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Productivity within trophic levels

Productivity within an ecosystem can be defined as the percentage of energy entering the ecosystem incorporated into biomass in a particular trophic level. Biomass is the total mass, in a unit area at the time of measurement, of living or previously living organisms within a trophic level. Ecosystems have characteristic amounts of biomass at each trophic level. For example, in the English Channel ecosystem the primary producers account for a biomass of 4 g/m 2 (grams per meter squared), while the primary consumers exhibit a biomass of 21 g/m 2 .

The productivity of the primary producers is especially important in any ecosystem because these organisms bring energy to other living organisms by photoautotrophy or chemoautotrophy. The rate at which photosynthetic primary producers incorporate energy from the sun is called gross primary productivity    . An example of gross primary productivity is shown in the compartment diagram of energy flow within the Silver Springs aquatic ecosystem as shown ( [link] ). In this ecosystem, the total energy accumulated by the primary producers (gross primary productivity) was shown to be 20,810 kcal/m 2 /yr.

Because all organisms need to use some of this energy for their own functions (like respiration and resulting metabolic heat loss) scientists often refer to the net primary productivity of an ecosystem. Net primary productivity is the energy that remains in the primary producers after accounting for the organisms’ respiration and heat loss. The net productivity is then available to the primary consumers at the next trophic level. In our Silver Spring example, 13,187 of the 20,810 kcal/m 2 /yr were used for respiration or were lost as heat, leaving 7,632 kcal/m 2 /yr of energy for use by the primary consumers.

Ecological efficiency: the transfer of energy between trophic levels

As illustrated in [link] , large amounts of energy are lost from the ecosystem from one trophic level to the next level as energy flows from the primary producers through the various trophic levels of consumers and decomposers. The main reason for this loss is the second law of thermodynamics, which states that whenever energy is converted from one form to another, there is a tendency toward disorder (entropy) in the system. In biologic systems, this means a great deal of energy is lost as metabolic heat when the organisms from one trophic level consume the next level. In the Silver Springs ecosystem example ( [link] ), we see that the primary consumers produced 1103 kcal/m 2 /yr from the 7618 kcal/m 2 /yr of energy available to them from the primary producers. The measurement of energy transfer efficiency between two successive trophic levels is termed the trophic level transfer efficiency (TLTE)    and is defined by the formula:

TLTE  =   production at present trophic level production at previous trophic level  × 100

In Silver Springs, the TLTE between the first two trophic levels was approximately 14.8 percent. The low efficiency of energy transfer between trophic levels is usually the major factor that limits the length of food chains observed in a food web. The fact is, after four to six energy transfers, there is not enough energy left to support another trophic level. In the Lake Ontario example shown in [link] , only three energy transfers occurred between the primary producer, (green algae), and the apex consumer (Chinook salmon).

Questions & Answers

What is the Molecular Biology?
Service Reply
The branch of biology that deals with the structure and function of the macromolecules (e.g. proteins and nucleic acids) essential to life.
Sam
what is the difference between mitosis and meiosis?
Fatima Reply
what is an element
Saidu Reply
Element is any one of the simplest chemical substances that cannot be decomposed in a chemical reaction.
Lucky
an element is a substance that cannot be broken down into any other substance
Akosua
explain why only one sperm fertilisers the ovum
Frazzy Reply
its because other sperms are destroyed on the way
Nasib
what is cell
Dau Reply
Cell is the smallest unit of life
Yodit
cell refers of the basic, structural and function unit of an organism
jacob
smallest functional unit of an organism
Nasib
explain for me for ecological factors affecting each of aquatic and terrestrial habitats
Ikeh Reply
Temperature, high humidity
Afriyie
50%
Yodit
temperature,light intensity,Co2
Nasib
what's meosis
Umoke Reply
meiosis this is the type of cell division which reduces the number of chromosomes in order to form a gamete
Caren
meiosis refers to the form of cell division in which a cell divides into four daughter nuclei each containing the same number of chromosomes as the parent cell
Bigenis
yes
Marah
cell division where one cell sprits into 4 daughter cells each having half number of chromosomes as parent cell
Nasib
The end of the linear chromosomes are maintained by
birabwa Reply
Gene
Afriyie
Telomerase
birabwa
is the process of undigested food in body
Enoch Reply
Hi
Afriyie
hello
birabwa
hi
Boame
Hello
kanahiya
What is biology
Hope Reply
What is DNA in full
birabwa
Deoxyribo Nucleic Acid
ibrahim
deoxyibonucleic acid
jacob
Deoxyribonucleic acid
Afriyie
is the study of living things and their interactions with the environment
jacob
is the energy production of studying in life (every living things)
Enoch
de-oxybonuclic acid
Fafali
Biology is the study of life.
Euchy
Biology is the study of plant, animal and it's environment
Eze
biology is the branch of science that deal with plants and living organism
Dominic
what's the difference between bi-enial crops and perennial crops
Johnson Reply
Bi-enial crops are crops that live/exist/can last for as long as 2 years while perennial crops are crops that are evergreen and can last eternity or an inestimable amount of time.
Joanna
what isrespiration
Massa Reply
Mg is very important part of enzymes which deal with DNA. It is a very simple reason but overlooked.
Eric Reply
what mitochondria means
ADEDAYO Reply
its is the most universal organelle among eukaryotes,it is surrounded by double membrane and in it are foldings and invaginationscalled cristae where areobic respiration takes place
Alex
an organelle found in large number in most cell ,in which the biochemical process of respiration and energy production occur
jacob
Mitochondria is the power house of a cell
Joanna
is the energy production in a female hormones
Enoch
how does a cell look like
Clara Reply

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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