Productivity of an Ecosystem

Introduction

Ecological productivity indicates the percentage of energy entering the ecosystem at a specific tropical level as biomass. In simple words, it is the rate of the formation of biomass in the ecosystem. A characteristic percentage of biomass is available at all trophic levels in the ecosystem. Many producers are present in the ecosystem to source energy. Productivity of the ecosystem refers to the rate of biomass production i.e. the amount of organic matter accumulated per unit area per unit time.

It is generally expressed in g-2 yr-1or (kcal m-2) yr-1 . Therefore, we measure the productivity of an ecosystem on the basis of the following:

• Primary productivity 
• Secondary productivity

Primary Productivity of an Ecosystem

It refers to the biomass generation by autotrophy: chemoautotrophs or photoautotrophs.

In the case of photoautotrophs, living organisms tend to use inorganic components to synthesize their food. Here, this process takes place in the presence of light which is the source of their energy. Plants are known as the main autotrophs that use photosynthesis to create organic materials from non-organic materials. 

On the other hand, Chemoautotrophy enables living organisms like archaea and bacteria to observe energy from other chemical proceedings instead of photosynthesis.  In per unit area, maximum productivity is found in tropical rainforest. In water, the least productive ecosystem is very deep lakes and the most productive ecosystem is coral reef.

  Primary productivity can be divided into-

-Gross primary productivity (GPP) 

– Net primary productivity (NPP)

 Gross primary productivity (G.P.P.) is the total amount of energy fixed (organic food) in an ecosystem (in producers) in unit time including the organic matter used up in respiration during the measurement period.

It is also known as total (gross) photosynthesis. A considerable amount of GPP is utilized by plants in respiration.   

 Net primary productivity (N.P.P.) is the amount of stored organic matter in plant tissues after respiratory utilization NPP=GPP-R(R=Respiration + Metabolic activities). Or GPP=NPP+R

Secondary Productivity

It refers to the biomass production rate by herbivores or consumers. Here, the organisms are not able to produce their own food and receive energy from primary productivity’s biomass production. In the secondary productivity of an ecosystem, we see different trophic levels, including: 

• Herbivores
• Carnivores
• Omnivores

Here every trophic level uses biomass but dissipates up to just 10% of the biomass into the energy. Further, the remaining unassimilated biomass is released as fecal waste. Additionally, these remains are used by other decomposers or different trophic levels.  

The assimilated energy is very useful for or running numerous processes for growth, metabolism, and reproduction, etc. Basically, the secondary productivity of an ecosystem represents the entire energy flow system through various topics levels. 

It is the energy percentage that each trophic level’s consumer tissues store within them. 

Primary consumer-

Terrestrial-Herbivores (key industry animal) of ecosystem, cow, grazing cattle, rabbit, They are also known as secondary producers as they synthesize complex materials in the cells, by the digestion of food which is obtained from the plant.

 Aquatic- common mollusca, tadpole and mosquito, zooplankton

 Secondary consumers or primary carnivores:

Those animals which feed upon primary consumers and obtain food. Those carnivores which kill and eat the herbivores, are called predators.

Terrestrial-  E.g. Dog, cat, snake. 

Aquatic-Hydra,frog, whale, and some small fish are secondary consumers. It is an example of a filter because it feeds on plankton.

Top (tertiary) consumers: Those animals which kill other animals and eat them, but they are not killed & eaten by other animals in nature are called tertiary consumers.

Terrestrial- E.g. Lion, man, peacock. 

 Aquatic- large fish

Unit of Productivity of an Ecosystem

Productivity = units of mass/ unit surface or volume per unit time. 

Energy Movements between Different Trophic Levels

Energy flow is the key function of an ecosystem.

It is determined by two basic laws of thermodynamics. First law of thermodynamics states that energy is neither created nor destroyed, but can be transferred from one component to another, or transformed from one state to another. Second law of thermodynamics states that every energy transformation involves degradation or dissipation of energy from a concentrated to a dispersed form due to metabolic functions, so that only a small part of energy is stored in the biomass.

Light falling on the plants is trapped by the producers in the presence of Mg++containing green pigment called chlorophyll and is used in assimilating the organic food called glucose by the process of photosynthesis. By photosynthesis, radiant energy of sunlight is transformed into potential energy of foodstuffs. Evidence shows that only a part of energy is trapped by the producers while the rest of energy is dissipated.

The energy conserving efficiency is– 1.15% for grasslands, 0.9% for Savannah, 0.8% for mixed forests, 5% for modern crops and 10-20% for sugarcane fields. The green plants or producers break down a part of organic food in respiration to obtain chemical energy for various body functions and overcoming entropy. Dissipation of energy  occurs as heat. The remaining energy is used in the synthesis of plant biomass called net photosynthesis which is then available to the next trophic level of food chains. This loss is not due to the inefficiency of the photosynthetic mechanism of the plants but due to the operation of the second law of thermodynamics.

Modal for energy flow-

  The amount of energy available decreases from step to step. Only about 10% of the biomass is transferred from one trophic level to the next one in a food chain. And only about 10% chemical energy is retained at each trophic level. This is called the 10% law of Lindeman (1942). When the food chain is short, the final consumers may get a large amount of energy. But when the food chain is long, the final consumer may get a lesser amount of energy.

Free energy travels from different trophic levels when an organism eats the organic molecules from the body of another organism.

The efficiency of energy transfer between different trophic levels is not that great. In fact, only 10% of the energy from one trophic level in the form of biomass reaches the next trophic level. It implies that energy transfers from primary producers and consumers only. 

Factors that Affect the Productivity of an Ecosystem 

Here are a few factors that affect the productivity of an ecosystem: 

Solar radiation:  With the increase in solar radiation, productivity increases.

Temperature: The most productive ecosystem can be found close by the equator terrestrial region. 

Moisture: Elements like soil moisture, precipitation fluctuation and transpiration, and leaf water potential rely upon the surrounding environment’s moisture content. 

Mineral nutrition: There is an increase in productivity due to the high mineral content uptake from the soil as well as the presence of nitrogen metabolism. However, the availability of heavy metals and salinity reduces the productivity of an ecosystem. 

Biotic activities: Herbivores who live above as well as below the ground parasites and predators decrease the level of primary productivity. 

Human population:

There is a reduction in productivity due to population increase as it causes a reduction in greenery. The lower parts do not get enough light and nutrition in aquatic ecosystems. Hence there is a hindrance to productivity. We can call the aquatic environment the least productive ecosystem. 

Conclusion

Here we learned about different types of ecological productivity and how energy transfers between various trophic levels of our ecosystem. Knowing about the factors that affect the productivity of an ecosystem is important, as well as the formula productivity unit we mentioned in the above article.