Feeding Relationships Flashcards
Food chains
What they are Arrows Trophic levels What are animals with trophic levels and what are plants? Decomposers
A food chain shows ‘who eats what’ in a habitat.
For example, owls eat shrews, shrews eat grasshoppers, grasshoppers eat grass.
The arrows in a food chain show the direction in which the food passes
Each level in a food chain shows a separate trophic level, or level at which that species is feeding. Therefore using the food chain above:
Grass - the producer level, because grass is a plant and produces its own food using light energy during photosynthesis.
Grasshoppers - these are the primary consumers, ‘consumer’ because they eat the grass and ‘primary’ because they are the first eaters of other organisms in the food chain. This level may also be called herbivores because they eat plant material.
Shrews - these are the secondary consumers because they eat the primary consumers. Also called carnivores, because they eat meat.
Owls - these are the tertiary consumers because they eat the secondary consumers. They are also carnivores.
All animals are consumers, because they eat other organisms to get their food, in contrast to plants that are producers.
What is not shown in a food chain is what halogens to all the dead plant and animal material that is no scavenged. This material decays as a result of the action of decomposers, for example, fungi and bacteria. Fungi digest their food, by secreting enzymes outside their hyphae, they then absorb the dissolved food materials. Many bacteria also fo this. However, only some of the digested food materials are absorbed - the rest are released released until the environment.
Trophic levels definitions
Producer level Primary consumers Secondary consumers Tertiary consumers Decomposers
Producer level - an organism that produces its own food, such as plants using light energy in photosynthesis to produce glucose.
Primary consumers - an animal that eats plants.
Secondary consumers - an animal that eats primary consumers
Tertiary consumers - an animal that eats secondary consumers
Decomposers - an organism that causes decay of dead material, such as many fungi and bacteria.
Food webs
Food chains within a habitat are linked together to form a food web. A food web is a better description of the feeding relationships in a habitat and shows how living organisms are interdependent.
Food webs still usually try to group the organisms according to their trophic level. There are usually many more species in a habitat than shown in a food web. So food web diagrams may focus on the relationships between key organisms rather than all of them. For example, they may only include the most numerous species or focus on the most vulnerable species. This could be helpful if you want to use the food web to predict what would happen to the ecosystem if the food web were changed in some way, such as by human activity.
Energy transfers in food webs
Food chains and food webs not only show who eats what but they also show the flow of energy through the trophic levels, from producers to top consumers.
Pyramids of numbers
A diagram that shows the number of individual organisms in different trophic levels of a food chain, often a pyramid shape.
Each bar in the pyramid represents a different trophic level, arranged in order starting with producers at the bottom and ending with the top consumers at the top. The width of each bar is drawn to scale, representing the numbers of individuals in the trophic level.
Gathering data for pyramid of number is relatively simple, because you must have to count the number of organisms in each trophic level within the area of observation.
Pyramids that have a very narrow base are sometimes called an inverted pyramid of number.
Pyramids of biomass
If you measure the biomass (the mass of living material) in the organisms instead of number you can avoid the problem of inverted pyramids.
The biomass of each trophic level is usually calculated as the average dry mass of one individual multiplied by the total number of individuals. This is usually within a given area, so the values will be in mass per unit area.
Pyramids of energy
A pyramid of energy in units of energy per area per time to show the amount of energy in each trophic level.
Although pyramids of energy always provide a pyramid shape each time, they are more difficult to calculate because you have to measure the energy content of each population within the area. This involves burning the plant or animal tissue in a calorimeter to measure the energy it contains and then multiplying by the number of individuals. Or you could use estimates of the average fat and muscle content of an individual animal, you can estimate the average energy content in an individual animal. All these phases of estimation reduce the reliability of the calculated values.
Efficiency of energy transfer
If you compare the amount of energy that enters a trophic level with the amount of energy available to the next trophic level, you can see that there are several sources of energy loss at each stage. From this you can calculate the efficiency of energy transfer, which is the proportion of energy passed to the next trophic level compared with the energy that entered the trophic level - for example, the amount of energy in the plants that a herbivore converts to animal tissue compared with the amount of energy in all the plants that it could eat.
Energy losses in plants
The amount of light energy that falls on the Earth’s surface varies at different times of day and year, and varies in different parts of the world. On average, tropical areas receive between 3 and 5 kWh/m^2 per day.
Plants only use a tiny proportion of this for many reasons. It has been estimated that most plants only convert about 1% to 2% of the light energy that falls on them into chemical energy in biomass. This is the energy available to a herbivore that eats the plant.
Energy losses in animals
When an animal eats, the food is digested in the alimentary canal and the soluble food molecules are absorbed into the body. The undigested food in the alimentary canal is egested as faeces. Absorbed food molecules may be used for different purposes in the body
- To produce new animal tissue or gametes for reproduction
- Used as a source of energy for respiration
- Converted to waste products in chemical reactions
The chemical energy in the food molecules remains as chemical energy in body tissue, or in the waste products, such as urea, which are excreted to the environment.
When food molecules are broken down during respiration chemical energy in the molecules is converted to heat energy. This heat energy is lost to the environment by conduction and radiation. So only a proportion of the chemical energy in the animal’s food is converted into chemical energy in its body tissues. This is what increases the animal’s biomass.
Different groups of animals have different efficiencies of energy transfer, depending on their food and on their body chemistry. For example, plant material is more difficult to digest than animal material, so carnivores generally have greater energy transfer efficiencies than herbivores. In addition, mammals and birds maintain their internal body temperature at a constant level, often above the temperature at a constant level, often above the temperature of the environment, and this requires the release of additional heat energy from respiration. So mammals and birds generally have a lower energy transfer efficiency than reptiles and amphibians, which do not maintain a constant internal body temperature. On average only about 10% of the energy in one trophic level is transferred to the next.
