Ecology and Ecosystems

Definition of Ecology

• Term was derived from the Greek words oikos (house or dwelling) and logos (science or study)
• The scientific study of distribution and abundance of organisms, and their interactions determines this abundance
• Ecology is the study of the ecosystem

Definition of Ecosystem

• Defined as the collection of living (biotic factors) and non-living (abiotic factors)
• A natural area containing living organisms interacting with non-living substances, producing a material exchange between them

Ecological Concepts: Biotic Factors

• Includes populations of living organisms and the resources they use

Ecological Concepts: Abiotic Factors

• Includes non-living resources, like space, and habitat characteristics, such as elevation, temperature, and humidity

Ecological Concepts: Species

• A collection of related living organisms able to interbreed and exchange genes

Ecological Concepts: Niche

• Describes the role an organism has in a community and how a certain species uses the environment

Ecological Concepts: Guild

• Species competing for similar resources, classified by nutrient acquisition, mobility, and feeding mode

Ecological Concepts: Population

• Individuals of one species in a defined geographical area

Ecological Concepts: Community

• Groups of populations in the same geographical area

Ecological Concepts: Diversity

• Variation in ecosystem organization, like species or genetic diversity

Ecological Concepts: Stability

• The capacity of an ecosystem to stabilize after disturbance

Ecological Concepts: Trophic Pyramid

• A representation of density at trophic levels
• The organization of relationships in biological communities; how food energy transfers through trophic levels
• Autotrophic species are the ecosystem's main producers and compose the base
• Heterotrophs are all other organisms that consume primary producers directly or indirectly for food/energy

Ecological Concepts: Trophic Web

• A diagram of connections between trophic levels representing feeding relationships within a community
• Transfer of food energy is implied source in plants through herbivores to carnivores, according to Hui (2012)

Ecological Concepts: Biological Magnification

• Pollutants concentrate in successive trophic levels via toxin concentration increasing up a food pyramid
• Defined by a rise in contaminated substances caused by the environment, such as heavy metals, arsenic, and polychlorinated biphenyls
• Organisms consume these substances through food, leading to toxin accumulation in higher food chain organisms

Ecological Concepts: Succession

• Progressive changes in community structure over time
• A process of species and habitat mixes changing, resulting in community replacement over time
• Natural communities replace each other, such as an abandoned field becoming a forest

Ecological Concepts: Selection

• The differential reproduction of genotypes

Ecological Concepts: Nutrient cycles

• The cyclic transition of nutrients through multiple forms
• The cyclic pathway in which nutrients pass, to be recycled and reused, comprising cells, organisms, community, and ecosystem
• Movement of nutrients from the environment to living organisms and back

Ecological Concepts: Productivity

• The amount of material or energy formed by a community within a period

Impact of Humans in the Ecosystem: Agroecosystem

• An ecosystem resulting from human intervention through domestication

Impact of Humans in the Ecosystem: Origin of Agroecosystem

• American agronomist Basil Bensin coined "agroecology" in 1928
• Only application of ecological principles to agronomic research processes at the time was Basil Bensin's understanding of agroecology
• The concept evolved from the 1960s-1980s into an ecosystem altered by human activities for economic gain

Natural Ecosystem vs. Agroecosystem

• Agroecosystems are simpler, have fewer predatory/parasitic species, and have less genetic variation. Natural ecosystems have more niches and species diversity
• Fewer trophic interactions in agroecosystems lead to fewer species controlling pest populations
• The low genetic diversity of agricultural species and landscapes makes agroecosystems more susceptible to pest outbreaks

Diversity in Agricultural Systems: Concepts and Example

• Increased plant diversity potentially decreasing pest attacks include non-host plants camouflaging host plants, or when acting as a physical barrier
• Alternative hosts diverting pests from at-risk crops and where natural pest enemies benefit
• Introducing asynchrony through staggered planting keeps pests from massing

Situations where decreased plant diversity might decrease pest attack

• Lack of alternate food, high amount of plant host, minimal perimeter effects
• Synchrony of crop development being out of phase with pests
• Decrease in diversity can benefit natural pest enemies and reduces physical barriers when searching for a pest species

Decreased diversity benefits pest enemies

• Reduces interfering natural enemies and hyper parasites
• Reduces likelihood of diverting key natural enemies or continuous sequence of annual crop monoculture creating opportunities for equilibria between natural enemies and the pest

Element of Ecosystem Diversity: Spatial diversity (patchiness)

• Refers to the influence of spatial arrangements of organisms, populations, and landscapes on ecological dynamics
• Emphasizes habitat loss/fragmentation caused by humans
• Patchiness is generally incompatible with mechanization and can be solved with strip cropping

Element of Ecosystem Diversity: Structural diversity

• Tall vs. short, shaded vs. open, etc., which provides different species habitats, increasing chances for species diversity at the primary producer level

Element of Ecosystem Diversity: Species diversity

• Increases chances for species diversity at higher trophic levels
• Enhanced by avoiding broad-spectrum pesticides

Element of Ecosystem Diversity: Trophic diversity

• Enhanced by avoiding broad-spectrum pesticides
• Maintained by not annihilating pest species and promoted by spatial, structural, and crop species diversity

Element of Ecosystem Diversity: Intraspecific diversity

• Genetic diversity within a crop species, such as multiline, synthetic hybrids, and cultivar mixes

Element of Ecosystem Diversity: Age diversity

• Not applicable to most cropping systems, but a key strategy in silviculture

Unique Features of Agroecosystems

• Agroecosystems experience frequent major disturbances, are dominated by domesticated plants, and have low species Agroecosystems nutrients from external sources, which makes the agroecosystem lush and nutrient rich
• A primary crop species is planted, grows, and is harvested simultaneously in agroecosystems
• These 5 features contribute to the unique feature of pest outbreaks

Agroecosystems Experience Frequent Major Disturbances

• Agroecosystems experience regular disturbances where farmers promote growth of weedy annuals by mimicking conditions in natural ecosystems
• Burning or tilling the land by farmers releases nutrients and provides space/light for crops to grow
• Disturbed agroecosystems also appeal to opportunistic pests
• Unstable ecosystems result in agroecosystems having more pest outbreaks than undisturbed ecosystems

Agroecosystems are Dominated by Domestic Plants

• Natural ecosystems have many plant species, filling a specific ecological niche, whereas agroecosytems have domestic plants and leave niches unfilled
• Domesticated plants have been selected by humans and can adapt to the agroecosystem
• Agroecosystems optimize crop conditions using tillage, pest management, watering, fertilization, and methods

Agroecosystems Have Low Species Diversity

• Agroecosystems are dominated by a single crop species, with low plant and perennial diversity
• Plants are habitats, so a low plant diversity leads to low diversity for other organisms
• Ecosystem stability is based on ecosystem biodiversity, therefore unstability is correlated with agroecosystems due to low biodiversity

Agroecosystems Feature a Main Crop Species that is Planted, Grown and is Harvested at the Same Time

• Crops are planted, grown, and harvested simultaneously in agroecosystems, known as phenological synchrony
• Synchrony simplifies tasks and provides a harvest food source, but an abundant food source is presented to pests growth

Agroecosystems Receive Nutrients from External Sources, Therefore the Main Crop is Lush and Nutrient-Rich

• Farmers provide nutrients in amounts that increase yield forms of chemical fertilizers, manures, green manures, composts, in optimally fertilized soils.
• Harvests mean nutrients are removed in the form of seeds, fruits, leaves, and others.
• Wild plants in natural ecosystems are nutrient-limited with recycled nutrients
• Excess nutrients to agroecosystems promote soft plant growth especially nitrogen fertilizers, and attract herbivorous pests prone to disease

Agroecosystems Experience Frequent Pest Outbreaks

• Pest outbreaks are rare in natural ecosystems, but are common in agroecosystems
• Agroecosystems are relatively unstable, disturbed, and contain abundant nutrient-rich food available in large quantities
• Number/diversity of beneficial organisms pest control is relatively small
• The pest situation differs between natural/agricultural ecosystems. While natural ecosystems have no serious pest issues, agroecosystems have frequent pest outbreaks
• IPM promotes managing agroecosystems like natural ecosystems.