Community (ecology)
In its simplest form it refers to groups of organisms in a specific place or time, for example, "the fish community of Lake Ontario before industrialization".
[1] The primary focus of community ecology is on the interactions between populations as determined by specific genotypic and phenotypic characteristics.
It is important to understand the origin, maintenance, and consequences of species diversity when evaluating community ecology.
[2] Community ecology also takes into account abiotic factors that influence species distributions or interactions (e.g. annual temperature or soil pH).
Humans can also affect community structure through habitat disturbance, such as the introduction of invasive species.
Robert Ricklefs, a professor of biology at the University of Missouri and author of Disintegration of the Ecological Community, has argued that it is more useful to think of communities on a regional scale, drawing on evolutionary taxonomy and biogeography,[1] where some species or clades evolve and others go extinct.
The next level is herbivores (primary consumers), these species feed on vegetation for their energy source.
Additional levels to the trophic scale come when smaller omnivores or carnivores are eaten by larger ones.
At the top of the food web is the apex predator, this animal species is not consumed by any other in the community.
Decomposers such as fungi and bacteria recycle energy back to the base of the food web by feeding on dead organisms from all trophic levels.
[11] A guild is a group of species in the community that utilize the same resources in a similar way.
A more precise guild would be vertebrates that forage for ground dwelling arthropods, this would contain certain birds and mammals.
Industrialization and the introduction of chemical pollutants into environments have forever altered communities and even entire ecosystems.
[16] Foundation species largely influence the population, dynamics and processes of a community, by creating physical changes to the environment itself.
Post fire disturbance the tree provides shade (due to its dense growth) enabling the regrowth of other plant species in the community, This growth prompts the return of invertebrates and microbes needed for decomposition.
This negatively affected the other organisms in the park; the increased grazing from the elks removed food sources from other animals present.
This starfish controls the abundance of Mytilus californianus, allowing enough resources for the other species in the community.
These changes influence the vegetation on the riparian zone, studies show biodiversity is increased.
Due to this communities are repeatable and easy to identify, with similar abiotic factors controlling throughout.
Frederic Clements developed the holistic (or organismic) concept of community, as if it were a superorganism or discrete unit, with sharp boundaries.
Henry Gleason developed the individualistic (also known as open or continuum) concept of community, with the abundance of a population of a species changing gradually along complex environmental gradients.
Varying environmental conditions and each species' probability of arriving and becoming established along the gradient influence the community composition.
Ecological drift leads to species' populations randomly fluctuating, whilst the overall number of individuals in the community remains constant.
It is considered an important limiting factor of population size, biomass and species richness.
The advantage of hunting in a group means bigger prey can be taken, however, the food source must be shared.
Whilst Rhizobium is a nitrogen fixing bacteria, providing amino acids or ammonium to the plant.
The mature tree also has a well-developed root system, helping it outcompete the sapling for nutrients.
Once developed to a zygote the parasite moves to the salivary glands where it can be passed on to a vertebrate species, for example humans.
[50] The cuckoo chicks eject the host's young from the nest meaning they get a greater level of care and resources from the parents.
Examples of neutralism in ecological systems are hard to prove, due to the indirect effects that species can have on each other.
