, by consumers, and by decomposers. Another term for a producer is autotroph.


Examples of producers include plants, algae, and certain bacteria.

Consumers cannot produce their own food. Instead, consumers ingest other organisms to obtain the energy and nutrients they need to survive. Consumers take in food, break it down, and release energy for required processes. The three types of consumers are herbivores, carnivores, and omnivores. Herbivores consume only plants, carnivores consume animals, and omnivores consume both plants and animals. Another name for a consumer is a heterotroph.


Deer are herbivores, crocodiles are carnivores, and humans are omnivores.

Within an ecosystem, energy is obtained from external sources and cycled through an energy pyramid. Each level in an energy pyramid is called a trophic level. On the bottom level, plants, algae, and some bacteria get energy from the Sun and perform photosynthesis to produce carbohydrates, oxygen, and energy. At the second level, herbivores obtain energy by eating the organisms of the first level. Consumers that eat herbivores make up the next level. Predators that eat the predators that eat herbivores represent the level above this. Some organisms eat at more than one trophic level. For instance, bears eat both berries and salmon. This places bears at the highest feeding level in the energy pyramid.


Bears are omnivores, eating both producers and other consumers.

As plants and animals die, they leave behind fur, skin, bones, leaves, and stems that are broken down by decomposers. Decomposers operate at the very bottom of the food and energy pyramid, on a sublevel. Decomposers convert leftover animal and plant parts into materials for other living organisms to use. Decomposers, which are mostly fungi and bacteria, convert leftover animal and plant parts into important nutrients, which are returned to the soil for use by succeeding generations of plants. Decomposers consume dead leaves, carcasses, and fecal waste as well, converting waste to nutrients and thereby cleaning the environment to prevent the spread of disease. Because of this, decomposers play a very important role in the ecosystem.


Decomposers such as these mushrooms help return nutrients to the soil.

Energy moves through an ecosystem from the sun to producers, consumers, and decomposers in turn, creating a pool of organic resources. Only about 10% of the energy at each trophic level is available to pass along to the next level of a food pyramid! There is less energy available to support the organisms in each increasing level, so the population numbers of species decrease as you move up the energy pyramid. This is why the energy flow is illustrated in the shape of a pyramid. This also explains why there are fewer organisms as you ascend an energy pyramid. For example, there are many more mice (primary consumers) than there are owls (secondary or tertiary consumers). There is simply not enough energy to support as many owls since energy on each level is “lost” (converted to heat, bodily functions, and waste, among other forms of energy).

Look at the example of an energy pyramid above. Then imagine a different food chain and energy pyramid: grass is eaten by a mouse, which is eaten by a snake, which is eaten by a hawk. The primary-producer level of grass contains 1,000 units of energy; the primary-consumer level of mice contains 100 units of energy; the secondary-consumer level of snakes contains 10 units of energy; the tertiary-consumer level of hawks contains only 1 unit of energy.

	→		→		→
(1,000 units of energy)		(100 units of energy)		(10 units of energy)		(1 unit of energy)

Ecosystems maintain a delicate balance as living things relate to one another. Living organisms can live only in habitats that supports their needs. Needs consist of food, water, shelter, and oxygen. If the balance is thrown off so much that an organism cannot survive, all other organisms in the ecosystem are affected, because all organisms are connected through food webs.

This food web is of a savanna in Africa; each ecosystem has its own unique food web in which every species has its own niche, or role in the ecosystem.

Some ecosystem changes have natural causes, such as forest fires, floods, hurricanes, earthquakes, volcanic activity, droughts, and rerouting of water (beaver dams or rockslides). When these changes happen and ecosystems change, some organisms may find that their needs are no longer being met in their habitat. For example, during a drought, a frog may need to move to a different location to find a wet environment. Conversely, if a beaver reroutes a river and a meadow suddenly turns into a large pond, a field mouse will have to search for a drier place for a habitat. Plants often suffer dying out because they are immobile and cannot move to a new location. When ecosystems experience changes and organisms either leave or suffer reductions in population, it affects all organisms living in an ecosystem. The greater the biodiversity of an ecosystem before it undergoes a change, the higher the likelihood that the ecosystem will survive.

A drought is a change in an ecosystem that may make it difficult for certain organisms to meet their needs. Those organisms must move to an ecosystem that meets their needs or face death. Such changes endanger not only the species that need water but also many of the species that are interconnected with that species. There is a domino effect.

There are several types of interactions experienced among species in ecosystems. Competition is one relationship. It occurs when two different species depend on the same food source. For example, both snakes and hawks eat mice. Another type of relationship is the predator-prey relationship. In the example above, hawks are a predator and mice are a prey. Finally, there are symbiotic relationships, in which at least one organism benefits. There are three types of symbiotic relationships: mutualism, commensalism, and parasitism.


Hawks and snakes are in a competitive relationship, while hawks and mice are in a predator-prey relationship.

Mutualism is a relationship in which both parties benefit. For instance, a bee gets nectar to make honey from a flower. While the bee is getting nectar, it pollinates the flower, allowing it to reproduce. Another example of mutualism involves crocodiles and plovers (birds). Crocodiles rest with their mouths open and plovers fly inside. Plovers clean crocodiles’ teeth of the stuck and decaying meat, and plovers get an easy meal. The crocodiles do not eat the plovers.

Bees and flowers both benefit from their mutualistic relationship. It is termed a service-resource relationship. The flower is pollinated and the bee obtains nectar to make honey.

Commensalism is a relationship in which one party benefits and the other party is not harmed. An example of commensalism involves remora fish and sharks. Remoras have a special fin that acts like a suction cup, allowing them to attach themselves to sharks’ skin. The sharks are not hurt, and the remoras receive free food by eating the scraps from sharks’ meals.

The remora benefits by gaining food while the shark is not harmed in this commensal relationship.

Parasitism is a relationship in which one party benefits while the other party is harmed. Sometimes parasitism results in death for the host organism, but not usually. An example of parasitism is a tick. A tick attaches itself to a warm-blooded animal and sucks its blood. The host can suffer from blood loss and loss of nutrients. In addition, since ticks carry diseases like Lyme disease, the host may become sick from a disease as well.

Ticks are parasites that benefit from their relationship with their hosts by gaining nutrients. Hosts suffer due to loss of blood and nutrients and by becoming infected with diseases.

These special relationships among organisms help maintain a healthy balance in an ecosystem. When a new species is accidentally or purposefully introduced into an ecosystem, the balance is thrown off and severe consequences often result. Unlike natural changes to ecosystems, introduction of a non-native species into an ecosystem is usually the result of human interference. Sometimes humans accidentally introduce species into new environments, such as when species catch a ride undetected on a boat or an airplane and are transferred to a new place. Other times, humans intentionally introduce a new species to a region, such as the cane toad that was introduced in Australia in 1935 to protect sugarcane crops from beetles. These non-native species that are introduced into ecosystems are called invasive species. The invasive species often outcompete native species for food, water, shelter, and other resources. Because invasive species often don’t have any natural predators in their new environments, they often multiply rapidly and take over a niche that once belonged to another organism, causing that organism to become endangered. In the case of the cane toad in Australia, cane toads not only killed the beetles that were destroying sugarcane, but also killed and ate any small pests that they encountered. In addition, it had no natural predator, since it produces deadly toxins, so its population grew out of control. The introduction of the cane toad created more problems than it solved.

The cane toad is a classic example of why introducing new species to an ecosystem can backfire.

Ecosystems are complex systems. A healthy ecosystem is one in which a wide variety of species are able to meet their needs as part of a relatively stable web of life. The greater the diversity of life, the stabler an ecosystem is and the better able it is to successfully survive a change.

English

Although roots absorb both water and nutrients from the soil for the plant, water is the ingredient necessary for performing photosynthesis.

Stems help maintain the physical structure of the plant and carry absorbed materials (such as water) and manufactured materials (such as glucose) to other plant structures. Xylem is vascular tissue that carries water throughout plants. Phloem is vascular tissue that carries sugars and other foods throughout plants.


The stems transport water for the process of photosynthesis and glucose to parts of the plant through vascular tissue called xylem and phloem.

Leaves are the location where most food is produced by the plant. The chlorophyll in leaves capture sunlight. Leaves combine this energy with water and carbon dioxide from the air to make plant food—glucose, a form of carbohydrate.


Leaves are the food-making factories of plants. Chlorophyll captures the sunlight used to make glucose.

Respiration, the process of releasing the energy stored in molecules, takes place in the cells of plants, just as it does for animals. Food molecules are broken down to release energy for growth and to fuel an organism’s metabolic processes.

Cellular respiration in plants takes place in cells just as it does in animals.

Flowers, seeds, and fruit are other structures of plants. Flowers function as the plant’s reproductive center and are the location where pollination (fertilization) takes place. Seeds formed as a result of pollination are scattered and produce new plants. The structure that forms to cover and protect seeds is called fruit. This structure can be soft and fleshy, such as the meat of an apple, or it can be hard, such as the shell of a nut. This provides nutrition for the seedlings after the seed germinates until the plant can produce its own food.


Flowers, fruit, and seeds are the reproductive system of the plant, and fruit stores the extra food from the plant.