species diversity quaternary consumers carnivore tertiary
TRANSCRIPT
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12 February 2021
Species Diversity Today�s topics: • Food webs
• Keystone species and indirect effects • Species diversity
• Richness and Evenness • Global patterns of diversity
• Islands and fragmentation • Equilibrium of colonization and
extinction • Species-area effects
Fig. 54-11
Carnivore
Carnivore
Carnivore
Herbivore
Plant
A terrestrial food chain
Quaternary consumers
Tertiary consumers
Secondary consumers
Primary consumers
Primary producers
A marine food chain
Phytoplankton
Zooplankton
Carnivore
Carnivore
Carnivore
A Food Web in the Grasslands of Yellowstone National Park
Removing Wolves Initiated a Trophic Cascade
With sea otters Without sea otters Another Trophic Cascade Another Trophic Cascade
Largemouth Bass removed
Source: Estes et al. 2011
Bass Planktivorous fish Zooplankton Phytoplankton
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Species interactions can evolve
A. ricordii
A. insolitus usually perches on shady branches.
A. distichus perches on fence posts and other sunny surfaces.
A. aliniger A. distichus
A. insolitus
A. christophei
A. cybotes A. etheridgei
Niche partitioning
Competition among lizards causes species to forage in different microhabitats.
Niche evolution in lizards
Green Anole Brown Anole
Green anoles perch higher in trees and evolved larger toepads on islands where Brown anoles were introduced.
Los Hermanos
G. fuliginosa G. fortis
Beak depth
Daphne
G. fuliginosa, allopatric
G. fortis, allopatric
Sympatric populations
Santa María, San Cristóbal
Beak depth (mm)
Perc
enta
ges
of in
divi
dual
s in
eac
h si
ze c
lass
60 40 20 0
60 40 20 0
60 40 20 0
8 10 12 14 16
Sizes of Galapagos finch beaks are more different on islands where two species compete.
Defense Mechanisms and Evolutionary Arms Races
Some places have high diversity
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Boreal forest
Desert
Other habitats have low species diversity
“Diversity” depends on species richness and evenness
A B C D
Community 1 A: 25% B: 25% C: 25% D: 25%
Community 2 A: 80% B: 5% C: 5% D: 10%
Which of these communities is more diverse?
Tropical habitats support much larger numbers of species than do temperate and polar regions.
Mammals and Plants show the same pattern
Plant Species Richness
Mammals
Imagine a newly formed island some distance from the mainland…
What will determine the rate of arrival of new species?
Species richness will be a balance between immigration and extinction
Number of species on island
Rat
e of
imm
igra
tion
or e
xtin
ctio
n
Extin
ctio
n
Imm
igration
How would these curves change for a larger island? How will that affect the equilibrium number of species?
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Area and Isolation Influence Species Richness on Islands
Number of plant species on the Galápagos Islands in relation to island area.
Endemic Galapagos prickly pear cactus tree
Species increase with area even at continental scales.
Area (hectares)
Num
ber o
f spe
cies
1,000
100
10
1 0.1 1 10 100 103 104 105 106 107 108 109 1010
The Theory of Island Biogeography Can Be Tested
Experimentally remove insects from small mangrove islands. Will the species number come back to equilibrium?
The Theory of Island Biogeography Can Be Tested (Part 2) How well does that experiment fit predictions of island biogeography theory?