1. Resource & Predation Controls on Ecosystem Production
Bottom-up Controls – refer to control of abundance or productivity of a species or functional group by supply of resources.

2. What controls production in an ecosystem?
The “bottom up” view of Ecosystem production
Nutrients

3. Global Ocean distribution of Chlorophyll
and Benthic Faunal Biomass
mg/m3

4. “Trickle Up” effect Increases in primary production propagate through the food web

5. What controls production in an ecosystem?
The “bottom up” view of Ecosystem production
The “top down” view of Ecosystem production
Nutrients

6. Top-Down Control & Inferences about
Trophic Cascades
Hairston, Slobodikin and Smith 1960
Basic Premise:
“Any population which is not resource limited must, of course, be limited to a level below that set by its resources.”
But, plants may become depleted whenever herbivores become numerous enough (insect outbreaks, e.g. adelgid)
World is Green
The remaining general method of herbivore control is predation”
Therefore the “usual condition is for populations of herbivores not to be limited by food supply….” and producers are limited by resources, not herbivores
“Predators and parasites in controlling herbivores … must be food limited.”

7. “Green World Hypothesis”
Limited by prey availability
Limited by predation and parasitism
Limited by nutrient availability, not herbivory
Nutrients

8. “Green World Hypothesis”
Although the authors did not explicitly call this series of interactions a “trophic cascade” , that was the idea that was implicit in the Green World Hypothesis.
Nutrients

9. Systems with and without predators
Brooks and Dodson (1965) examined 9 lakes:
Four lacked Alewifes
Four had natural Alewife populations
One had introduced Alewifes
sampled before and after the introduction

10. Zooplankton Size Distribution in Lakes with:
LARGE
DOMINANT ZOOPLANKTERS
Dioplomus
Cyclops
Daphnia
Mesocyclops
Lepiodore
5 mm
Epischura
No Alewife
SMALL
Bosmina
Tropocyclops
Cyclops
DOMINANT ZOOPLANKTERS
Ceriodaphnia
Asplanchna
Alewife
Size-efficiency Hypothesis.
Larger zooplankton more effectively graze phytoplankton than smaller zooplankton.
Therefore if zooplanktivorous fish are absent, large herbivorous zooplankton will increase and phytoplankton abundance will be reduced.
Large zooplankton out compete small zooplankton. Populations of small zooplankton increase in abundance when large zooplankton are depleted.

11. A “Trophic Cascade” Food web manipulations in
If piscivores added to lake, they will eat and deplete zooplanktivorous fish.
Populations of larger herbivorous zooplankton will grow.
Phytoplankton populations will be reduced.
Food web manipulations in
Peter, Paul and Tuesday Lakes
- Bass
Control
+ Bass

12. Lakes with piscivore removed have higher chl a
Food web manipulation experiments of in 3 lakes (from Carpenter et al., Ecology 68: ).
ZOOPLANKTON
PHYTOPLANKTON
Control
+Bass
-Bass
Lakes with bass (piscivore added), zooplanktivorous fish depleted, large zooplankton increase, chl a is lower
Lakes with piscivore removed have higher chl a

13. TROPHIC CASCADE IN KELP ECOSYSTEMS
Sea Otters
and urchin grazers
And Killer Whales

14. Effect of Killer whale predation on Sea Otters
Sea Otter Abundance
100 80 60 40 20
# Otters (% max count)
Amchitka I.
N. Adak I.
Kagalaska I.
L. Kiska I.
400
300
200
100
gms 0.25 m -2
Sea Urchin Biomass
Grazing Intensity 60 50 40 30 20 10
% Loss 24 hr -1
No. per 0.25 m2 10 8 6 4 2
Year
Total Kelp Density
From Estes et al Science 282:473

15. Trophic Cascades and Feedbacks
And nutrients or other factors limiting producers can still increase producer biomass and have effects that propagate up the food web
Both Top-down and Bottom-Up controls influence abundance and productivity of populations CX
But organisms feeding at multiple trophic levels can complicate picture
Nutrients P H P C3 - + C2 - + C1 - +
Links
1 (odd)
2 (even)
3 (odd)
4 (even)
For simple food chains:
An odd number of trophic links results in control of primary producers by grazing (top-down)
An even number of trophic links results in control of primary producers by resources (bottom-up) -

16. Are Trophic Cascades All Wet?

17. Reasons Why Trophic Cascades Might be Stronger in Aquatic Ecosystems than in Terrestrial Ecosystems
Herbivores are bigger relative to plants in aquatic ecosystems (e.g. zooplankton vs. phytoplankton compared with insects vs. trees)
Aquatic primary producers are more nutritious and have element composition more like their herbivores
Terrestrial plants have lower P:B ratios than aquatic plants (is this a cause or a consequence??)
Aquatic herbivores consume about 3X more autotrophic production than terrestrial herbivores (but why??)

18. Comparison of Herbivory in Aquatic and Terrestrial Ecosystems (Cyr and Pace, 1993 Nature 361:148)
Frequency distributions showing the proportion of NPP removed by herbivores in ecosystems with different primary producers
Median, 79%
Median, 30%
Median, 18%

19. Regardless of amount of NPP, rates of Herbivory are on average about 3X higher in Aquatic than Terrestrial Ecosystems (note: log scale)

20. Ratio B+predators/B-predators for Plants
Comparative Strength of Trophic Cascades Across Ecosystems based on Manipulations of Predators in Six Types of Ecosystems (102 studies) Plot loge (Abundance+predators/Abundance-predators)
Ratio B+predators/B-predators for Plants
0.7% % 5.0% % % 100%
20.0
7.4
2.7
Herbivore response greatest in lentic & marine systems (e.g. density with predators ~6% to13% of that without predators) and least in terrestrial (density + predators ~71% of density - predators)
Plant response greatest in marine benthos (biomass 4.7X > in systems with predators) vs. terrestrial (1.1X > with predators)
Across systems, as Herbivores ⇩ plant biomass response ⇧
(modified from Shurin et al. 2002, Ecology Letters 5:785)

21. Reasons why we might not ‘see’ top down cascades in land ecosystems
Many terrestrial plants have complex structural tissue that is harder to digest and have evolved ‘anti-herbivore’ compounds
Perhaps grazing in terrestrial ecosystems is inhibited by Antiherbivore Compounds/Lignin Derivitives

22. Effect of Tannins on palatability of grass to Geese
Relative Amount Eaten
From Buchsbaum et al

23. Reasons why we might not ‘see’ top down cascades in land ecosystems
Many terrestrial apex predators have been hunted to near or local extinction

24. WOLVES AND WILLOWS Percent Browsing <2 m 2-3 m 3-4 m
100 50
<2 m
Percent Browsing
2-3 m
3-4 m
400
200
Willow Height (cm)
Wolves
Re-introduced
Ripple et al For. Ecol & Mgt. 230:96

25. Reasons why we might not ‘see’ top down cascades in terrestrial ecosystems
Plants have complex tissues and anti-herbivore compounds
Terrestrial may have more complex and more detritus based food webs, less direct grazing.
Many terrestrial apex predators have been hunted to near or local extinction
Longevity of the plant community (decades to centuries for mature plants) makes it hard to measure the results
Terrestrial ecosystems are less experimentally tractable than their aquatic counterparts, in part because of extreme longevity of the plant community
Many of the more charismatic species now enjoy stringent legal protection, which hampers manipulation;

26. "The ecology of fear" Defensive strategies to avoid predation
Reduced energy intake
Alternate food sources
Increased susceptibility to other predators
Lower mating success
Emigration

27. Creek Infauna Abundance was lower
Mummichog Reduction
No Trophic Cascade :
Creek Infauna Abundance was lower
Algae
Inverts
Mummichog
Expected 60
Total Annelids
(# / m 2 x 10 3) 40
Observed 20
-Fish
Fish
-Fish
Fish
Fleeger et al.
Accepted JEMBE
Reference
Nutrient

28. Behavior alters species roles in ecosystem
Algae
Inverts
Mummichog
(Shrimp)
Nutrients P H P C1 -

29. Behavior alters species roles in ecosystem
Removal of mummichogs allows shrimp to forage in more open areas and become more carnivorous. 6 8 10 12
Shrimp d 15N
Fish -Fish
Reference
Nutrient enrichment
David Johnson Kari Galvan
Linda Deegan

30. SUMMARY Top down controls can be important in ecosystem dynamics
Can affect more than just the level below (cascade), including effects on adjoining ecosystems
Interact with nutrient level
Indirect trait mediated effects may be as important as direct consumption effects
Stronger in Aquatic or Terrestrial?
No consensus just yet.