Energy in Ecosystems

• Producers


  The driving force in all ecosystems is solar energy. Green plants (including algae and plankton) are referred to as autotrophs because they have the ability to produce their own food by converting the sun’s energy into chemical energy (stored in food) by the process of photosynthesis.
• Carbon dioxide + water → sunlight + chlorophyll → glucose + oxygen
• Green plants absorb light energy using chlorophyll, a green pigment which is found in cells in leaves. They use it to react carbon dioxide with water to make simple sugars such as glucose which provides food and energy for the plant to grow.
• Animals and non-green plants (including fungi) cannot produce their own food from solar energy, and are known as heterotrophs. They are consumers as they must consume plants or other animals in order to stay alive and grow.
• Herbivores

  Eat plant or vegetable matter only
• Carnivores


  Consume meat only
• Omnivore


  Eat a mixture of plant and animal material
• A food chain is a sequence of organisms, each of which feeds on a type of organism from the preceding food level.
• In a food chain, the direction of arrow indicates the transfer of energy (energy flow). However, they tend to be very simplistic and rarely give us an idea of the complex feeding relationships which occur in nature.
• Almost all food chains within an ecosystem are interconnected showing the interdependence between species, and form complex food webs. A food web can be organised into different feeding or trophic levels.
• Primary producers


  Include green plants, algae, and blue-green bacteria
• Secondary Consumers


  Feed on primary consumers
• Primary Consumers


  Herbivores which feed on green plants (primary producers)
• Tertiary consumer


  At the top of the food web, they eat animals from all 3 levels below them, although may concentrate specifically on secondary consumers
• Each organism within a food web has its own particular function or niche which it fulfils. Essentially this is the habitat it occupies, what it eats and what may predate it.
• Detritus includes partly broken down dead plant and animal material, such as fallen leaves, seeds and berries, animal faeces and dead organisms. This material still has critical value to the flow of energy within an ecosystem and supports populations of detritivores and decomposers.
• Detritivores are organisms such as wood lice and earthworm, which feed directly on this material. Decomposers are micro-organisms, including bacteria and fungi, which chemically break down waste materials and dead organisms using enzymes. Apart from cleaning up the ecosystem of dead matter, they also perform a vital function by making nutrients available to the ecosystem. Effectively they are nature’s recyclers and allow vital minerals to be used by other organisms.
• Technically energy is not ‘lost’ but converted to other forms such as heat and sound energy. Within ecosystems, energy is said to be ‘lost’ when it is not made available to the trophic level above. Generally only 10% of the energy consumed by an organism is made available to the next trophic level, and food chains can usually sustain no more than 6 energy transfers before all the energy is used up.
• Reasons for energy loss


  1. Animals use up energy to build up their body weight. However when some of this is eaten by a predator, some parts may have no nutritional value such as cellulose, bones, skin or horns. These are left uneaten or expelled as undigested waste or faeces, and as a result energy is effectively ‘lost’ from the food chain.
  2. Energy gained by a consumer in its food is used for moving around, and in warm blooded animals such as mammals, for keeping warm. Only a tenth of the energy in is used for building up body tissue, with most being lost as heat or through respiration.
• The productivity of an ecosystem is the rate of production or the amount of organic matter (biomass) formed or accumulated per unit area in unit time.
• Gross productivity is the measure of all photosynthesis, or creation of chemical energy, that occurs in an ecosystem.
• Net productivity is the energy which is left after losses as a result of respiration, growth, heat and movement.
• Endotherms, which include mammals and birds, are organisms which can control their internal body temperature, and this is usually kept higher than the surrounding environment. They are often referred to as ‘warm blooded’ animals and can live in areas where ectotherms struggle to survive such as polar and mountain areas. As they have higher metabolic rates, they have to eat frequently to obtain energy. Endotherms tend to digest food more completely and as a result food chains are typically quite short, with only 3 or 4 trophic levels.
• Ectotherms, which include invertebrates, most fish, reptiles and amphibians, are animals that rely on their external environment for temperature control instead of generating their own body heat. Ectotherms have lower metabolic rates and often feed less regularly. However physical activity is restricted to certain times of the day (night time). As a result food chains composed chiefly of ectotherms tend to be slightly longer. Although ectotherms are referred to as ‘cold blooded’ animals, this is incorrect as their blood temperatures can be 35-40C, similar to endotherms.