Biology 2483A Lecture 14: 14-commensalism.docx
2 Jan 2015
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Agriculture could be considered a form of mutualism. A colony may contain hundreds of gardens, each the size of a football; they can feed 2 8 million ants. Nonresident fungi, pathogens, and parasites can sometimes invade the colonies. Ants respond to escovopsis by increasing garden weeding rate: weeding effort on ants" part becomes more intense. They also enlist the help of other species: The ants carry a bacterium that makes chemicals that inhibit escovopsis. The bacteria also secrete compounds that promote the growth of the cultivated fungi. The bacteria also benefit: they get a place to live (in specialized structures called crypts on the ant"s exoskeleton), and a source of food (glandular secretions) from the ants. Thus, the bacterium is a third mutualist. Positive interactions occur when neither species is harmed and the benefits of the interaction are greater than the costs for at least one species: facilitation is a synonym for positive interactions.
