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Lecture 13

BIOB50Winter2012 Lecture 13. - notes from lecture and text (includes images!)

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University of Toronto Scarborough
Biological Sciences
Marc Cadotte

Lecture 13 Chapter 14 Mutualism and CommensalismCase Study The First FarmersThe fungusgrowing ants started cultivating fungi for food at least 50 million years before the first human farmers The fungi produce specialized structures called gongylidia on which ants feedWhen a queen leaves the nest to mate and begin a new colony she carries in her mouth some of the fungi from her birth colonyThe fungi are cultivated in subterranean gardens A colony may contain hundreds of gardens each the size of a football they can provide enough food to support 28 million antsA The mound above the ground is made up of soil excavated by the ants the fungus is cultured in garden chambers each about the size of a football and the dump chambers contain refuse from the fungal gardens Picture is a representation of an AttaLeafcutter ant colony B Photo is a cutaway view of a garden chamber in a central Paraguay colony of the leafcutter antPositive InteractionsPOSITIVE INTERACTIONS OCCUR WHEN NEITHER SPECIES IS HARMED AND THE BENEFITS OF THE INTERACTION ARE GREATER THAN THE COSTS FOR AT LEAST ONE SPECIESMUTUALISMmutually beneficial interaction between individuals of two species COMMENSALISMindividuals of one species benefit while individuals of the other species do not benefit and are not harmed 0SYMBIOSISa relationship in which the two species live in close physiological contact with each other such as corals and algaeParasites can also form symbiotic relationshipsSymbiosis can included parasitismcommensalism 0 and mutualism Mutualistic associations are everywhere Most plants form MYCORRHIZAE symbiotic associations between plant roots and various types of fungi The fungi increases the surface area over which the plants can extract soil nutrients over 3m of fungal hyphae may extend from 1cm of plant rootThere are two categories of MYCORRHIZAEECTOMYCORRHIZAEthe fungus grows between root cells and forms a mantle around the exterior of the root
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