Download Getting to Know: Relationships Among Organisms

Getting to Know: Relationships
Among Organisms
If you are looking for examples of organisms from many different scientific kingdoms, just visit your local grocery store! Fish, chicken, and beef are from the Animal kingdom. Apples, bananas, and carrots are from the Plant kingdom. Mushrooms are not animals or plants. They are from the kingdom Fungi. People can meet their needs for energy by eating the variety of foods from a grocery store.
How do organisms meet their needs in
ecosystems?
In ecosystems, organisms meet all their needs through interactions with other organisms and the environment. Plants and many protists such as algae and diatoms are producer organisms. Producer organisms produce their own food through photosynthesis.
What is the relationship between producer
and consumer organisms?
The plant obtains energy
by producing its own food
through photosynthesis.
The caterpillar obtains
energy by feeding on the
plant.
During photosynthesis, light energy is used to combine carbon dioxide and water. The
products of photosynthesis are glucose and oxygen. Glucose is a food molecule that contains
stored chemical energy. Consumer organisms
must feed on other living organisms to obtain this
energy. All consumer organisms are either directly or
indirectly dependent on producer organisms for food
and energy.
Animals that feed on plants are called herbivores. For
example, a caterpillar is an herbivore that feeds on
plant leaves.
The mountain lion is an example of a
carnivore.
Animals that feed on other animals are called
carnivores. A mountain lion that feeds on a deer is
a carnivore. Animals that feed on both plant and
animal matter are called omnivores. Bears and
raccoons are good examples of omnivores. Humans
are also omnivores.
How do predator–prey relationships affect populations of organisms?
Predator–prey relationships are an important part of ecosystems. Predator–prey relationships
do not happen randomly or arbitrarily. They are developed over many generations between
species. When a prey population changes, the predator population also changes. Likewise,
when a predator population changes, the prey population also changes. For example, if
the mountain lion population is removed from an area, the deer population may increase
significantly because an important predator is no longer present.
Concept: Relationships Among Organisms
Getting to Know
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Misconception 1: Food chains often show large predators at the end, or top, of the
diagram. Do food chains actually end with large predators?
Food chains do not have an actual end point or top organism. Bacteria decompose even
a large predator like a mountain lion when it dies. In fact, decomposers can break down
each organism in a food chain.
What are some other relationships between organisms?
In a parasite–host relationship, one organism benefits at
the expense of the other organism. Typically, the host organism is not killed by the parasite. A tick attaching itself to a deer is an example of a parasite–host relationship. The tick feeds on blood from the deer, but the deer is typically not killed by the interaction.
In symbiotic mutualism, both organisms benefit each other. A good example is the relationship between ants and acacia trees. Acacia trees have large thorns that the ants can hollow out and live inside. The trees also excrete sweet nectar that feeds the resident ants. In return, the ants benefit the acacia tree by attacking
any insects that attempt to eat the tree.
Fungi such as these mushrooms
are important decomposer organisms.
Decomposers recycle nutrients in an
ecosystem.
Commensalism refers to a relationship in which one
organism benefits and the other organism is not
significantly affected. The relationship between cattle
and birds called cattle egrets is a good example of commensalism. As cattle graze in grasslands,
they disturb many insects that hide among the grasses. Egrets follow the cattle and eat the
insects that are disturbed by the grazing cattle. The egrets benefit, but the cattle are not
significantly affected by this behavior.
In this lesson, you will learn more about the relationships among organisms in ecosystems.
Misconception 2: Don’t all species compete for the same resources in an ecosystem?
That is not always true. Some species actually work together in ways that benefit both
species. Organisms can have mutualistic or commensal relationships, which help them
maximize their use of limited resources.
Concept: Relationships Among Organisms
Getting to Know
www.discoveryeducation.com
2
© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.