Ecosystem :
An ecosystem is a biological environment consisting of all the
organisms living in a particular area, as well as all the nonliving, physical
components of the environment with which the organisms interact, such
as air, soil, water, and sunlight. It is all the organisms in a given area,
along with the nonliving (a biotic) factors with which they interact; a
biological community and its physical environment.
The entire array of organisms inhabiting a particular ecosystem is
called a community. In a typical ecosystem, plants and other
photosynthetic organisms are the producers that provide the food.
Ecosystems can be permanent or temporary. Ecosystems usually form a
number of food webs.
Ecosystems are functional units consisting of living things in a
given area, non-living chemical and physical factors of their environment,
linked together through nutrient cycle and energy flow.
Central to the ecosystem concept is the idea that living organisms interact
with every other element in their local environment. Eugene Odum, a
founder of ecology, stated: "Any unit that includes all of the organisms
(ie: the "community") in a given area interacting with the physical
environment so that a flow of energy leads to clearly defined trophic
structure, biotic diversity, and material cycles (i.e.: exchange of materials
between living and nonliving parts) within the system is an ecosystem.
A population is all the organisms that both belong to the same species
and live in the same geographical area. The area that is used to define the
population is such that inter-breeding is possible between any pair within
the area and more probable than cross-breeding with individuals from
other areas. Normally breeding is substantially more common within the
area than across the border.
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In biological terms, a community is a group of interacting species
sharing a populated environment. In human communities, intent, belief,
resources, preferences, needs, risks, and a number of other conditions
may be present and common, affecting the identity of the participants and
their degree of cohesiveness.
A habitat (which is Latin for "it inhabits") is an ecological or
environmental area that is inhabited by a particular species of animal,
plant or other type of organism. It is the natural environment in which an
organism lives, or the physical environment that surrounds (influences
and is utilized by) a species population.
Components of an Ecosystem
You are already familiar with the parts of an ecosystem. You have
learned about climate and soils from past lectures. From this course and
from general knowledge, you have a basic understanding of the diversity
of plants and animals, and how plants and animals and microbes obtain
water, nutrients, and food. We can clarify the parts of an ecosystem by
listing them under the headings "abiotic" and "biotic".
A biotic
Biotic
Sunlight
Primary producers
Temperature
Herbivores
Precipitation
Carnivores
Water or moisture
Omnivores
Soil or water chemistry (e.g., P, NH4+)
Detritivores
Etc.
etc.
All of these vary over space/time
By and large, this set of environmental factors is important almost
everywhere, in all ecosystems.
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Usually, biological communities include the "functional groupings"
shown above. A functional group is a biological category composed of
organisms that perform mostly the same kind of function in the system;
for example, all the photosynthetic plants or primary producers form a
functional group. Membership in the functional group does not depend
very much on who the actual players (species) happen to be, only on what
function they perform in the ecosystem
An autotroph:, also called a producer, is an organism that produces
complex organic compounds (such as carbohydrates, fats, and proteins)
from simple inorganic molecules using energy from light (by
photosynthesis) or inorganic chemical reactions (chemosynthesis). They
are the producers in a food chain, such as plants on land or algae in water.
They are able to make their own food and can fix carbon. Therefore, they
do not utilize organic compounds as an energy source or a carbon source.
Autotrophs can reduce carbon dioxide (add hydrogen to it) to make
organic compounds. The reduction of carbon dioxide, a low-energy
compound, creates a store of chemical energy. Most autotrophs use water
as the reducing agent, but some can use other hydrogen compounds such
as hydrogen sulfide. An autotroph can produce its own energy through
photosynthesis through the inputs of light, carbon dioxide and H 2O.
Autotrophs can be phototrophs or lithotrophs (chemoautotrophs).
Phototrophs use light as an energy source, while lithotrophs oxidize
inorganic compounds, such as hydrogen sulfide, elemental sulfur,
ammonium and ferrous iron. Phototrophs and lithotrophs use a portion of
the ATP produced during photosynthesis or the oxidation of inorganic
compounds to reduce NADP+ to NADPH in order to form organic
compounds.
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A heterotroph : is an organism that cannot fix carbon and uses
organic carbon for growth. This contrasts with autotrophs, such as plants
and algae, which can use energy from sunlight (photoautotrophs) or
inorganic compounds (lithoautotrophs) to produce organic compounds
such as carbohydrates, fats, and proteins from inorganic carbon dioxide.
These reduced carbon compounds can be used as an energy source by the
autotroph and provide the energy in food consumed by heterotrophs.
1. Herbivores are organisms that are adapted to eat plants. Herbivory
is a form of predation in which an organism consumes principally
autotrophs. such as plants, algae and photosynthesizing bacteria.
More generally, organisms that feed on autotrophs in general are
known as primary consumers.
Herbivores form an important link in the food chain as they
consume plants in order to receive the carbohydrates produced by a
plant from photosynthesis.
2. Carnivores in turn consume herbivores . carnivore
meaning
'meat eater' is an organism that derives its energy and nutrient
requirements from a diet consisting mainly or exclusively of
animal tissue, whether through predation or scavenging. Animals
that depend solely on animal flesh for their nutrient requirements
are considered obligate carnivores while those that also consume
non-animal food are considered facultative carnivores.
3. Omnivores are species that eat both plants and animals as their
primary food source. They are opportunistic, general feeders not
specifically adapted to eat and digest either meat or plant material
primarily. Pigs are one well-known example of an omnivore.
Crows are another example of an omnivore that many people see
every day. Humans are regarded as omnivores.
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Decomposers (or saprotrophs) are organisms that break down dead or
decaying organisms, and in doing so carry out the natural process of
decomposition. Like herbivores and predators, decomposers are
heterotrophic, meaning that they use organic substrates to get their
energy, carbon and nutrients for growth and development. Decomposers
use deceased organisms and non-living organic compounds as their food
source. The primary examples are (Fungi , Bacteria ,Worm).
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Food chains :
Food chains and food webs are representations of the predator-prey
relationships between species within an ecosystem or habitat.
Many chain and web models can be applicable depending on habitat or
environmental factors. Every known food chain has a base made of
autotrophs, organisms able to manufacture their own food (e.g. plants,
chemotrophs).
Organisms represented in food chains
In nearly all food chains, solar energy is input into the system as light and
heat, utilized by autotrophs (i.e., producers) in a process called
photosynthesis. Carbon dioxide is reduced (gains electrons) by being
combined with water (a source of hydrogen atoms), producing glucose.
Water splitting produces hydrogen, but is a nonspontaneous (endergonic)
reaction requiring energy from the sun. Carbon dioxide and water, both
stable, oxidized compounds, are low in energy, but glucose, a highenergy compound and good electron donor, is capable of storing the solar
energy. This energy is expended for cellular processes, growth, and
development. The plant sugars are polymerized for storage as long-chain
carbohydrates, including other sugars, starch, and cellulose.
Glucose is also used to make fats and proteins. Proteins can be made
using nitrates, sulfates, and phosphates in the soil.When autotrophs are
eaten by heterotrophs, i.e., consumers such as animals, the carbohydrates,
fats, and proteins contained in them become energy sources for the
heterotrophs.
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Chemoautotrophy
An important exception is lithotrophy, the utilization of inorganic
compounds, especially minerals such as sulfur or iron, for energy. In
some lithotrophs, minerals are used simply to power processes for
making organic compounds from inorganic carbon sources.
In a few food chains, e.g., near hydrothermal vents in the deep sea,
autotrophs are able to produce organic compounds without sunlight,
through a process similar to photosynthesis called chemosynthesis, using
a carbon source such as carbon dioxide and a chemical energy sources
such as hydrogen sulfide, H2S, or molecular hydrogen, H2.
Unlike water, the hydrogen compounds used in chemosynthesis are high
in energy. Other lithotrophs are able to directly utilize inorganic
substances, e.g., iron, hydrogen sulfide, elemental sulfur, or thiosulfate,
for some or all of their energy needs.
Involvement in the carbon cycle
Carbon dioxide is recycled in the carbon cycle as carbohydrates, fats, and
proteins are oxidized (burned) to produce carbon dioxide and water.
Oxygen released by photosynthesis is utilized in respiration as an electron
acceptor to release chemical energy stored in organic compounds.
Dead organisms are consumed by detritivores, scavengers, and
decomposers, including fungi and insects, thus returning nutrients to the
soil.
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The sequence of eating and being eaten in an ecosystem is known as
the food chain. It is the path of transfer of food energy from the producers
through a series of organisms i.e herbivores to carnivores to decomposers.
There are three basic types of food chain as discussed below:
1.
Grazing food chain
2.
Detritus food chain
3.
Parasitic food chain
1. Grazing food chain: The primary producers are the living green plants
which are grazed on by grazing animals. It is found in aquatic and
grassland ecosystem.
E.g. of aquatic ecosystem
Phytoplankton →Zooplankton→ Fish→ Hawk
E.g. of grassland ecosystem
Grass→Rabbit→Fox→Wolf→Tiger
Grass→ Grasshopper→ Frog→Snake→Hawk
2. Detritus food chain: This type of food chain starts from dead organic
matter and so it is less dependent on solar energy. The dead organic
matter is broken down into simple nutrients by microorganisms like fungi
and bacteria. This type of food chain is found in forest ecosystem.
Dead organic matter→ Detritivores→Predators
3. Parasitic food chain: In this type of food chain either the producer or
the consumer is parasitized and therefore the food passes to the smaller
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organism. The energy transfer through this kind of food chain is not
significant.
Producer→ Herbivores→ Parasite→ Hyperparasites
Trees→ Fruit eating birds→ Lice and bugs→ Bacteria and fungi
Food web:
Food chains are overly simplistic as representatives of the relationships of
living organisms in nature. Most consumers feed on multiple species and
in turn, are fed upon by multiple other species.
For a snake, the prey might be a mouse, a lizard, or a frog, and the
predator might be a bird of prey or a badger. The relations of detritivores
and parasites are seldom adequately characterized in such chains as well.
A food web is a series of related food chains displaying the movement of
energy and matter through an ecosystem. The food web is divided into
two broad categories: the grazing web, beginning with autotrophs, and the
detrital web, beginning with organic debris. There are many food chains
contained in these food webs.
In a grazing web, energy and nutrients move from plants to the herbivores
consuming them to the carnivores or omnivores preying upon the
herbivores. In a detrital web, plant and animal matter is broken down by
decomposers, e.g., bacteria and fungi, and moves to detritivores and then
carnivores.
There are often relationships between the detrital web and the grazing
web. Mushrooms produced by decomposers in the detrital web become a
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food source for deer, squirrels, and mice in the grazing web. Earthworms
eaten by robins are detritivores consuming decaying leaves.
Flow of food chains
Food energy flows from one organism to the next and to the next and so
on, with some energy being lost at each level. Organisms in a food chain
are grouped into trophic levels, based on how many links they are
removed from the primary producers. In trophic levels there may be one
species or a group of species with the same predators and prey.
Autotrophs such as plants or phytoplankton are in the first trophic level;
they are at the base of the food chain. Herbivores (primary consumers)
are in the second trophic level. Carnivores (secondary consumers) are in
the third. Omnivores are found in the second and third levels. Predators
preying upon other predators are tertiary consumers or secondary
carnivores, and they are found in the fourth trophic level.
Significance of Food Chains and Food webs
1.
2.
They help in maintaining the ecological balance.
They help in understanding the feeding relations among
organisms.
3.
Energy flow and nutrient cycling take place through them.
4.
It explains the concept of biomagnification.
biomagnification :Some metallic pollutants and pesticides are non
biodegradable. These poisonous substances are not easily broken down in
the body; instead they accumulate in the tissues. As they are consumed by
higher trophic levels through the food chain their concentration keeps on
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increasing. This phenomenon is referred to as biomagnification. The
permissible safe limit of DDT in human body is 0.2 ppm whereas it is
found on an average human body contains 11 ppm of DDT.
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