Ecologists study environmental systems. These systems are biotic factors, which are the living parts of an ecosystem, and abiotic factors, which are the nonliving parts. The items that consumers eat depends upon whether they are herbivores, carnivores or omnivores.
Producers, consumers and decomposers make up the main parts of the biotic factors. Producers are organisms that make their own energy, like flowers do with photosynthesis. Consumers do exactly what their name suggests: they consume either producers or other consumers. Humans are consumers as are all animals in some form. The items that consumers eat are dependent on if they are herbivores, carnivores or omnivores. The final group, the decomposers are often made up of organisms we can't see or function at a level that we do not typically observe.
Bacteria that feed on nonliving material are decomposers. These organisms break down material to create things like compost and dirt, and they return nutrients back to the soil.
The abiotic factors fall into four categories, which are physiographic factors, climate factors, edaphic factors and gases. Physiographic factors include the physical aspects of the area where the biotic factors exist, such as the topography and distance of a place from water. Climate factors are the weather and climate of a given area. The edaphic factors consist of things such as soil makeup and water-holding capacity. The gases category includes oxygen, carbon dioxide and nitrogen as well as their cycles.