Producers: Algae, Bacteria and Plants are examples of producers; organisms that 'produce' or make their own energy or food via photosynthesis, using the energy from sun and water, or chemosynthesis, to create their needed nutrients in organic compounds. Producers are essential for the rest of the habitat to uphold.
Primary Consumers: Animals or plankton that are first to eat the producers, and are usually herbivores, are the primary consumers, as they receive the largest amount of energy from the producers as the energy travels up the food web, so they play a important role in transferring energy from the producers towards the higher 'trophic' levels of the ecosystem.
Secondary Consumers: These are animals that eat the primary consumers in order to obtain their energy and nutrients, and are typically omnivores or carnivores. Because they are higher up the food web, they must eat more than what a primary consumer would eat as they do not intake as many nutrients from the producers.
Apex Predator: These animals are at the top of the Food Web. They have little to no natural predators of its own. Apex predators are needed in an ecosystem to balance the food hierarchy and regulate the population of other species to order to prevent over population. They need to eat the most in the food web as they receive the least amount of depleting energy from the original producers.
Decomposers: While not listed in the Food Web, decomposers are in charge of breaking down dead plants, animals and other organic matter to recycle their nutrients back into the cycle. The two main decomposers are bacteria and fungi, but also includes invertebrates. They are important to keep the continuious cycle of energy flowing.