GEOGRAPHY (UG), SEM - VI, PAPER - DSC - 3T : SOIL AND BIO ...

GEOGRAPHY (UG), SEM - VI, PAPER - DSC - 3T : SOIL AND BIO-GEOGRAPHY, (CONCEPT OF TROPIC STRUCTURE & FOOD CHAIN AND FOOD WEB)

The concept of trophic level was developed by Raymond Lindeman (1942), based on the terminology of AugustThienemann(1926): "producers", "consumers" and "reducers" (modified to "decomposers" by Lindeman).

A trophic level is the group of organisms within an ecosystem which occupy the same level in a food chain.

GEOGRAPHY (UG), SEM - VI, PAPER - DSC - 3T : SOIL AND BIO-GEOGRAPHY, (CONCEPT OF TROPIC STRUCTURE)

Energy moves from one organisms to another when it is eaten.

Each step in this transfer of energy is know as a trophic level.

The main trophic levels are Producers, Consumers, and Decomposers.

Each step in a food chain or food web is called a trophic level.

Primary producers always make up the first trophic level.

Various consumers occupy every other level. Some examples are

shown.

TROPHIC LEVELS


Trophic levels can be represented by numbers, starting at level 1 withplants. Further trophic levels are numbered subsequently according to howfar the organism is along the food chain.

Level 1: Plants and algae make their own food and are called primaryproducers.

Level 2: Herbivores eat plants and are called primary consumers. Level 3:Carnivores which eat herbivores are called secondary consumers.

Level 4: Carnivores which eat other carnivores are called tertiaryconsumers.

Level 5: Apex predators which have no predators are at the top of the foodchain

Trophic Level Where It Gets Food Example

1st Trophic Level: Producer Makes its own food Plants make food

2nd Trophic Level: Primary Consumer Consumes producers Mice eat plant seeds

3rd Trophic Level: Secondary ConsumerConsumes primary consumers

Snakes eat mice

4th Trophic Level: Tertiary ConsumerConsumes secondary consumers

Hawks eat snakes


There are five main trophic levels within a food chain, each of which differs in its nutritional relationshipwith the primary energy source.

First trophic level: The solar radiation from the Sun provides the input of energy which is used by

autotroph or Primary producers. Primary producers are usually plants and algae, which perform Photosynthesis inorder to manufacture their own food source. Primary producers make up the first trophic level.

In terrestrial ecosystems, almost all of the primary production comes from vascular plants such as trees,ferns, and flowering plants. In marine ecosystems, algae and seaweed fill the role of primary production.

There are also some deep-sea primary producers that perform oxidization of chemical inorganic compoundsinstead of using photosynthesis; these organisms are called ”chemoautotrophs”.

Producers

Quaternary Consumers

Tertiary Consumers

Secondary Consumers

Primary Consumers



Second trophic level: The consists of herbivores (Consumers), these organisms gain energy by eating primary

producers, they cannot produce their own food and are called primary consumers.Herbivores are generally split into two categories: grazers, such as cows, sheep and rabbits, whose diets consist at least

90% of grass, and browsers, such as deer and goats, whose diets consist at least 90% of tree leaves or twigs.Primary consumers may also consume other forms of plant material. Many bats, birds and monkeys eat fruit

(frugivores); birds, insects, bats and arachnids (spiders) eat nectar (nectarivores); and termites and beetles eat wood(xylophages).

In marine ecosystems, primary consumers are Zooplankton, tiny crustaceans which feed off photosynthesizing algaeknown as Phytoplankton.


Third trophic level: The consists of carnivores (Consumers) which eat herbivores; these are the secondary

consumers. This includes animals and carnivorous plants that feed on herbivorous insects (insectivores).Secondary consumers are usually small animals, fish and birds such as frogs, weasels, and snakes, although larger

apex predators, such as lions and eagles, may consume herbivores, and can also exist within the second trophic level of an ecosystem.

In marine ecosystems, all species that consume zooplankton are secondary consumers; this ranges from jellyfish to small fish such as sardines and larger crustaceans such as crabs and lobsters, as well as whales, which filter feed, and basking sharks.


Consumer categories based on

material eaten (plant: green

shades are live, brown shades

are dead; animal: red shades are

live, purple shades are dead; or

particulate: grey shades) and

feeding strategy (gatherer: lighter

shade of each color; miner:darker shade of each color)


Fourth trophic level: The contains omnivores (Consumers) which

eat secondary consumers (carnivores) and are known as tertiary consumers.Owls are an example of tertiary consumers; although they feed off

mice and other herbivores, they also eat secondary consumers such asstoats. In turn, owls may be hunted by eagles and hawks, and are thereforenot apex predators.

Fifth trophic level: The consists of apex predators; these animals

have no natural predators and are therefore at the top of the food chain.Decomposers or detritivores are organisms which consume dead plant andanimal material, converting it into energy and nutrients that plants can usefor effective growth. Although they do not fill an independent trophic level,decomposers and detritivores, such as fungi, bacteria, earthworms andflies, recycle waste material from all other trophic levels and are animportant part of a functioning ecosystem.

Energy is lost with each trophic ~90% is released to the environment as heat

~10% of the energy is used

Only about 10% of the

energy from one level is

passed on to the next level



The definition of the trophic level, TL, for any consumer species i is –

𝑻𝑳𝒊 = 𝟏 + 𝒊 𝑻𝑳𝒋 −𝑫𝑪𝒊𝒋

where TLi is the fractional trophic level of the prey j, and DCij represents the fraction ofj in the diet of i.

In the case of marine ecosystems, the trophic level of most fish and other marineconsumers takes value between 2.0 and 5.0. The upper value, 5.0, is unusual, even forlarge fish, though it occurs in apex predators of marine mammals, such as polar bearsand killer whales.

There is a very definite limit to the number of possible links in a food chain, andconsequently also to the number of trophic levels in any ecosystem. The reason forthis is that only about 10 percent of the available energy is assimilated in passingfrom one trophic level


The mean trophic level of the world fisheries catch has steadily declinedbecause many high trophic level fish, such as this tuna have been overfished.

In fisheries, the mean trophic level for the fisheries catch across an entire area

or ecosystem is calculated for year y as:

𝑻𝑳𝒚 = 𝒊 𝑻𝑳𝒊 − 𝒀𝒊𝒚

𝒊𝒀𝒊𝒚where Yiy is the catch of the species or group i in year y, and TLi is the fractional

trophic level for species i as seen earlier. It was once believed that fish at higher trophic levels usually have a higher

economic value; resulting in overfishing at the higher trophic levels. Earlierreports found precipitous declines in mean trophic level of fisheries catch, in aprocess known as fishing down the food web.


(a)What is a trophic level in an ecosystem? What is 'standing crop' withreference to it?

(b)What are trophic levels? Give an example of a food chain and state thedifferent trophic levels in it.

(c)Explain the role of the 'first trophic level' in an ecosystem.(d)Explain how energy limits the number of trophic levels in a food chain or

web.


Odum, W. E.; Heald, E. J. (1975) "The detritus-based food web of an

estuarine mangrove community". Pages 265–286 in L. E. Cronin,

ed. Estuarine research. Vol. 1. Academic Press, New York.Gorlova, E. N.; Krylovich, O. A.; Tiunov, A. V.; Khasanov, B. F.; Vasyukov, D. D.;

Savinetsk y, A. B. (March 2015). "Stable-Isotope Analysis as a Method ofTaxonomical Identification of Archaeozoological Material". Archaeology, Ethnologyand Anthropology of Eurasia. 43 (1): 110–121.

Pauly, D.; Christensen, V; Walters, C. (2000). "Ecopath, Ecosim and Ecospace as toolsfor evaluating ecosystem impact of fisheries". ICES J. Mar. Sci. 57 (3): 697–706.

Preisser, E. (2008). Trophic Structure. Encyclopedia of Ecology, 3608–3616.

GEOGRAPHY (UG), SEM - VI, PAPER - DSC - 3T : SOIL AND BIO-GEOGRAPHY, (CONCEPT OF TROPIC STRUCTURE & FOOD CHAIN AND FOOD WEB)

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