part3 energy in ecological system

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CAVITE STATE UNIVERSITY(CvSU)

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General EcologyPART III: ENERGY IN ECOLOGICAL SYSTEM

I. LAWS OF ENERGY

Laws of EnergyStatement:

Energy may be transformed from one type to another but is never created nor destroyed. The total inflow of energy into a system must equal the total outflow of energy from the system, plus the change in the energy contained within the system.

The entropy of the universe is defined as disordered randomized state of energy that is unavailable to do work. In almost all energy transformation, there is a loss of energy in the form of heat. This form of energy is no longer available to do work.

Flow of energyStatement:

Although the energy of the universe to do work is constant, it is decreasing with time, because their energy is degraded to heat which is the least useful form of energy because entropy in the universe is continually increasing.

Explanation: Energy enters an ecosystem in the form of sunlight (yellow arrow).

Phytoplanktons as producers convert light energy to chemical energy through the process of photosynthesis. Zooplanktons and fishes as consumers take in some of this chemical energy in the form of organic compounds when they eat the phytoplanktons or other smaller zooplanktons. Decomposers obtain chemical when they feed on the dead remains of producers and consumers. Every use of chemical energy by organisms involves a loss of some energy to the surroundings in the form of heat.

In contrast to energy flow, chemical cycling (white arrow) involves the transfer of materials within an ecosystem. While most ecosystems have constant input of energy from sunlight or another source, the supply of chemical elements used to construct molecules is limited. Chemical elements such as carbon and nitrogen are cycled between the abiotic components of the ecosystem. Producers acquire these forms from air or soil and fix it into organic molecules. Animals consume some of these organic molecules. When the plants and animals become detritus, decomposers return most of the elements to the soil and air in inorganic form. Some

elements are also returned to the soil and air as the by- products of plant and animal

metabolism.

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II. FOOD CHAIN, FOOD WEB AND TROPHIC LEVELS IN AN ECOSYSTEM

Statement:Trophic level is the position occupied by organisms in a food chain. It is numbered subsequently according to how far the organism is along the food chain.

Level 1: Plants and algae make their own food and are called primary producers.

Level 2: Herbivores eat plants and are called primary consumers.

Level 3: Carnivores which eat herbivores are called secondary consumers.

Level 4: Carnivores which eat other carnivores are called tertiary consumers.

Level 5: Quaternary consumers or Apex predators which have no predators are at the top of the food chain.

Food chain is the sequence of transfers of matter and energy in the form of food from organism to organism or from one trophic level to trophic level.

Food web is a network of feeding interactions among species.

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III. ECOLOGICAL PYRAMID

Transfer of EnergyStatement:

Each day, Earth receives 1019 kcal of solar energy, the energy equivalent of about 100million atomic bombs. Most of this energy is absorbed, scattered, or reflected by the atmosphere or by the

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surface of Earth. Producers convert only about 1% of the energy in the sunlight available to them to primary production. 10% of the energy available to each trophic becomes incorporated into the tissues of the next higher level. Actual energy efficiencies of energy transfer are usually in the range of 5-20%. In other words, 80-95% energy at one trophic level never reaches the next.

Explanation:When energy flows as organic matter through the trophic levels of an

ecosystem, much of it is lost at each link in the food chain. In most ecosystems, herbivores manage to eat only a fraction of the plant material produced and they cannot digest all of what they do consume.

A caterpillar feeding on leaves passes about half the energy in the leaves as feces. Another 35% of the energy is expended in cellular respiration. Only about 15% of the energy in the food is transformed into biomass of caterpillar.

Factors Affecting the Reduction of Energy Transfer1. Respiration2. Growth and reproduction3. Defecation4. Non-predatory death

Factors Affecting the Number of Trophic Levels in an Ecosystem1. Amount of energy entering the ecosystem2. Amount of energy loss between trophic level3. Form, structure and physiology of organisms at each level

Productivity in an Ecosystem

Statement:Gross Primary Productivity (GPP) is the rate at which organic matter

is produced during photosynthesis by producers in an ecosystem. Primary productivity in an ecosystem sets the energy budget. It determines the maximum amount of energy available to all the higher trophic levels in an ecosystem.

Net productivity (NP) is the rate at which organic matter stored in plants that produces growth.

Explanation:Different ecosystems vary in their productivity. Productivity in land

ecosystems generally rises with temperature up to about 30°C, after which it declines, and is positively correlated with moisture. On land primary productivity is highest in warm, wet zones in the tropics where tropical forest biomes are located. In contrast, desert scrub ecosystems have the lowest productivity because their climates are extremely hot and dry.

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Terrestrial Productivity

In the oceans, light and nutrients are important controlling factors for productivity. Light penetrates only into the uppermost level of the oceans, so photosynthesis occurs in surface and near-surface waters. Marine primary productivity is high near coastlines and other areas where upwelling brings nutrients to the surface, promoting plankton blooms. Runoff from land is also a source of nutrients in estuaries and along the continental shelves. Among aquatic ecosystems, algal beds and coral reefs have the highest net primary production, while the lowest rates occur in the open due to a lack of nutrients in the illuminated surface layers.

Ocean Productivity

Ecological Pyramids

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Statement: Ecological pyramids emphasize the energy loss from one trophic level

to the next.

Types of Ecological pyramids:

Productivity Pyramid illustrates the energy loss with each transfer in a food chain.

Biomass Pyramid illustrates the total weight of dry matter present in the ecosystem.

Pyramid of Numbers depicts the number of organisms at each trophic level.

IV. NUTRIENT CYCLING / BIOGEOCHEMICAL CYCLES

Nutrient cycles is also called biogeochemical cycles because chemical cycles in an ecosystem involve both biotic and abiotic components. Cycles have Abiotic reservoirs where chemical accumulates or is stockpiled outside the living organisms.

General scheme for Biogeochemical cycle

1. Producers incorporate chemicals from the abiotic reservoirs into organic compounds.

2. Consumers feed on the producers, incorporating some of the chemicals into their own bodies.

3. Both producers and consumers release some chemicals back to the environment as waste products.

4. Decomposers play a central role by breaking down complex organic molecules in detritus.

Water Cycle

The continuous movement of water in the biosphere is known as Water Cycle. Of all the water in the planet, 96.4% is the salt water. Water

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Decomposer

Producer

Consumer

Nutrients

Abiotic reservoirs

Geologic processes

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cycle has three major processes: evaporation or transpiration, condensation, and precipitation. Most of the water falls on the oceans, since these covers most of the surface of the Earth. The water that falls on land is pulled back to the ocean by the force of gravity.

1. Evaporation: This is the change of water from a liquid to a gas. On average, around 47 inches is evaporated into the atmosphere from the ocean each year.

2. Transpiration: This is the evaporation of liquid water from plants and trees into the Earth’s atmosphere. Nearly all water that enters the roots transpires into the atmosphere.

3. Sublimation: This is the process where ice and snow changes into a gas without moving through the liquid phase.

4. Condensation: This is the process where water changes back into a liquid. This is when we begin to first see clouds.

5. Transportation: This is the movement of solid, liquid and gaseous water throughout the atmosphere. Without this movement, all of the water evaporated over the ocean would not precipitate over land.

6. Precipitation: This is water that falls to the earth. Most precipitation falls as rain but includes snow, sleet, drizzle and hail. On average, about 39 inches of rain, snow and sleet fall each year around the world.

7. Deposition: Water vapor changes into without going through the liquid phase. This is most often seen on clear and cold nights when frost forms on the ground.

8. Infiltration: This is the movement of water into the ground from the surface. Percolation is movement of water past the soil going deep into the groundwater.

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9. Surface flow / Run off: This is the river, lake, and stream transport of water to the oceans. The water may return to the surface in springs or eventually seep into the oceans.

10.Plant uptake: This is water taken from the groundwater flow and soil moisture. Only 1% of water that a plant draws up is used by the plant. The remaining 99% is passed back into the atmosphere.

Carbon Cycle

All living things need carbon and oxygen. Carbon is the element found in all living things. It is considered as the backbone of all carbohydrate molecules. Oxygen is required for the process of respiration. Plants obtain carbon from the carbon dioxide absorbed during the process of photosynthesis and animals obtain their carbon from plants or other animals they eat. Animals cannot use carbon dioxide from the atmosphere.

1. Photosynthesis removes CO2 from the atmosphere and incorporates it into organic molecules, which are

2. passed along the food chain by consumers.3. Cellular respiration returns CO2 to the atmosphere.4. Decomposers break down the carbon compounds in detritus.5. However, increasing level of CO2 in the atmosphere is caused by the

burning of wood and fossil fuels which contributes to global climate change.

Phosphorus Cycle

Organisms require phosphorus as an ingredient of nucleic acids, phospholipids and ATP. Phosphorus cycle does not have an atmospheric component. Rocks are the only source of phosphorus for the terrestrial ecosystem. Because weathering is generally a low process, the amount of phosphates available to plants in natural ecosystem is often quite low. Farmers and gardeners use crushed phosphate rock, bone meal (finely

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ground bones from slaughtered livestock or fish), or guano (droppings of seabirds and bats manure) to add phosphorus to the soil.

1. The weathering or breakdown of rocks gradually adds inorganic phosphate (PO4) to the soil.

2. Plants absorb dissolved phosphate from the soil and assimilate it by building the phosphorus atoms into organic compounds.

3. Consumers obtain phosphorus in organic form from plants.4. Phosphates are returned to the soil by the action of decomposers on

animal wastes and remains of dead plants and animals.5. Some of the phosphates drain from terrestrial ecosystems into the

sea, where they may settle and eventually become part of new rocks. Phosphorus removed from the cycle will not be available to living organisms until

6. geologic processes like uplift of rocks and expose them to weathering.

Nitrogen Cycle

As an ingredient of proteins and nucleic acids, nitrogen is essential to the functioning and structure of all organisms. Nitrogen has two abiotic reservoirs, the atmosphere and the soil. Almost 80% of the atmosphere is nitrogen gas. However, plants cannot assimilate nitrogen in the form of gas. The process of nitrogen fixation converts gaseous N2 to ammonia and nitrates which can be used by plants. A small amount of nitrogen is fixed by high-energy processes such as lightning strikes.

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1. Some bacteria live symbiotically in the roots of certain species of plants, supplying their hosts with a direct source of usable nitrogen. The largest group of plants with this mutualistic relationship is the legumes, a family that includes peanuts, soybeans, and kudzu.

2. Free-living nitrogen-fixing bacteria in soil or water convert N2 to ammonium (NH4). The N2 is available in air pockets in the soil and dissolved in water.

3. After nitrogen is “fixed”, some of the NH4 is taken up and used by plants.

4. Nitrifying bacteria in the soil also convert some of the NH4 to nitrate (NO3),

5. which is more readily assimilated by plants.6. When an herbivore eats a plant, it digests the proteins into amino

acids and then uses the amino acids to build the proteins it needs. Higher-order consumers get nitrogen from the nitrogen-containing organic molecules of their prey.

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7. Organisms that are not consumed eventually die and become detritus, which is decomposed by bacteria and fungi. Decomposition releases NH4 from organic compounds back into the soil, replenishing the soil reservoirs.

8. Under low-oxygen conditions, soil bacteria known as denitrifying bacteria strip the oxygen atoms from the NO3, releasing N2 back into the atmosphere and depleting the soil reservoir of usable nitrogen.

Definition of Terms:Biomass: mass of living organic material in an ecosystem.Ecosystem productivity: refers to the amount of energy stored.Energy: capacity of a system to perform work.Energy flow: the passage of energy through the components of ecosystem.Entropy: a measure of biodiversity in the study of biological ecology.

Prepared by

Ms. SHELA B. LEBASNONInstructor Date: August 02, 2013

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