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GENERAL PRINCIPLES OF ECOLOGY
The term Ecology was coined in 1866 by the German scientist Ernst Haeckel. The word Ecology is derived from the Greek root word Oikologie where oikos means ‘home’ or habitation or a place to live in. Logos means study or discourse. Hence, literally speaking, Ecology is the study of organisms at home.
Definitions According to Kendeigh (1961), Ecology is the study of animals and plants in their relations to each other and to their environment. The term Ecology is defined by Odum (1969) as ‘the study of interrelationships between organisms and environment.’
Subdivisions of ecology Kirchner and Schroter (1902) broadly divided Ecology into the following two subdivisions on the basis of nature of study:
Autecology- the study of individual organism or an individual species in relation to environment. Ex: Study of a Maple tree in its environment.
Autecology has great significance in economic Biology such as a) Fish culture b) Prawn culture c) Pearl culture d) Sericulture e) Poultry f) Dairy g) Agriculture h) Horticulture i) Silvi cultureIt is also important for soil conservation and wild life conservation.Autecology is experimental and inductive. Synecology: the study of groups of organisms which are associated
together as a unit in relation to the environment EX: Study of a forest.(of which Maple tree is a component), study of a desert, study of a cave etc.
Synecology Includes study of community and ecosystem. Synecology is deductive and largely descriptive. Both autecology and Synecology are studied together. According to Herreid (1977), the Synecologist paints the outline of a picture With a broad brush and an autecologist paints the finer details.
Other sub divisions Animal Ecology-study of animals in their environment. Plant Ecology- study of plants in their environment. Habitat Ecology-study of habitats (living spaces).
Marine Ecology- Study of marine habitat. Fresh water Ecology- study of fresh water habitat. Terrestrial Ecology-study of terrestrial habitat. Population Ecology-study of populations. Community Ecology-study of communities. Applied Ecology- study of application of ecological concepts in
relation to human needs. Paleo Ecology-study of environmental conditions and organisms of
past ages. Space Ecology- study of travel to different planets. Radiation Ecology- study of radioactive substances, radiation and
their applications. Human Ecology- study of the environment with man as the central
theme.
SCOPE OF ECOLOGY Maintenance of natural resources-ecology provides knowledge for
the proper maintenance of natural resources. Pollution control-helps to control environmental pollution. Discovery of new sources of food. Application in human welfare-Ecology helps to determine the utility
of habitats for human welfare. Application in Evolution-provides means to detect and measure the
rate of evolution in wild population. Application in Genetics- helps to bring the rare genetic materials
into plants and domestic animals. Application in the survival of human race-full knowledge of Ecology
is needed for survival of human race from the hazards of population explosion leading to encroachment of unsuitable habitats and the dangers of atomic energy.
FOOD CHAIN AND FOOD WEB
Food chains
Food chains and food webs show the transfer of energy from one organism to the next. (Energy goes to the organism the arrow is pointing
at.)All living things (plants and animals) need energy to live and all living things get this energy from food. A food chain shows how energy and nutrients are transferred from one organism to another in the form of food. A food chain shows the transfer of energy from one organism to another. The arrows point to the organism that receives the energy. The arrows are called strands.
Plants, algae and some types of bacteria make their own food using the sun's energy, carbon dioxide (CO2) and water. They are called producers because they produce or make their own food. Organisms that get their energy from consuming other organisms are called consumers.
Organisms that eat plants are called herbivores or primary consumers. Cows and deer are herbivores, as are many insects. Organisms that eat other animals are called carnivores. Owls are carnivores because they eat rodents and birds. Some insects are carnivores. If a carnivore eats an herbivore, it is called a secondary consumer. A carnivore that eats another carnivore, it's called a tertiary consumer. Owls and shrews are both carnivores. Because the owl eats the shrew, this is an example of a tertiary consumer eating a secondary consumer. Organisms that eat both plants and animals are called omnivores. People are omnivores, and so are rats, raccoons, & skunks. So... is an omnivore a primary, secondary or tertiary consumer? Well, it depends on what it's eating at the moment. If it's eating grass, it is a primary consumer. But when it's eating a rabbit, it's a secondary consumer. And when it eats a salmon (that eats insects and crustaceans), it's a tertiary consumer. Organisms that break down dead or decaying organisms for their food are a special kind of consumer called detritivores and decomposers. Some examples of decomposers include fungi and bacteria. Some detritivores have mouths and eat dead plants and animals. Examples are worms and certain insects. Decomposers do not have mouths to eat with, but they break down or digest dead organisms using special enzymes and then absorb the nutrients (like sponge absorbing water).
A food web is composed of interconnecting food chains.
Because organisms in a habitat generally eat more than one thing, the energy produced in plants connects with several organisms living together. For example, an owl eats many types of rodents, including rats, voles, shrews and birds. Since shrews eat insects, and rats and birds are omnivores, you can see that the food chains become interconnected and more complex.
FOOD WEB IN A POND
FOOD WEB IN OCEAN
A more complex marine food web might look like the one to the right. Despite the visual complexity of the diagram, many species and many links between species are not shown. Organisms may have more than one trophic role because they eat a variety of food types.
Types of food webs There are different kinds or categories of food webs:
Source web - one or more node(s), all of their predators, all the food these predators eat, and so on.
Sink web - one or more node(s), all of their prey, all the food that these prey eat, and so on.
Community (or connectedness) web - a group of nodes and all the connections of who eats whom.
Energy flow web - quantified fluxes of energy between nodes along links between a resource and a consumer.
Paleoecological web - a web that reconstructs ecosystems from the fossil record.
Functional web - emphasizes the functional significance of certain connections having strong interaction strength and greater bearing on community organization, more so than energy flow pathways
(Node: Node is one of the words or pictures that arrow go towards or away from them. A link connects two nodes.)
Application of food webs1. Food webs are constructed to describe species interaction
(Direct relationships). 2. Food webs can be used to illustrate indirect interaction among
species.3. Food webs can be used to study bottom-up or top-down control
of community structure.( bottom up effects occur when a density of a source affects the density of its consumer. Top down effects occur when the population density affects the density of its resource)
4. Food web can be used to reveal different patterns of energy transfer in terrestrial and aquatic Ecosystems aquatic Ecosystems.
TROPHIC PYRAMID The word trophic is derived from the Greek word ‘trophe’ referring to food of feeding. Definition: Trophic pyramid, also referred to as ecological pyramid or energy pyramid, is a graphical representation designed to show the bio-mass or bio-mass productivity at each trophic level in a given ecosystem.
Trophic level of an organism is the position it occupies in a food chain.
Each trophic pyramid is made up of a series of interconnected feeding relationships called food chain
A food chain represents succession of an organism that eats another organism and is eaten themselves.
Food chain that starts at trophic level 1 with primary producers such as plants move to herbivores at level 2, predators at level 3 and
finish with carnivores or apex predators at level 4 and 5. The path along the chain can form either a one way flow or food web.
Most food chains consist of three or four trophic levels. A typical sequence is plant, herbivore, carnivore and top carnivore. Another sequence is plant, herbivore, parasite of the herbivore and
parasites of the parasites. Many herbivores, detritivores, carnivores and parasites eat more
than one species and many eat different foods at different stages of their life histories.
In addition many species eat both plants and animals and therefore feed at more than one trophic level.
Consequently food chains combine into highly complex food webs. The use of ecological pyramid was first described by Charles Elton in 1927.
TROPHIC LEVELS
Producers- The bottom level of the trophic pyramid is made up of the producers. Producers are organism that makes their own food. These include plants and algae that use the energy of the sun to make their own food. It also includes certain types of bacteria that use chemicals to make their own food (Chemotrophs). These bacteria live near underwater volcanoes that are so deep in the ocean that no sunlight can penetrate and they live in total darkness.
Primary consumers - All consumers get their energy by eating other organisms. Organisms that eat plants are called herbivores. Because they get their energy from organisms in the first trophic level (producers), they are Called primary consumers
Secondary consumers are consumers that eat primary consumers (or Herbivores). They are also called carnivores.
Tertiary consumers are consumers that eat secondary consumers (or other carnivores).
There are also higher trophic levels (fourth and fifth) depending on the food chain. For example, algae plankton small fish large fish human shark (or shark human!)
Omnivores are organisms that eat producers and other consumers. Based on the transfer of energy to different trophic levels, an omnivore is a primary consumer when it is eating a producer and a secondary consumer when it is eating a primary consumer and a tertiary consumer when it is eating a secondary consumer, and so on.
Detritivores and decomposers can also be primary, secondary, and tertiary consumers depending on which level of the trophic pyramid they are eating from. Decomposers include bacteria and fungi. Detritivores such as worms get their energy by eating dead and decaying organisms. A worm that eats a dead plant is a
primary consumer, while a worm that eats a dead deer is a secondary consumer.
TROPHIC PYRAMIDS
There are three types of trophic pyramids: Pyramid of Numbers Pyramid of Biomass Pyramid of Energy
1. PYRAMID OF NUMBERS
This shows the relationship between producers, herbivores and carnivores at successive trophic levels in terms of the number. Here there will be a gradual decrease in the number of individuals from the lower to the higher trophic levels. This may be studied by taking the example of trophic levels in grassland.
In a Grassland Ecosystem
The grasses occupy the lowest trophic level and they are abundantly present in the grassland ecosystem. The deer’s occupy the second level; their number is less than compared to the grasses. The wolves, which feed upon the deer’s, are far less in number when compared to the number of deer’s. The lions, which occupy the next trophic level, feed upon wolves, and the number of individuals in the last trophic level is greatly reduced.
In a Cropland Ecosystem
In croplands the crops are more in numbers. The grass hoppers feeding on crop plants are lesser in number. The frogs feeding on grass hopper are
still lesser in number. The snakes feeding on frogs are fewer in number. Hawks feeding on snakes are all the more lesser in number.
Crop -> Grasshoppers - > Frogs - > Snakes ->Hawks
In Pond Ecosystem The number in a pond Ecosystem decreases in the following order:
Phytoplankton- >Zooplankton -> Fishes->Snakes
Inverted Pyramid of Numbers In the parasitic food chain, the pyramid of numbers is founds to be inverted. Here, a single plant or tree might support varieties of herbivore. These herbivores like birds in turn, support varieties of parasites like lice, bugs that outnumber the herbivores. Subsequently each parasite might support a number of hyper parasites like bacteria and fungi, which will outnumber the parasites. Thus from the producer level onwards, towards the consumers, in the parasitic food chain there is a gradual increase in the number of organisms, instead of the usual decrease. As a result of this, the pyramid becomes inverted in the parasitic food chain. There is a gradual increase in the numbers of individuals from autotrophs to the higher trophic levels. Inverted pyramid occurs in a tree Ecosystem also. A single tree (producer) contains many fruit eating birds (primary consumers). The birds carry numerous parasites (secondary parasites).
Salient features of Pyramid of numbers1. It shows the number of organisms at different levels.2. The pyramid is erect. 3. The smaller animals are preyed upon larger animals and smaller animals
Increase faster in number of organism at each stage of food chain, makes a triangular figure that is known as pyramid of number.
2. PYRAMID OF BIOMASS
Biomass refers to the total weight of living matter per unit area in an Ecosystem. The biomass decreases from the producer level to the consumer level.
The pyramid of Biomass indicates decrease of biomass in each trophic level from base to the apex.
Pyramid of Biomass
In a Grassland: The biomass of grass is maximum. It gradually decreases towards the consumer level in the following order:
Grass- > Mouse- >Snake-> Hawk Grass -> Grasshopper-> Lizard-> Hawk
In a forest: The biomass of tree is maximum and the biomass of top consumer is minimum. The decrease in weight occurs in the following order.Plants-> Deer->Fox -> TigerPlants-> Rabbit->Fox->Lion
Inverted Pyramid of Biomass When the biomass of the producer is less and that of consumer is more the pyramid will have inverted shape. It occurs in a pond or Lake Ecosystem. Here the biomass of the diatoms and phytoplankton’s (producers are less as compared to that of crustaceans (Primary consumers) and small fishes (secondary consumers).
Significance1. This pyramid shows the total biomass at each trophic level in a food chain.
2. Pyramid in erect.
3. It indicates a decrease in the biomass at each trophic level from the base to apex of pyramid.
Example: Total biomass than herbivores, which is again more than carnivorous.
Pyramid of Energy
Energy flows in an Ecosystem from the producer level to the consumer level.
At each trophic level energy is lost in the form of heat (as much as 80 to 90%) as organisms expand energy for metabolic processes.
The higher the organism on the trophic pyramid the lower is the amount of energy it has..
For example plants and other autotrophs (Primary producers) convert only a fraction of the enormous solar energy they have access to into food energy.
Herbivores and detritivores (primary Consumers) take in less available energy because they are limited by the biomass of the plants they devour.
Carnivores (secondary consumers) that feed on herbivores, detritivores and those that eat other carnivores (tertiary consumers) have the lowest amount of energy available to them. Salient features:
1. The energy pyramid always upright and erect. It shows the rate of energy flows at different trophic levels. It shows that energy is maximum at producer level and minimum at
The carnivores' level. At every successive trophic level there is a loss of energy in the
form of heat, respiration etc.
Desert Energy Pyramid
Grassland Energy Pyramid
