BIOEE1610 Agroecology

Species that differ in at least one aspect of their resource use, and thereby experience less intense competitive interactions, allowing them to coexist.

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.

• Insurance effect, negative covariance effect
• Less pest attacks

• 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.

• 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)

• 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

• Increased global cereal production
• Increased irrigated land
• Increased use of nitrogen and phosphorus fertilizers
• Increased global pesticide use and imports

• 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.)

• Maximization of productivity
• Minimization of labor

• Moderate to high diversity
• A mixture of annuals and perennials
• Infrequent, moderate disturbance
• High nutrient retention and recycling
• Low subsidies

• Maximization of stability
• Minimization of risk

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.

• Shifting cultivation in humid tropical forests (most diverse while they recover)
• Home gardens
• Polycultures
• Genetic mixtures
• Wheat varieties
• Maize hybrids
• Clonal crops

• Tropical rainforests
• Temperate forests
• Natural grasslands
• Boreal forests
• Spartina marshes
• Geothermal pools

• 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)

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.

• 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

• 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

• 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.

• Loss of biodiversity
• Loss of wildlife habitat
• Nutrient runoff
• Sedimentation of waterways
• Pesticide poisoning
• Greenhouse gas emissions

• Food
• Fiber
• Bioenergy

• Expansion of agricultural land
• Increase in field size
• Loss of field margin vegetation
• Loss of biodiversity

• 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

• Labor
• Capital markets
• Climate
• Water
• Soil nutrients
• Land