Definition of ecosystem succession

Succession?  The observed process of change in the species structure of an ecological community over time  Succession occurs in all natural environments Ecology succession 1st year Horseweed dominant; crabgrass, pigweed 2nd year Asters dominant; crabgrass 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 oakhickory forest 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 Early 20th century E Warming in Denmark and Henry Cowles in the United States developed the concept of ecological succession 1936 Frederick Clements developed a theory of plant succession and community dynamics Ralph 1954 Slatyer E Egler proposed: the process of succession is dependent on which species get there first 1977 Joseph Connell (University of California) and Ralph Slatyer (Autralian National University) proposed a generalized framework for viewing succession Generalized framework for viewing succession Facilitation model • Early successional species modify the environmental becomes more suitable for later successional species to invade and grow to maturity Inhibition model • Involves strong competitive interactions • No one species is completely superior to another Tolerance model • Later successional species are neither inhibited nor aided by species of earlier stages • Later species can invade a newly exposed site Types of succession P/R • Degradative succession • Autotrophic Succession Driven • Allogenic Succession • Autogenic Succession Area • Primary Succession • Secondary Succession Primary Succession The process of creating life in an area where no life previously existed wps.prenhall.com Continuing change  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 The Climax Community  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 earlier stage  Structure of climax community in different geographic areas are different These are Climax Communities 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 Temperature Cold Cold desert Tundra Taiga Moderate Temperate forest Grassland Deciduous forest Hot Hot desert Savanna Tropical forest Rainfall 0-10 10-20 20-30+ A summary of enegy changes that occur during succession: Total Biomass Respiration Net primary production organic matter A summary of structures changes that occur during succession: Age andsize Population Age Structures Size of Number ofProducer species A summary of other changes that occur during succession: Factors Early stages Climax stages Food chains Linear, predominantly grazing Weblike, predominantly detrius Inorganic nutrients Extrabiotic Intrabiotic Niche specialization Broad Narrow Life cycles Short, simple Long, complex Mineral cycles open closed A summary of other changes that occur during succession: Factors Early stages Climax stages Nutrient exchange rate, between organism and environment rapid Slow Role of detritus food chain Unimportant Important Population growth form r - selection K - selection production quantity quality A summary of other changes that occur during succession: Factors Early stages Climax stages Internal symbiosis Undeveloped Developed Nutrient conservation poor good Stability poor good Information Low High How humans affect ecological succession? 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 restructures and disrupts a previously stabilized ecosystem The disturbed ecosystem will immediately begin a process of ecological succession • Plant species that adapt to the sunny conditions and the broken soil will rapidly invade the site and will become quickly and densely established These invading plants are what we call "weeds“ in which we consider a nuisance or invaders 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 ... succession • Autotrophic Succession Driven • Allogenic Succession • Autogenic Succession Area • Primary Succession • Secondary Succession Primary Succession The process of creating life in an area... developed the concept of ecological succession 1936 Frederick Clements developed a theory of plant succession and community dynamics Ralph 1954 Slatyer E Egler proposed: the process of succession is... Primary Succession Secondary Succession The process of re-stabilization that follows a disturbance in an area where life has formed an ecosystem wps.prenhall.com Secondary Succession Degradative Succession