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. 1 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. 2 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. 3 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. 4 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). 5 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. 6 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. 7 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 8 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 9 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 10 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. 11