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 Height above Sea Level BIG SMALL

7. Oxystele variegata Height above Sea Level BIG SMALL

9. 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

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

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

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

13. Conflicting demands…………. Manipulating densities of competitors and predators Hyla chrysoscelis in artificial ponds 1)Controls without predators or competitors 2)Intra-specific competitors 3)An inter-specific competitor 4)Predator 1: Notophthalmus 5)Predator 2: Ambystoma 6)Predator 3: Enneacanthus 7)Predator 4: Tramea Trade-offs - maximize gains and minimize risks Resetarits & Wilbur (1989) Ecology 70: 220-228 Resetarits & Wilbur (1991) Ecology 72: 778-786

14. Male calling Female egg-laying

15. Depth DayNightDay & Night Fish No Fish DayNight Diel vertical migration by zooplankton Abundant Food

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

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

18. Maximizing growth rate – minimizing mortality risk Size influences mortality………………… 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 Two habitats – 1 & 2 – of differing growth potential A species grows at rate g: g 1 and g 2 Mortality rate – μ: μ 1 and μ 2 Size specific mortality rate – μ: μ 1 /g 1 and μ 2 /g 2 g1g1 g2g2 Size (s) Growth rate Switching point Mortality does not vary between habitats

19. g1g1 g2g2 Size (s) Rate μ 1 /g 1 μ 2 /g 2 Mortality varies between habitats

20. 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