Ecology Definition and Scale

Ecology Definition

• Originates from the Greek words "Oikos," meaning household or home, and "Logos," meaning study or research.
• Literally the study of the "homes" or environment of organisms.
• Coined from the term "oekologie" by Ernst Heinrich Haeckel in 1866.
• The study of interrelationships among living organisms, and between organisms and their environment.
• Physical environment includes non-living elements like light, heat, moisture, and gases.
• Biological environment includes living things, such as plants, animals, and microorganisms.
• Biotic interactions are interactions among living organisms.
• Abiotic interactions are interactions between organisms and their non-living environment.

Scale or Levels of Ecology

• Historically studied under two headings: Autecology and Synecology.
• Autecology focused on the study of individuals or their populations.
• Synecology focused on the study of the community as a whole.
• Modern ecology studies are conducted at several levels including:
  • Individual organism
  • Population
  • Community
  • Ecosystem
  • Biosphere

Ecology Terms and Concepts

• Ecology uses many unique terms and concepts.

Species

• Are groups of similar organisms that can interbreed.
• Defined as a group of reproductively isolated individuals.
• Examples are Magnifera indica, Rattus rattus, and Agama agama.

Population

• Is a group of organisms of the same species in a defined location at a given time.
• Can also be grouped organisms of the same species living in the same geographic area.

Community

• Consists of multiple populations of different species interacting within an environment at a specific time.
• Composed only of biotic factors.
• i.e. A pond, grassland, or a rotten log.

Ecosystem

• A functional unit of living (biotic community) and non-living components that interact to create a stable system.
• Ecosystems must be self-sustaining and self-regulating.
• Can be as small as a pond or as large as an ocean.
• Can be as small as a field of grasses, or as large as a forest.
• Can be temporary such as a freshwater pool, or permanent, such as a forest or an ocean.
• Can be natural or man-made like an aquarium.

Types of Ecosystems

• Aquatic
• Terrestrial

Niche

• Refers to the position a species occupies in its community and/or the role it plays within that ecosystem.
• For i.e. in a grassland ecosystem, green plants are producers, and microorganisms are decomposers.
• While two species may be related they will not occupy the same niche, like:
  • Grasshoppers and aphids living on the same plant (cassava), but occupy different niches on that plant.

Environment

• Is the totality of all factors and conditions affecting a living organism in its habitat.
• Includes physical aspects like air, water, soil, sun, temperature, and pH.
• Includes biological aspects like plants, animals, and microorganisms.

Habitat

• A place or physical environment where an organism or population lives i.e. inhabits.
• Categorized as:
  • Aquatic relating to water
  • Terrestrial relating to land
  • Arboreal relating to above-ground
• Can be a smaller unit within a larger one, called a microhabitat (i.e. the back of a leaf).

Energy Flow

• Refers to the movement of energy through an ecosystem in a straight line.
• The sun is the primary energy source.
• Producers (green plants, algae) trap around 1% of solar energy and convert it to chemical form using photosynthesis.
• Organisms rely on the food stored by producers.
• Feeding relationships are represented as food chains and food webs.

Food Chain

• Is a linear representation of feeding relationships among living organisms in an ecosystem.
• Each organism derives energy from the preceding organism.
• Each feeding level in the food chain is called a trophic level (with different species occupying different trophic levels).
• The first trophic level is usually occupied by producers/primary producers (autotrophs).
• All other levels are occupied by heterotrophs (consumers).
• The second trophic level is occupied by primary consumers (herbivores and detritivores).
• Followed by carnivores feeding on herbivores (secondary consumers), predators that feed on those (higher carnivores), etc.
• Food chain examples:
  • Plants > Deer > Lion
  • Plants > Worm > Bird > Cat
  • Grass > Grasshopper > Frog > Snake > Hawk
  • Algae > Small animal > Small fish > Big fish > Bird

Food Web

• In reality an organism may feed on more than one organism at the same time.
• In nature, an animal may feed in more than one food chain creating a food web.
• Consists of multiple food chains linked at different points, which creates many alternative feeding pathways.

Ecological Pyramids

• Ecological pyramids graphically depict energy flow through the ecosystem.
• They show the disproportionate relationship between the numbers of producers, primary, secondary, and tertiary consumers.
• Constructed in a triangular pyramid shape.
• Three main types:
  • Pyramid of numbers shows the number of individual organisms at each level.
  • Pyramid of biomass shows the amount of living tissue or total mass of organisms within each trophic level.
  • Pyramid of energy depicts the amount of energy at each trophic level.

Nutrient Flow

• Refers to the movement of nutrients through an ecosystem.
• Unlike energy from the sun, nutrients (chemical elements) are available only in limited supply.
• Nutrients have to be recycled through biogeochemical cycles like:
  • Nitrogen Cycle
  • Carbon Cycle
  • Hydrological cycle (Water Cycle).

Nitrogen Cycle

• The major pathways of the nitrogen cycle are:
  • Nitrogen Fixation
  • Nitrification
  • Ammonification
  • Assimilation
  • Denitrification

Nitrogen Fixation

• The conversion of atmospheric nitrogen into nitrates achieved through:
  • Direct fixation by electrochemical means during lighting or thunderstorm.
  • Fixation by microorganisms, especially bacteria that use an enzyme (hydrogenase) to convert atmospheric nitrogen (N₂) into ammonia (NH3) or ammonium (NH₄⁺).
  • Bacteria examples are Azobacter, Clostridium, Nostoc, and Anabena.
  • Rhizobium lives in the root nodules of legumes (beans, groundnuts, peas) in mutualistic association.

Nitrification

• The process by which soil microorganisms convert ammonia (NH3) or ammonium (NH4+) to nitrate (NO3).
• Completed in two stages:
  • Ammonia is oxidised to nitrites (NO₂) by bacteria such as Nitrosomonas, Nitrococcus, and Nitrospira.
  • Nitrites (NO₂) are converted to nitrates (NO₃) by bacteria such as Nitrobacter and Nitrocystis.

Ammonification

• Decomposes proteins in dead organic matter by microorganisms to produce amino acids and ammonia.
• The ammonia formed is either released into the atmosphere or retained in the soil for plants to absorb.
• Under certain conditions, it may be oxidised to nitrates.
• The most common pathway for nitrogen to enter the soil as many soils lack adequate nitrifying bacteria.
• Organisms responsible are mostly fungi (Actinomycetes) and bacteria (Bacillus subtilis, B. mesenterilus).

Assimilation

• The process by which inorganic nitrogen compounds are used to form organic nitrogen compounds.
• Organisms assimilate nitrogen by taking up NH3, NH4+, and NO3 formed through nitrogen fixation and nitrification.
• Plant roots absorb these forms of nitrogen, while animals assimilate it from plant tissues.

Denitrification

• The reduction of some nitrates (NO3) in the soil to gaseous nitrogen (N₂) or oxides of nitrogen or ammonia.
• Occurs mainly under anaerobic conditions, where denitrifying bacteria use the oxygen in nitrate molecules to oxidize carbohydrates.
• Important bacteria include Bacillus cereus, B. licheniformis, Pseudomonas denitrificans, etc.
• Delivers only a relatively small amount of nitrogen to the atmosphere.

Carbon Cycle

• Movement of carbon from the atmosphere into organisms and back.
• Complex due to carbon's ability to exist in different compounds in plants, animals, rocks etc.
• Oceans serve as a major reservoir of CO2, containing 50 times mores than in air.
• Carbon is stored in oceans as bicarbonate mineral deposit on the ocean floor.
• Oceans regulate the CO₂ in the atmosphere.
• Cycle operates through CO2 exchange among the atmosphere, biosphere, and the oceans.