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