Niches
A Niche is a particular role that an organism can play in an ecosystem to be able to successfully and consistently survive and reproduce there. By their nature, all organisms will want to find and fill all the available niches of an ecosystem, so that they may survive and procreate. This will lead to constant competition and evolution, with only the best adapted species managing to fill each niche. If a species is particularly well adapted, it may even fill several niches at once.
A niche can also be thought of as a combination of resources consumed by an organism.
Overview
Niches can be highly variable, as they depend on both the ecosystem's biome, and the species present in that ecosystem. Furthermore, environmental events could temporarily or permanently alter the biome and species present in the ecosystem, which can drastically change the available niches.
Characteristics
Though it is hard to define a specific list of niches, there are many characteristics that can be used to define niches.
By Adaptability
Generalist: A species that is well adapted to live in a wide variety of environments. Because it is not specialized, it will have a hard time dominating any one environment in particular. However, in return, it is much more resistant to extinction, since if a natural event afflicts one biome it still has remaining members in others. This causes generalist species to be the most successful immediately after extinction events.
Specialist: A species that is highly adapted to living in a particular environment, at the cost of being less adapted to living in all other environments. Such a lifestyle will make it easy for a specialist species to outcompete all generalist species in that environment, but at the cost of making the species highly dependent on the stability of that environment. If a natural event were to occur in that environment killing many organisms or permanently altering its conditions, this could spell disaster for a specialist species.
By Diet
There are many different combinations of diets organisms can have, as such, there are many different ways of classifying them.
By Energy Source
All organisms must use energy (or ATP if microbes) to build the biomolecules (sugars, fats, proteins, DNA) they need to survive and reproduce. Depending on the source of this energy, the organism may be classified in different ways:
Phototroph: Receives their energy from light.
Thermotroph: Receives their energy from temperature gradients.
Chemotroph: Receives their energy from energy rich molecules (ex. glucose)
By Nutrient Source
Organotroph:
Lithotroph:
By Nutrient Source
Autotroph: