Definition of ecosystem succession

3rd to 18th year Grass scrub community; broomsedge grass, pines coming in during this stage 19th to 30th year Young pine forest 30th to 70th year Mature pine forest; Understory of you

3rd to 18th year

Grass scrub community;

broomsedge grass, pines coming in during this stage

19th to 30th year

Young pine forest

30th to 70th year

Mature pine forest;

Understory

of young hardwoods

70th to 100th year

Pine to hardwood transition

100th year plus

Climax hickory forest

oak-Ecology succession

Process of Succession

 Early successional species – pioneer species

 high growth rates

 smaller size

 high degree of dispersal

 high rates of per capita population growth

 Late successional species

 lower rates of dispersal and colonization

 slower per capita population growth

 larger and longer - lived

Terrestrial succession

Lake or pond succession

Why Does Ecological Succession Occur?

• it is the process of life for plants, soil and other living organisms

• Organisms alter soil structure, chemistry, and microclimates, the

species composition of ecological communities constantly

changes over time.

• Succession will continue until the environment reaches it’s final

stage…the Climax Community.

Historical study of Succession

Frederick Clements developed a theory

of plant succession and community dynamics

Early

20 th century 1936

Ralph Slatyer1954

1977

Joseph Connell (University of California) and Ralph Slatyer (Autralian National University) proposed a

generalized framework for viewing succession

Generalized framework for viewing succession

1 Facilitation model

• Early successional species modify the environmental

becomes more suitable for later successional species to invade and grow to maturity

2 Inhibition model

• Involves strong competitive interactions

• No one species is completely superior to another

3 Tolerance model

• Later successional species are neither inhibited nor

aided by species of earlier stages

• Later species can invade a newly exposed site

wps.prenhall.com

Primary Succession

The process of creating life in an area where no life previously existed

Primary Succession

Secondary Succession

Degradative Succession

 Decomposers breaking down organic matter

 Leads to disappearance of everything, species included

 B/P, B/R, B/E reduce

 P/R < 1

 It is characterised by early and continued dominance of autotrophic organisms

 Does not lead to degradation

 Habitat continually occupied by living organisms

 P/R > 1

 B/P, B/R, B/E (E = P + R) increase

Autotrophic Succession

Autogenic Succession

 Autogenic succession is succession driven by the biotic

components of an ecosystem

 Change of species driven by biological processes changing

conditions and/or resources

 Example: organisms living, then dying, on bare rock

Species diversity changes during succession

http://sky.scnu.edu.cn/life/class/ecology/chapter/chapter20.files/image061.jpg

Species diversity changes during succession

http://www.scielo.br/scielo.php?pid=S0100-204X2009000200011&script=sci_arttext

Species diversity changes during succession

http://mrhalverson.com/a pessays_ecology.html

Species diversity changes during succession

http://www2.mcdaniel.edu/Biology/eco/suc c/successionweb.html

 Colonizers joined by other species suited for modified habitat

 Eventually replace colonizers

 Better competitors in modified habitat

 Less r-selected, more K-selected

 Communities gradually become dominated by K-selected

species

 Good competitors, able to coexist with others for long periods

of time

Continuing change

 Communities become stabilized

 Reach equilibrium

 Little or no change in species composition, abundance over long periods of time

 Climatic climax community

 End stage of succession

The Climax Community

 Rarely is climax stage reached quickly

 Community usually affected by some major disturbance (e.g., fire) before climax stage is reached

 Resets succession, forces it to start again from some

These are Climax Communities

• Two main physical factors determine the nature of the community that develops in an area

• These are temperature and the amount of rainfall

Hot Hot desert Savanna Tropical forest

These are Climax Communities

A summary of enegy changes that occur

during succession:

Biomass Total organic matter

Respiration

Net primary production

A summary of structures changes that

occur during succession:

Number of species

Population sizeAge and

Age Structures

Size of Producer

A summary of other changes that occur

during succession:

Food chains Linear, predominantly

grazing

Weblike, predominantly detrius

Inorganic nutrients Extrabiotic Intrabiotic

Niche specialization Broad Narrow

Life cycles Short, simple Long, complex

A summary of other changes that occur

during succession:

Nutrient exchange rate,

between organism and

environment

Role of detritus food

Population growth form r - selection K - selection

A summary of other changes that occur

during succession:

Internal symbiosis Undeveloped Developed

1 How do humans affect ecological succession?

2 Does ecological succession ever stop?

How Do Humans Affect Ecological Succession?

• Clearing the land for the garden and preparing the soil for planting represents a major external event that radically re-structures and disrupts a previously stabilized ecosystem The disturbed ecosystem will immediately begin a process

How Do Humans Affect Ecological Succession?

• A gardener's only course of action is to spend a great

deal of time and energy weeding the garden or using

chemicals to infringe upon the weeds and the ecosystem around it

• The farmers and gardeners who are growing our foods incur an immense cost in terms of time, fuel, herbicides and pesticides that humans pay every growing season because of the force of ecological succession

Does Ecological Succession

Ever Stop?

• We must recognize that any ecosystem, no

matter how inherently stable and persistent,

could be subject to massive external disruptive forces (like fires and storms) that could re-set and re-trigger the success ional process

• As long as these random and potentially

catastrophic events are possible, it is not

absolutely accurate to say that succession has stopped

Does Ecological Succession

Ever Stop?

• Also, over long periods of time (“geological

time”) the climate conditions and other

fundamental aspects of an ecosystem change

• These geological time scale changes are not

observable in our “ ecological” time, but their

fundamental existence and historical reality

cannot be disputed

• No ecosystem, then, has existed or will exist

unchanged or unchanging over a geological time scale.