Productivity and Energy Flow

Productivity and Energy Flow


Productivity in ecosystems refers to the rate of biomass production, or the amount of organic matter produced by living organisms through photosynthesis or chemosynthesis over a certain period of time. It is expressed in terms of weight (g-2 ) or energy (kcal m-2 ). The rate of biomass production is called productivity. It is expressed in terms of g-2 yr-2 or (kcal m-2) yr-1  Productivity can be categorized into two main types: primary productivity and secondary productivity.


Primary Productivity:


    • Primary productivity refers to the rate at which producers (usually plants or algae) convert solar energy into organic compounds through photosynthesis. This process forms the base of the food chain, as it produces the organic matter that supports all other organisms in the ecosystem.
    • Primary productivity can be further classified into gross primary productivity (GPP) and net primary productivity (NPP):
      • Gross Primary Productivity (GPP): This is the total rate at which producers convert solar energy into chemical energy through photosynthesis. It represents the entire biomass production by autotrophs.
      • Net Primary Productivity (NPP): NPP is the rate at which producers convert solar energy into chemical energy, minus the energy used by the producers for their own respiration (cellular respiration). It represents the energy available to heterotrophic organisms (consumers) at higher trophic levels.
      • GPP(Gross Primary Productivity) - R (Respiratory Losses) = NPP (Net Primary Productivity)


Secondary Productivity:


    • Secondary productivity refers to the rate at which consumers convert organic matter into biomass through feeding activities. This includes herbivores consuming plants (primary consumers), carnivores consuming herbivores (secondary consumers), and so on. Secondary productivity measures the efficiency with which energy is transferred between trophic levels.
    • Secondary productivity is influenced by factors such as the availability of food, energy transfer efficiency, and the metabolic rates of consumers.




Decomposition in ecosystems is a vital ecological process where organic matter, such as dead plants and animals, is broken down into simpler substances by decomposers like bacteria, fungi, and detritivores. This breakdown releases nutrients like nitrogen, phosphorus, and carbon back into the soil, making them available for uptake by plants, thus completing the nutrient cycle.


The process of decomposition typically involves several stages:


  1. Fragmentation: Larger organic matter is physically broken down into smaller pieces by mechanical action, such as by earthworms, insects, or weathering.

  2. Leaching: Water-soluble compounds like sugars, amino acids, and minerals are dissolved and carried away by water, entering the soil or nearby water bodies.

  3. Chemical breakdown: Decomposers like bacteria and fungi break down complex organic molecules into simpler compounds through enzymatic reactions. This includes the breakdown of proteins into amino acids, fats into fatty acids and glycerol, and carbohydrates into simple sugars.

  4. Humification: The remaining organic material undergoes further breakdown into humus, a stable organic substance that contributes to soil fertility and structure.

  5. Mineralization: In this final stage, nutrients are released in inorganic forms, such as ammonium, nitrate, phosphate, and carbon dioxide, which can be absorbed by plants or taken up by microorganisms.



Factor Affecting Decomposition


1. Chemical Composition – Decomposition rate will be slow when detritus is rich in lignin and chitin and rate increases when detritus is rich in nitrogen and water soluble substances like sugars.

2. Climate factors affecting decomposition include:

  1. Temperature: Higher temperatures accelerate decomposition, while cold temperatures slow it down.

  2. Precipitation: Moisture availability affects microbial activity, with high precipitation promoting decomposition and drought conditions slowing it.

  3. Seasonality: Decomposition rates typically increase during warmer, wetter seasons and decrease during colder, drier seasons.


Energy Flow


Energy flow in an ecosystem refers to the movement of energy through various levels of the ecosystem, from producers to consumers and eventually to decomposers. This flow of energy is essential for sustaining life within the ecosystem.


The components involved in energy flow in an ecosystem include:


  1. Producers: Producers, primarily green plants, algae, and some bacteria, are the organisms that can photosynthesize and convert sunlight into chemical energy through the process of photosynthesis. They form the base of the energy pyramid in most ecosystems by capturing solar energy and converting it into organic compounds like glucose.

  2. Consumers: Consumers are organisms that obtain their energy by consuming other organisms. They can be divided into several categories based on their feeding habits:

    • Primary consumers (herbivores): These are organisms that feed directly on producers. Examples include deer, rabbits, and grasshoppers.
    • Secondary consumers (carnivores): These are organisms that feed on primary consumers. Examples include lions, wolves, and snakes.
    • Tertiary consumers: These are organisms that feed on secondary consumers. These are also referred to as secondary carnivores. Examples include apex predators like eagles and sharks.



Energy flow within an ecosystem follows the laws of thermodynamics, particularly the second law, which states that energy tends to flow from areas of higher concentration to areas of lower concentration and that energy transformations are not 100% efficient, resulting in some energy loss as heat at each trophic level.


Therefore, due to this independence of food/energy between organisms,the chains or web are formed in the ecosystem.


Food Chain


In an ecosystem, a food chain is a series of organisms, each dependent on the next as a source of food. It represents the transfer of energy and nutrients from one organism to another. Typically, a food chain starts with a producer, like plants, which convert sunlight into energy through photosynthesis. Then, consumers, such as herbivores, eat the plants, and predators eat the herbivores, forming a chain of energy transfer.


There are three main types of food chains:


Grazing Food Chain (GFC): This type of food chain occurs on land. It typically starts with green plants as the primary producers, which are then consumed by herbivores (primary consumers), followed by carnivores (secondary consumers) that eat the herbivores, and possibly tertiary consumers that eat the carnivores.




Detritus Food Chain (DFC): In this type of food chain, decomposers, like bacteria and fungi, break down dead organic matter (detritus) into simpler compounds. These decomposers are then consumed by detritivores, such as earthworms or maggots, which in turn may be eaten by predators.




These food chains are interconnected and form complex networks called food webs, which depict the multiple paths of energy flow within an ecosystem. Each organism in a food chain plays a crucial role in maintaining the balance of the ecosystem.


Food Web 


A food web is a more complex representation of the feeding relationships within an ecosystem compared to a simple linear food chain. It consists of multiple interconnected food chains, illustrating the various paths along which energy and nutrients flow through an ecosystem.


In a food web, each organism can occupy multiple trophic levels, as they may consume and be consumed by multiple other species. This interconnectedness reflects the complex interactions among organisms within an ecosystem.


Food webs provide a more realistic depiction of the flow of energy and nutrients and better illustrate the dynamic nature of ecosystems compared to simple food chains. They help us understand the intricate relationships among organisms and the stability of ecosystems.




Trophic Level


Trophic level refers to the position of an organism in a food chain or food web, determined by its feeding relationship and its source of energy and nutrients. Organisms within an ecosystem can be categorized into different trophic levels based on how they obtain their food and energy.


There are typically four main trophic levels:


  1. Primary Producers (Trophic Level 1): Primary producers, such as plants, algae, and some bacteria, are at the base of the food chain. They convert sunlight into chemical energy through photosynthesis or derive energy from inorganic compounds in the case of certain bacteria (chemosynthesis). They are the primary source of energy for all other organisms in the ecosystem.

  2. Primary Consumers (Trophic Level 2): Also known as herbivores, primary consumers are organisms that feed directly on primary producers. They obtain energy by consuming plants or algae. Examples include various insects, herbivorous mammals, and some fish.

  3. Secondary Consumers (Trophic Level 3): Secondary consumers are carnivores that feed on primary consumers. They obtain energy by consuming herbivores. Examples include carnivorous mammals, birds of prey, and predatory fish.

  4. Tertiary Consumers (Trophic Level 4): Tertiary consumers are carnivores that feed on other carnivores. They obtain energy by consuming secondary consumers. In some ecosystems, there may be additional trophic levels beyond tertiary consumers, such as quaternary consumers that feed on tertiary consumers.



  • Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.
  • Organisms at each trophic level depend on those at the lower trophic level for their energy demands
  • The number of trophic levels in the grazing food chain is restricted,as the transfer of energy follows 10% law. It means only 10% of the energy is transferred to each trophic level from the lower trophic level. It was given by Lindemann in 1942.
  • Each trophic level represents a transfer of energy and nutrients from one group of organisms to another within an ecosystem. Trophic levels help us understand the flow of energy through ecosystems and the interactions among different organisms.


Ecological Pyramids


Ecological pyramids are graphical representations of the trophic structure and energy flow within an ecosystem. They illustrate the relative amounts of energy, biomass, or number of organisms at each trophic level.


There are three main types of ecological pyramids:


  • Pyramid of Energy: This type of ecological pyramid depicts the amount of energy present at each trophic level in an ecosystem. Since energy is lost as it moves through trophic levels due to metabolic processes, heat loss, and inefficiencies in energy transfer, the pyramid of energy typically shows a decrease in energy availability as you move from lower to higher trophic levels. This means that the energy available to higher trophic levels is less than that available to lower trophic levels. As a result, the pyramid of energy always appears upright.



  • Pyramid of Biomass: The pyramid of biomass represents the total biomass (the total mass of living organisms) at each trophic level in an ecosystem. Biomass decreases as you move up the trophic levels because energy is lost as heat and through metabolic processes. Therefore, similar to the pyramid of energy, the pyramid of biomass typically shows a decrease in biomass from lower to higher trophic levels.It can be of two types:

    a) Upright (in case of grassland ecosystem)
    b) Inverted (in case of pond ecosystem)




  • Pyramid of Numbers: This type of ecological pyramid depicts the number of individual organisms at each trophic level in an ecosystem. The pyramid of numbers can take different shapes depending on the ecosystem. In some ecosystems, where large numbers of small organisms (such as phytoplankton) support a smaller number of larger organisms (such as fish), the pyramid of numbers may be upright. However, in other ecosystems, where a few large organisms support a larger number of smaller organisms (such as in a forest ecosystem where a few trees support numerous herbivores and even more smaller organisms), the pyramid of numbers may be inverted.




These ecological pyramids provide valuable insights into the structure and dynamics of ecosystems, helping ecologists understand the flow of energy and the relationships between organisms within ecosystems.


Limitations of Ecological Pyramids


Ecological pyramids are useful tools for visualizing energy flow and biomass distribution in ecosystems, but they have limitations:


  1. Oversimplify complex food webs.
  2. Ignore the roles of omnivores and detritivores.
  3. Don't account for temporal variability.
  4. Assume a fixed trophic efficiency.
  5. Provide static representations, not capturing dynamic changes.
  6. Less applicable to aquatic ecosystems.


Despite these limitations, they offer valuable insights into ecosystem structure and function when used alongside other ecological models and empirical data.


Ecological Succession


  • Ecological succession refers to the process by which an ecological community undergoes changes in species composition over time. These changes occur due to various factors such as disturbances, environmental conditions, and interactions among species.
  • The entire sequence of communities that successively change in a given area are called seres.
  • The individual transitional communities are termed as seral stages or seral communities.
  • Succession typically follows a predictable pattern, though the specific trajectory can vary based on local conditions. There are two main types of ecological succession:
  1. Primary Succession: This occurs in an area where there is no soil present or where the soil is incapable of sustaining life. Primary succession begins with the colonization of barren land by pioneer species such as lichens, mosses, and certain plants capable of surviving harsh conditions. Over time, as these pioneer species die and decompose, they contribute to the development of soil, paving the way for more complex plant communities. Examples of primary succession include the colonization of volcanic rock, newly formed sand dunes, and areas left barren after glacier retreat.

  2. Secondary Succession: Secondary succession occurs in areas where the soil remains intact, despite being disturbed by events such as fires, floods, hurricanes, or human activities like deforestation or agriculture. In secondary succession, the process starts with the regeneration of plant life from seeds, roots, or spores present in the soil or brought in by wind or animals. Unlike primary succession, where the initial colonizers are usually pioneer species, secondary succession often begins with more established plant species. Over time, the community undergoes changes as more species colonize the area, eventually leading to the restoration of a stable ecosystem resembling the pre-disturbance state.




Understanding these types of succession helps ecologists predict and manage ecosystem dynamics, especially in contexts such as land management, conservation, and restoration efforts.


Succession of Plants


Succession of plants refers to the predictable series of changes in plant communities over time in a particular area. There are two main types of plant succession: Hydrarch and Xerarch.

  • Hydrarch Succession:

    • Definition: Hydrarch succession occurs in wet environments such as ponds, lakes, or marshes.
    • Initiation: It begins with the colonization of bare substrate, often by pioneer species like algae or floating aquatic plants.
    • Progression: Over time, these pioneer species modify the environment, creating conditions suitable for the growth of other plants. As they die and decompose, they contribute to the formation of organic matter and soil.
    • Intermediate stages: In the intermediate stages, emergent plants like reeds and grasses establish themselves. These plants have adaptations for living in waterlogged conditions.
    • Climax community: The climax community in hydrarch succession often consists of woody plants like trees and shrubs. These species are better adapted to stable, moist conditions and can outcompete many of the earlier successional species.




  • Xerarch Succession:

    • Definition: Xerarch succession occurs in dry environments such as sand dunes, rock crevices, or abandoned agricultural fields.
    • Initiation: It typically begins with colonization by pioneer species adapted to dry conditions, such as lichens and mosses. These organisms are capable of surviving in harsh environments with limited water availability.
    • Progression: As pioneer species colonize and begin to break down rocks or stabilize sand, they create patches of soil. This allows for the establishment of herbaceous plants like grasses and wildflowers.
    • Intermediate stages: With the accumulation of organic matter and the development of soil, larger plants such as shrubs and small trees can establish themselves. These plants further stabilize the soil and create more favorable microclimates for other species.
    • Climax community: The climax community in xerarch succession often consists of drought-resistant trees and shrubs, such as cacti or mesquite trees. These species are well-adapted to dry conditions and can thrive in areas with limited water availability.




Both hydrarch and xerarch successions lead to medium water conditions (mesic), neither too dry (xeric) nor too wet (hydric). The important fact is that all successions whether taking place in water or on land, proceed to a similar mesic climax community.

These successions play crucial roles in ecosystem development and contribute to biodiversity and habitat formation.


Nutrient Cycle


  • The nutrient cycle, also known as the biogeochemical cycle, describes how nutrients move and are recycled through ecosystems. These cycles involve the exchange of nutrients between living organisms, the atmosphere, soil, water, and geological formations.
  • The amount of nutrients present in the soil at any given time, is referred to as the standing state. It varies in different kinds of ecosystems and also on a seasonal basis. 
  • Nutrient cycles are of two types - Gaseous and Sedimentary.
  • Atmosphere is the reservoir for gaseous type of nutrient cycle (e.g. nitrogen and carbon cycle).
  • Earth's crust is the reserviour of sedimentary cycle (e.g. sulphur and phosphorus cycle).


Ecosystem - Carbon Cycle


The carbon cycle is the process by which carbon is exchanged between the atmosphere, oceans, soil, and living organisms.


  1. Carbon dioxide (CO2) in the atmosphere is absorbed by plants during photosynthesis, converting it into organic carbon.
  2. Animals consume these plants, transferring carbon through the food chain.
  3. Carbon is released back into the atmosphere through respiration by plants and animals, and through decomposition of organic matter by microbes.
  4. Carbon is also stored in long-term reservoirs such as fossil fuels, soil, oceans, and forests.
  5. Human activities, such as burning fossil fuels and deforestation, have disrupted the carbon cycle, leading to increased CO2 levels in the atmosphere and contributing to climate change.
  6. Balancing the carbon cycle is crucial for maintaining a stable climate and supporting life on Earth.



Ecosystem - Phosphorus Cycle


The phosphorus cycle is a crucial biogeochemical process that involves the movement of phosphorus through the Earth's lithosphere, hydrosphere, and biosphere.


  1. Phosphorus is primarily found in rocks and minerals in the Earth's crust.
  2. Weathering and erosion release phosphorus from rocks, making it available for uptake by plants.
  3. Plants absorb phosphorus from the soil through their roots and incorporate it into their tissues.
  4. Animals obtain phosphorus by consuming plants or other animals.
  5. Phosphorus is returned to the soil and water through the decomposition of plant and animal matter.
  6. Phosphorus can also enter aquatic ecosystems through runoff and erosion, where it can become trapped in sediment or taken up by aquatic plants and algae.
  7. Human activities, such as the use of fertilizers and the discharge of wastewater, can disrupt the phosphorus cycle, leading to nutrient imbalances and ecosystem degradation.
  8. Balancing the phosphorus cycle is essential for maintaining healthy ecosystems and water quality.




Ecosystem Services


Ecosystem services are the essential benefits that ecosystems provide to humans. They include:

  • Provisioning services: Tangible resources like food, water, and timber.
  • Regulating services: Processes like climate regulation, water purification, and pollination.
  • Supporting services: Fundamental roles like soil formation, nutrient cycling, and biodiversity maintenance.
  • Cultural services: Non-material benefits such as recreation, aesthetics, and cultural identity. Recognizing and preserving these services are critical for human well-being and sustainability.