Quick questions on Relationships Between Organisms - TCE Biology (Tasmania)

Predation is an interaction in which one organism, the predator, kills and eats another, the prey. It directly transfers energy up the food chain and is a powerful selection pressure: predators tend to catch the slowest or least wary prey, while prey evolve defences such as camouflage, speed, or toxins. Predator and prey numbers are linked, so a rise in prey can be followed by a rise in predators, which then drives prey numbers down again, producing cyclic patterns.

Competition occurs when organisms need the same limited resource, such as food, water, light, space, or mates. It comes in two forms:

Mutualism is a symbiosis in which both species benefit. Examples include:

Commensalism is a symbiosis in which one species benefits and the other is neither helped nor harmed. An example is a bird nesting in a tree: the bird gains shelter while the tree is unaffected. True commensalism is hard to confirm, because careful study often reveals a small benefit or cost to the second partner, but it remains a useful category.

Parasitism is a symbiosis in which one species, the parasite, benefits while the other, the host, is harmed. Parasites usually live in or on the host and take nutrients from it. Examples include tapeworms in the gut, ticks on the skin, and many disease-causing organisms. Successful parasites usually do not kill the host quickly, because the host is their food and habitat; weakening the host while keeping it alive maximises the parasite's success.