Levels of Organization in Ecology

Levels of Organization in Ecology

• Ecology is a science that studies the interdependent, mutually reactive and interconnected relationship between the organisms and their physical environment on the one hand and among the organisms on the other hand.
• Ecology not only deals with the study of the relationship of individual organisms with their environment, but also with the study of populations, communities, ecosystems, biomes, and the biosphere as a whole.
• Ecology encompasses the study of individuals, organisms, populations, communities, ecosystems, biomes and biosphere, which form the various levels of ecological organisation. These levels describe the hierarchy of life, with each stage representing increased complexity and interaction, from a single organism to global planetary systems.
  1. Individual
  2. Population
  3. community
  4. Ecosystem
  5. Biome
  6. Biosphere

Individual and Species

• An individual is any living thing or organism. An organism is an individual living being that can act or function independently.
• A species is a group of living organisms consisting of similar individuals capable of exchanging genes (interbreeding). They are considered the basic unit of taxonomy and are denoted by a Latin binomial, e.g., Homo sapiens.
  • Closely related species—with only a slight difference in their genetic makeup—though not capable of interbreeding, share many of their hereditary characteristics.
    • For instance, approximately 98.4 per cent of human and chimpanzee genes are identical.
• For Example, The Tiger (Panthera tigris) is a type of individual organism; The Royal Bengal Tiger (Panthera tigris tigris) is a species of tiger among others, like the Sumatran tiger. (Panthera tigris sumatrae) etc. Similarly, The Elephant is an Individual type of organism. Among them, the African elephant (Loxodonta africana), Asian Elephant (Elephas maximus) are different species.

Population

• A population is a group of organisms usually of the same species, occupying a defined area during a specific time.
  • The population growth rate can be positive due to births and immigration, or negative due to deaths and emigration.
  • The main limiting factors for the growth of a population are abiotic and biotic components.
• Every individual species is represented in populations. The populations of Royal Bengal Tigers can be seen in Sundarbans, etc., whereas Sumatran tigers can be seen in the Pacific islands of Sumatra.

Community

• In ecology, the term community, or more appropriately, ‘biotic community, refers to the populations of different kinds of organisms living together and sharing the same habitat.
• Communities are named after the dominant plant form. For example, a grassland community is dominated by grasses, although it may also include herbs, shrubs, and trees.
• The characteristic pattern of the community is termed as the structure of the community and is determined by:
  • the roles played by its various populations
  • the range of its various populations
  • the type of area that is inhabited by the populations of the community
  • the diversity of species in the community
  • the interactions between various populations of the community inhabiting the area.
• Members of a community also actively interact with their environment. In a community, only those plants and animals survive that are adapted to a particular environment. The climate determines the type of environment, hence, the type of organisms in a community.
  • For example, it is the climate of the area that determines whether a given area becomes a desert or a forest.
• Communities created by humans, such as lawns, crop communities, gardens, and parks, are considered man-made communities. These are relatively simple and consist of only one species as opposed to a natural community characterised by a large number of species.
• Man-made communities are very unstable and require a great deal of care and constant manipulation, and maintenance.

Types of Community

• On the basis of size and degree of relative independence, communities may be divided into two types:

Major Communities

• A major community is the smallest ecological unit capable of self-sustenance and self-regulation.
• Independence: These are large-sized units that are relatively independent of other communities.
• Energy Source: They rely solely on external energy from the sun.
• Composition: A major community is a functional combination of:
  • Floral community (plants)
  • Faunal community (animals)
  • Microbial community (micro-organisms)
• Examples: Ponds, forests, grasslands, or lakes. 

Minor Communities

• Minor communities, also known as societies or merocenoses, are smaller ecological units that function within larger systems.
• Dependence: They are not individually self-sustaining and rely on interactions with neighboring communities for survival.
• Resource Needs: They depend on other communities for their essential energy and nutrients.
• Structure: They serve as the building blocks that make up major communities.
• Example: A group of organisms living within a piece of deadwood on a forest floor, or a mat of lichen on a cow dung pad.

Stable Community: In a stable community, productivity varies little from year to year. It is either resistant or resilient to occasional disturbances (natural or human-made) and invasions by alien species.

Community Structure

• Community structure describes the composition of an ecological group, specifically the variety and quantity of species within it.
• Size and Scale: Communities can be small, with few species in a limited space, or large, covering wide areas with numerous populations.
• Core Components: It is defined by the total number of species present and their relative abundance.
• Influencing Factors: The structure is shaped by environmental and biological drivers, including:
  • Climatic patterns and weather.
  • Interactions between different organisms.
  • Species density and overall abundance.
  • Frequency of disturbances, such as storms or fires.

Characteristics of a Biological Community

• A community’s nature is defined by how its species interact and adapt to environmental factors. While features are highly variable, the following are the most prominent:
  • Dominance: One or two species at each trophic level typically exert the most influence over the community’s structure and function.
    • These ecological dominants can alter the habitat’s abiotic conditions over time.
    • Despite their influence, every species remains vital for a balanced ecosystem. For example, a dominant tree may control light and nutrients, but its reproduction might rely on a rare insect for pollination.
  • Interdependence: Organisms within a community (plants, animals, and microbes) have a fundamental dependence on at least one other organism.
    • These interactions are essential for nutrition, reproduction, or protection.
  • Stratification: Communities often display vertical or horizontal layering, where populations are distributed into defined strata.
    • Some organisms move between these layers daily (diurnal basis), such as a bird that feeds on the forest floor but roosts in the high canopy.
  • Diversity: This refers to the variation of species and their relative abundance within an area.
    • Higher species diversity generally leads to a more stable community.
  • Ecotone: This is the transitional area where two different biomes or communities meet and integrate.
    • Ecotones are environmentally important as they often support a high number of species, attracting animals for nesting or food.

Ecosystem

• An ecosystem is defined as a structural and functional unit of the biosphere consisting of a community of living beings and the physical environment, both interacting and exchanging materials between them.
• The term ‘ecosystem ‘was coined by A.G. Tansley in 1935. An ecosystem is a functional unit of nature encompassing complex interactions between its biotic (living) and abiotic (nonliving) components. For example, a pond is a good example of an ecosystem.
• Ecosystems vary greatly in size and elements, but each is a functioning unit of nature. Everything that lives in an ecosystem is dependent on the other species and elements that are also part of that ecological community. If one part of an ecosystem is damaged or disappears, it has an impact on everything else. The ecosystem can be as small as a single tree or as large as the entire forest.

Biome

• Biomes are very large ecological units characterised by a major vegetation type and associated fauna adapting to a specific climate zone.
• A Biome is not an ecosystem, but it can be seen as a form of a massive ecosystem.
• The boundaries and abundance of organisms in a biome is often defined by abiotic factors such as climate, relief, geology, soil and vegetation.
• Many units of an ecosystem may be found in one biome. Moreover, no two biomes are alike.
• Biomes play a crucial role in sustaining life on Earth. For example, the Aquatic biome is home to millions of fish species and is the source of the water cycle. It also plays a very important role in climate formation.
• The terrestrial biomes provide food, enrich the air with oxygen and absorb carbon dioxide and other harmful gases from the air. They also help regulate the climate.

Variants in Biomes

• There are five major variants of biomes on earth. In these five, there are many sub-biomes, under which there are many more well-defined ecosystems.
  • Desert Biomes: They are the Hot and Dry Deserts, Semi-Arid Deserts, Coastal Deserts and Cold Deserts.
  • Aquatic Biomes: Aquatic biomes are grouped into two categories i.e. Freshwater Biomes (lakes, ponds, wetlands, rivers and streams) and Marine Biomes (oceans, coral reefs and estuaries).
  • Forest Biomes: There are three main biomes that make up Forest Biomes. These are the Tropical Rainforest, Temperate and Boreal Forests (also called as Taiga). Example: Amazon biome contains a moist tropical rainforest.
  • Grassland Biomes: There are two main types of grassland biomes: the Savanna Grasslands and the Temperate Grasslands. Example: African Savanna and Prairies.
  • Tundra Biomes: There are two major tundra biomes – The Arctic Tundra and The Alpine Tundra.

Biosphere

• The biosphere is a part of the Earth where life can exist. The biosphere represents a highly integrated and interacting zone comprising the atmosphere (air), hydrosphere (water) and lithosphere (land).
• It is a narrow layer around the surface of the Earth. If we visualize the earth to be the size of an apple the biosphere would be as thick as its skin.
• It is that part of the earth in which many smaller ecosystems exist and operate. It extends from the deepest root systems of trees to the dark environment of ocean trenches, to lush green rainforests and high mountain tops.
• However, living organisms are mostly confined to the areas that receive solar radiation, which includes the atmosphere, the land surface, the upper layers of soil and the upper region of water bodies. In the ocean, the biosphere does not end where light ceases and goes a little further as gravity enables the energy flow to continue downward.
• Similar to the existence of an underwater biosphere, it extends upwards in the atmosphere to a certain limit. On high mountains, like the Himalayas, the limit above which chlorophyll-bearing plants cease to exist is around 6.2 km.
• The biosphere is absent at extremes of the North and South poles, the highest mountains and the deepest oceans since existing hostile conditions there do not support life. Occasionally, spores of fungi and bacteria do occur at a great height beyond 8,000 meters, but they are not metabolically active and hence represent only dormant life.
• Living organisms are not uniformly distributed throughout the biosphere. Only a few organisms live in the Polar Regions, while the tropical rainforests have an exceedingly rich diversity of plants and animals.

Divisions of the Biosphere

• Biosphere is composed of three primary interconnected layers: lithosphere, atmosphere and hydrosphere.
• The Atmosphere (Air)
  • The Atmosphere is the gaseous envelope surrounding the Earth, commonly referred to as “air.”
  • Composition: A blend of various gases that protect and sustain the planet.
  • Significance: It provides the essential conditions and gases necessary for the existence of life.
• The Hydrosphere (Water)
  • The Hydrosphere encompasses all the water found on the Earth’s surface. It covers approximately 70% of the Earth’s surface.
  • Components: Includes oceans, seas, lakes, ponds, rivers, and streams.
  • Significance: Water is a vital component for every form of life.
• The Lithosphere (Land)
  • The Lithosphere is the rigid, outermost shell of the Earth, forming its hard top layer.
  • Composition: It consists of rocks and minerals and is topped by a thin layer of soil.
  • Topography: An irregular surface featuring various landforms such as mountains, plateaus, plains, and valleys.
  • Structure: It is broken into large and small tectonic plates and is categorized into two types:
    • Oceanic Lithosphere: Associated with the oceanic crust.
    • Continental Lithosphere: Associated with the continental crust.