Top-Down vs Bottom-Up Trophic System

Grazer vs. Decomposer Systems

Food Webs

• Two or more trophic systems linked within a given ecosystem or landscape.

• Three main categories in agroecosystems:

– Animal-based (animal production systems)

– Above-ground, plant based (Crop Production Systems [CPS])

– Soil food web in CPS’s

• The two CPS webs interact but are usually managed separately

Components Soil Food Web

• Herbivores – Root feeders (arthropods, microbes)

• Pathogens – Microbes that attack underground organisms

• Shredders – Chew up organic matter, increasing surface area & decomposition rate

• Decomposers – Decompose organic matter

• Predators – Maintain stability of above populations

Limiting Resources & Competition

• Populations can be limited in several ways

– Food & water

– Shelter/Reservoir

• Limitation can occur at any stage or time (e.g. overwintering)

• Effectiveness dependent on population ecology of individual pest. Life history strategy important part of that ecology.

r- vs. K-selected pests

Managing for one may help other

Interactions Between Pest Categories

Read Chapter 7, Ecosystem Biodiversity & IPM

Interactions Between Pest Categories

• Trophic Relationships

• Environmental (Habitat) Modification Result

• Mechanical Effects

• Response to Control Tactics

– Non-pesticide

– Pesticide-related

• “Interactions” may be:

– Pest-pest or pest-crop

– Measured in injury or damage

This subject excludes the direct effects of:

• Interactions within pest categories (i.e. – pathogen – pathogen). But note that viruses, bacteria, fungi, & nematodes are different “categories” for Norris et al.

• Interactions between pests and their natural enemies

Direct vs. Indirect According to Brown

• Direct:

(Pest A + Pest B) -> Outcome

– Outcome may be biological or economic

– If Spp. A & B are present, outcome is realized

• Indirect:

Pest A -> Affector -> Pest B -> Outcome

– “Affector” may be another pest, management action, environmental effect, etc.

– A & B & Affector must all be present for outcome to occur

Direct Interaction
(A + B) -> Outcome

Four possibilities

Examples by Category

• Green vegetable bug becomes a problem if provided with non-pest weeds.

• Ants tending aphids.

• Weeds as alternate hosts for pathogens.

Overwintering hosts for aphids.

4. cf. item 4 on p. 136 (cutworms & chinch bugs) & item 5 on p. 137 of text.

Read these sections closely

• Habitat Modification – Understand and be able to ‘compare & contrast’:

– Altered Resource Concentration

– Altered “Apparency”

– Microenvironment Alteration

• Interactions Due to Physical Phenomena

– Physical Damage to Host

– External Transport

– Internal Transport

Ecosystem and Biodiversity in IPM

• Why did monocultures become so widespread?

• Can we expect monocultures to continue?

• If so, how can we make biodiversity relevant? At what spatial scale will this relevancy be realized (cf. p. 157).

Frequent Disadvantages of Biodiversity in CPS

• Increasing plant diversity decreases density of marketable commodities

• Increased density/diversity of herbivores (cf. p. 136 – 137)

• Increased alternative hosts for pathogens

• Larger complex of species to be managed

• More complex production system/equipment needed to deal with mixed plantings

• Dilution of inputs (fertilizer, water)

• Decreases in commodity quality common (size, color, texture, etc.)

• Increased cost of commodity as a result of the above