Food chainA food chain is a linear sequence of links in a food web starting from species that are called producers in the web and ends at species that are called decomposers in the web. A food chain also shows how the organisms are related with each other by the food they eat. The transfer of energy from the source in plants through a series of organisms, by eating and being eaten, constitutes the food chain. At each transfer a large proportion of energy is lost in the form of heat. Food chains were first introduced by the African-Arab scientist and philosopher Al-Jahiz in the 9th century and later popularized in a book published in 1927 by Charles Elton, which also introduced the food web concept.

Food chains vary in length from three to six or more levels. A food chain consisting of a flower, a frog, a snake and an owl consists of four levels; whereas a food chain consisting of grass, a grasshopper, a rat, a snake and finally a hawk consists of five levels. Producers, such as plants, are organisms that utilize solar or chemical energy to synthesize starch. All food chains must start with a producer. In the deep sea, food chains centered around hydrothermal vents and cold seeps exist in the absence of sunlight. Chemosynthetic bacteria and archaea use hydrogen sulfide and methane from hydrothermal vents and cold seeps as an energy source (just as plants use sunlight) to produce carbohydrates; they form the base of the food chain. Consumers are organisms that eat other organisms. All organisms in a food chain, except the first organism, are consumers.

The most obvious aspect of nature is that energy must pass from one living organism to another. When herbivores animals feed on plants, energy is transferred from the plants to the animals. In an ecosystem, some of the animals feed on other living organisms, while some feed on dead organic matter; the latter form the detritus of the food chain. At each link in the chain, a large part of the energy from the food is lost through daily activities. Each chain usually has only 4 to 5 such links. However a single species may be linked to a large no. of species.

Food webIn an ecosystem, there are a very large number of interlinked chains; together, these form a food web. A food web (or food cycle) is the natural interconnection of food chains and generally a graphical representation (usually an image) of what-eats-what in an ecological community. Another name for food web is a consumer-resource system. If the links in the chains that make up the web of life are disrupted due to human activities that lead to the loss of extinction of species, the web breaks down.

The linkages in a food web illustrate the feeding pathways, such as where heterotrophs obtain organic matter by feeding on autotrophs and other heterotrophs. The food web is a simplified

illustration of the various methods of feeding that links an ecosystem into a unified system of exchange. There are different kinds of feeding relations that can be roughly divided into herbivory, carnivory, scavenging and parasitism. Some of the organic matter eaten by heterotrophs, such as sugars, provides energy.

Ecological pyramidAn ecological pyramid (also trophic pyramid, energy pyramid, or sometimes food pyramid) is a graphical representation designed to show the biomass or biomass productivity at each trophic level in a given ecosystem.

Biomass is the amount of living or organic matter present in an organism. Biomass pyramids show how much biomass is present in the organisms at each trophic level, while productivity pyramids show the production or turnover in biomass.

Ecological pyramids begin with producers on the bottom (such as plants) and proceed through the various trophic levels (such as herbivores that eat plants, then carnivores that eat herbivores, then carnivores that eat those carnivores, and so on). The highest level is the top of the food chain.

An ecological pyramid of biomass shows the relationship between biomass and trophic level by quantifying the biomass present at each trophic level of an ecological community at a particular time. It is a graphical representation of biomass (total amount of living or organic matter in an ecosystem) present in unit area in different tropic levels. Typical units are grams per meter2, or calories per meter2. The pyramid of biomass may be "inverted". For example, in a pond ecosystem, the standing crop of phytoplankton, the major producers, at any given point will be lower than the mass of the heterotrophs, such as fish and insects. This is explained as the phytoplankton reproduce very quickly, but have much shorter individual lives.

One problem with biomass pyramids is that they can make a trophic level appear to contain more energy than it actually does. For example, all birds have beaks and skeletons, which despite having mass are not eaten by the next trophic level.

There is also pyramid of numbers which represent the number of organisms in each trophic level. They may be upright (e.g. Grassland ecosystem), inverted (parasitic ecosystem) or dumbbell shaped (forest ecosystem)

In an ecosystem, green plants (the producers) utilize energy directly from sunlight and convert it into matter. A large number of these organisms form the most basic or first tropic level of the food pyramid. The herbivores that eat plants are at the second tropic level and are called primary consumers. The predators that feed on them form the third tropic level and are known as secondary consumers. Only a few animals form the third tropic level consisting of the carnivores at the apex of the food pyramid. This is how energy is used by living creatures and flows through the ecosystem from its base to the apex.

EcosystemAn ecosystem is a community of living organisms (plants, animals and microbes) in conjunction with the nonliving components of their environment (things like air, water and mineral soil), interacting as a system. These biotic and abiotic components are regarded as linked together through nutrient cycles and energy flows. As ecosystems are defined by the network of interactions among organisms, and between organisms and their environment, they can be of any size but usually encompass specific, limited spaces (although some scientists say that the entire planet is an ecosystem). There are two types of ecosystems, called terrestrial ecosystems and aquatic ecosystems. Forests, grasslands, semi-arid areas, deserts, mountains, islands are examples of terrestrial ecosystems and pond, lake, wetland, river, delta, marine are examples of aquatic ecosystems.

Ecosystem goods and services

Ecosystems provide a variety of goods and services upon which people depend. Ecosystem goods include the "tangible, material products" of ecosystem processes—food, construction material, medicinal plants—in addition to less tangible items like tourism and recreation, and genes from wild plants and animals that can be used to improve domestic species. Ecosystem services, on

the other hand, are generally "improvements in the condition or location of things of value". These include things like the maintenance of hydrological cycles, cleaning air and water, the maintenance of oxygen in the atmosphere, crop pollination and even things like beauty, inspiration and opportunities for research. While ecosystem goods have traditionally been recognized as being the basis for things of economic value, ecosystem services tend to be taken for granted. While Gretchen Daily's original definition distinguished between ecosystem goods and ecosystem services, Robert Costanza and colleagues' later work and that of the Millennium Ecosystem Assessment lumped all of these together as ecosystem services.

Forest EcosystemA forest ecosystem is defined as an area dominated by trees and other woody plants. Forests aren't only trees, however. Healthy forests have a lot going on in them, and many different species of both animals and plants that call them home. There are many different types of forests in the world, ranging from tropical rain forests to the dense sub-polar taiga. To truly understand a forest ecosystem, it is easiest to break it down into the five layers that most healthy forests have. Animals that live in a forest move between the layers to feed and hunt.

A forest ecosystem has two parts :

The non living or abiotic aspects of the forest : The type of forest depends on the abiotic conditions at the site. Forests on mountains and hills differ from those along river valleys. The vegetation is specific to the amount of rainfall and local temperature which vary according to latitude, altitude and soil type.

The living, biotic aspects of the forest : the plants and animals form communities that are specific to each forest type. For instance, coniferous trees occur in the Himalayas; mangrove trees in the river deltas; thorn trees in arid areas.

Forest types in IndiaThe forest types depends on abiotic factors such as the climate and soil characteristics of a region. Forests in India can be broadly divided into coniferous and broad leaved forests.

They can also be classified according to the nature of their tree species – evergreen, decidious, xerophytes or thorn trees, mangroves and so on. They can also be classified according to the most abundant species of trees, such as sal or teak forest.

Coniferous forests grow in Himalayan mountain region, where the temperatures are low. These forests have tall stately trees with needle like leaves and downward sloping branches, so that the snow can slip off the branches. They have cones instead of seeds and are called gymnosperms.

Broadleaved forests are of several types, such as evergreen forests, deciduous forests, thorn forests, mangrove forests. Broad leaved trees usually have large leaves of various shapes and are found in the middle to the lower latitudes.

Evergreen forests grow in the high rainfall areas of the western Ghats, north eastern India and Andaman and Nicobar islands. These forests grow in areas where the monsoon lasts for several months. These shed a few of their leaves throughout the year. The trees overlap with each other to form a continuous canopy. Thus, very little light penetrates down to the forest floor. The forest is rich in orchids and ferns. The forests abounds in animal life and is very rich in insect life.

Deciduous forests are found in regions with a moderate amount of seasonal rainfall that lasts for only a few months. The deciduous trees shed their leaves during the winter and hot summer months. The forest frequently has thick undergrowth as light can penetrate easily onto the forest floor.

Thorn forest are found in semi- arid regions of India. The trees, which are sparsely distributed, are surrounded by open grassy areas. Thorny plants called xerophytic species, are able to conserve water. Thorn forests trees have long or fibrous roots to enable them to reach water at great depths. Many of these plants have thorns which reduce water loss and protect them from herbivores.

Mangrove forests grow along the coasts, especially in the river deltas. These plants are uniquely adapted to be able to grow in a mix of saline and fresh water. They grow luxuriantly in muddy areas covered with silt that the rivers have brought down. They have breathing roots that emerge from the mud banks.