The nested arrangement of the tanks creates partially separated ecological zones or microhabitats . In nature, different microhabitats can occur naturally because of the physical size and structural diversity of the environment. Each microhabitat contains a different community of organisms that thrive there because they are all well adapted to the local conditions. Subdivision of an environment into smaller, partially separated microhabitats creates more niches , lowers competition between organisms and often allows more species to live in the same physical space. The diversity of this system is also affected by factors such as immigration , succession , predation , local extinction and by the availability of resources .
Immigration occurs when new species are introduced.
The organic material gradually breaks down and releases dissolved nutrients to the water. Succession is the gradual change in the relative numbers of different species over time. These changes occur because of maturation, differential reproduction, predation and subtle changes in the physical conditions. In some ecosystems, such as oak forests, succession may occur until a climax state is reached. In other ecosystems, such as coral reefs, factors such as disturbance cause succession to continue indefinitely.