1. Producers: These are organisms like plants and algae that make their own food through photosynthesis. They form the base of the food web and provide energy for all other organisms in the ecosystem.

2. Consumers: These organisms obtain energy by eating other organisms. Consumers can be divided into categories:

* Herbivores: Eat plants.

* Carnivores: Eat other animals.

* Omnivores: Eat both plants and animals.

* Decomposers: Break down dead organic matter (plants and animals), releasing nutrients back into the ecosystem for producers to use.

3. Decomposers: These are organisms like bacteria and fungi that break down dead organic matter, releasing nutrients back into the ecosystem for producers to use. They play a crucial role in recycling nutrients and maintaining the balance of the ecosystem.

4. Scavengers: These are animals that feed on dead animals. They help clean up the environment and prevent the spread of disease. Examples include vultures, hyenas, and some types of beetles.

It's important to note that these roles are not always distinct. For example, some organisms might act as both a producer and a consumer, or a scavenger and a decomposer.