Biotic pollination vector
**Ecology** is the branch of biology that studies the biota (living things), the environment, and their interactions. It comes from the Greek *oikos* = house; *logos* = study. 

Ecology is the study of ecosystems. Ecosystems describe the web or network of relations among organisms at different scales of organization. Since ecology refers to any form of biodiversity, ecologists research everything from tiny bacteria in nutrient recycling to the effects of tropical rain forests on the Earth's atmosphere. Scientists who study these interactions are called *ecologists*. 

Terrestrial ecoregion and climate change research are two areas where ecologists now focus.

There are many practical applications of ecology in conservation biology, wetland management, natural resource management (agriculture, forestry, fisheries), city planning (urban ecology), community health, economics, and applied science. It provides a framework for understanding and researching human social interaction.

Population ecology
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See also: Overpopulation
A graph of a population which reaches carrying capacity
Population ecology measures the size of a population: all the living things from one species that live in an place. A population gets bigger because of birth and movement into a place, and it gets smaller because of death and movement out of a place. Growth rate is the change in population size divided by the current population size. When a population is small, growth rate does not change, so the population shows exponential growth. Rate of exponential growth depends on how a living thing reproduces. If it has only a few offspring (children) which grow slowly, like a human, the rate will be low. If it has a lot of offspring which grow quickly, like a fruit fly, the rate will be high. Any environment only has enough natural resources, such as food, water, or space, for a certain size of population. This size is called the carrying capacity. When population size is near the carrying capacity, growth rate will become less. The graph of population growth will be an S-shape, called logistic growth.

Community and ecosystem ecology
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A soil food web
A community is all populations of different species that live in the same place. An ecosystem is a community and its environment. Ecosystem ecology studies how energy and nutrients move through an ecosystem. All living things need energy to survive, move, grow, and reproduce. A trophic level is the number of times energy moves from one living thing to another, before reaching a particular living thing. The first trophic level, called producers or autotrophs, gets energy from the environment. They use the energy to make organic compounds. Most producers, such as plants, take in energy from sunlight, but some take it from inorganic compounds. Other trophic levels, called consumers or heterotrophs, get their energy by eating other living things. All animals are consumers, and there are three kinds: herbivores, carnivores, and omnivores. Herbivores eat only plants, carnivores eat only other animals, and omnivores eat both. Decomposers are living things which break down dead things. A food web shows the movement of energy in an ecosystem.

Humans and ecology
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### Ecology in politics

Ecology starts many powerful philosophical and political movements - including the conservation movement, wellness movement, environmental movement, and ecology movement we know today. When these are combined with peace movements and the Six Principles, they are called green movements. In general, these put ecosystem health first on a list of human moral and political priorities, as the way to achieve better human health and social harmony, and better economics. 

People with these beliefs are called political ecologists. Some have organized into the Green Parties, but there are actually political ecologists in most political parties. They very often use arguments from ecology to advance policy, especially forest policy and energy policy.

Also, ecology means that it is the branch of biology dealing with the relations and interactions between organisms and their environment, including other organisms.

### Ecology includes economics

Many ecologists also deal with human economics:

* Lynn Margulis says that economics studies how humans make a living, while ecology studies how every other animal makes a living.
* Mike Nickerson says that "economy is three-fifths of ecology", since ecosystems create resources and dispose of waste, which the economy assumes is done "for free".

Ecological economics and human development theory try to separate the economic questions from others, but it is difficult. Many people think economics is just part of ecology now, and that economics that ignores it is wrong. "Natural capital" is an example of one theory combining both.

### Ecology and anthropology

Sometimes ecology is compared to anthropology. Anthropology includes how our bodies and minds are affected by our environment, while ecology includes how our environment is affected by our bodies and minds. There is even a type of anthropology called ecological anthropology, which studies how people interact with the environment. 

Antoine de Saint-Exupery stated: "The earth teaches us more about ourselves than all the books. Because it resists us. Man discovers himself when he measures himself against the obstacle".

Related pages
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* Prey-predator equations
* Ecological economics
* Ecomuseum
* Environmentalism
* Sustainable development

Other websites
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* "Restoration Ecology". Wiley Online Library. doi:10.1111/(ISSN)1526-100X.