Trophic Levels and Energy Flow
Probably one of the most important aspects of ecology involves the energy flow throughout the populations in a biome. The way that energy flows between organisms is represented through visuals called food webs which are made up of smaller interactions called food chains. Because all organisms must take in materials to live, food webs are vital to the world of ecology.
Because many organisms do not exclusively eat one thing, food webs can become very complex very quickly. On top of this, the arctic has an extra quirk; polar bears do not fit into the traditional terrestrial food web because they primarily eat marine organisms. In order to account for this, I made two food webs for the arctic.
Producers convert sunlight into usable energy through photosynthesis. In the arctic, the producers tend to be small shrubs and lichen such as arctic willow, caribou moss, and labrador tea. The permafrost makes it difficult for plants to ground themselves with their roots, so in turn the plants are smaller. The herbivores, or primary consumers, include caribou, ermines, harlequin ducks, arctic hares, musk oxen, and lemmings. Arctic wolves, arctic foxes, and snowy owls are at the top of the food web as secondary consumers because they consume the primary consumers. Not included in this food web is the energy source for producers which comes from the sun. |
As for polar bears, they are considered both tertiary consumers and quaternary consumers. Polar bears consume ringed seals (which are tertiary consumers) as well as fish like trout, salmon, and cod (which are secondary consumers). For this particular food web the producers are arctic moss and arctic algae which are prey for arctic grasshoppers, arctic krill, and arctic shrimp. Not included in this food web is the source of energy for producers - the sun. |
Food pyramids are similar to food webs, however they include a very important concept that food webs lack. Just like with cellular respiration, not all energy taken in is used. So, with the food pyramid, you are able to see that only 10% of the initial energy that is contained within producers is transfered to a primary consumer. As you go up the pyramid, only 10% of the energy from the tropic level below it is available. The rest of this energy is typically given off as heat. So, if a musk ox consumes some lichen, they would only be able to use 10% of the initial energy contained within the lichen. Once a secondary consumer, like an arctic wolf, eats that musk ox, they will only be able to get 1% of that initial energy transfered from the producer. This means that the further up you go on the food pyramid, the more an organism must consume in order to survive. That musk ox would have to eat ten lichen in order to receive that 100% of energy that the lichen a,ready has available.