1. The hierarchical nature and processes of different levels of ecological systems:

2. Species Interactions Ch 17 Herbivory

3. Objectives Herbivory Effects on plants
How demonstrate herbivory effects
Herbivore selectivity
Plant deterrents to herbivory
What limits herbivory?

4. Pairwise interspecific interactions
***Which is: +/-, +/0, +/+, -/-, -/0 ?
Mutualism
Commensalism +,0
Amensalism ,0
Herbivory
Predation
Parasitism
Disease
Competition
Amenalism: huge tree and seedling competing for resources; seedling makes infinitesmal dent into tree’s resources. Really very asymmetrical competition.
Commensalism: epiphytes on trees; remoras (sharpsuckers) have sucker on dorsal fin; attadh to shark or rays 1) saves energy due to limited swimming 2) gathers food ccraps when host is feeding
Parasite: consumes part of blood or tissues of host, usually without killing the host.
Pathogen: parasitic organism that causes a disease in its host.

5. Pairwise interspecific interactions
Mutualism (+/+)
Commensalism (+, 0)
Amensalism (-, 0)
Herbivory (+/-)
Predation (+/-)
Parasitism
Disease
Competition (-/-)
Amenalism: huge tree and seedling competing for resources; seedling makes infinitesmal dent into tree’s resources. Really very asymmetrical competition.
Commensalism: epiphytes on trees; remoras (sharpsuckers) have sucker on dorsal fin; attadh to shark or rays 1) saves energy due to limited swimming 2) gathers food ccraps when host is feeding
Parasite: consumes part of blood or tissues of host, usually without killing the host.
Pathogen: parasitic organism that causes a disease in its host.

6. Fluidity of interspecific relationships:
Can evolve from one type to another.
Switch + and - signs of interaction, e.g. +/+ to +/-.

7. In food chains, all life forms are both consumers and victims of consumers.
Predators
Parasites
Parasitoids
Pathogens
Herbivores

8. Herbivory: Effects on plants
C41.7 Larva of moth eating way through mesophyll of oak leaf.

9. Outbreaks of herbivorous insects can defoliate forests.
Canada
Tent caterpillars, gypsy moths, fungus on chestnut…pine bark beetle in BC on trainride
Spruce budworm

10. Herbivory has great effects on plants: 1) individual/ecosystem 2) population 3) community
If prefer dominant species--->
What is a keystone
herbivore?
If prefer subdominant
species--->
Mauna Loa Hawaii: area at L is protected from cattle grazing.
GB: Herbivores can change relative densisites of plants species:
Herbivores that prefer dominant plants cause increased diverstiy
Herbivores that prefer subordinant plants cause decreased diversity.
Figure 1

11. How do we test the hypothesis that
herbivores control plant populations?
Describe, then explain these results.

12. Herbivores feed on plants - and also inoculate
them with pathogens and rot-causing microbes.

13. Does herbivore control plant species? If…. then…
Natural enemies hypothesis:
Biological control:
Prickly pear introduced into Australia without natural enemy.
Biological control: introduced cactus moth from SA; moth feeds on growing shoots and introduces pathogens - greatly reduced cactus.
But not eradicated…manages to disperse to predator-free areas.
Figure 2

14. (biological control agent)
In spite of plant defenses, herbivores can control plant population size.
Weed introduced to west; from Europe ; has high amounts of alkaloids - toxic to cattle and sheep.
Biological control: introduced beetles of genus Chrysolina from Australia.
Reduced weed abundance by 99%..
Klamath weed + beetle
(biological control agent)

15. ***What are plant deterrents to herbivory?
Structural defense
Low nutritional content;
sequester nutritious parts
Mutualistic defense (ant-acacia)
Secondary compounds
Figure 3

16. Chemical defenses (secondary compounds)
are toxic to herbivores.

17. Types of secondary compounds
growth regulators
toxins against generalist herbivores
specialists evolve to detoxify toxin
often N-based
lignin, alkaloids, non-protein amino
acids,
cyanogenic glycosides--->HCN
digestive inhibitors against specialists
often C-based
tannins, phenolics, terpenoids
Digestive inhibitors bind to proteins and inhibit their digestion. So slow growth of larvae

18. Chemical defenses Constitutive: high levels at all times
Induced: increase greatly after
attack
Theory: Cost of defense is too high to maintain under light herbivory.
(but how quickly can they make them?
Hypothesis: Plants ‘eavesdrop’ on neighbors - signal to make defense.
Refer to article they read at beginning of semester.Wild tobacco growing near clipped sagebrush became more resistant to herbivores than tobacco plants near unclipped sagebrush.
Eavesdropping may be restircted to species that are strongly inducible and to those species that relase high concentrations of cues.

19. What is evidence that plant defenses are induced by herbivory?#2 to #1
Mite 2 lower on cotton plants that had been previously exposed to closely related mite sp 2 than on control plants with no previous mite exposure.
Inductionof chemical defenses by cotton plants following exposure to one mite species results in reduced populations of adult mites of another species.- and their eggs.
Mite sp 1 attacks.
Plant responds by making defense chemical.
Mite sp 2 attacks but in much lower numbers.

20. Are herbivores ‘lawnmowers’ or selective feeders
***Are herbivores ‘lawnmowers’ or selective feeders? What 3 factors may explain results?
K Selectivity is major reason why the world is not completely green for a herbivore. Selectivity may be caused by plant secondary substances such as phenols.Also differences in nutritional quality.
Figure 4

21. Describe the major pattern in this figure. Generate a WHY
***Describe the major pattern in this figure. Generate a WHY ? Develop an ‘If…then’.
Herbivores
of oak
leaves
More species of caterpillars eat oak leaves in spring than later in season.
April
October
Figure 5

22. Hypothesis/prediction:
If oak leaves become less suitable insect food as they age,
then caterpillars fed young leaves will grow better than if fed slightly older leaves.
Diet larval weight % adults emerge
young leaves
old leaves
***What is conclusion?
Do data support the hypothesis?
“Figure” 6

23. H1: Increase in toughness H2: Increase in secondary chemicals
***What are three changes as a leaf ages that could account for the previous results? (3 alternative hypotheses)
H1: Increase in toughness
H2: Increase in secondary chemicals
H3: Decrease in nutrient quality
Toughness index
Figure 7
Leaf age

24. ***Develop predictions for H1 toughness and H2 chemical defense.
If leaf toughness explains seasonal feeding pattern of oak insects,
then larvae should grow equally well when eating ground-up old vs. young leaves.
If chemical defenses have increased with leaf age,
then larvae should grow better on ground-up leaves of young than old leaves.
***Are predictions ‘operational’?
Do they contain independent and dependent variables?
‘Figure’ 8

25. ***Results Larvae fed ground-up leaves Larval weight Young leaves 37
Old leaves
***Which hypothesis is supported?
Why hasn’t NS favored insect mouth parts able to cope with tough leaves?
3rd alternative hypothesis is still possible; Maybe poorer nutrition in later summer; then NS toward early feeding.
“Figure” 9

26. ***What factors limit herbivory? Predators Herbivores Plants Nutrients
Herbivores consume 10% of plant productivity (up to 30-60% in grasslands). Why so little?
***What factors limit herbivory?
Predators
Herbivores
Plants
Nutrients
Abiotic factors
The ‘world is green’ hypothesis: Herbivores consume a small % of vegetation because they are held in check by a variety of factors.
What limits herbivory?
top-down vs. bottom-up control:
predators limit number of herbivores?
vs. plants deter herbivores?

27. Top-down control. Tri-trophic predators interactions. herbivores
Top-down control Tri-trophic predators interactions herbivores plants nutrients/light Bottom-up control
Top-down: predators control herbivores
Bottom up: plants (or nutirents that control plants) control herbivore
(e.g. light or nutrients lower plant productivity which lowers herbivore producitify
Also intraspecific competition may control herbivores; or other abioltic factors
“Figure” 10

28. Observation/question: Despite many potential herbivores, why do leaves lose low leaf area?
Observation: Birds eat insect herbivores.
***Hypothesis:
If bird predation on insect herbivores indirectly
reduces the amount of leaf area consumed,
***Prediction:
then leaf area consumed will be greater for plants with bird-exclusion cages than those without cages.
‘Figure ‘ 11

29. Experimental set-up…caged tree saplings

30. Results: 1) number of insects: 70% greater on saplings without birds than with birds.
“Figure” 12
2) % leaf area missing:
35% without birds
22% with birds
*** What’s conclusion?
Support for hypothesis?
Tri-trophic interaction; top-down control.
Bird predation:
directly reduces # of herbivores
indirectly reduces leaf damage by herbivores
New questions: Will 1) decreases in bird populations due to forest fragmentation or 2) change in phenology increase insect damage?