Ecology in One Page:
Ecology is the study of living things interacting with their environment, both the abiotic (non-living) factors such as water and oxygen and the biotic factors (living) such as predators and parasites. The area of the Earth that is studied is referred to as an ecosystem. It could be a rain forest or a lake. All of the organisms that interact in that ecosystem are called the community. All of the organisms of one species in the community are called a population (e.g. a population of wolves).
One of the ways organisms interact with the environment is taking food from the environment to make energy. Energy is originally placed in food by green plants (known as producers) in a process called photosynthesis. Inn photosynthesis, energy from the sun is locked up in glucose molecules and stored for later use within these plants. If another organism (a 1st order consumer) eats these plants, it can use the energy stored in that glucose. Later, still other animals (2nd order consumers) can eat the 1st order consumers and also use the glucose. A picture of this sequence of eating that shows what organisms use glucose and its energy is called a food chain.
(Example: grass -> cow -> wolf ) A different picture which includes all of the alternate choices in an organisms diet is called a food web.
As you live, your body uses some of the energy, (for movement, for warmth, for chemical processes, and as waste heat) and stores the rest. Since some of your energy is used up, it is not available for the next organism in the food chain. In fact, each level looses about 10% of the energy as waste heat. This means that each level of the food chain has less energy stored than the one below it. This can be shown in a picture called a food pyramid. It is wider at the bottom where the producers are and narrower at the top where consumers are).
Some organisms have specially defined relationships called symbiosis. This is where one organism lives on or in another. There are three types of symbiosis, including mutualism, where both organisms benefit by the symbiosis. There is also commensalisms, where neither organism benefits or is harmed, and parasitism where one animal benefits while the other is harmed.
Because there is a limited amount of food, habitat, water etc. in an ecosystem, there will be competition for it by the organisms present. The number of individuals in a population that can be supported by an ecosystem is called it carrying capacity. Species that exist together over long times are called a climax community.
Both natural and man-made disasters can have an impact on an ecosystem. Some are sudden such as volcanic eruption and some are gradual such as climate change. These often kill off the climax community resulting in a succession or a series of new temporary communities occupying the ecosystem one after the other, until eventually the climax community return returns.
Humans have impacted ecosystems by stripping or hunting away species of plants and animals; for example, they have removed predators to deer and end up causing deer population explosions. They also introduced non-native species (exotics) like purple loosestrife and zebra mussels, which took over their ecosystems. They have polluted the water and air causing species to become extinct; for example, DDT pesticides caused bald eagles to almost go extinct because it prevented eagle eggs from being produced normally. In other cases man simply removed or destroyed habitats, thus wiping out whole ecosystems.