Topic 2: The Ecosystem


Ecosystems are the biotic and abiotic factors in a specified area that interact with one another.The term environment means surroundings. It comes from the French word environner (to encircle or to surround). It is a composite term for the conditions in which organisms live and thus consists of air, water, soil and sunlight which are the basic needs of all living beings and plant life, to carry on their life functions. The environment also includes others like temperature, wind, energy etc. Thus it consists of both biotic and abiotic substances. Environment creates favourable conditions for the existence and development of living organisms.

2.1. Structure

  • biotic factor - A living, biological factor that may influence an organism or ecosystem, such as producers-plants,consumers-animals etc
  • abiotic factors – A non-living or physical factor that may influence an organism or ecosystem. For example, precipitation, wind, sunlight, soil, temperature, pH, salinity, light, temperature. Understanding the interaction of the biotic and abiotic factors in an ecosystem can help us to see why particular human activities may be a problem for human survival.
    Example: The loss of ozone in the stratosphere increases the quantity of UV radiation on the surface of the planet. In the same way that humans experience sunburn from too much sun exposure, so do plants. Excessive UV may damage or destroy plant protein and DNA, killing the plant.
  • Trophic level - The position that an organism occupies in a food chain, or a group of organisms in a community that occupy the same position in food chains. And is mainly considered as feeding level.
  1. Producers/Autotrophs - Organisms that make their own food. Usually plants through photosynthesis.
  2. Primary consumers - Organisms that consume producers.
  3. Secondary consumers - Organisms that consume primary consumers.
  1. Herbivores - Organisms that eat plants, but no meat.
  2. Carnivores - Meat-eaters.
  3. Omnivores - Organisms that eat both plants and meat
  4. Saprotrophic - Decomposers

  1. species - A group of organisms that interbreed and produce fertile offspring.
  2. population - A group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.
  3. community - A group of populations living and interacting with each other in a common habitat.
  4. ecosystem - A community of interdependent organisms and the physical environment they inhabit.
  5. habitat - The environment in which a species normally lives.

niche - A species' share of a habitat and the resources in it. An organism's ecological niche depends not only on where it lives but on the role it plays in the ecosystem.

  • fundamental niche - The part of the habitat in which a species can live in the absence of competitors and predators
  • realized niche - The part of the habitat that the organism actually occupies.

biome – large, relatively distinct terrestrial region characterized by similar climate (temperature and precipitation), soil, and organisms.

  • competition – [– ,–] Two species (interspecies competition) or two populations of the same species (intraspecies competition) compete for the same resources. Both sides are harmed.
  • symbiosis – biological interaction where two different species are in direct contact with each other.
    • commensalism – [0 , +] One species benefits, the other is unaffected
    • mensalism – [0 , –] One species is harmed, the other is unaffected
    • mutualism – [+ , +] Both species benefit
    • predation – [+ , –] One species benefits, the other is harmed. The prey is usually killed quickly.
    • parasitism – [+ , –] One species benefits, the other is harmed. The host is killed slowly if at all.

2.2. Function


photosynthesis – 6CO2 + 6H2O + light energy ⇒ C6H12O6 + 6O2 + heat – Carbon Dioxide, Water and Sunlight go in, Glucose, Oxygen and Heat are produced.

respiration – C6H12O6 + 6O2 ⇒ 6CO2 + 6H2O + released energy (heat) – Glucose and Oxygen go in, Carbon Dioxide and Water and Heat are produced.

2.3. Changes


Reproductive Strategies: r and K


  1. Short-lived
  2. Large broods
  3. Reproduce early in life
  4. Little to no care for young
  5. Relatively small


  1. Long-lived
  2. Few offspring per reproductive period
  3. Reproduce later in life
  4. Nurture young
  5. Relatively large

succession – a change over time in the types of species that occupy a given area.

  • primary succession – ecological succession in an environment that has not been previously inhabited (no soil is present).
  • pioneer communities – the first organisms to colonize (or recolonize) an area.
  • secondary succession – ecological succession in an environment that was exposed to some type of disturbance (soil is already present).

sere – a sequence of communities over ecological time. Each stage of succession is called a seral stage.

  • lithosere – succession on bare rock
  • hydrosere – succession in freshwater lakes
  • psammosere – succession on sand dunes
  • halosere – succession on salt marshes

climax community – species composition no longer changes over time; secession stops. Community retains an overall uniform appearance.