WELCOME BACK!!! Hope you all had a lovely break

BR: What do you know about

succession?

Succession notes

Lab Measurements

Wrap-up: What is a disturbance?

May 18th, 1980

Erupted with force comparable to a

hydrogen bomb

Killed 62 people and damaged

surrounding ecosystems

Killed nearly all plants and animals within

650 square km

Located 96 miles south of Seattle, WA

http://www.history.com/topics/us-states/washington/videos/mount-st-helens-erupts

http://www.history.com/topics/us-states/washington/videos/mount-st-helens-erupts

Plants started to grow back the following

summer which attracted animals

› Chipmunks, insects, squirrels and their predators birds, snakes, coyotes

Within a few years young trees

appeared

After more than 2 decades, forest has

started to cover some of the area

http://earthobservatory.nasa.gov/Features/WorldOfChange/sthelens.php

Ecosystems are constantly affected

by/are responding to disturbance

Succession: the change in plant and

animal communities that follows a

disturbance

› Describes how ecosystems respond to natural and man-made disturbances

Volcanic eruptions, fires, tornadoes, etc.

Agriculture, mining, logging, etc.

Ecosystems are NEVER static!

Constantly being affected by

disturbances

Disturbance: A discrete, punctuated

killing, displacement, or damaging of

one or more individuals that directly or

indirectly creates an opportunity for new

individuals to become established.

Bell-ringer: What is succession?

Collect any labs/BRs

Pass back/Go over quiz

Notes

Mount St. Helen’s Reading

(finish for HW)

Wrap-up: What is one

biological agent of a

disturbance?

Fires

› Burn large areas creating open space

Winds

› Blow through an area

Storms

Droughts

Floods

Disease

Predation

Grazing

Disease reduced the population of seas

urchins that lived in coral reefs

Urchins eat macro algae (sea plants)

Plants overgrow coral reefs and create

an algal bloom that threatened reefs

survival

http://gallery.usgs.gov/videos/223.VrOfuDZhPvE

Effect of a disturbance depends on its:

1. Spatial scale

2. Turnover rate

3. Frequency

4. Predictability

The geographic area that is disturbed

May vary greatly depending on location

Ex.)Appalachian forests

› Winds, storms, and lightning usually topple

only few trees at a time and their loss opens

about 322 square feet of land

Minnesota forests

› Fire is the predominant agent of disturbance

and opens gaps from 988-9,884 acres

Average time required to disturb an

entire area

Ex.) Chaparral has higher turnover rate

than tropical rain forest b/c there are

more frequent fires

The number of disturbances over time.

The variance in the average time

between disturbances.

Ex.) Forest fires or windstorms may seem

unpredictable but history indicates that

they are relatively predictable.

› Fires occur at fairly regular intervals

› As trees age they are more likely to be knocked down by wind

After a disturbance plant and animals

communities follow each other in a fairly

regular pattern.

At first areas are covered with annuals

plants that live for a single growing

season

Annuals are often replaced by perennials plants that live for several

growing seasons

Bell-ringer: Can scientists

predict disturbances?

Why or why not?

Go over/collect Mount St.

Helen’s reading

Notes

Wrap-up: What is a

macroenvironment?

As time passes short bushes and young

trees may appear which will in time be

overshadowed by maturing trees

Eventually the process of change slows,

and the plant and animal species tend to remain for an extended period

CLIMAX COMMUNITY

Climate causes patterns of succession to

vary by location

Heather plants dominate the landscape

Birch trees begin to grow which starts a

transition that changes the plants that

live underneath the trees

Within 20 years, heather bilberry herb

After 40 years bilberry wavy hair grass

After 60 years bent grass is the dominant

plant living around the birch trees

Succession is initiated by disturbances

that open up space

First species to colonize area = pioneer

species

› Green algae and acorn barnacles red

algae

Succession that occurs in areas where

there was no soil or where the

disturbance destroys the soil

Ex.) Mount St. Helens

Occurs when a disturbance destroys a

climax or intermediate community

without destroying the soil.

The first plants and animals to appear in

an area after a disturbance.

Macro: Characteristics of a large area.

Micro: Small-scale conditions at which

plants and animals live.

Fraction of sunlight reaching the ground

› Important role in soil temp, soil moisture, etc.

Succession seems to be an orderly

process, but in reality it can be quite

unpredictable

Driving forces vary among ecosystems

and over time

› Ex.) Forces that drive succession in the

intertidal zone of shallow temperate seas differ from those that drive succession in

temperate forests

1. Facilitation

2. Tolerance

3. Inhibition

Species in early and middle successional

communities change their

microenvironments in ways that make

them less hospitable for their own needs

or more hospitable to species that

inhabit later successional communities

Species create the conditions for their

own demise

Succession can start with any species

An early successional species may be

more likely to first colonize a disturbed

area

Should a species that normally inhabits a

middle or late successional community

arrive first, it too can start the process of

succession

Species appear and disappear based

on competition

› Demand by two or more individuals for

limited environmental resources such as food, water, space, and so on

Any species can start the process of

succession

The first species to arrive depends on its

ability to disperse and the luck of being

in the right place at the right time

Whichever species establishes itself FIRST

can persist for a relatively long period by

inhibiting the growth of other species.

The direct or indirect harmful effects of

one plant on another through the

production and release of chemical

compounds known as allelochemicals

Produces a nonprotein amino acid in its

leaves and foliage that inhibits the

growth of other tress but not its own

seedlings

Inhibit a limited number of species

May be a good alternative to human-made herbicides and pesticides

Most successional processes return an ecosystem to its original state › Late successional community after a

disturbance looks like the late successional community that was present before the disturbance

Some disturbances generate ecosystems that are very different from the previous ones

Certain ecosystems flip back and forth between alternate states

Some landscapes alternate between

woodlands and grasslands

Some lakes alternate between

ecosystems dominated by submerged

plants and ecosystems dominated by

phytoplankton

Human impact!

Succession will not move the lake from a plant dominated system to a phytoplankton dominated system because both are positive feedback loops.

The plant ecosystem can flip as humans add nutrients to the lake as the concentration of nutrients increases, it passes some critical threshold and phytoplankton grow faster than fleas can eat them!

As phytoplankton multiply, they absorb more sunlight which reduces light to bottom dwelling plants

Plants ability to filter nutrients is slowed which leaves more nutrients for phytoplankton

Reduction of light kills plants leaving fleas no where to hide and their pop decreases from predation

Phytoplankton grow even faster taking over the ecosystem

Lake is now eutrophic green color

In historic times, most human

disturbances mimic natural disturbances

› Fires to flush out animals/clear land

› Effect was similar to natural fires

Presently, humans are accelerating rates

of extinction and climate change which

affect the food webs of entire biomes

Some ecologists use human health as an

analogy to measure ecosystem health

Two components:

1. The absence of disease

2. The ability to cope with disease

Has no disease

If exposed to disease, can withstand and

recover from disease

Most physicians look for disease so

absence of disease is the biggest

indicator of health

The potentials of an ecosystem to

withstand and recover from disturbance

If succession can cope with effects of

human activity, these disturbances can

be managed in a sustainable manner

If human activities disturb the env. to the

point where there is catastrophic

change, those activities are not

sustainable

The degree to which an ecosystem

changes following a disturbance

An ecosystem that changes little in

response to a disturbance is said to be

resistant

› High resistance = healthy

› Loss of resistance may be associated with stress from human disturbance

The size of the change that an ecosystem can undergo and still be able to reestablish its original structure and behavioral patterns

Unstable ecosystems have no resilience because they do not return to original state

Resilient or stable ecosystems, can return to their original state following a disturbance

The ability to recover is reduced by

stresses that are associated with human

activities

A healthy ecosystem can return to its

original state further from its set point

than what an unhealthy ecosystem can

recover from

Resistance determines how big a

disturbance is required to make an

ecosystem sick

Resilience determines how sick an

ecosystem can get and still recover.

Relationship between stability and

diversity depends on the redundancy of

functional groups and the strength of

predator-prey interactions

Describes the role that a species plays in

the ecosystems

Ex.) Fish living on coral reefs can be

divided among 14 functional groups:

› Large fish that eat large fish, fish that eat

corals, fish that eat plankton, etc.

The presence of more than one species

in a functional group

Ex.) Used to compare the health of coral

reefs in the Caribbean to those of the

Australian Great Barrier Reef

› Caribbean lack redundancy in 3 critical fish

groups

Ability of ecosystems to resist and recover

from disturbances is determined by strength

of linkages, not just number of links

Weak interaction: implies that the likelihood of consumption of one species by another is small species eat different types of

food (generalist)

Strong interaction: eats only a few types of

food so likelihood of consumption of one

species by another is high (specialist)

Enhance by a food web that contains

many weak interactions

Trophic Cascades: population changes

from one trophic position to the next

The process of reestablishing to the

extent possible the structure, function,

and integrity of indigenous ecosystems

and sustaining the habitats they provide

A “new science” trying to compensate

for so much human damage

Restoring original species?

Restoring ecosystem capabilities?

1st step: Reestablish healthy soil

2nd step: Reestablish indigenous

ecosystem using principles based on

succession

› Ex.) establish climax community