Download 2006-05-10 – Dynamic and Succession of Ecosystems

Dynamic and Succession
of Ecosystems
Kristin Heinz, Anja Nitzsche
10.05.06
Basics of Ecosystem Analysis
Structure
• Ecosystem dynamics
– Basics
– Rhythms
– Fundamental model
• Ecosystem succession
– Basics
– Energy flow
– Diversity
– Examples
Ecosystem dynamics
• Because of the open character there is a
flow between different ecosystems
• It is a flow of
– Energy → transformation
– Stocks
– Dynamics in populations
–…
Ecosystem dynamics
• Biological rhythms
– Circardian rhythm
– Annual rhythm
– Longer annual rhythm
– Tides
– Lunar rhythm
–…
Biological rhythms
• Circardian rhythm
– Production of plants
– Vertical drift of limnic and marine animals
– Roost fly of birds in winter
• Annual rhythm
–
–
–
–
Falling down of the leaves
Hibernation
Bird migration
Diapause
Ecosystem dynamics
• Longer annual rhythm
– In population dynamics
• Tides
– Along the cost side very different and complex
structure of time
– Characteristic vertical zoning of the animals
and alga
Ecosystem dynamics
• Lunar rhythm
– Agitation in migration by birds, tropical
mammals and insects
Ecosystem dynamics
• Human made rhythms
– Land use activities
– Change of land use
– Emission dynamics
– Environmental policy
– Global change
– Continuous climate change
–…
Fundamental model of ecosystem dynamics
Conservation
Renewal
- Accessible Carbon,
- Nutrients ad Energy
(Miineralisation)
2
- k-Strategy
- Climax
- Consolidation
RA
S
W
LO
LY
(Adult Stage)
Y
DL
PI
Stored Capital (Storage)
4
1
Exploitation
- r-Strategy
- Pioneers
- Opportunists
(Juvenile Stage)
Creative
Destruction
3
- Fire
- Storm
- Pest
- Senescence
( Disturbance Incorporation)
Organization
Connectedness
(Holling 1986)
A hypothetic trajectory of the adaptive cycle
Maturity / Conservation
Exergy
stored
Renewal /
Reorganization
Release /
Creative destruction
Pioneer stage / Exploitation
connectedness
Disturbance
• Stability
– Ability of an ecosystem to recover or to return to the
original constitution after disturbance
• Resiliency
– Dimension for the ability of an ecosystem to survive a
disturbance
• Capacity
– Intensity of resiliency factors which can be buffer in
an ecosystem
– Only stable ecosystems can buffer
Disturbance
• Difference from the original ecological
factors
• Direct and indirect damages
Ecosystem Succession - Definition
• A fundamental concept in ecology
• Refers to more-or-less predictable and orderly changes in the
composition or structure of an ecological community
• Initiation by:
¾ Formation of a new, unoccupied habitat (e.g., a lava flow or a severe
landslide) → primary succession
¾ Some form of disturbance (e.g. fire, severe windthrow) of an existing
community → secondary succession
Ecosystem Succession - Definition
• The trajectory of ecological change can be influenced by:
¾ site conditions
¾ the interactions of the species present
¾ more stochastic factors such as availability of colonists or seeds
Ecosystem Succession - Definition
• Stable end-stage called climax, sometimes referred to as the 'potential
vegetation' of a site, shaped primarily by the local climate
• Has been largely abandoned by modern ecologists in favour of
nonequilibrium ideas of how ecosystems function
• Most natural ecosystems experience disturbance at a rate that makes a
"climax" community unattainable
Æ climate change
Æ expansions and introductions
Ecosystem Succession - Factors
• Succession usually occurs in areas where no other species offer
competition in the area
• The type of organisms' that occupy areas in such circumstances
depends on a number of factors
• Climate → Temperature, precipitation, sunlight
• Soil → pH, composition of the soil
• Human Intervention → pollution, acid rain
Ecosystem Succession – Energy Flow
• Energy flow is fundamentally changed → demonstrated in the
quantity of standing crop in the ecosystem
• During early seral stages → energy inputs > outputs
• Disturbance by external factors → the energy loss > inputs
• Accumulation of energy as biomass → high metabolic rates → high
productivity which maximises the energy flow in the system
Ecosystem Succession - Productivity
• Increases proportional to the amount of standing crop
• The percentage gross productivity is fixed as net productivity is not
continuous with progression
• Early seral stages: small short-living plants dominate, have a high
yield and individual plants require very little energy for
maintenance
Æ r-selected life-histories
• Later seral stages: large long-living plants dominate which use high
levels of their gross productivity for respiration to maintain their
bodies
Æ k-selected life-histories
Ecosystem Succession - Diversity
• Number of species progresses rapidly as plants and animals colonise
the area
• In later seres the rate of increase decreases
• Increasing interspecific competition → it is the intermediate seres
which contain the largest number of species present at any one time
during the succession
Ecosystem Succession - Trophic Structure
• Early seres are short, linear food chains which are easily upset if one
element in the food chain is removed
• As the succession progresses the ecosystem becomes more layered
and species diversity increases creating a complex food web
• The more complex food webs → greater stability → allows
alternative energy flows when one element of the food chain is
disrupted
Ecosystem Succession -
st
1
Example
• Primary Succession: colonisation of bare rock
¾ Pioneer community: lichens → provide enough nutrients to support
a community of small plants such as mosses → typically replaced by
ferns
¾ With erosion of rock and increasing amounts of organic material a
large layer of soil is gradually built up
¾ This soil allows plants such as grasses and small flowering plants to
grow followed by shrubs and trees → climax community?
Ecosystem Succession -
nd
2
Example
• Secondary succession: after forest fire
¾ Spores, seeds and vegetative organs may remain viable in the soil
¾ Influx of animals and plants through dispersal and migration from
the surrounding area
¾ Succession does not begin with pioneer species but with species
from intermediate seres