Parasites are symbiotic species that rely on their host for nutrients, like predators rely on prey. This is at the expense of the host, which often suffers illness as a result, or a damaged reproductive function. Unlike predators that have a lower reproductive capacity compared to their prey, parasites have a higher reproductive potential than their host.
An ecological niche is the set of tolerances and requirements a species has in its immediate living space. For example, birds make use of a tree’s branches to house nests, while fungi make use of a tree’s trunk to grow. The same habitat can have many different niches that can be populated by different species.
Parasites have very narrow niches because they are specific to their host. Human head lice cannot survive anywhere except the human scalp. This also means that the molecular processes that parasites rely on in their host are very similar and overlap with those of the host – one reason developing effective treatments against them is challenging. This interdependence means that some processes carried out by the host on behalf of its parasite renders the parasite degenerate i.e. unable to fulfil them by itself, and lacking in structures and…