BRAINCAKEParasitism and Disease
A parasite is an organism that lives in or on another organism, the host, and obtains nutrients from it, harming the host. Parasites usually do not kill their host quickly, because they depend on it. Examples include tapeworms in the gut, and fleas, ticks and lice on the skin. Pathogens are microorganisms, such as bacteria, viruses, fungi and protoctists, that cause disease.
Effects on the host population. Parasites and pathogens reduce host fitness: infected individuals may be weaker, grow more slowly, produce fewer offspring or be more easily caught by predators. Some diseases kill many individuals. For example, myxomatosis, a viral disease spread by fleas, killed over 99% of rabbits in parts of Britain in the 1950s, and ash dieback, caused by a fungus, is killing many ash trees across the UK.
Sign in free to see the rest of this lesson, the R.E.C.I.P.E. recall steps and the quiz
BrainCake is free. Make an account in seconds and pick up where this page stops.
Key terms in this lesson
- coevolution
- A process in which two interacting species, such as a host and a parasite, each evolve in response to selection pressure from the other.
More in The Nature of Ecosystems
- Edaphic Factors
- Predation
- Finding a Mate
- Territory
- Case Study: Snowshoe Hare and Lynx
- Case Study: Red Grouse and Parasites
- Density Dependent Factors
- Density Independent Factors
All 39 lessons in The Nature of Ecosystems · All Edexcel A-level Biology topics