Biology 1 Food Chains and Pyramids
-A food chain shows who eats what in a particular habitat. For example, grass seed is eaten by a vole, which is eaten by a barn owl. The arrows between each item in the chain always point from the food to the feeder. This is the direction in which energy flows in the food chain.
-Food chains always start with producers, which are almost always green plants. The other organisms in the food chain are consumers – they all get their energy and biomass by consuming (eating) other organisms.
-Most food chains are quite short, and they rarely consist of more than four steps. This is because a lot of energy is lost at each step. After about three steps, very little energy is still available for use by living organisms. This also explains why there are few organisms at the top of food chains, compared with those lower down.
-In more complex food chains, we can draw a pyramid for them. Let's look at this food chain:
oak tree → caterpillar → blue *** → sparrow hawk
There need only be one oak tree to feed one caterpilla, but lots of caterpilla's are needed to fill a blue *** and lots of blue ***'s are needed to fill a sparrow hawk, which is at the end of the chain. Here is what the pyramid would look like if it were a pyramid of numbers:
Oak Tree: - As you can see, the longer the lines, the
Caterpilla: --------- more of that animal or plant you will need
Blue Tit: ---- to fill the others. In this case, the catapilla
S. Hawk: - has the longest line as that's needed most.
Biology 1 Biomass; Animal and Plant Competition; P
-The dry mass of an organism is called its biomass. Biomass is the amount of biological material. The total biomass at a particular step in a food chain is always less than the total biomass at the step before it. Let's look again at the food chain:
grass → vole → barn owl The biomass of all the grass plants is the greatest in the chain, and the biomass of all the barn owls is the least. We can show information like this using a pyramid of biomass.If we looked at the more complex food chain (ie the oak tree to sparrow hawk), we could see that the large biomass of the oak tree is bigger than the small biomass of the sparrow hawk, at the other end of the chain.
-Animals and plants compete for different things in their habitats because if they don't get what they need from their homes they'll die. Here are what they both compete for:
Food; Water; Space; Mates Light; Water; Space; Mineral Salts.
-With population counts, there is a continuous tussle between predator and prey. For example, if the predators numbers increased, the preys numbers would decrease. However this would then lead to the predators number declining as there would not be enough food eventually. This would then mean the preys numbers would go up and the cycle would begin again. This is very clear when comparing the predator/prey relationship with the Canadian Lynx (Predator) and the Snowshoe Hare (Prey).