1. Community Structure: Top-Down vs. Bottom-Up Control

2. Hairston, Smith and Slobodkin (1960) Community Dynamics Carnivores HerbivoresPlants Detritivores Frees plants from herbivore control Resource limited control HairstonSlobodkin

3. Other inferences of Hairston et al, 1960 1) Exceptions not important 2) All communities have 3 trophic levels 3) Omnivory not important 4) External abiotic factors - not controllers ?? X X X

4. Critiques Too Simple 1) Species differences matter 2) Plant dominance could be explained by good defences

5. Menge, 2000. J.exp.Mar.Biol.Ecol

6. Early example of top-down control P. Dayton All predators present Predators excluded

7. Menge and Sutherland, 1976 Predation is weak High wave energy - effects of predation -weak Moderate wave energy - effects of predation - strong Effects of predation by whelks. MengeSutherland Top-down forces along environmental gradients

8. Bottom Up Control Fretwell, 1977, 1987 - availability of plant material governs structure of food chains - Low productivity - 1 link (plants) - Higher productivity - add links

9. Bottom up control Gardner 2013. Mar. Ecol Progr. Ser. Wellington Harbour Cook Strait Mytilus galloprovinciales

10. Bottom up control Gardner 2013. Mar. Ecol Progr. Ser. Cook Strait Lab Intertidal Looked at 1)Mortality 2) Growth rate 3) Gonad condition

11. Bottom up control Gardner 2013. Mar. Ecol Progr. Ser. Cumulative Mortality Oct Nov Dec Jan Feb Mar Apr May 30 20 10 0 Cook Strait Lab Intertidal

12. Bottom up control Gardner 2013. Mar. Ecol Progr. Ser..05.04.03.02.01 Growth Rate (mm/day) Cook Strait Lab Intertidal

13. Bottom up control Gardner 2013. Mar. Ecol Progr. Ser. Oct Nov Dec Jan Feb Mar Apr May Cook Strait Lab Intertidal Gonad condition

14. Top-down vs Bottom-up in tide pools Boiler Bay, Oregon Nielsen, K. 2001. Ecological Monographs 71: 187 Karina Nielsen

15. Top-down vs Bottom-up in tide pools Artificial Tide Pools Top-down vs Bottom-up in tide pools Nielsen, K. 2001. Ecological Monographs 71: 187 Karina Nielsen

16. Top-down vs Bottom-up in tide pools Nielsen, K. 2001. Ecological Monographs 71: 187 Karina Nielsen

17. Top-down vs Bottom-up in tide pools Predictions Top-down vs Bottom-up in tide pools Nielsen, K. 2001. Ecological Monographs 71: 187 Karina Nielsen

18. Top-down vs Bottom-up in tide pools Nielsen, K. 2001. Ecological Monographs 71: 187 Karina Nielsen

19. Top-down vs Bottom-up in tide pools Nielsen, K. 2001. Ecological Monographs 71: 187 Karina Nielsen

20. Top-down vs Bottom-up in tide pools Nielsen, K. 2001. Ecological Monographs 71: 187 Karina Nielsen

21. Orca Sea Otter Kelp Urchins Ecological Relationships in Kelp Forests

22. Transplant mussels and barnacles (filter feeders) to urchin-dominated and kelp-dominated substrates

23. Transplant mussels and barnacles (filter feeders) to urchin-dominated and kelp-dominated substrates Expected (top down) Urchin - dominated Kelp - dominated

24. Transplant mussels and barnacles (filter feeders) to urchin-dominated and kelp-dominated substrates Expected (top down)Observed (bottom up) Urchin - dominated Kelp - dominated Urchin - dominated

25. Clearly - can be a complex interaction Increased nutrient Increased algae Increased benthic filter feeders Increased consumers (predation) control

26. Interaction of Systems Leonard, Levine, Schmidt & Bertness. 1998. Flow-driven variation in intertidal community structure in a Maine estuary. Ecology 79:1395-1411 G.H. Leonard SchmidtLevineBertness Damariscotta River

27. Interaction of Systems Leonard et al, 1998 Low flow High flow

28. Interaction of Systems increased seaweed growth increased filter feeder growth increased larval settlement low consumer efficiency higher densities of organisms with planktonic larvae more spatial competition increased consumer pressure increased sedimentation increased consumer mortality lower densities of organisms with planktonic larvae less spatial competition

29. Leonard et al, 1998 Hydrodynamics Time Flow rate

30. Leonard et al, 1998 Community structure barnacles musselsBare space Fucus High flowLow flow Percent cover TideheightTideheight

31. Leonard et al, 1998 Recruitment rates Density (#/100 cm 2 ) High flow Low flow BarnaclesMusselsSnails

32. Leonard et al, 1998 Crab predation Predation Intensity (% mortality) High flow Low flow On Littorina, Nucella, Mytilus

33. Leonard et al, 1998 diatoms grazers crabs musselsbarnacles NutrientsLarvaePlankton

34. Leonard et al, 1998 diatoms grazers crabs musselsbarnacles Nutrients Larvae Plankton diatoms grazers crabs musselsbarnacles whelks High flow Low flow

35. Plants Consumers Predators Interference competition, exploitative competition for resources other than food (-) Depletion of more nutritious, palatable or accessible prey (-) Induced morphological or chemical defenses, hiding, retreat to refuges (-) Stimulation of area- specific primary productivity (+) Powers. ‘92. Ecology 73: 733 Cover from (for) predators - (+) + (-)