Role of Insect Herbivores in Plant Population Dynamics, Ecology, &
Succession
I. Introduction:
A. Revisiting Hairston, N.G., Smith, F.E., & Slobodkin, L.B. 1960.
1. Less emphasis on plant abundance than on plant
composition and community structure
B. Succession Theory
1. Each stage alters environment so as to favor next
stage
Are insects & pathogens part of that process?
2. Implications to Global Change
II Types of Evidence & their Interpretations:
Altered Systems
A. Agricultural Systems
1. Continual outbreak
2. Early successional plant species
B. Introduced Insects into Natural Ecosystems
1. Gypsy moth
2. Fall Web worm in Europe
3. Balsam Woolly Adelgid in US
4. Wood wasps in Australia
C. Biological Control of Introduced Weeds
1. Exotic weeds
2. Biological control
D. Types of Evidence & their Interpretations:
Natural ecosystem interactions
1. Large-scale outbreaks are relatively rare
2. Some ecosystems exhibit more herbivory than others
3. Largely Anecdotal
III. Natural ecosystems: Mechanisms Impacting Succession
A. Compensatory growth, or Differential Impact
1. Chronic herbivory in grasslands
2. Certain species favored - mostly tolerance
3. Keeps plant community in continual state of early
succession
4. Chronic and episodic herbivory in forests
1. Altered within species age structures
2. Accelerate Succession
B. Increased light penetration
1. Effects on understory plants
2. Effects on soil
3. Consequences of altered light penetration
a. Reduced competition among plants
b. Altered Plant species composition
c. Altered Soil Communities
1. Decomposers, Root Herbivores, Mycorhyzzae
C. Altered Patterns of Nutrification
1. Increased rate of nutrient leaching from foliage
2. Increased rate of fall of nutrient - rich litter
a. Autumn Abscission is nutrient - poor litter
3. Litter is often induced
4. Deposition of frass
5. Consequences of Altered Nutrification Patterns
a. Altered Plant Architecture
1. Stimulation of Nutrient redistribution within
plants - increased turnover rates
2. Adventitious branching
3. Increases or decreases in reproductive parts
b. Stimulated activity of decomposer organisms
c. Effects on wildlife
d. Effects on Aquatic Ecosytems
D. Soil Erosion
E. Solar Reflectance
F. Altered Fire Cycles
1. Reverse Succession
G. Altered Genetic Structure
1. Herbivores - Select for diversity?
2. Pollinators - Promote outcrossing
3. Seed Dispersors - Generate Spatially Local Genetic
Structure? Ants?
IV. Role in ecosystem disturbance
A. Examples
1. Saratoga Spittle Bug
2. Root organisms
3. Bark Beetles
B. Plant and plant community factors favoring insect - induced
disturbance events
1. Homogeneity: Species, Age, Genetics