BIOEE1610 Agroecology

  1. What is niche complementarity?
    Species that differ in at least one aspect of their resource use, and thereby experience less intense competitive interactions, allowing them to coexist.
  2. What is overyielding?
    Polycultures having a greater yield than the total that their individual components would yield in monocultures due to complementarity or facilitation. Note that not all combinations overyield, grass-legume combinations typically do.
  3. Why greater yield stability in polycultures?
    • Insurance effect, negative covariance effect
    • Less pest attacks
  4. Explain the relationship between ecosystems and landscapes?
    • Agricultural activities can have important effects on natural ecosystems through the movement
    • of organisms, pesticides, nutrients, and soil. Spillover may positively or negatively affect the landscape
    • At the same time, the landscape context
    • can strongly influence ecological processes that occur within
    • agroecosystems, such as pollination and pest regulation. The
    • spatial structure of the landscape, including the size, shape,
    • and connectedness of different ecosystem types can have
    • dramatic effects on these ecological processes.
  5. What are planned components of agroecosystems?
    • Spatial or temporal arrangement of domesticated plants or animals that farmers purposefully include in the agroecosystem. It may also include beneficial organisms that are purposefully included in the ecosystem such as nitrogen fixing bacteria or biological control agents.
    • Crop and livestock selection
    • Planting densities and arrangement
    • Tillage (the preparation of land for planting crops)
    • Pest management
    • Nutrient management (manure or fertilizer)
  6. What are unplanned components of agroecosystems?
    • Organisms that persist in the ecosystem after it’s been converted into an agricultural system or organisms that invade it from the surrounding landscape.
    • Natural enemies and pest regulation
    • Pollinators
    • Soil organisms, decomposition and nutrient cycling
    • Water flow and purification / contamination
  7. What are the components of the global increase of agriculture?
    • Increased global cereal production
    • Increased irrigated land
    • Increased use of nitrogen and phosphorus fertilizers
    • Increased global pesticide use and imports
  8. What are the characteristics of larger agroecosystems?
    • Low diversity
    • Annual crops rather than perennial crops
    • Frequent disturbance (you can tell from bare ground)
    • Low nutrient retention and recycling (resulting from frequent disturbance like harvesting etc.)
    • High subsidies (fertilizer etc.)
  9. What are the main goals of larger ecosystems?
    • Maximization of productivity
    • Minimization of labor
  10. What are the characteristics of smaller agroecosystems?
    • Moderate to high diversity
    • A mixture of annuals and perennials
    • Infrequent, moderate disturbance
    • High nutrient retention and recycling
    • Low subsidies
  11. What are the main goals of smaller agroecosystems?
    • Maximization of stability
    • Minimization of risk
  12. What is the scientific reason to conserve sources of biodiversity?
    The genetic information is used to find resistance to certain diseases etc. For example, the hybrid rice created to be resistant to rice blast fungus in Yunnan China. Mixtures of the hybrid rice and glutinous rice show less occurrences of the disease.
  13. Highest to lowest plant diversity in agroecosystems:
    • Shifting cultivation in humid tropical forests (most diverse while they recover)
    • Home gardens
    • Polycultures
    • Genetic mixtures
    • Wheat varieties
    • Maize hybrids
    • Clonal crops
  14. Highest to lowest plant diversity in natural ecosystems?
    • Tropical rainforests
    • Temperate forests
    • Natural grasslands
    • Boreal forests
    • Spartina marshes
    • Geothermal pools
  15. What are the types of diversity in agroecosystems? How are they achieved?
    • Genetic diversity:
    • Varietal mixtures
    • 2. Species diversity:
    • Polycultures
    • Cover crops / green manures
    • Pest repellent crops
    • 3. Structural diversity:
    • Agroforestry (reduced erosion and increased biodiversity by growing trees and shrubs around croplands)
    • Shade plantations (slightly less productivity for coffee, but far more longevity for the plantation as a whole.
    • Home gardens
    • 4. Landscape diversity (In the Andes, at different elevations to prevent frost and grow a wider variety of crops adapted to different temperature / humidity conditions)
  16. What are cover crops?
    Cover crops are commonly used to suppress weeds, manage soil erosion, help build and improve soil fertility and quality, control diseases and pests, and promote biodiversity. Green manures are the crops that are left to wither.
  17. What are the mechanisms that would allow polycultures to yield more than the component monocultures?
    • Complementarity, higher yield and higher productivity
    • More resilience to environmental perturbation
    • Insurance effect (Under stressful conditions, when one species / genotype suffers, others do well)
    • Drought resistance
    • Resistance to invasion (less specialist insects, more predator insects)
    • Negative covariance effect
    • Better soil health (intraspecific competition is higher than interspecific competition, different species have different phenologies and use different nutrients at different levels of the soil)
    • Yield stability (due to insurance effects)
    • Fewer weed problems (due to shading)
    • Support more unplanned biodiversity and more ecosystem services
  18. Why does pest suppression occur in polycultures?
    • Herbivores are typically less abundant due to:
    • More difficulty finding host plants
    • Move more often and lose their host
    • Have lower reproductive rates due to limited resources
    • 2. Predators and parasitoids are typically more abundant
    • Have a greater diversity of foods (greater diversity of herbivores). Higher diversity of insects means higher diversity of predators
    • Have more options for nest sites
  19. Explain ecosystem services and agriculture
    • Agriculture is both a consumer and provider of ecosystem services. Agroecosystems are localized in landscapes and influence both the services and disservices produced in the landscape.
    • In turn, landscapes influence the ecosystem services flowing to the agroecosystems from other ecosystems.
  20. What are agroecosystem disservices (once called externalities and ignored but currently counted and accounted for within the system)
    • Loss of biodiversity
    • Loss of wildlife habitat
    • Nutrient runoff
    • Sedimentation of waterways
    • Pesticide poisoning
    • Greenhouse gas emissions
  21. What are agroecosystem provisioning services?
    • Food
    • Fiber
    • Bioenergy
  22. What is landscape simplification?
    • Expansion of agricultural land
    • Increase in field size
    • Loss of field margin vegetation
    • Loss of biodiversity
  23. What are the effects of landscape simplification
    • Pest density increases, predator density decreases due to natural enemies not being able to survive in long distances without patches to nest etc.
    • Simplification increases virus occurrence / disease
    • Less pollinator visits
  24. What are the constraining factors of agroecosystems?
    • Labor
    • Capital markets
    • Climate
    • Water
    • Soil nutrients
    • Land
Card Set
BIOEE1610 Agroecology
Week 16