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Community Ecology BCB331

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  1. Community Ecology BCB331 Mark J Gibbons, Room Z108, BCB Department, UWC Tel: 021 959 2475. Email: mgibbons@uwc.ac.za Image acknowledgements – http://www.google.com

  2. Habitat Selection Mobile organisms – many animals – which can move between habitats and select those that will favour survival, growth and reproduction Decisions based on: Avoiding physiological stress Avoiding or limiting competition and predation Maximizing prey availability Settlement cues How study? Correlation – field study Experimentation - manipulation Correlation – HOW?

  3. Settlement cues.......................

  4. Settlement Success……….. Graphs showing the percentage settlement of larvae of Spirobis borealis on filmed panels treated with Fucus extracts (open triangles), on filmed panels (circles), and on untreated panels (solid triangles). The panels were presented to the larvae (A) immediately after release, (B) after delay of 6 h, (C) after a delay of 12 h

  5. Physiological stress Design an experiment to determine habitat selection by woodlice: keep everything else constant What phylum? What subphylum? What order? Characteristics?


  6. Oxystele variegata BIG SMALL Height above Sea Level

  7. Oxystele variegata BIG SMALL Height above Sea Level

  8. Melaraphe neritoides makes use of both light and gravity as directional stimuli to control its position Response to these cues influenced by submersion and orientation, so that behaviour is flexible When immersed in seawater, they are negatively geotactic: when immersed and the right way, they are negatively phototactic: when immersed and upside down, they are positively phototactic: when emersed, they are negatively phototactic Such behaviours allow individuals to return to splash zone following down-shore displacement

  9. Prey availability Large mammals in fynbos Anthopleura and Mytilus Sebens (1981) Science 213: 785-787

  10. Competitor avoidance Clonal tunicate (Botryllus) – a major space occupier Manipulated densities of settling larvae on glass slides….. Avoidance Tolerance Grosberg (1981) Nature 290: 700-702

  11. Predator avoidance Notonecta (water boatman) – carnivore but also a size- selective cannibal: manipulated densities Sih (1982) Ecology 63: 786-796

  12. Conflicting demands…………. Trade-offs - maximize gains and minimize risks Manipulating densities of competitors and predators Hyla chrysoscelis in artificial ponds • Controls without predators or competitors • Intra-specific competitors • An inter-specific competitor • Predator 1: Notophthalmus • Predator 2: Ambystoma • Predator 3: Enneacanthus • Predator 4: Tramea Resetarits & Wilbur (1991) Ecology 72: 778-786 Resetarits & Wilbur (1989) Ecology 70: 220-228

  13. Male calling Female egg-laying

  14. Diel vertical migration by zooplankton Abundant Food Depth Day Night Day & Night Day Night No Fish Fish

  15. Depth of occupation at night influenced by vertical distribution of food What happens when food is scarce?

  16. Primarily plankton feeders: open water when large, shallow water when small Lepomis macrochirus Werner et al. (1983) Ecology 64: 1540-1548

  17. Two habitats – 1 & 2 – of differing growth potential A species grows at rate g: g1 and g2 Mortality rate – μ: μ1 and μ2 g1 g2 Growth rate Switching point Size (s) Mortality does not vary between habitats Maximizing growth rate – minimizing mortality risk Size influences mortality………………… Size specific mortality rate – μ: μ1/g1 and μ2/g2 Conceptualize a model to indicate when the juveniles of a species (population with R = 1) should move from habitat 1 to habitat 2 when a) mortality is constant between habitats, b) when mortality varies between habitats

  18. μ1/g1 μ2/g2 Mortality varies between habitats Rate g1 g2 Size (s)

  19. Community Ecology BCB331 Mark J Gibbons, Room Z108, BCB Department, UWC Tel: 021 959 2475. Email: mgibbons@uwc.ac.za Image acknowledgements – http://www.google.com