Can decomposers and parasites be included in food webs and food chains?
Decomposers and parasites can both be included in food webs and food chains.
Decomposers and parasites can both be included in food chains/webs. A parasite is simply an organism that lives in or on another organism in order to survive. Parasites definitely belong in a food chain as they do alter energy flow. Parasites are essentially consumers. Thus, you could add parasites to an existing food chain by linking them to the organisms they consume. They are often ignored or forgotten in food chains, but they still consume energy and affect energy transfer.
Here's another example with multiple decomposers:
The fungus, maggots, bacteria, pillbug and so forth are all decomposers. As you can see, decomposers are typically shown at the bottom of the food chain/web in a diagram.
If you're a go-getter, here's a really excellent academic article that you may want to read parts of summarizing parasites and food webs: Lafferty et al., 2008 .