BIOEE 1610 1st Edition Lecture 13Outline of previous lectureI. What is a community?II. Community change and successionA) DisturbancesB) Mechanisms of successionIII. Food websA) TypesB) Interaction strengths and keystone speciesC) Trophic cascadesOutline of current lectureI. Trophic cascadesII. DiversityA) ComponentsB) Shannon indexC) Rank-abundance curvesIII. Spatial scales of diversityA) Alpha, beta, gamma diversityCurrent lectureI. Trophic cascades*Why is the world green?-Hypothesis: top-down control (trophic cascading)-Hypothesis: plants develop their own defenses*Studies: -More predators  less herbivores  MORE PLANTS-Fertilization  MORE PLANTS  little to no effect no herbivores*Conclusion: top-down control appears to be happening*Example of trophic cascading: -Kelp  sea urchins  otters-Sea otter recovery, it is very successful, huge populations of sea otters return-They grazed on sea urchins, who could no longer consume as much kelp-Kelp urchins grew significantly-Without the sea otters, there would be a whole bunch of urchins and very little kelp-Killer whales (0) otters (+) urchins (-)  kelp(+)*Example of trophic cascading:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-Later, killer whales’ food sources began to decline-The killer whales switched to consuming sea otters-Killer whales (+) Otters (-)  urchins (+)  kelp (-)-Different effects of top-down control depending on if you have an odd or even number of levelsII. DiversityA) Components*”Diversity” is a complex combination of species richness and evennessB) Shannon index*H'=−∑j=1Spᵢ ln ⁡( pᵢ)C) Rank-abundance curves*Rank abundance curve (greater species evenness is shown by a lower slope)Proportional abundanceABAbundance rank*Sampling: How do you know if you have enough samples/samples are large enough?-As you continue to increase the number of individuals in your samples, the number of species will begin to even out (at some point you will be capturing essentially all of the speciesProportion of species in sampleProportion of individuals in sampleIII. Spatial scales of diversityA) Alpha, beta, gamma diversity*Robert Whittaker: spatial scales of diversity*Alpha diversity: number of species within a uniform habitat*Beta diversity: rate of species turnover between habitats (expressed as gamma/alpha diversity)*Gamma diversity: number of species observed in all habitats within a region*Example (looking only at richness and not evenness)-In region one: mountain one has species A, B, C, D, E, F; mountain two has B, C, D, E, F; mountain three has A, B, C, D, E, F, G-Alpha=6; gamma=7; beta=gamma/alpha=1.2*Local species richness vs regional diversity-As one goes up, the other also tends to, but not necessarily in a one-to-one rate*Human microbes*Different types of microbes in out bodies (alpha), different combinations of these in different people (beta), variety of microbes across all of the human population