The Earth has many different ecosystems ranging from deserts to the icy tundra. In these ecosystems live many different organisms. The different organisms on the planet include: animals, plants, fungi, protists, and bacteria.
Within each ecosystem there are many, many different habitats. A habitat is the place where an organism lives and what provides that organism with the things that it needs. In a forest the habitat for a fern is the forest floor. In that forest the habitat for termites is the wood they are living in (like a dead tree). On that same wood there also will be bacteria and most likely mushrooms also sharing that same habitat.
A niche is the 'role' that an organism plays in an environment. It involves: where it lives, what it eats, what eats it, what time of day it is active, what time of year is reproduces etc.
An organism interacts with both the living and nonliving things in its environment. The living parts of the ecosystem are called the biotic factors. Organisms interact with each other in a millions of ways. For example, some organisms provide a habitat for other organisms (bacteria in your intestines etc). Another example is when one organism is food for another organism (grass to a cow).
Abiotic factors are the nonliving parts of an ecosystem and include:
All living things require water. It is the main component of cytoplasm. Cytoplasm keeps the shape of the cell so that it doesn't become a flat. It is impossible to move things around the cell (diffusion) and do chemical reactions (ie. stay alive) when there is no water. Water also plays a direct role in many chemical reactions (including photosynthesis).
Sunlight is an important source of energy for organisms to do photosynthesis-
water+carbon dioxide ---> sugar +oxygen
Oxygen is required by most organisms on the planet (some bacteria don't require it and some are actually killed by it!). Oxygen is required to convert sugar into another energy molecule called ATP. ATP is the main energy molecule that directly provides the energy required by cells to function.
Soil and rock provides a habitat for many organisms. The type of soil and rocks in a particular area can determine what kind of plants and bacteria can grow in the soil.
A species is a group of animals that are able to interbreed in the wild and have fertile offspring.
A population is the number of one species living in a particular area. The population of Homo sapiens in Vienna in 2011 was 1,731,236. In 2006 the population of Eurasian beaver (Castor fiber) in Europe/Asia was 639,000 (and growing!).
Ecosystems contain more than one population of species. Communities are a group of different species inhabiting (living in) the same region and interacting with each other-----all the plants, animals, fungi, protists and bacteria living in a certain area.
So how is a community different than an ecosystem? The answer is that a particular ecosystem involves the community of organisms living in that area PLUS the abiotic factors (soil, sunlight etc.)
Ecology is the study of ecosystems. Ecologists therefore study how organisms interact with other organisms and their abiotic environment.