Law 3: Everything is Always Changing

• Succession– How the ecosystem changes over time

• Natural Selection– The survival and reproduction of organisms with

particular traits

Ecological Succession

The gradual process of change and replacement of some or all of the species in a community.

– May take place over hundreds or thousands of years

– Each new community makes it harder for the previous community

Primary Succession

• Occurs on a surface where no ecosystem existed before

• No soil• On rock or sand dunes• Takes many years to

establish an ecosystem.

How Primary Succession Happens• Where?– Begins where there is no soil– Volcanic islands, areas exposed after a glacier,

deserted parking lots• What happens?

1. Bacteria and lichens or wind tolerant plants 2. Rock begins to break down or sand becomes

stable3. Soil begins to build up

Examples of Primary Succession

• Coastal sand dunes• Hawaii

Sand Dunes1. Dune building – wind causes sand to

build up next to coastline2. Pioneer stage – wind tolerant grasses

begin to move in, stabilizing the sand3. Yellow or White dune - spurges, plants

with waxy, succulent leaves and horizontal growing roots, start to grow further stabilizing the sand

4. Grey dune – continuous plant cover, soil beginning to form on the sand

5. Scrub dune – small shrubs such as hawthorn that can grow in poor, sandy soil move in

6. Conifers – final stage.

Hawaii – Volcanic Island

1. Lava flows cool2. Colonization begins

immediately rate relies on surrounding areas and moisture

- Kipuka – fragmented forests, surrounded by lava flow.

3. Windblown soil, seeds, spores fall into cracks

4. Organic matter builds up on top of volcanic rock allowing for shrubs and trees to move in

Secondary Succession

• Occurs where an ecosystem has previously existed.

• Occurs in ecosystems that have been disrupted by humans, animals or natural processes such as fires storms, floods, or earthquakes

How Secondary Succession Happens

• When?– After a disturbance– Fire, storm, flood– Old field

• How?– Pioneer species start the process

• Moss, weeds

– Middle species• Tall grass• Wildflowers• Bushes and small trees

– Climax species are the end• Tall trees with a dense canopy

After a Forest Fire

1. “Weeds” move in first, deep rooted plants

2. Berry bushes, blueberries, raspberries

3. Tree species that require full sunlight move in first

4. Jack pine requires fire to release seeds from cone and germinate

5. Aspen and birch trees can sprout from underground root systems

Yellowstone Fires 1988

• 790,000 acres were burnt

• Forest floor was thick and dry after a drought

• Grasslands returned first

• Aspens grew next• Douglas fir and spruce• Lodgepole pines last

Abandoned Farm Field

1. Grasses2. Cedar, shrubs3. Pines4. Oak, Maple

Pond Succession• Ponds are formed when lakes get smaller or

when potholes or sinkholes are formed

1. New ponds have sandy, sterile bottoms and small water plants like duckweed and algae– Fish from lake could be present

2. Floating plants– Frogs, turtles and small fish become abundant

3. As the pond matures, bottom becomes thicker and emergent plants take hold– Bottom becomes thick with organic matter

4. Plants become thicker, pond becomes marsh– Marsh can become swamp if trees take over

Pond Succession

How does Succession Effect the Animals?

• Pioneer plant species favor small herbivores

• As the forest grows, more predators move in

• As succession continues the diversity changes

Natural Selection• If an ecosystem changes,

the animal populations have to adapt or move

• Only the animals with the characteristics to survive will populate the new ecosystem

• Animals gain new characteristics by chance genetic mutations

Examples of Natural Selection

• Darwin’s finches– Galapagos Islands– Similar finches on each island – The finches have a unique beak

shape– Specialized for food source on it’s

island

• Isolated species – Mountain Sheep– One species, two populations that

become isolated– Dall Sheep of Alaska, Bighorn Sheep

of US, Desert Sheep of Mexico and

Artificial Selection

• The selective breeding of organisms by humans for specific characteristics

Natural Selection and Resistance

• The ability of an organism to tolerate a particular chemical designed to kill it– Herbicides

• Roundup Resistant weeds

– Pesticides• Colorado Potato Beetle

– Antibiotics• Methicillin-resistant Staphylococcus aureus

(MRSA)