What is Rhizobium Why is it important Soil bacteria that fix nitrogen by

What is rhizobium why is it important soil bacteria

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2. What is Rhizobium? Why is it important? Soil bacteria that fix nitrogen by infecting 3. Describe how the relationship between two organisms could change from mutualistic to parasitic or competitive. Give an example.Midterm 2+Nature of Communities: Structure and Diversity (primarily Chapter 16, 19—see exceptions below) Terms/Concepts: Diversity- a measure of diversity that increases with species evenness and species richness
Relative abundance-how abundantRichness- the number of species in a communityEvenness- the relative abundance of individuals within a communityRank-abundance diagram- a curve that portrays the number of species in a community and their relative abundance; constructed by plotting the relative abundance of species against their rank in abundanceSimpson’s Index of diversity-a measure of the diversity of a given area at a given time. D= diversity index, N= total number of organisms of all species found, n=number of individuals of a particular species. D=N(N-1) / sum of n(n-1)Dominant vs. rare speciesDominant-strongly interacting species, comprises a large amount of the biomass in a community (Douglas fir in NW Pacific old growth forests)Keystone species- species that, despite low biomass, exert strong effects on the structure of the communities they inhabitOrganismic vs. individualistic community concepts (chapter 17)Organismic- Clements viewed the community as a quasi-organism made up of interdependent species;; Communities are integrated units Communities have few species in common with narrow transmission between them. Suggests a common evolutionary history Individualistic- Gleason saw the community as an arbitrary concept and stated that each species responds independently to the underlying features of the environment; Species associate because of similarities in their requirements and tolerances, not becauseof strong interactions or common evolutionary historyEquilibrium theory of island biogeography (chapter 18)-Theory of island biogeography published by Robert MacArthur and Edward Wilson in 1967-Studies dynamics of species being established on islands through immigration and being lost from islands through extinctionDirect vs. indirect species interactionsDirect- Occur between two species; Competition, predation, facilitation.Indirect- Relationship between two species is mediated by a third (or more) speciesTrophic level (basal, intermediate, top predator)- position in food web determined by number of energy transfer steps; Basal species feed on no other species but are fed upon by othersBottom-up vs. top-down controlBottom-up-interactions is controlled by the primary producer popTop-down- interactions is controlled by Secondary and Tertiary consumersTrophic cascade-chains of interactions extending among multiple trophic levelsCommunity structure- attributes such as the number of species, relative abundance of species and the kinds of species comprising a community; includes attributes such as

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