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Ecology- lec 15 summary- mutualism & commensalism.docx

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Biology 2483A
Hugh Henry

Ecology- lec 15 summary- Mutualism & commensalism Fungi cultivating ants- ant farmers feed fungi leaves by scraping away a waxy covering, & fertilize fungi & fungi digest chemicals in plants.. then ants eat the fungi Ants cant survive when a parasite destroys the fungi—they respond by increasing weeding rate rd 3 mutualist—ants carry a bacterium that inhibits the fungal parasite Symbiosis- a relationship in which 2 species live in close physiological contact (parasitism +/-, mutualism or commmensalim Positive interactions (AKA facilitation)- nethier is harmed, atleast one benefits - Mutualism (+/+) - Commensalism (+/0)—eg. Buffalo walks and grasshoppers come out, seagulls can pick out Sometimes there is a cost to one or both, but net effect is positive Mutualism is everywhere - Mycorrhizae- association between plant roots & fungi 1. Ecomycorhizae- fungus between root cells & forms a sheath around root 2. Arbuscular mycrorrhizae- penetrates into some root cells, but extends away from root - Corals- protect, provide nutrients (P & N), sunlight Algae- photosynthesize carbohydrates for corals - Bacteria in gut of animals to digest for them Commensalism is everywhere - Lichens etc grow on trees without affecting them - Bacteria on our skin Mutualism can arise from a host-parasite interaction - Amoeba infected by a bacterium- bacterium used to cause smaller, slow growing amoeba & killed it 5 years later, bacteria was harmless & amoeba was dependant on bact for metabolic function Some positive interactions- highly species specific & obligate (neither can survive w/o other) - Wasps & figs have coevolved & figs have evolved specific suctures that help wasps- very sophisticated & specific Some positive interactions- not specific, no coevolution & facultative (not necessary) - Adult nurse plant creates shade-- cooler, moist conditions for many diff species under it - Herbivores pass seeds in feces- dispersal mechanism- no coevolution Interactions between 2 species: - Positive (benefis>costs) Negative (costs>benefits) Neutral (costs=benefits) - But costs & benefits can vary e.g. soil temp low- typha & myositis are commensals (typha helps myosotis) soil temp high- typha & myositis are competitors (typha competes with myosotis) Each partner in a mutualistic interaction acts in ways that serve its own ecological/evolutionary interests Types of mutualisms - Trophic mutualism- mutualist receives energy or nutrients from partne
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