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BIOLOGY 157: LIFE SCIENCE: AN ENVIRONMENTAL APPROACH (Communities and Succession)

BIOLOGY 157: LIFE SCIENCE: AN ENVIRONMENTAL APPROACH (Communities and Succession). COMMUNITIES I. DEFINITION: a community is a unit composed of two or more interacting species in a given area How many communities are there on the earth?

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BIOLOGY 157: LIFE SCIENCE: AN ENVIRONMENTAL APPROACH (Communities and Succession)

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  1. BIOLOGY 157: LIFE SCIENCE: AN ENVIRONMENTAL APPROACH (Communities and Succession)

  2. COMMUNITIES I • DEFINITION: • a community is a unit composed of two or more interacting species in a given area • How many communities are there on the earth? • One ??? Hundreds ??? Thousands ???Millions ??? • It all depends on how you ‘define’ it.

  3. COMMUNITIES II • Community Diversity:the number of species and strains in a community • Community Complexity:(= Ecological Diversity )the number of trophic levels and how the species are distributed among the trophic levels • Communities have boundaries in space and time.

  4. ECOTONES • Ecotonezone between communities where composition very rapidly changes from that typical of one community to that typical of the other • Ecotones are ‘pressure’ or ‘tension’ zones • Ecotones often have a greater biodiversity than either of the adjacent communities • Ecotones can be narrow or wide • Ecotones and adjacent communities can shift over time

  5. ECOTONES (narrow)

  6. ECOTONES (narrow)

  7. EDGE EFFECT (I) • Related to ecotones • Size of the area and shape of the area interact • Two areas of the same size may have very different shapes and thus very different amounts of ‘edge’. • How does this affect species in those areas?

  8. EDGE EFFECT (II)

  9. COMMUNITY PRODUCTIVITY

  10. EMERGING CHARACTERISTICS IN COMMUNITIES • Dominant (= Keystone) Species and Subordinate Species (may not always be related to abundance) • Stratification (= Layering) • Succession:a non-cyclic process during which species / communities in a particular area are replaced by other species / communities over time= the ‘life history’ of a community

  11. ECOLOGICAL SUCCESSION (I)

  12. ECOLOGICAL SUCCESSION (II)

  13. ECOLOGICAL SUCCESSION (III) • What causes it? • Organisms and the changes they create are the driving force. • Types of Succession • Primary • occurs on a primary bare area • Secondary • occurs on a secondary bare area

  14. ECOLOGICAL SUCCESSION (IV) • Pioneer (species or community) • the first species to invade an area • Seral (species or community) • those which occupy intermediate positions in a succession (early, mid, late, etc.) • Climax (species or community) • those occupying the final position in a succession

  15. CLIMAX COMMUNITY (I) • DEFINITION:a steady state community whose characteristics are determined by the characteristics of its habitat & environment • Primary Climax • does not depend on recurrent disturbances by fire or animals to maintain floristic / faunal composition • Climatic Climax --- forms on normal soils, with average topography, and thus only the macroclimatic conditions are controlling it. • Edaphic Climax --- develops differently from what one expects for the macroclimatic conditions due to an unusual soil • Topographic Climax --- develops differently from others in the same region due to a distinctive microclimate

  16. CLIMAX COMMUNITY (II) • Disclimax • all climaxes that maintain their floral / faunal composition only as a result of persistent disturbances of the same kind, frequency and intensity • - Fire • NJ Pine Barrens • Some Grasslands • - Zootic • Some Grasslands

  17. TRENDS DURING SUCCESSION (I) • Stage in Ecosystem DevelopmentAttribute Young Mature-------------------------------------------------------------------------------- • Biomass low high • Trophic Relationships simple complex • Food Chains short, grazing long, detritus • Food Webs simple complex • Stratification less more • Species Diversity low high • Niche Specialization broad narrow • Feeding Relations general specialized • Life Cycles short, simple long, complex • Population ControlMechanisms physical biological

  18. TRENDS DURING SUCCESSION (II) • Stage in Ecosystem DevelopmentAttribute Young Mature-------------------------------------------------------------------------------- • Fluctuations greater lesser • Stability low high • Potential Yield toHumans high low • Net CommunityProduction higher lower (0 ??) • Community Respiration lower higher • Community P / R Ratio P > R P = R

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