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Unit 12: Biodiversity
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Dilution effectDilution effect
As suburbs developed in New England, the forest habitat became more patchy, resulting in the disappearance of some species and the proliferation of mice -- which are the reservoir for the Lyme spirochete -- and ticks, which carry the disease to humans. This increased the proportion of infected ticks, and led to an increase in human disease.
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Mass ExtinctionsMass Extinctions
A graph showing the five major recognized mass extinctions over the last 600 million years. Trilobites went extinct at the end of the Permian era, while dinosaurs were casualties of the most recent mass extinction at the Cretaceous/Tertiary period border.
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Species Richness vs. Lyme DiseaseSpecies Richness vs. Lyme Disease
Ostfeld's study found that as species richness declined, the incidence of Lyme disease increased.
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Test Strip ę Cedar Creek Test Strip - Cedar Creek
Each year, David Tilman collects the plant matter from a strip 10 cm by 3 m from each of his experimental plots to examine the effects of species diversity on biomass.
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Tilman¨s Experimental Plots Tilman's Experimental Plots
Tilman compares plots with few species (on left) to those with more species (as on the right). He has found that more diverse plots recover from disturbances like drought more quickly than those with fewer species.
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Asteroid Asteroid
A re-creation by NASA scientists of the impact made by an asteroid 500 miles in diameter at Chicxulub, on the Yucatan Peninsula. This impact is thought to be the cause of the K/T mass extinction 65 million years ago.
Biomass vs. species numberBiomass vs. species number
Tilman's experimental data showing that productivity rose with the number of species grown in a plot
Black MamoBlack Mamo
Another animal that has gone extinct in the ¸sixth mass extinction”
Cedar Creek aerial photoCedar Creek aerial photo
Aerial photo of Cedar Creek research fields at the University of Minnesota
Cedar creek aerial photoCedar creek aerial photo
Aerial photo of Cedar Creek research fields at the University of Minnesota
Deer tick Deer tick
The tick that causes Lyme disease
Greater Koa finchGreater Koa finch
Mass extinctionsMass extinctions
The graph shows an approximate time line of loss of families of species from the earth during the five so-called ¸mass extinctions.” The trilobite, top left, was a victim of the extinction at the end of the Permian period, and the familiar T. rex died out with the K/T extinction 65 million years ago.
Mouse with ticks on ear
Mouse ear with engorged ticksMouse ear with engorged ticks
Mouse ear with engorged ticks attached to it
Passenger pigeonPassenger pigeon
Once a common bird of eastern North America, the last passenger pigeon died in a zoo in 1914.
Pie chart of speciesPie chart of species
A pie chart of the hypothesized distribution of species living on earth today
Spriochetes of Borelia burgdorferei, the bacterium that causes Lyme disease
T. rexT. rex
Illustration of Tyrannosaurus rex, a casualty of the mass extinction at the end of the Cretaceous period
Close-up of tick body
Tick on the end of a piece of grass, waving pincers, waiting to attach for a bloodmeal
Tick photoTick photo
The tick that causes Lyme disease
Adult, nymph, and larval stages of the tick
Adult, nymph, and larval stages of the tick
Tree phylogenyTree phylogeny
Simple phylogeny of plants
Trilobite, a casualty of the mass extinction at the end of the Permian period

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