Food chains (ecosystem)

ECOSYSTEM - Food chains  

   An ecosystem consists of structural and functional components. The structural components consist of abiotic and biotic factors.

BIOTIC FACTORS

Biotic factors are producers, consumers and decomposers.

Producers

According to ecosystem green plants are called producers. They prepare food by their own using sunlight (solar energy). Hence, they are known as autotrophs. Certain bacteria fix the CO₂ by breaking down of certain chemical substances.  E.g.: Iron and sulphur bacteria. They are called as chemoautotrophs. The producers are the first trophic level in most food chains. They constitute the main source of food for the organisms of the second or next higher trophic level the ‘consumers’.

Example: herbaceous and woody plants in the terrestrial ecosystem, Microscopic phytoplanktonic organisms, algae some higher plants in the Aquatic ecosystem.

Consumers

The consumers are dependent either directly or indirectly on producers for food. Hence, they also known as heterotrophs.   Consumers are further categorised into primary consumers who feed upon producers (e.g.: deer, insect, iguana, horse etc.). They also called as herbivores. Secondary consumers are those feed upon primary consumers, also called primary carnivores (e.g.: frog feed upon insects).  Tertiary consumers feed upon secondary consumers, also called secondary carnivores (e.g.: snakes feed upon frogs).

Decomposers

Decomposers feed upon the detritus (dead decaying matter). E.g.: Earthworm. They breakdown complex organic matter into simple inorganic substances like carbon dioxide, water and nutrients and the process called decomposition.

detritus : It is the raw material for decomposition. It constitutes plant parts such as leaves, bark, flowers and dead remain of animals, including faecal matter.

Example: Earthworms, these are often called as “farmer’s friend”.  These help in the breakdown of complex organic matter as well as in loosening of the soil (making the soil pores). Hence, these are known as Detritivores. The process of decomposition involves the following steps:

1.   Fragmentation: Break down of complex particles into small fragments. This process is called fragmentation.

2.   Leaching:  In this process the water-soluble inorganic nutrients go down into the soil and get precipitated as unavailable salts.

3.   Catabolism: Breakdown of complex particles into smaller particles is called catabolism.  In this process bacterial and fungal enzyme degrade detritus into simpler particles.

4.   Humification: it leads to accumulation of dark coloured amorphous substance called humus. It is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.  

5.   Mineralization: the humus is further degraded by some microbes and release of inorganic nutrients occurs by the process known as mineralization.            

Generally, food chains end with decomposers.

 https://www.youtube.com/watch?v=REU1n_esNeM&feature=youtu.be

FOOD CHAINS

There will be transfer of energy in the form of food from one organism to other organism, this process is called food chain. Simply says organisms ‘who eats whom’ is called a Food chain.

E.g.:    Grass      -      Deer       -     Lion

               (producer)   (herbivore)  (carnivore)

     Primary             secondary

       consumer         consumer

In the above example we observe producers are the starting point of the food chain. Primary consumer dependent upon producer for food while secondary consumer feed upon primary consumer.

          A food chain represents a unidirectional transfer of energy. It couldn’t be in reverse direction (lion à deer), deer cannot feed upon lion.  The study of food chains helps us knowing various interactions among organisms, their habitat and also their interdependence.

          Energy flows into biological systems(ecosystems) from the Sun. The biological systems of environment include several food levels called Trophic levels. Trophic level means the position in which organism is present i.e., what it eats and what eats it.

           A trophic level is composed of those organisms which have the same source of energy and having the same number of steps away from the sun.

FIRST TROPHIC LEVEL	Producers		Autotrophs	E.g.: plants
SECOND TROPHIC LEVEL	Primary consumers	Herbivores	Heterotrophs	e.g.: Insect
THIRD TROPHIC LEVEL	Secondary consumers	Primary carnivores	Heterotrophs	e.g.: Frog
FOURTH TROPHIC LEVEL	Tertiary consumers	Secondary carnivores	Heterotrophs	e.g.: Snake

         An organism may occupy more than one trophic level simultaneously                                                               

E.g.:  Sparrow is a primary consumer when it eats seeds, leaves, fruits and a secondary consumer when it eats insects and worms.

   

Types of food chains:

1.    Grazing food chain

2.    Parasitic food chain

3.    Detritus food chain

The two main food chains are Grazing and detritus food chain.

1.                Grazing food chain:

  Photosynthetic organisms come under this type. They are source for the next trophic level primary consumers. The secondary consumers which is above to this trophic level dependent on primary trophic level. This continues up to tertiary and quaternary trophic levels.

In this process the living organisms gain energy by consuming food from their respective trophic level.

These are multiple and interconnecting pathways, as well as number of species participated at each trophic level. These show interrelation among different species. These complex pathways resemble  a web rather than a simple chain. Hence, are referred to as food webs.  It represents a picture like a web showing energy transfer among organisms at each trophic level.

Food web

Difference between food chain and food web

Detritus food chain:

It begins with dead organic matter(detritus) and goes from non- living organisms to detritivores and their predators.

The large amount of organic matter is generated by the death of plant’s parts, animals and their excretion products of all ecosystems. Hence this food chain is present in all ecosystems. These are also known as saprotrophs (sapro: to decompose).

Plants prepare food by the process called photosynthesis.

6CO₂         +             6H₂O     ---->      C₆H₁₂ O₆         +        6O­₂

Carbon dioxide     water                carbohydrate      oxygen

The difference between these two trophic levels is in the flow of energy. In the GFC the flow of energy is in unidirectional. In detritus food chain the flow is recycled. It is not in unidirectional. The flow of energy in dingle food chain is termed as the single channel energy flow model. In all the ecosystems the GFC and DFC are interconnected. Not all the food is completely digested and absorbed, it is diverted to faecal matter or detritus pathway. The two-channel energy flow model explains the interconnection between GFC and DFC. It is also termed as Y-shaped model as given below.

Difference between grazing food chain and detritus food chain

Parasitic food chain:

    This is also referred to as GFC. The energy flows from large to small organisms. 

For example, trees (1^st trophic level) provides shelter and food to the successive trophic levels.  The organisms in the trophic host many ecto and endo parasites. Hence, by this way the energy is transferred from large organisms sized (trees) to small sized (parasites) organisms.

Energy flow: 

    The energy flow in the ecosystem is consistent with the two basic laws of thermodynamics. According to 1^st law of Thermodynamics

 Energy flows continuously

 from one body to other body. It is neither created nor destroyed. This is also called as law of conversation of energy. The energy is being transferred among different trophic levels.

 The source of energy obtains from sun light called solar energy.  This consumption starts from producers which occupies the 1^st trophic level.  Plants prepare their food by the process of photosynthesis. In this process solar energy is converted to chemical energy. In this process the energy is same but does not change. It is emitted as heat energy which is also utilised by photosynthetic organisms.

 According to 2^nd law of thermodynamics energy flow is not 100% efficient some energy is lost as heat. It states that the energy transfer will increase the entropy of the universe.