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.