of fungi in individual colonies. Ant populations defend against the horizontal transmission of foreign fungi to their fungal colony, as this transmission may lead to competitive stress on the local fungal garden. Invaders are identified and removed by the ant colony, inhibiting competition and fungal interbreeding. This active isolation of individual populations helps maintain the genetic purity of the fungal colony, and this mechanism may lead to sympatric speciation within a shared habitat. See also Evolutionary pressure Ring species Selection Pieris oleracea References Bibliography Ecology Evolution