Ecological communities are made up of the total organisms in a habitat or region. These communities are multifaceted and are therefore made of complex interactions between species, the resources that they use and the environment as a whole.
Ecological communities are (often interdependent) populations of multiple species within a single habitat. The interdependent interactions between species form ecosystems. As species in an ecosystem interact, they influence resources in the habitat, exchange minerals with organisms, produce energy and consume organisms of other species.
For example, the vegetation that caterpillars eat, known as host plants (which include willow, lilac, milkweed, and aspen) use sunlight to produce nutrients which caterpillars depend on to survive. Species of caterpillars serve as food for American Robins, Carolina wrens and other caterpillar-larvae ingesting birds. If one were to remove American Robins (or any other caterpillar-larvae eating birds) from the an ecosystem, that would have a causal effect on both the caterpillar populations, but also the abundance of vegetation that’s allowed to grow. Removing a single species, especially the predators, has implications which can be felt throughout the entire ecological system.
The point is: factors like predators, vegetation, sunlight and the availability of nutrients are crucial in shaping ecosystems. A community’s structure can be partly understood in terms of its species richness. Species richness is the sum total of different species represented in a given pool of organisms. Species richness is one of the most commonplace metrics used for comprehending the extent of diversity of within a community.
Community structures are essentially the labyrinth of interactions between organisms within the region and their interactions with their environments. However, not all species are equally important in ecological communities. A keystone species is the species which disproportionately affects other organisms in the ecosystem relative to its population abundance. If the keystone is removed from the environment, then a chain reaction of events will be set off that cause falling survival rates for the dependent species.
The foundation species likewise plays a crucial role in the populations of other species in the ecosystems. Foundation species are are likely to have the large populations, making them onipresent throughout the ecological system. Foundation species therefore make up the structural bedrock of the ecosystem. The difference between the keystone and foundation species is that the keystone species is likely to be few, yet powerful. In other words, the continued functionality of the ecological system depends upon their influence. The foundation species is likely to be the most abundant creature in the ecosystem and structures the environment physically.