Ecology Exam III - Ecology Exam I I I Friday November 13th...

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Ecology, Exam III, Friday, November 13th Chapters: Unit III: Interactions Among Organisms o 14: Mutualism and Commensalism Unit IV: Communities o 15: The Nature of Communities o 16: Change in Communities o 17: Biogeography o 18: Species Diversity in Communities Unit V: Ecosystems o 19: Production Chapter 14: Mutualism and Commensalism Positive Interactions (one or both species benefit, none are harmed) have influenced colonization of land & growth & survival of organisms today. Positive Interactions : Concept 14.1 : Positive interactions occur when neither species is harmed and the benefits of the interaction are greater than the costs for at least one species. o Symbiosis : relationship where both organisms are in close physiological contact with each other. Can be (+/+), (+/0), (+/-) o Mutualism and Commensalism are ubiquitous (everywhere) Mycorrhizae : mutualistic relationships between plant roots and fungi. Fungi increase root surface area and prevent plant pathogens. Plant provides carbohydrates. Ectomycorrhizae : fungi between plant root cells, mantle Arbiscular mycorrhizae : fungi penetrates plant root cells o Mutualism and Commensalism can evolve in many ways Lichen and tree can be initially (+/0), but when the lichen gets too large, reduce sunlight for tree, turning into (+/-). The tree can evolve (chlorophyll), turning the (+/-) back to a (+/0).
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o Positive Interactions can be obligate and coevolved or facultative and loosely structured. Obligate: Not optional, species cannot survive without each other. Coevolved: Each partner evolves unique features that benefit the other species. Facultative: Not obligate. Deer eating seeds, dispersing with feces. Nurse plants: desert plants providing shade & “nurse” seedlings. Commensalism: ALWAYS facultative for (0) species. o Positive Interactions can cease to be beneficial under some circumstances The costs and benefits experienced by interacting species can vary from one place and time to another due to temperature or… Experiment: At high soil temp, Typha has (-) effect on Myosotis . At low soil temp, Typha has (+) effect on Myosotis. o Positive Interactions may be more common in stressful environments Experiment: Neighboring plants increased target plant performance at high elevation sites (colder) than low sites. Characteristics of Mutualism: Concept 14.2: Each partner in a mutualism acts to serve its own ecological and evolutionary interests. o Mutualisms can be categorized according to their effects. Trophic mutualism: a mutualist receives energy or nutrients from its partner food in exchange for Phosphorous (mycorrhizae) Habitat mutualism: One partner provides the other with shelter, a place to live, or a favorable habitat. “Seeing-eye fish”
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Service mutualism: One partner performs an ecological service for the other. i.e. Pollination, dispersal, defense.
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