Ecosystems and Communities

Community and Population

• A community is a group of different species living together with mutual tolerance and benefits in a specific area.
• Different species in a community share common characteristic features due to uniform environmental conditions.
• The size and characteristic features of communities are varied, e.g., forest, desert, pond, and mangrove communities.
• A community has its own specific features, including different plant and animal species, growth forms, and structures.

Dominant Species

• A dominant species is a prominent species in a community that has a significant impact on the environment.
• Example: Dipterocarpus (Hora) species are dominant in a lowland tropical rain forest such as Sinharaja forest.

Successional Communities

• Communities that change their composition with time due to variation/fluctuation of environmental factors are known as successional communities.
• These communities eventually attain a stable condition known as the climax stage.

Ecosystem

• An ecosystem is defined as the living and non-living things in an environment and all their interactions.
• Ecosystems can be recognized as a basic fundamental unit in ecology.
• Different types of ecosystems exist in nature, e.g., pond, forest, estuary, and grassland.
• The boundaries of one ecosystem are often overlapping and no clear margins are recognizable in most ecosystems.

Structure and Function of an Ecosystem

• The structure of an ecosystem mainly consists of living and non-living components.
• The two main components of an ecosystem are:
  • Abiotic (non-living) components: space, energy, and raw materials.
  • Biotic (living) components: producers, consumers, and decomposers.
• The functions of an ecosystem are:
  • Flow of energy: energy enters the ecosystem from the sun and is trapped in green plants, converted to chemical energy, and utilized in metabolic processes.
  • Cycling of raw materials: raw materials are the building blocks of an ecosystem, and they are divided into three pools according to their origin: atmosphere, hydrosphere, and lithosphere.

Abiotic Components

• Space: physical and biological space.
• Energy: solar, chemical, gravitational, heat, and wind energy.
• Raw materials: atmosphere (gases), hydrosphere (water), and lithosphere (soil).

Biotic Components

• Producers (autotrophs): organisms that can synthesize their own food through photosynthesis, e.g., green plants and algae.
• Consumers (heterotrophs): organisms that require energy fixed in the form of chemical bonds of organic molecules for survival, e.g., herbivores, carnivores, and omnivores.
• Decomposers (heterotrophs): organisms that obtain their energy from dead organisms or organic compounds dispersed in the environment, e.g., fungi and bacteria.

Competition

• Intra species competition: competition between individuals of the same species for limited resources, leading to the survival of the fittest.
• Inter species competition: competition between different species for limited resources.
• Competition can shape the ecosystem, e.g., taller trees shielding the understory from sunlight, making it hard for other plants to grow.

Evolution and Natural Selection

• Competition within and between species for resources is important in natural selection.
• Scientists believe that competitive relationships may be partially responsible for the evolutionary process.
• The evolution of species is influenced by competition, e.g., the giraffe's long neck adaptation to eat food with little to no competition.

Niche and Habitat

• Niche: the total range of environmental conditions that are suitable for the existence of a species.
• Habitat: the specific environment in which an organism lives.
• Fundamental niche: the total range of environmental conditions that are suitable for the existence of a species without any ecological disturbances.
• Realized niche: the part of the fundamental niche that is actually occupied by the species.