In order to study ecology, scientists need to see how organisms are related to one another and also to the environment in which they live. To do this, it is useful to think about a hierarchy of ecosystem organization ranging from the individual organism to the biosphere.
To begin with, consider a single organism, the individual. An “organism” is any living thing, whether it is a human being, a germ, a rose bush, or a panda bear.
A group of organisms of the same kind is a population. A “population” can be defined as a group of interbreeding organisms living in the same area. You might imagine a human population such as the population of the city in which you live or the population of a certain country. The humans within that population live in the same area and can interbreed and have babies. Similarly, a population of dandelions might all live in the same field and share pollen or a population of dolphins might all live in the same body of water and have babies.
A community is the next largest level of organization. A “community” includes all the organisms, sometimes hundreds of different types, in a given area. Several different populations are usually found in a community. The populations within a community are interdependent because of the food webs that bind them together. Communities can vary greatly in size. For instance, you could consider the community within a certain forest or you could think about a community in a garden. In MyScienceBox, students study microhabitats and look at a community within a single square meter. Communities can be even smaller such as the community that lives on and inside a single human being. On our skin are various molds, yeasts, and bacteria. In our hair we may have lice. In our intestines are E. coli and other bacteria. Many microscopic critters live in our mouth. Thus, there is a community of organisms living in and on your body!
Until now, we have only considered the living things in an area. The next level of the organization, an ecosystem, begins to include the nonliving parts as well. An “ecosystem” includes all organisms in a defined area and their nonliving environment. When you study an ecosystem, you look at how the nonliving and living parts affect one other. When you study a community, you only look at how the living things affect each other. Like a community, an ecosystem can be large or small. The Earth is the largest of all ecosystems which is called the “biosphere”.
The Earth ecosystem can be divided into several major biomes. A “biome” is one of several major types of ecosystems found on the planet. Each biome is characterized by a particular type of vegetation. Biomes generally encompass large geographical areas and are not sharply delineated (one will blend into another). You probably are already familiar with the major biomes already: desert, rainforest, grassland, tundra, coniferous forest, deciduous forest, and mountain. Some include the ocean as a non-terrestrial biome. One important point is that even though a biome like a rainforest will be similar anywhere in the world – all will have large trees, vines, many bird and animal species, etc. – the exact type of species of tree and the exact type of vine will vary from rainforest to rainforest. Thus in one kind of biome, different organisms will occupy the same niche. These organisms tend to be similar in form but often come from very different evolutionary backgrounds (for instance, consider the numbat, an Australian marsupial anteater, and other mammalian anteaters around the world including the giant anteater and the armadillo).
Some understanding of food webs is useful but not required.