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Roles in an Ecosystem
Dana Desonie, Ph.D.
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Printed: September 6, 2018
Dana Desonie, Ph.D.
Chapter 1. Roles in an Ecosystem
Roles in an Ecosystem
Learning Objectives
• Define and describe the common roles in an ecosystem.
Can you pick out the organisms at the bottom and at the top of this food chain?
What’s at the bottom of the food chain? A bit of the food energy comes from above, where plankton photosynthesize.
Most comes from the coral. Coral are animals that live with tiny zooxanthellae that also photosynthesize. Of course,
you know what’s at the top of this food chain!
Roles in Ecosystems
All ecosystems have living things that play the same basic roles. Some organisms must be producers. Others must
be consumers. Decomposers are also important.
Producers are living things that use energy to make food. Producers make food for themselves and other living
things. There are two types of producers:
• By far the most common producers use the energy in sunlight to make food. This is called photosynthesis.
Producers that photosynthesize include plants and algae. These organisms must live where there is plenty of
• Other producers use the energy in chemicals to make food. This is called chemosynthesis. Only a very few
producers are of this type, and all of them are microbes. These producers live deep under the ocean where
there is no sunlight. An example is pictured below (Figure 1.1).
Microbes use chemicals to make food.
The chemicals pour out of a crack on the
ocean floor at a mid-ocean ridge. What
consumers live in this ecosystem?
Consumers can’t make their own food. Consumers must eat producers or other consumers. Listed below are the
three main types of consumers (Figure 1.2): herbivores, carnivores, and omnivores. Which type are you?
Examples of the main types of consumers. Can you name other consumers of each type?
Consumers get their food in different ways (Figure 1.3). Grazers feed on living organisms without killing them.
Chapter 1. Roles in an Ecosystem
A rabbit nibbles on leaves, and a mosquito sucks a drop of blood. Predators, like lions, capture and kill animals
for food. The animals they eat are called prey. Even some plants are consumers. Pitcher plants trap insects in their
sticky fluid in their “pitchers.” The insects are their prey. Scavengers eat animals that are already dead. This hyena
is eating the remains of a lion’s prey. Decomposers break down dead organisms and the wastes of living things
(Figure 1.3). This dung beetle is rolling a ball of dung (animal waste) back to its nest. The beetle will use the dung
to feed its young. The mushrooms pictured are growing on a dead log. They will slowly break it down. This releases
its nutrients to the soil.
Ways consumers get food. Do you know how earthworms get food?
• Herbivores eat plants, carnivores eat meat, and omnivores eat both.
• Predators are animals that eat a prey animal. Scavengers eat organisms that are already dead. Decomposers
break down dead plants and animals into component parts, including nutrients.
• Producers create food energy. They are the base of all life on Earth. Most producers use photosynthesis but a
very small number use chemosynthesis.
1. What are consumers? What are the three types of consumers and what do they eat?
2. Compare and contrast photosynthesis and chemosynthesis.
3. What role do decomposers play in an ecosystem? What would happen if there were no decomposers?
Explore More
Use the resource below to answer the questions that follow.
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/1511
What is competition?
What is predation?
What is symbiosis?
How do stable communities develop?
What is succession?
What is a niche? What does a niche include?
What causes competition?
1. Christopher Auyueng. A picture of an ecosystem on the ocean floor . CC BY-NC 3.0
2. Grasshopper: Renato Targa (Flickr:renatotarga); Mole: Peter Paquet/ Northwest Power and Conservation
Council; Raccoon: Flickr:ZeMoufette. Herbivores, carnivores, and omnivores are the three main types of co
nsumers . CC BY 2.0
3. Rabbit: Dan Perry; Mosquito: Courtesy of James Gathany, CDC; Pitcher plant: Tim Mansfield; Hyena:
Demetrius John Kessy (Flickr:Diamond Glacier Adventures Ltd); Dung Beetle: Teddy Fotiou (Flickr:EpochCatcher);
Mushrooms: Flickr:The_Gut. The different ways consumer get food . Rabbit: CC BY 2.0; Mosquito: Public
Domain; Pitcher plant: CC BY 2.0; Hyena: CC BY 2.0; Dung Beetle: CC BY 2.0; Mushrooms: CC BY 2.0
Chapter 1. Roles in an Ecosystem