Intraspecific and interspecific relationshipsSpec C4.1.9, C4.1.10, C4.1.11
In short
Intraspecific relationships are between members of the same species. They compete for limited resources such as food, territory and mates, but may also cooperate, for example by hunting in packs. A community is all the interacting populations in an area. Interspecific relationships include herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity.
Within a species
Members of the same species have the same needs, so intraspecific competition happens whenever a resource is in short supply. Reasons include limited food, water, space or territory, light (plants), nest sites and mates.
| Relationship | Example |
|---|---|
| Competition for mates | Red deer stags roar and fight in the rut; winners mate with groups of hinds |
| Competition for light | Dense tree seedlings shade each other; only the tallest survive to form the canopy |
| Competition for territory | Robins defend feeding territories against other robins |
| Cooperation in hunting | Grey wolves hunt in packs, bringing down prey such as elk that one wolf could not kill |
| Cooperation in defence and care | Meerkats take turns as sentinels; worker honeybees rear the queen's offspring and defend the hive |
| Cooperation in keeping warm | Emperor penguins huddle in groups through the Antarctic winter, reducing heat loss |
Communities
A community is all of the interacting organisms in an ecosystem: every population in the area, including plants, animals, fungi and bacteria. An ecosystem is the community together with its abiotic environment.
Between species
| Relationship | What happens | Example |
|---|---|---|
| Herbivory | A primary consumer feeds on a plant or alga | Dromedary camels browsing acacia shoots |
| Predation | A consumer kills and eats another animal | Canada lynx hunting snowshoe hares |
| Interspecific competition | Two species use the same limited resource, and both are harmed | Red and grey squirrels competing for seeds in British woodland |
| Mutualism | Both species benefit | Rhizobium bacteria in root nodules of legumes |
| Parasitism | A parasite lives on or in a host and takes nutrients from it, harming but not usually killing it | Ticks feeding on the blood of cattle |
| Pathogenicity | A pathogen causes disease in its host | Mycobacterium tuberculosis causing tuberculosis in humans |
Intra- means within (one species); inter- means between (different species). Mixing these up costs easy marks.
Written and checked against the IB Biology HL specification · Updated October 2026