Some ants win by blocking rivals' nest entrances with pebbles
Competition in nature is not always a head-on fight. The ant Novomessor cockerelli plugs the entrances of red harvester ant colonies with small rocks to stop them foraging, and male bowerbirds pilfer decorations from neighbours' display structures. Both are interference, one of three distinct ways that organisms compete for scarce resources.
Ecologists define competition as an interaction in which organisms need the same limited resource, whether food, water or territory, so each lowers the other's fitness simply by existing. It happens within species, called intraspecific competition, and between them, called interspecific, and it helps shape community structure, species diversity and population swings.
Interference, or contest, competition is direct. Large aphids evict smaller ones from the best spots on cottonwood leaves, and red deer stags battle during the rut. It carries clear risks of injury but real rewards, and tends to favour larger, stronger animals, producing cycles in which juveniles stay stunted until they reach adulthood. Rivals adapt: red deer hinds and fawns feed when the dominant males are absent. Plants interfere chemically through allelopathy, releasing compounds that inhibit neighbours.
Exploitation, or scramble, competition is indirect. Organisms may never meet; one simply uses up what the other needs, as when a daytime and a nocturnal species share food, or a plant hogs light and soil nitrogen until nearby plants die. It rewards whoever gets there first, often smaller creatures with faster foraging rates. The two modes frequently mix: a 2019 study found a native thrip, Frankliniella intonsa, beat an invasive relative by both feeding longer and guarding its food more. The third mode, apparent competition, involves no shared resource at all, only a shared predator.
Competition's grand role is debated. The competitive exclusion principle says weaker competitors must adapt or disappear, yet clear cases are rare in natural ecosystems. Competition has long been seen as central to natural selection, but the newer Room to Roam hypothesis proposes that vertebrate diversity grew mainly as animals spread into empty habitable space rather than by outcompeting one another.
Source: Competition (biology)
