From our Naturalist, Siena:
We’ve talked a lot recently about larger animals in our forest ecosystems. However, today I wanted to bring another group to light: parasites. People would often rather forget about these vilified organisms. So much so, that they are often neglected from food webs. Let us take a look at this example food web:
In this food web, grass is eaten by rabbits and deer, which are then eaten by hawks and wolves respectively. Humans can also be part of this food web as rabbits and deer are both common game that are hunted. Many would not find an issue with this example food web. However, I feel there is a very important organism that is being left out of this web: ticks. Ticks are often linked with the diseases they may carry and the unpleasant idea of their feeding methods. However, not all ticks carry disease and are a common organism in many ecosystems.
Let us take a look at the same example food web, but we’ll add in our parasite:
As you can see, this food web looks a bit more complicated. This right here may be the reason parasites are often not included in food webs. In our original food web, hawks, humans, and wolves were the top consumers and we often think of consumers as predators. However, in our new food web, our top consumer is not quite a predator, nor does it fully consume its prey. A parasite does not always aim to kill or even injure its host. A healthy host, means a longer life for most parasites. Ticks require a blood meal to continue their lifecycle. While they intend to feed on a host for a period of time, a healthy tick does not aim to kill. A diseased tick does not even spread its disease intentionally. For example, a tick that is infected with Lyme disease, that is a tick that is technically playing host to a parasite itself. Let us take one more look at our food web, but this time, we’ll add Lyme disease:
In this web, we’ve added two parasites, which has made our food web more complex. With so many organisms in an ecosystem, every one plays a part. The introduction of Lyme disease in various populations can have debilitating affects on these ecosystems. Food webs can become even more complex if the parasites have multiple hosts. However, that may be a discussion for another day.
If you would like to learn more about the importance of parasites in food webs, here is a great scientific article on the topic by Kevin D. Lafferty (https://doi.org/10.1111/j.1461-0248.2008.01174.x).