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1
After Snowball Earth (600 mya – present)
• Ice melts
• New habitats available (land)
• Oxygen in atmosphere
• Result -> adaptive radiation
– First multicell organisms
– Land colonized by plants and animals
– Animals diversified
• Rapid
diversification in
body forms
• All 20-30 modern
phyla present by
the end of the
Cambrian (500
mya)
• Some phyla
extinct, no new
phyla
Mass Extinctions Mass Extinctions
2
Extinction is a natural process
• Fossil record indicates the average species lives 4-22 million years
• 99.9 % of all species are extinct
• Mass extinctions usually followed by rapid speciation
One of the oldest ecological questions…
• What occurs where and why?
A great ecological mystery…solved?
• What occurs where and why? • mammals (including marsuipals) diversified ~60-70 mya
3
Put the pieces together How do we know all this?
• Hypothesis – marsupial mammals restricted to Australia due to evolutionary history and continental movements.
– Is this a testable hypothesis?
– How?
Similar patterns in other groups
Evolutionary fallacies
• Evolution is directional
• Evolution is random
• Species “change from one to another”
• “If X evolved into Y, why do we still have X?”
4
Experimental Evidence leading to present biodiversity
• Genetic change is observable
• Speciation is observable
• Radiometric dating of the earth
• Fossil record
• Rates of speciation and extinction
• Continental movements and the distribution of biota (biogeogrpahy)
Incorrect view of life.
Why?
Correct view
Biodiversity
• What is it?
• Where is it?
• Why is it important?
5
Biodiversity
• What is it?
– Simplest form - number of species
– 1st problem – what is a species?
– 1.4 million described species
– Estimated 11 million undescribed• 8 million insects
• 1 million fungi
• 500,000 nematodes
• 400,000 bacteria
• 50,000 vertebrates (about 90% described)
Biodiversity
• What is it?
– Number of species in an area (species diversity)
– Genetic diversity within those populations is also related (genetic diversity)
– Indices of diversity:• Species richness (S)
• Shannon Index (H`)
– Where ni=individuals of species I
– S = number of species
– N = total number of individuals
– Pi = relative abundance of each species
Area 1 pi ln(pi) Area 2 pi ln(pi) Area 3 pi ln(pi)
Species 1 5 0.16 -1.824549 9 0.36 -1.021651 3 0.20 -1.609438
Species 2 4 0.13 -2.047693 2 0.08 -2.525729 4 0.27 -1.321756
Species 3 8 0.26 -1.354546 1 0.04 -3.218876 2 0.13 -2.014903
Species 4 3 0.10 -2.335375 0 0.00 5 0.33 -1.098612
Species 5 8 0.26 -1.354546 2 0.08 -2.525729 0 0.00
Species 6 1 0.03 -3.433987 3 0.12 -2.120264 1 0.07 -2.70805
Species 7 2 0.06 -2.74084 8 0.32 -1.139434 0 0.00
S 7 6 5
N 31 25 15
H` 15.09154 12.55168 8.752759
6
• S – easiest to determine
• H` - accounts for abundance of species, gives a measure of “evenness” in diversity
Area 1 pi ln(pi) Area 2 pi ln(pi) Area 3 pi ln(pi)
Species 1 5 0.16 -1.824549 9 0.36 -1.021651 3 0.20 -1.609438
Species 2 4 0.13 -2.047693 2 0.08 -2.525729 4 0.27 -1.321756
Species 3 8 0.26 -1.354546 1 0.04 -3.218876 2 0.13 -2.014903
Species 4 3 0.10 -2.335375 0 0.00 5 0.33 -1.098612
Species 5 8 0.26 -1.354546 2 0.08 -2.525729 0 0.00
Species 6 1 0.03 -3.433987 3 0.12 -2.120264 1 0.07 -2.70805
Species 7 2 0.06 -2.74084 8 0.32 -1.139434 0 0.00
S 7 6 5
N 31 25 15
H` 15.09154 12.55168 8.752759
Spatial component of diversity
• Alpha diversity (α)
– Number of species (S) within a given habitat
• Beta diversity (β)
– Proportion of species in common among two areas
• Gamma diversity (γ)
– Total biodiversity over a broad area (ecosystem level biodiversity)
Spatial component of diversity example
• Alpha diversity (α)
– 20 species in A
– 15 species in B
• Beta diversity (β)
– 8 species in both A and B
• Gamma diversity (γ)
– 100 species in the region as a whole
A
B
Biodiversity
• Where is Biodiversity?
– Larger areas have more species
– Question is, which regions have the greatest gamma diversity?
– Where do you find the most number of species within a given area?
7
Woody plant species over 3 m tall.
Where is diversity
– Obvious trend is for greater diversity as you move towards the equator…why?
• History
• Stability
• Energy
• Area
Ecological Gradients
• Abiotic variables do not naturally change abruptly
• Gradual changes in variable are called gradients
8
Ecological Gradients
• Most species have optimal conditions where they are most fit, populations are most dense
• Results in unimodal distributions across gradients
Ecological Gradient
Popu
latio
n D
ensity
Latitude
SouthernNorthern
Tem
pe
ratu
re
History and the diversity gradient
What areas were most favorable when a
group radiated?
Stability and the diversity gradient
• Topical ecosystems are productive all year
• There are no “crunch periods”with limiting resources
• No seasonal freeze
9
Energy and the diversity gradient
• More light, more precipitation = more photosynthesis
• More food = more populations supported
Area and the diversity gradient
Rare Species
• Most species are rare.
– Widespread species tend to be patchy
– Species with limited ranges tend to be more locally abundant
– Very few widespread species that are abundant everywhere (called generalists)
• Why?
– Jack of all trades, master of none
– Natural selection works to maximize fitness in an environment. Maximizing fitness in one environment will decrease it in another.
Generalist vs. Specialist
– Generalists – poor competitors, wide spread, never very abundant, tolerant of a variety of abiotic factors.
– Specialist – good competitors in their habitat, often very abundant, only tolerant of specific abiotic conditions
10
Biodiversity
• Why is it important?
– Economics
– Aesthetics
– Medicinal
– Rivet hypothesis
– Intangible value of a healthy ecosystem
Abiotic Environment - Climate
• Major components – temperature, moisture, light
All directly or indirectly due to solar input.
Solar input is greatest at the equator, light is
perpendicular to surface.
Seasonal Variability in Day Length
• Equatorial regions more stable.
11
Nature and Fate of Solar Radiation
Sunlight, temperature and moisture drive climate
• Downdraft areas are warm and dry
• Updraft areas moist
Coriolis Effect
• Object at equator is traveling 1,030 mph…at poles, not moving
12
Ocean currents – conveyor belts of heat
Climate Summary – short term effects
• Local climate due to
– Rotation of Earth
– Earth orbit
– Tilt of Earth
– Air currents
– Water currents
– Atmospheric conditions
– Surface albedo
– Solar output – 11 year cycle
13
Glacial Periods
• Typically last ~100,000 years
• ~ 20 ice ages in last 4 million years
• Global temperatures 4-9 C cooler
• Ice over a mile thick
• Sea levels much lower
• Interglacial periods = rapid speciation
Snowball Earth
• Earth covered in ice
– Ice reflects sunlight, increases surface albedo
– Decrease in solar input -> colder -> more ice
– How was this positive feedback loop broken?
Nutrient cycles – ecosystem function
• All vital nutrients are recycled
• Nutrients often limiting resources
• Most important cycles
– Water
– Carbon
– Nitrogen
– Phosphorus
• Nutrient Cycle properties
– Residence time
– Various pool volumes (source/sink)
– Temporal and spatial nutrient availability
– Biotic/abiotic processing times (ecosystem function)
– Role of decomposers
Hydrologic cycle
14
Carbon cycle
• Carbon fixation –ultimate energy supply for all ecosystems
• Sinks
– Ocean
– Plant material
– Sediment
– Detritus
• Climate change implications