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Chapter 14

Chapter 14 - mutualism and commensalism

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BIOL 2050
Christopher Lortie

Chapter 14 – Mutualism and Commensalism  Ants and fungi, example of co-evolution and positive interaction  Positive interaction – one in which both species benefit and neither is harmed  There is +,+ and +,0  What is facilitation? Generally commensalism which is +,0 but it could be mutualism which is +,+ but it generally describes plant, plant interaction so facilitation is a positive interaction between two plant species or two individuals of the same plant species where one plant helps another plant and generally we don’t measure whether there is a cost back or benefit back to the nurse plant or the plant that helped the other plant which is why facilitation is generally +,0 or commensalism  Diff between mutualism and commensalism? In mutualism its +,+ so both interactors get a benefit and commensalism is +,0 so one of the individuals definitely gets a benefit and the other is neutral, there is no cost  Whats symbiosis? When two species live in close physiological contact with each other such as coral and algae. So symbiosis includes commensalism, mutualism (therefore also facilitation) but also parasitism which is +,- so one individual (or species) benefits and there is a cost to the other. Symbiosis encapsulates all these terms or concepts  What are mycorrhizae? Associations between roots and various fungi this was a big paradigm shift where plants actively try to cultivate these fungi to live near the roots (remember, there is two kinds ones that live outside, ECTOmycorrhizae, and ones that can be between the cells within the root or right in the cells in the root and both of these are called ENDOmycorrhizaes or they can also be called ARBUSCULAR mycorrhizae).  So the fungus grows into the soil in both cases and this gives the plants an extended root network and fungi make hyphae which are really tiny threads which are hard for a plant to make which allows for greater nutrients and water and resource capture for the plant and the benefit back to the fungi is that it gets carbohydrates and sugars through the roots (this is a good example of mutualism because they both benefit) – Figure 14.4  Corals do very similar things but with algae  Some positive interactions are obligate meaning that both interactors need it and some are facultative in that there could be some free living bacteria that don’t need the roots but the same species of free living bacteria and fungi
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