Ecological Succession –Syllabus Topics to – Describe the concept and processes of succession in a named habitat. –2.3.6 Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stages of succession. –2.3.7 Describe factors affecting the nature of climax communities.

Ecological Succession –orderly process of change over time in a community” (IB definition) What is a “community”?community Sequence of appearance and disappearance of species Pattern of colonization and extinction Directional, non-seasonal, continuous Two types: primary and secondary

Primary Succession Occurs after the creation of a new habitat e.g. lava flow, glacier retreat, sand dune formation, artificial ponds, artificial reefs Areas which have never had organisms growing on them Conditions are unfavorable for life at first

Fig. 7-11, p. 156 Exposed rocks Lichens and mosses Small herbs and shrubs Heath mat Jack pine, black spruce, and aspen Balsam fir, paper birch, and white spruce forest community Time

Secondary Succession Community development in areas that were previously occupied by a community Occurs after a disturbance e.g. loss of trees by disease, wind or fire; logs clearing areas in intertidal zone; overturning of boulders in intertidal zone Conditions are therefore favourable since seeds, spores and even resistant animals or plants may remain and there is often a well developed soil More rapid than primary succession

Fig. 7-12, p. 157 Time Annual weeds Perennial weeds and grasses Shrubs and pine seedlings Young pine forest with developing understory of oak and hickory trees Mature oak-hickory forest

IN YOUR NOTEBOOK… Describe the steps you would take to measure PRIMARY succession in the wake of a melting glacier in glacier national park. In another paragraph describe what you would do to measure SECONDARY succession in the forest in the abandoned farms of Long Valley.

Why does succession occur? –Ecosystem changes result from: –Changes in physical environment - disturbance or creation of new habitat –Competition between organisms –Shift in energy flow from production to respiration

How does succession occur? Through a series of stages: –Pioneer species arrive –Early colonizers with good dispersal mechanisms (r- selected species); fast growth rate; high photosynthetic rate; minimal environmental demands –Opportunistic organisms settle –e.g. diatoms, sea lettuce, scotch broom

Stages of Succession Sere - “set of communities that succeed one another over the course of succession at a given location” (IB definition) process of succession from beginning to end –Seral stages waves of temporary organisms displace pioneer species through competition –Climax community –End point of succession

Climax Community Most permanent of all the stages Stage at which system has reached steady-state equilibrium May take 100’s or 1000’s of years to reach this stage Difficult to identify Determined by climatic or edaphic (soil) factors unless humans maintain an equilibrium at subclimax (e.g. poor soil quality, grazing, preventing forest fires, selective logging)

During succession species modify the physical environment making it more suitable for new species and less suitable for those already there Pioneer species are often poor competitors and are replaced by stronger competitors that have greater environmental demands Later communities are often more complex than earlier communities

Changes in Community with Succession Biomass Size of individuals Biodiversity increases then may stabilize or slightly decline as size of individuals increases Shift from linear food chains to complex food webs Gross productivity (GPP is low initially, rising in the middle stages of succession, then GPP declines again in the climax phase)

More Changes… –Net productivity from goes from high in the early stages to zero as succession approaches climax –Initially low amount of energy lost through respiration therefore high NPP Respiration with shift in community to more consumers so net productivity approaches zero as Photosynthesis:Respiration ratio (P:R) approaches 1Respiration with shift in community to more consumers so net productivity approaches zero as Photosynthesis:Respiration ratio (P:R) approaches 1 –internal cycling of materials –mineral cycles become more closed