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

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

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

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

Menge, J.exp.Mar.Biol.Ecol

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

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

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

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

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

Bottom up control Gardner Mar. Ecol Progr. Ser. Cumulative Mortality Oct Nov Dec Jan Feb Mar Apr May Cook Strait Lab Intertidal

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

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

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

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

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

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

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

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

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

Orca Sea Otter Kelp Urchins Ecological Relationships in Kelp Forests

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

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

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

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

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

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

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

Leonard et al, 1998 Hydrodynamics Time Flow rate

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

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

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

Leonard et al, 1998 diatoms grazers crabs musselsbarnacles NutrientsLarvaePlankton

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

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 - (+) + (-)