Ecology is a branch of biology which is focused on the examination of living organisms in the natural environment. Ecologists look at how organisms interact with the environment and each other, and they study the complex and interconnected systems which influence life on Earth. Ecology is also sometimes known as environmental biology, and there are a number of subdisciplines within this branch of the sciences which deal with specific topics of interest, such as the relationship between humans and the natural environment.
Researchers in ecology can study individuals, populations, communities, and ecosystems. At each level, there are more things to learn about. The natural environment is usually heavily interconnected; researchers can focus on a single population of plants or animals, for example, and find much fodder for study, ranging from how that population shapes the physical environment to how other organisms interact with it. For example, ruminant populations can create paths and watering holes, shaping the land, and they can also influence plant populations by eating some plant species, leaving others alone, and excreting seeds which plants can use to spread themselves.
In the 20th century, ecologists became especially interested in human activities which had a deleterious effect on the environment, recognizing that humans could have a tremendous and not always beneficial influence on nature. For example, dumping pollutants into a river can cause a variety of changes in nature, just as paving over a wetland can eliminate a habitat and put stress on the animals and plants which are used to living there.
Ecologists are often interested in looking at entire ecosystems, and studying all of the organisms which live in them and influence them. Each ecosystem hosts unique plant and animal species which have adapted to the environment and each other, and studying this can provide scientists with information about the history of that ecosystem, and the evolutionary roots of the animals which live there. Ecology can also be studied in urban environments.
The study of ecology is not limited to the terrestrial environment; marine environments, lakes, and streams can also provide a great deal of food for thought and inspiration for study. The marine environment in particular is not very well understood, with researchers constantly finding that there is more to learn about the ocean, the creatures which live there, and its underlying geography and geology. For example, for centuries people assumed that the bottom of the ocean was inactive and bleak, but in the 20th century, researchers discovered areas of biological activity around hydrothermal vents, with organisms which had adapted to the dark, high pressure, low oxygen environment of the deep sea.