Interdependency
Objective
The student knows that there are relationships, systems, and cycles within environments. The student is expected to observe the way organisms live and survive in their ecosystem by interacting with the living and nonliving elements.
Foundation
Nonliving elements are parts of the ecosystem that are not living, such as sunlight, air (which includes oxygen and carbon dioxide), water, rocks, and soil. Living elements are organisms like plants and animals that require energy to survive and have basic needs that must be met. Plants and animals both need water, air (includes oxygen and carbon dioxide), rocks, soil for nutrients, and shelter. In a natural environment many organisms depend or rely on other organisms to survive. Because animals need food, water, and some need shelter, and plants need nutrients, sunlight, and water, all organisms must depend on other organisms and nonliving things in their environment to survive. Some birds need trees for nest building and food. Foxes and groundhogs need proper soil to dig tunnels and dens for shelter. Deer need trees and plants for food and camouflage. Plants need a proper balance of appropriate soil and water. This is true for any environment from a rain forest to an aquarium. The fish in an aquarium depend upon their owner to furnish food and keep the water clean. The pet of a child depends upon its owner for food and water. In turn the aquarium owner or pet caregiver receives enjoyment or companionship. In a natural environment where food, water, shelter, sunlight, and good soil are always in high demand, the competition for these resources creates a much more intense struggle for survival than in an aquarium or pet’s home. Organisms must fend for themselves, and organisms have different adaptations and methods to gain the energy (food) that they need.
The source of all energy on Earth is the light of the Sun. However, in the form of sunlight, that energy is not useable for animals. It must first be changed to a useable form and is done so by plants. Through the process of photosynthesis, plants are able to change the light of the Sun and carbon dioxide into sugar (energy) and store it in their leaves and roots. Because plants are able to produce a useable form of energy for other organisms, they are called producers. Animals, not being able to produce their own food, are required to eat plants or other animals to gain energy and are called consumers. Consumers can be classified into four groups. Herbivores are animals which consume only plants. Carnivores are animals which eat only other animals, and omnivores are animals which eat a combination of plants and other animals. Decomposers, such as bacteria and fungi, are organisms that break down dead organisms and their wastes.
As a plant produces energy (food) which is then eaten by an animal, which in turn gets eaten by another animal, it is possible to observe the flow of energy as it is passed from one organism to another. This “chain” of energy passage is called a food chain. An example would be grass that is eaten by a grasshopper, which is eaten by a toad, which gets eaten by a snake, which finally gets eaten by a hawk. The energy from the plant has moved through all the organisms to end with the hawk. In time the hawk dies, and its body decays and is broken down by the decomposers which return the nutrients back to the soil. The nutrients in the soil are then collected and used again by nearby plants. Sometimes a food chain becomes more complicated, and the hawk may also eat a mouse, squirrel, or some other animal. The snake may also eat a beetle or a caterpillar. When there are several food chains which interconnect it is called a food web.
In order to ensure a successful interactive ecosystem, there must be a proper balance in the populations of organisms. The relationship of organisms is such that any change in the population of any organism in the food chain will affect other organisms. In the example above, if all the snakes in an area were to be killed or removed, there would be fewer predators eating toads, and the toad population would increase. If there were no snakes, the hawk might have a smaller food supply, and the number of hawks might dwindle. If a fire were to destroy the grass, there would be fewer insects in the grass for the toads to eat and once again another population of organisms is affected. If any population of organisms changes in some way, either increasing or decreasing, it will affect other organisms in the community.