feeding relationships

• An ecosystem is the interaction between a community of living organisms and their environment. A community is two or more populations of organisms. An ecosystem is the interaction of two or more populations of organisms in their environment.
• Feeding relationships show what organisms eat or are eaten by others and through this the levels of organisation in an ecosystem. These can be shown in food chains, which add together to make food webs for a habitat.
• At the base of almost every food chain is a producer. These are plants or algae, which photosynthesise. This means they convert energy from the sun into glucose during photosynthesis producing biomass. It is this which feeds the rest of the food chain.
• All animals above the producer are called consumers. The first is the primary consumer, the next is the secondary consumer. Animals that hunt and kill others are called predators, and those that are hunted and killed are called prey. The top animal in the feeding relationship is called the apex predator.
• Decomposers are bacteria and fungi, which break down dead organisms in a process called decomposition or rotting. They do this by releasing enzymes onto the dead matter and afterwards, consume the broken down substances. They form a vital role in the recycling of matter. When organisms die and decompose plants absorb the broken down nutrients through their roots.
• In a healthy, balanced ecosystem the numbers of predators and prey remain fairly constant. They can go up and down during each year but generally over the years, these increases and decreases remain fairly constant.

  If numbers of either predators or prey increase or decrease it could be due to a change in the abiotic factors, like water or sunlight, or biotic factors, like a new predator or pathogen. This would result in a less healthy, balanced ecosystem.
• The numbers of predators and prey for certain ecosystems such as the Canadian Lynx (wild cat) and hare have been recorded over many years and found to change in a regular cycle.
• It is important to estimate the number of organisms in a population to better understand the relationships in a community. This information is useful for monitoring the impact of conservation projects that aim to conserve endangered species or habitats It is almost always impossible to count all of the organisms in a population. So we look at a small section of a population to draw conclusions about the rest. This process is called sampling and the area or part of population looked at is called a sample.
• It is important to estimate the number of organisms in a population to better understand the relationships in a community. This information is useful for monitoring the impact of conservation projects that aim to conserve endangered species or habitats It is almost always impossible to count all of the organisms in a population. So we look at a small section of a population to draw conclusions about the rest. This process is called sampling and the area or part of population looked at is called a sample.
• Another method is to use large nets to sweep through grasses or leaves of trees in a process called sweep netting. To catch aquatic organism nets are often held downstream of an area of river bed which is then gently disturbed by the person doing the sampling. The small animals float into the net. This is called kick-sampling.
• Pooters are small devices used when sampling to suck up small insects safely without them going into your mouth.
• Quadrats are square frames of wire usually 0.25 m2. These are placed on the ground to look at the plants or slow-moving animals within them.
• Sampling methods in plant studies using a quadrat:

  • Number of an individual species: records the total number of individuals of one species (e.g., daisies)
  • Species richness: records the number of different plant or animal species, not the number of individuals within a species
  • Percentage cover: records the percentage of the quadrat area covered by one species (e.g., grass); useful when identifying individual plants is challenging, like with grasses or moss
• Random sampling using a quadrat involves the placing of quadrats at random coordinates. Regardless of whether you are investigating the number of individual species, the species diversity or the percentage cover in different areas you would use random sampling.
• Most sampling is random, but systematic sampling can be used if there is a trend or pattern across the habitat, such as distance up a beach, or altitude on a hillside. If you are using the wrong kind of sampling method for your experiment, this can lead to biased results.
• Sometimes we want to see if the number of species or percentage cover changes within an area. This is often as a result of a change in an abiotic factor.
• Sampling example: investigating if seaweed growth depends on the distance from the tide on the seashore
• Systematic sampling is used to link a linear change, like the number of hours seaweed is covered by the tide
• In systematic sampling, a quadrat is placed at regular distances along an imaginary line called a transect running down the shore
• Systematic sampling along the transect helps link changes in species to abiotic factors influenced by the tide, like immersion by water, temperature fluctuations, and light intensity
• Results from transects can be represented in kite diagrams, where the width of the bar from the middle at any distance shows how many individuals were observed at that point
• Method

  1. choose a starting point on the school field in an area where the grass is often cut
  2. use random numbers to generate a set of coordinates to place your first quadrat
  3. count the number of different plant species within this quadrat (the species richness)
  4. return to your starting position and repeat steps two and three a further 14 times using different random numbers
  5. repeat steps one to four for a part of the school field which the grass is infrequently cut
  6. compare your results by calculating a mean for each location
• Atoms exist in different forms or compounds at different times in history and cycle between them. We can see this cycling in the element carbon and the compound water. Just as rocks can cycle between igneous, sedimentary and metamorphic, carbon and water can exist in different forms at different times.
• Other elements and compounds also exist in cycles. Many humans eat protein in the form of meat from other animals. Our bodies break this down into its constituent parts called amino acids and then use these to make proteins within our own bodies for growth and repair. When we eventually die these building blocks are returned to the environment to be used by other living organisms.
• Decomposing bacteria and fungi help dead organisms break down and rot. They help recycle minerals and nutrients to the environment, which can then be used by other organisms. As they decompose dead matter, the decomposers also respire and so release carbon dioxide to the environment, contributing to the carbon cycle.
• Carbon is an essential element for life on Earth and parts of each of the cells in our bodies are made from it. The carbon cycle shows how atoms of this element can exist within different compounds at different times.
• 1. Carbon enters the atmosphere as carbon dioxide from respiration and combustion.

  2. Carbon dioxide is absorbed by producers to make carbohydrates in photosynthesis.

  3. Animals feed on plants, passing the carbon compounds along the food chain. Most carbon they consume is exhaled as carbon dioxide during respiration. The animals and plants eventually die.

  4.Dead organisms are eaten by decomposers and carbon in their bodies is returned to the atmosphere as carbon dioxide. In some conditions decomposition is blocked. material may then be available as fossil fuel in the future for combustion.
• Water is a key compound for life on Earth. All living organisms need water. Some can survive in a dormant state without it for long periods of time, but all organisms will quickly or eventually die without it.
• EvaporationWater turns from a liquid to a gas when it evaporates. Energy from the Sun can evaporate water from all places on the Earth’s surface such as puddles, ponds, lakes and oceans.
• Condensation-After evaporation water can cool and convert from gas to liquid, often forming clouds.
• Transport-Water within clouds can be blown many miles by strong winds and so transported to other areas.
• Precipitation-Precipitation occurs when rain, snow, hail and sleet fall from the sky.
• Surface runoff-Much water will be absorbed into the ground after precipitation but if a large volume falls or the ground is already wet some water can run along the surface of the ground.
• Infiltration-This occurs when water that has fallen as precipitation is absorbed into the ground. This can then be stored within underground rocks called aquifers.
• Transpiration-Plants need to maintain a constant stream of water to their leaves for transport and support. So they allow some water to evaporate as water vapour from their leaves to mean that more is continually ‘pulled’ to their leaves from the soil.
• Decomposition is the breakdown of dead matter, which is often called rotting. Decomposing bacteria and fungi are organisms that help the process of decomposition. Decomposition is crucial to the cycling of elements, such as carbon from one living organism to another.
• The rate of decay is the speed at which dead matter is broken down by decomposers. The rate can be estimated by measuring changes in pH, (for example in milk), change in mass (decaying fruit and vegetables) or change in temperature (grass cuttings). Rates of decay are affected by a number of key factors.
• At colder temperatures decomposing organisms will be less active, thus the rate of decomposition remains low. This is why we keep food in a fridge. As the temperature increases, decomposers become more active and the rate increases. At extremely high temperatures decomposers will be killed and decomposition will stop.
• With little or no water there is less decomposition because decomposers cannot survive. As the volume of available water increases, the rate of decomposition also increases. Many decomposers secrete enzymes onto decaying matter and then absorb any dissolved molecules. Without water these reactions cannot occur.
• Similar to water, decomposers need oxygen to survive and without it there is little or no decomposition. Oxygen is needed for many decomposers to respire, to enable them to grow and multiply. This is why we often seal food in bags or cling film before putting it in the fridge. As the volume of available oxygen increases, the rate of decomposition also increases. Some decomposers can survive without oxygen. We use these in biogas generators.