DynamicDynamic andand SuccessionSuccession ofof EcosystemsEcosystems
Kristin Heinz, Anja Nitzsche Basics of Ecosystem Analysis 10.05.06 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
Stored 4 Renewal Conservation 2 - Accessible Carbon, - k-Strategy - Nutrients ad Energy - Climax Ca - Consolidation pital (Storage)
LY W R O (Miineralisation) A L (Adult Stage) P S ID L Y
1 Exploitation Creative 3 - r-Strategy Destruction - Pioneers -Fire - Opportunists -Storm -Pest - Senescence (Juvenile Stage) ( Disturbance Incorporation) Organization Connectedness
(Holling 1986) A hypothetic trajectory of the adaptive cycle
Maturity / Conservation
Renewal / Exergy Reorganization stored 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 - 1st 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 - 2nd 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