FINAL3-BIODIVERSITY Flashcards
Unplanned Biodiversity
Weeds (in field) Surrounding (none – all) Soil Biota Arthropods (except releases of biocontrol agents) Non-domesticated animals
Planned Biodiversity
Crop Varieties
Some surrounding vegetation (none – all)
(e.g., other monocrops, intercrops, non-crops)
Domesticated animals
Loss of Biodiversity in agriculture
Conventional practices
Conventional practices work primarily to manage a few factors perceived to be of direct importance to the system The crop plants A few nutrients (N,P,K) Tillage/herbicides Insecticides
Loss of Biodiversity in agriculture
TREND:
simplification / homogenization
Homogenization + Simplification = Productivity/Profitability
Biodiversity: The Challenge
As agroecologists: the challenge we face is to:
try and understand what the identities of the larger, unplanned biota,
what function they serve,
what value we wish to assign to their functions,
How management practices can be modified to optimize biodiversity, taking into consideration both short-term (profit) and long-term (sustainability) goals
Biodiversity includes:
genetic variability~
Within and between species
Biodiversity includes:
Alpha diversity~
Measure of a species richness and abundance within a community
Biodiversity includes:
Beta Diversity~
species diversity across communities or along gradient transects
Biodiversity includes:
Gamma Diversity~
Species diversity along a biogeographic region
Identifying biodiversity
Alpha biodiversity!~
Spatial component: Within field
Identifying biodiversity
Beta Diversity!~
Spatial Component:
Number and evenness of species over a landscape
Gamma Diversity!~
Number and evenness of species over region
Can you have a high alpha biodiversity low beta biodiversity agroecosystem?
YES
Shannon-Weiner index
Accounts for #species and evenness
Ecosystem functions:
Processes critical to ecosystem vitality
Nutrient, water, air cycling
Biomass production
Decomposition
Ecosystem services:
Functions that are valued by us
Pollination services
Biological control
Soil fertility
Stability
Ability to withstand disturbance
resistance
ability to resist stress
resilience
ability to recover after stress
Biodiversity…
alpha diversity: species richness and relative abundance, planned & unplanned)
Genetic Diversity
within species
Structural Diversity…
*or Habitat Diversity defined in 4-parts:
(e.g., Plant architecture, habitat diversity, constructed)
(- Living fences, Deciduous borders)
*Major habitat system: e.g., terrestrial, aquatic;
*Formation type: e.g., woodland, open ground;
*Vertical layers: e.g., ground flora, shrub, high canopy;
-Traditional shaded coffee
systems
*Qualifiers: e.g., deciduous, coniferous, annual, etc
Functional: complexity of interactions among system components
Constructed diversity - terraces, ponds, etc
Temporal Diversity
(e.g., Variable planting times, life histories)
Crop rotation
Spatial Diversity
(e.g., beta diversity of vegetation types, or crop varieties, or crop stages, gamma diversity)
Landscape complexity
(% natural habitat in landscape)
Functional biodiversity
Biological pest control Pollination services Nutrient cycling Synergistic interactions eg. -legume/non-legume -Plant mycorrhizae -Microclimate modification – windbreaks, shade Risk aversion: -Multiple products -Spread workload Landscape stability: -Perennial ground cover, hedgerows etc reduce runoff/erosion
Functional diversity
Ladybugs and carabids and pea aphid control (Losey 1998)
Do Intercrops reduce pest damage?
Proposed mechanisms include:
Enemies Hypothesis
Resource Concentration Hypothesis
Resource Concentration Hypothesis
more difficult for pests to find desired host and/or tend to leave more quickly
Enemies Hypothesis:
increase in predators and parasitoids due to increased availability of alternate food sources
Effect of polycultures on herbivore populations
decreased population: 52% of studies
increased populations: 15% of studies
no effect on population of 13% of studies
variable effect on population of 20% of studies
Effect of polycultures on natural enemy populations:
increased population: 53% of studies
decreased population: 9% of studies
no effect on population of 13% of studies
variable effect on population of 25% of studies
Non-Synchronous Planting Not Only Leads to More Stable Arthropod Ecology, … but
More Stable Labor Requirements More Stable Input Costs More Stable Harvest Prices Left to their own, Farmers Drift away from Enforced Synchronous plantings
Summary: Some measures of Stability
Ecosystem-Level Nutrient cycling (ability of plant-soil microbe systems to process nutrients) Soil Erosion (physical sustainability of soil system over time)
Community-Level
Species Richness (conservation as well as agronomic issue)
Functional Redundancy (systems “buffered” by multiple species having similar functions)Population-Level
Insect Pest Suppression (by “beneficials”)
Disease Suppression (e.g., rice blast example)
Economic-Level
Yield, costs and price stability (reduced reliance on volatile purchased inputs; “spreading the risk” through a variety of crops)
Input Availability (avoiding demand “bottlenecks” when costs can rise)
Demand for Labor (spread over year to provide stable work force)
Overall Profit and sustainability (integrates all of the above)