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Transcript
Why is the competition paradigm so prevalent? • based on mathematical theory • so, straight forward to test in field & lab • subsequent models developed as spin-offs of competition theory: i. Coexistence ii. Theory of the niche iii. Resource division Prior to 1980s: Several researchers felt that competition was more NB than other ecological processes After 1980s: Researchers questioned why competition was necessarily the most NB interaction. Predation seems more NB in marine habitats. Do communities have to be in equilibrium? Does competition ever depart from equilibrium? Findings suggest that species diversity is affected by: competition disturbances predation Community Structure - Chapter 21 Communities: an assemblage of plants & animals that occur together in the same place & dominated by > dominant species Communities as assemblages of species… Do communities exist as well defined units? There are 2 historical viewpoints Open Community H.A. Gleason Closed Community F.E. Clements Coincidence associations Superorganism Diffuse Sharp boundaries Ricklefs 2001 Fig. 21.4 F.E. Clements H.A. Gleason Ecotone: a zone of transition between habitat types Ricklefs 2001, Fig. 21.5 Molles 2002, Fig. 1.9 Ricklefs 2001, Fig. 21.6 Some species grow only in nonserptine soils Some spp. have no preference Others grow in ecotone. Others grow in serpentine soils. Ricklefs 2001, Fig. 21.6 Concentration of soil minerals determine the plants that make up each community Ricklefs 2001, Fig. 21.6 But, evidence supports Gleason (open communities) This is true even though some communities have very distinct boundaries. e.g., boundary between aquatic & terrestrial communities