A major research theme among community ecology has been whether ecological communities have a (nonrandom) structure and, if so, how to characterise this structure. Forms of community structure include aggregation and nestedness. Aggregation
Overdispersion or statistical aggregation, where the variance of a distribution is higher than expected. Nestedness
Nestedness is a measure of order in an ecological system, referring to the order in which the number of species is related to area or other factors. The more a system is "nested" the more it is organized.
Habitat and Niche
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant, or other type of organism. It is the natural environment in which an organism lives, or the physical environment that surrounds (influences and is utilized by) a species population. Within each ecosystem, there are habitats which may also vary in size. A habitat is the place where a population lives. A population is a group of living organisms of the same kind living in the same place at the same time. All of the populations interact and form a community. The community of living things interacts with the non-living world around it to form the ecosystem. The habitat must supply the needs of organisms, such as food, water, temperature, oxygen, and minerals. If the population's needs are not met, it will move to a better habitat.
Niche is a term describing the way of life of a species.
The ecological niche describes how an organism or population responds to the distribution of resources and competitors and how it in turn alters those same factors. Fundamental niche
The fundamental niche is the potential niche, in other words the niche that would prevail in the absence of competition and other factors that might constrain its acquisition and use of the resources. All resources that could be used in absence of competition...