Ecosystem

The decomposers like fungi and bacteria are heterotrophs i.e., they are not able to prepare their own food and they are saprotrophs as it depends on dead and decaying material. They are not autotrophs as they can not make their own food like plants and they are also not chemo-autotrophs as they cannot use inorganic energy sources to synthesize food from carbon dioxide.

Thus, decomposers like fungi and bacteria are heterotrophs and saprotrophs.

Mineralization is defined as the process by which humus is degraded further by the action of the microbes, this leads to the release of inorganic nutrients from humus. The other options are incorrect as mineralization by microorganisms only helps in the release of inorganic humus.

Productivity is the amount of biological mass produced in a given ecosystem. It expressed in units of mass per unit volume) per unit time. Here in the given options, the correct units which are expressed are g–2 yr–1 and (kcal m–2) yr–1. The rest of the given options are incorrect.

The inverted pyramid signifies that the number of consumers is more than the producers. In the case of the marine ecosystem, the food chain in the marine ecosystem is generally depicted as Phytoplankton → zooplankton → predatory fish. Now, the total biomass of zooplankton is greater than that of phytoplankton because the life span of zooplanktons are longer and phytoplankton multiply at a much faster rate but they have a shorter lifespan. Therefore, a single generation of zooplankton can consume a number of generations of phytoplankton. Also, the biomass of the fish is larger because the fishes are larger in size and they have a longer lifespan and thus they can consume a generation of zooplankton.

Therefore increases from Phytoplankton → zooplankton → predatory fish and we obtain an inverted pyramid.

Agaricus is a fungus which is not a producer as it is non-photosynthetic. Thus, they are not able to make their own food unlike the other options – Spirogyra, Volvox and Nostoc. The other options are all able to produce their own food.

The Estuaries are the most productive in terms of net primary production as they are very much diverse and they have the highest productive biomass as compared to the other options. The Algal beds and reef-based ecosystem (i.e., Estuaries) have an average productivity rate of 2500g/m²/yr.

The pyramid of numbers can be upright or inverted depending upon the ecosystem. For example, In the grassland ecosystem, the pyramid of numbers is upright whereas in case of marine ecosystem the pyramid of numbers is inverted.

About 2-10% of the solar energy which falls on the leaves of a plant is converted into chemical energy by the process of photosynthesis. The other options are incorrect as the values are either very low or very high. The optimum percentage should be between 2-10%.

The tropical forest receives less solar radiation and the soil in these regions are very rich in minerals and humus so, the moisture and the temperature conditions of these environments are very much favourable for high microbial activity and the presence of leaves and other organic components makes the decomposition rate higher and faster.

The net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores is 10%. As per the 10 percent rule the herbivores utilize 10% of their net primary productivity and pass it on to the next tropic level while the rest of the 90% is used up in metabolic activities like breathing, thermoregulation, osmoregulation, etc.

The successive replacement of communities that results in gradual changes in the species composition of a given area to attain the climax stable community is called ecological succession.

It is the final stable community which appears in an area at the end of biotic succession, which is well adapted according to the climate.

Only the Carbon and Oxygen cycle is affected by the process of respiration.

Pioneer species in hydrosere is plankton which is followed by various stages to attain climax stage which lives in harmony with the climate.

Nutrients cycle is of two types-

a. Gaseous nutrient cycle- reservoir exists in the atmosphere. E.g. Nitrogen, Carbon.

b. Sedimentary nutrient cycle- reservoir is present in Earths crust.

If CO₂ fixed by producers is passed through other three species then it can be said that total four trophic levels are involved , fourth trophic level is occupied by the tertiary consumer.

Characterised by very high temperature at day time and very less precipitation (rainfall).

Based upon the availability of light, aquatic habitat is categorised into four zones- littoral zone, pelagic zone, lentic zone and benthic zone.

Littoral zone represents the coastal region which is exposed to light, air and immersed in water.

It includes the texture of soil, mineral composition, topography and pH of soil.

Ecosystem provides wide range of economic, enviormental and aesthetic services.

Siluriformes or Catfish are a secondary carnivorous organism in an aquatic ecosystem. It feeds on primary consumers for its energy. The Catfish is a predator of many fishes and small aquatic organisms like zooplankton and phytoplankton. They are purely carnivorous (i.e., meat-eating) organisms.

The base tier of the ecological pyramid represents the producers in an ecosystem. Producers are the organisms which make their own food. For example, plants are producers. Producers are the organisms from which further higher tropic levels arise which are known as consumers.

A particular stage in the process of succession revert back to an earlier stage when there occurs a natural calamity like earthquakes, landslides, volcanic eruptions or human-induced activities like fire, deforestation etc.

The vertical stratification of a forest signifies the vertical layering of a given ecosystem. It is the classification of vegetation in accordance to the plant height. Here the forest vertical stratification order is : Grass, Amaranths, Shrubby plants, Teak. The grass is the smallest in height whereas the teak trees are the highest in height.

Crow is a very common example of an omnivore which is present in the grazing food chain and it is also present in the decomposer food chain. Crow is able to obtain food from both grazing and decomposing food material.

Pitchers plants have the green pigments known as chlorophyll and therefore, they are photosynthetic. Being photosynthetic they can prepare their own food. This characteristic makes them producers. But they grow in the soil which is either nutrient deficient or too acidic. To compensate for the soil nutrition deficiency and acidity, they prey upon the insects and obtain the necessary nutrients and minerals for their survival.

Examples of two organisms which can occupy more than one trophic level in an ecosystem are Human and sparrow. They are both omnivorous and thus, they can be categorized under herbivorous as well as carnivorous organism. Therefore, they occupy two trophic levels at the same time.

When the forests are cleared by burning and left for regrowth after a year of cultivation it has been observed that the soil nutrient levels have increased. This is due to the increased microbial activity which improves the soil quality by increasing inorganic minerals content in the soil. This phenomenon is known as secondary succession.

In primary succession, the process begins from a bare rock whereas during the secondary succession the soil is already left behind containing nutrients and minerals. Thus, the succession in secondary succession is much quicker than primary succession.

• Lichens are the pioneer species, which are the first to invade the bare land.

• Lichen releases acidic chemicals which cause weathering in rocks.

• Weathering results in formation of soil and releases minerals required for the growth of seral communities.

Solar energy is considered to be the primary source of energy.

Edible mushrooms belong to the Kingdom fungi, which are achlorophyllus and can’t synthesise their own food. Hence depends on other organisms for food, called heterotrophs.

Due to following reasons:

• Limited solar light.

• Limited nutrients present, especially Nitrogen.

• Highly saline water.

As the consumers assimilate primary products synthesised by producers, it results in formation of new organic mass. Therefore, the rate of production of organic matter by heterotrophs is called secondary productivity.

Biogeochemical cycle refers to the biological cycle in the geo i.e. rocks, air etc. It involves the cycling of nutrients.

Lithosere- takes place on rocks

Psammosere- takes place on the sandy habitat

The ability of ecosystem to maintain itself is termed as self sustainability.

I) It is showing Tropical deciduous ecosystem

II) E.g. Amla, Palas tree etc.

All these organisms are detrivore, a part of DFC.

The organisms at a higher level have less energy available as compared to the lower trophic level organism. This can be explained by the 10 percent law which states that each successive higher trophic level organism transfers 10% of its energy and the rest of the 90% energy is consumed for various metabolic processes like respiration, thermoregulation, osmoregulation, etc.

In the ecosystem in each successive trophic level, there is a 10 percent transfer of energy. As the number of trophic levels starts to increase in an ecosystem the energy starts to decrease as well. So, after a few trophic levels, the energy becomes zero and thus the trophic level succession stops and therefore, the number of trophic levels in an ecosystem are limited.

A complete ecosystem can be defined as the community of abiotic and biotic components interacting with each other. An aquarium consists of all the biotic components like bacteria, plants, small aquatic organisms, etc and abiotic components like water, light, temperature, oxygen in the water, non-living decoration, the filter, substrate, etc. Thus, it is a complete ecosystem.

The tropics receive less solar radiation and the moisture the level is high in these regions and soil is very rich in minerals and humus so, the moisture and the temperature conditions of these environments are very much favourable for high microbial activity and the presence of leaves and other organic components make the decomposition rate higher and faster.

Two major human activities which interfere with the carbon cycle is:

i) Deforestation of trees: The deforestation of trees means less production of oxygen in the air as well as less consumption of carbon dioxide from the atmosphere by the trees. Thus, carbon levels would rise.

ii) Rapidly burning of fossil fuels: The fossil fuels like coal, petroleum, etc are used for cooking and transport. These fossil fuels are burned and they emit carbon components in the environment which leads to an increase in carbon and interferes with the normal carbon cycle.

The flow of energy through the various trophic levels in an ecosystem starts with the producers which receive energy from the sun. The producers pass the energy to the next higher trophic level. Only 10% of the energy is passed and the rest is used by the organism itself for carrying out various metabolic processes such as respiration, osmoregulation, thermoregulation, etc. This energy cannot be passed back to the previous trophic level. Thus, it is only unidirectional and non-cyclic.

Micro-organisms are a group of heterotrophic organisms which are known as saprotrophs. They are responsible for the decomposition of the organic remains i.e., dead and decaying plants and animals in an ecosystem. The Micro-organisms obtain their energy requirements from the organic matter which is obtained by dead and decaying animals and plants.

Poaching of tigers would lead to the extinction of the organism. This would remove the predator species from the ecosystem and it will lead to an increase in the number of the tiger’s natural prey. The increase in the number of prey of tigers would cause an imbalance of the natural population of the preys. Therefore, the poaching of tigers would lead to an imbalance in the natural ecosystem.

Energy transfer in an ecosystem follows a ten percent rule which states that 10% of energy is transferred to the next trophic level. So, if the lion eats 10 kg of deer meat then only 10% energy would be passed to the lion i.e., 1 kg of lion’s flesh.

The primary productivity varies from ecosystem to ecosystem as it depends on the plant species and the environmental surrounding and its ability to carry out photosynthesis. It also depends upon other factors like soil conditions, moisture, temperature, etc.

Due to sudden climatic changes, sometimes the climax species form a pre climax stage, abiotic and biotic factor affects the sereal stage.

It is seen in seeds and vegetative propogules. Due to absence of favourable condition seeds don’t germinate forming a pre climax stage.

The ecosystem in which either a biotic or abiotic factor is absent is called an incomplete ecosystem.

e.g.- Benthic zone- It is the bottom most part of the water body where light isn’t available.

Limitations of ecological Pyramids;

a. It doesn’t take into account the same species belonging to two or more trophic level.

b. It assumes a simple food chain, which never operates in the world.

c. It doesn’t accommodate food web.

d. Saprophytes are not given place in the ecological pyramids.

Humification: It involves the formation of amorphous topmost layer of soil called the humus. Formed by degradation of soil.

Mineralisation: Humus degrades to release inorganic nutrients.

1) producers

2) Primary consumers

3) Secondary consumers

4) Tertiary consumers (Topmost carnivore)

• Decomposition is largely an oxygen requiring process.

• Plant material rich in cutin and lignin are difficult to decompose.

• High temperature and high humidity favours process of decomposition.

• Low pH reduces the growth of decomposer microbes, therefore the process of decomposition slows down.

The meaning of the above statements are different. Each expression means different meaning.

Explanation:

a. I have harvested 10 quintals of wheat.

This statement signifies the total amount of wheat harvested by the farmer i.e., Only the quantity of the wheat is given but the area and time in which it is harvested is not given.

b. I have harvested 10 quintals of wheat today in one acre of land.

This statement signifies the total primary production of wheat by the farmer and area i.e., the total yield of wheat of an area. The time taken to harvest the wheat is not given in this statement.

c. I have harvested 10 quintals of wheat in one acre of land, 6 months after sowing.

This statement signifies the total primary production of wheat by the farmer and the area and time period of its harvesting.

Gross Primary Productivity is defined as the rate of production of the organic matter during the photosynthesis in an ecosystem.

Gross Primary Productivity (GPP) is utilized by the plant during respiration. The 100% GPP only 10% is left for the next trophic level. 90% of the net GPP is utilized by the plant for metabolic activities like respiration, osmoregulation, and thermoregulation. Thus, the GPP utilized by the plants minus the metabolic activities i.e., respiration losses (R) is defined as the net primary productivity (NPP).

The ecosystem tends to increase the rate of Gross Primary Productivity (GPP) for producing more food from solar energy.

Whereas, Human tends to increase the Net Primary Productivity (NPP) to ensure that food is available for the human population.

Among the given ecosystems a young forest will be the most productive because primary productivity in an ecosystem depends upon the plant species in a given area and the rate of plant growth and number of plants growing.

So, a young forest has a higher rate of plant growth and it develops more rapidly as compared to a natural old forest. A shallow polluted lake and alpine meadow have a lower number of producers and therefore they have less productivity.

An ecological pyramid is a graphical representation which is used for showing the various ecological features like the number of individuals present at a trophic level, the amount of energy and the biomass at each trophic level.

The three types of ecological pyramids are:

i) Pyramid of number.

ii) Pyramid of biomass.

iii) Pyramid of energy.

The above can be explained further:

i) Pyramid of number:

• It is an ecological pyramid which represents the number of individual organisms at each trophic level in an ecosystem.

• Pyramid of numbers can be either upright or inverted.

ii) Pyramid of biomass:

• It is an ecological pyramid which represents the amount of organic matter present at each trophic level in an ecosystem.

• It can be either upright or inverted pyramid.

iii) Pyramid of energy:

• It is an ecological pyramid which represents the total amount of energy present at each trophic level in an ecosystem.

• It can be either upright or inverted pyramid.

i) Pyramid of number:

• It is an ecological pyramid which represents the number of individual organisms at each trophic level in an ecosystem.

• Pyramid of numbers can be either upright or inverted.

ii)Pyramid of biomass:

• It is an ecological pyramid which represents the amount of organic matter present at each trophic level in an ecosystem.

• It can be either upright or inverted pyramid.

The inverted pyramid signifies that the number of consumers is more than the producers. In the case of the marine ecosystem, the food chain in the marine ecosystem is generally depicted as Phytoplankton → zooplankton → predatory fish. Now, the total biomass of zooplankton is greater than that of phytoplankton because the life span of zooplanktons are longer and phytoplankton multiply at a much faster rate but they have a shorter lifespan. Therefore, a single generation of zooplankton can consume a number of generations of phytoplankton. Also, the biomass of the fish is larger because the fishes are larger in size and they have a longer lifespan and thus they can consume a generation of zooplankton.

Therefore increases from Phytoplankton → zooplankton → predatory fish and we obtain an inverted pyramid.

This linkage established is known as food web.

Food web is the interlocking between two or more types of food chains at different trophic levels, it results in a trophic level to serve as food for more than one organisms of same or different trophic levels.

• Second law of Thermodynamics states that energy can neither be created nor be destroyed, it can only be transformed from one form to another form.

• Energy flows in the ecosystem through external environment to the series of organisms back again to the external environment.

• During this process 90% of the energy is utilised by the each trophic level and only 10% energy is passed to next trophic level,

• The utilised energy later on transforms into heat.

A. If all the producers are removed, it will result in net zero primary productivity, therefore, no biomass would be available for the next trophic levels. This will result in death of all the organisms.

B. If all the herbivores are eliminated then organisms depending on herbivores (carnivores) will die. And as their will be no one to consume primary products, producers would flourish and primary productivity would increase.

C. If all the top carnivores are removed it will result in the increase in population of herbivore which would start to destroy producers and this will lead to ecological disbalance.

Man made ecosystem- Agricultural fields and Aquarium.

Man made ecosystem involves few organisms as compared to natural ecosystem which leads to comparatively low productivity.

Man made ecosystem requires proper input for maintenance whereas natural ecosystems are self sustainable.

• When one moves from pioneer species to the climax community, biodiversity increases.

• During ecological succession a stage is reached at which all the biotic species are in a state of fine balance among themselves and with the abiotic condition.

• These stable and suitable conditions help in niches specialisation therefore, it can be said that climax communities are more diverse.

The cyclic movement of nutrients from their reservoirs to the plants and then back to the reservoir is called biogeochemical cycle.

The function of biogeochemical cycle is to provide enough amount of nutrients to meet the deficit caused in the ecosystem due influx and efflux.

Phosphorus cycle is the example of sedimentary cycle.

• The reservoir of P is present in rocks.

• As the rocks weather, it releases phosphate dissolved in soil solution.

• Plant absorbs the PO₄^3- present in soil solution.

• Herbivores and other organisms gets P from plants.

• When they excrete or die, decomposed excreta or dead body releases P in the soil. In this manner P again comes back in soil and the cycle continues.

P/R ratio refer to Production/Respiration ratio, it represents the relationship between the productivity and its consumption. For a stable community P/R ratio = 1.

For Pioneer species P/R >1, in order to establish a community organic matter is needed to be accumulated.

For climax communities P/R=1. Climax communities being stable, utilise all the products.