Ecosystems Knowledge-Based Study

Study notes

1. What is an Ecosystem?

   An ecosystem consists of a biological community of interacting organisms and their physical, non-living environment. Ecosystems can vary greatly in size, ranging from a small puddle or rotting log to vast forests, coral reefs, or open oceans.

   Every ecosystem is shaped by two fundamental components:

   • Biotic factors: The living components of an environment. These include plants, animals, fungi, protists, and bacteria.
   • Abiotic factors: The non-living chemical and physical parts of the environment that affect living organisms. Examples include sunlight, temperature, precipitation, soil composition, water pH, and air currents.

   The survival and distribution of living organisms depend directly on how well they are adapted to these abiotic conditions and how they interact with other biotic components.

   Hierarchical Levels in Ecology

   Ecologists study the natural world across distinct levels of biological organization, each building upon the previous level:

   1. Organism: An individual living entity, such as a single oak tree or a wolf.
   2. Population: A group of individuals belonging to the same species that live in the same geographic area at the same time and can interbreed.
   3. Community: All the different populations of various species that live and interact within a shared environment.
   4. Ecosystem: The combination of the living community (biotic) and its surrounding physical environment (abiotic).
   5. Biosphere: The global ecological system integrating all living beings and their relationships; the zone of life on Earth.

   Understanding these distinct levels helps scientists determine whether an ecological change is localized to a single species or affects the broader system as a whole.

   Trophic Structure and Energy Transfer

   Energy enters most ecosystems as sunlight and is converted into chemical energy through photosynthesis. Organisms are categorized into functional feeding roles known as trophic levels:

   • Producers (Autotrophs): Organisms that produce their own organic food from inorganic substances using light or chemical energy (such as green plants, algae, and phytoplankton).
   • Primary Consumers (Herbivores): Animals that feed directly on producers.
   • Secondary and Tertiary Consumers (Carnivores and Omnivores): Predators that feed on primary consumers or other predators.
   • Decomposers (Saprotrophs): Organisms such as bacteria and fungi that break down dead organic matter, returning essential chemical nutrients to the soil and water.

   Unlike matter, energy does not cycle indefinitely. Energy moves in a one-way flow through the trophic levels, and approximately 90% of energy is lost at each step primarily as metabolic heat, leaving only about 10% to be transferred to the next trophic level.

   Biogeochemical Cycles and Homeostasis

   While energy flows unidirectionally and dissipates, chemical elements are conserved and continuously recycled within ecosystems through biogeochemical cycles.

   Key Nutrient Cycles

   • Carbon Cycle: Carbon moves between the atmosphere, living organisms, oceans, and geological deposits through photosynthesis, cellular respiration, decomposition, and combustion.
   • Nitrogen Cycle: Nitrogen gas is fixed into biologically accessible forms (like nitrates and ammonium) by nitrogen-fixing bacteria, assimilated by plants, and returned to the atmosphere by denitrifying bacteria.
   • Water (Hydrologic) Cycle: Water circulates through evaporation, transpiration, condensation, and precipitation.

   The stability and resilience of an ecosystem rely on complex interactions and biodiversity. When biodiversity is high, ecosystems are generally more capable of recovering from natural disturbances such as fires, storms, or disease outbreaks.