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Community Ecology BDC331

Community Ecology BDC331. Mark J Gibbons, Room 4.102, BCB Department, UWC Tel: 021 959 2475. Email: mgibbons@uwc.ac.za. Image acknowledgements – http://www.google.com. Lotka-Voltera models mimic reality in some respects: Outcomes of competition are predictable. > 1. 5.95. 12.68.

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Community Ecology BDC331

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  1. Community Ecology BDC331 Mark J Gibbons, Room 4.102, BCB Department, UWC Tel: 021 959 2475. Email: mgibbons@uwc.ac.za Image acknowledgements – http://www.google.com

  2. Lotka-Voltera models mimic reality in some respects: Outcomes of competition are predictable

  3. > 1 5.95 12.68 A word about models….. A balance between reality and understanding

  4. A more mechanistic approach – Tilman (1977, 1982) Two limiting resources – e.g. light and nutrients Amounts set limits to population growth Population increases A Limitation by resource 1 B Amount of resource 2 ZNGI Limitation by resource 2 Amount of resource 1 Population must decrease Rate of resource consumption important (differs between species) – influence consumption vectors Population A is limited by resource 1, whilst Population B is limited by resource 2

  5. Putting two species together…… a b A B B A Amount of resource 2 Amount of resource 1 In a, above, Species B needs more resources than species A and it is driven to extinction (Blue). Yellow is area where A naturally present and B absent. In b, above, species A needs more resources than species B and it is driven to extinction (Brown). Green is area where A naturally present and B absent. NO EQUILIBRIUM POINT WITH BOTH SPECIES

  6. Here, the ZNGI overlap – equilibrium point: Stable or unstable? Need information on consumption rates. At the equilibrium point, Species A is limited by resource 2, and Species B by resource 1. IF, A consumes more resource 1 than B, unstable – extinction of B (blue) IF B consumes more of resource 2 than A, unstable – extinction of A (brown) Else – stable co-existence

  7. Consumption rates variable What do the models tell us? 1) Competition can lead to winners and losers 2) Some competitive interactions lead to co-existence 3) Can understand competitive interaction ONLY with knowledge of resources and mechanisms

  8. Apparent Competition – Competition for enemy-free space Imagine a predator that eats two species of prey Both prey species suffer from the predation, and the predator (enemy) benefits from both species of prey Increases in the predator abundance caused by its consumption of one prey species, increase the harm done to the other prey species, indirectly. Therefore each prey species adversely affects the other prey species – even if no obvious limiting resource The limiting resource that the prey species compete for is “enemy-free” space – the persistence of one prey species will be favoured by avoiding attacks from the predator, which also attacks the other prey species. This can be achieved if the two species occupy a habitat that is sufficiently different from the other prey species – niche differentiation

  9. Venturia canescens Coupled Oscillations Ephestia kuehniella Plodia interpunctella No Competition between hosts Bonsall and Hassell (1997) Nature 388: 371-372

  10. Coupled Oscillations Low r Venturia canescens Bonsall and Hassell (1997) Nature 388: 371-372 Ephestia kuehniella Plodia interpunctella

  11. THE END Image acknowledgements – http://www.google.com

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