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Bibliographic Information

As a subset of the general study of ecology, this field of specialization explores the organization and functioning of biological communities. Community ecologists protect the environment and save species from extinction by assessing and monitoring environmental conditions such as global warming.

One of the earliest formal definitions of community ecology was suggested by Cornell professor Robert Whittaker in Whittaker characterized community ecology as an assemblage of living organisms that interact and form a community with a unique structure and species composition. Knowing how a community functions is vital to promoting and preserving biodiversity. Community ecology examines how coexisting organisms interact and compete in a particular niche or geographical location such as a woodland, prairie or a lake.

Community ecology encompasses all populations of all species that live together in the same area. Community ecologists study ecological interactions and consider such things as how to intervene when a rising deer population is destroying the understory layer of a woodland.

Community ecology encompasses many types of ecological interactions that continue to change over time. A forest community includes the plant community, all trees, birds, squirrels, deer, foxes, fungi, fish in a forest stream, insects and all other species living there or migrating seasonally.

Similarly, a coral reef community includes a vast number of different species of corals, fish and algae. Abundance and distribution are strong forces that shape the biological community.

Community (Ecology): Definition, Structure, Theory & Examples | Sciencing

Community ecology focuses on how interactions between different species affect health, growth, dispersion and abundance of the ecological system. At the community level, species are often interdependent.

Several short food chains are common in most biological communities. Food chains often overlap and form food webs of producers and consumers. American, European and British scientists have long held many differing theories on the definition of community ecology, which was first called plant sociology. In the 20th century, opinions differed as to whether ecological niches were self-organized organismic communities or random assemblages of species that thrived because of their particular traits.

By the 21st century, theories broadened to include such ideas as the metacommunity theory that focuses on community structures and the evolutionary theory that incorporates principles of evolutionary biology into community ecology. Currently held community ecology theory is based on the supposition that ecological communities are the result of different types of assembly processes.

Conservation Biology

Assembly processes involve adaptation, speciation in evolutionary biology, competition, colonization, altitude, climate, habitat disturbances and ecological drift. The theory of community ecology expands upon niche theory , which has to do with an organism having a specific place and role in an ecosystem.

Species richness refers to the richness, or number, of species found. For example, an annual bird count might yield a species richness of 63 different species of birds spotted in a nature center. One pileated woodpecker is counted the same as 50 chickadees in determining species richness of the area.

Species richness does not factor in the total number of individuals found within each species. The number and type of species present in a community gradually increases toward the equator. Species richness decreases towards the polar region. Fewer plant and animal species are adapted to cold biomes. Species diversity looks at overall biodiversity. Species diversity measures species richness as well as the relative number of species present.

High species diversity characterizes stable ecological communities. Sudden or significant changes in a community such as an influx of predators can disrupt the predator-prey ecological balance and reduce species diversity. Community ecologists study the interaction between structure and organisms. Structure describes characteristics of ecological niches, species richness and species composition. Species interact with each other and with their environment in many different ways, such as competing for finite resources or working together to trap game. Population dynamics play a pivotal role in communities.

The trophic pyramid is made up of trophic levels , and food energy is passed from one level to the next along the food chain see below Food chains and food webs. The base of the pyramid is composed of species called autotrophs, the primary producers of the ecosystem. They do not obtain energy and nutrients by eating other organisms. Instead, they harness solar energy by photosynthesis photoautotrophs or, more rarely, chemical energy by oxidation chemoautotrophs to make organic substances from inorganic ones.

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All other organisms in the ecosystem are consumers called heterotrophs, which either directly or indirectly depend on the producers for food energy. Within all biological communities, energy at each trophic level is lost in the form of heat as much as 80 to 90 percent , as organisms expend energy for metabolic processes such as staying warm and digesting food see biosphere: The flow of energy.

The higher the organism is on the trophic pyramid, the less energy is available to it; herbivores and detritivores primary consumers have less available energy than plants, and the carnivores that feed on herbivores and detritivores secondary consumers and those that eat other carnivores tertiary consumers have the least amount of available energy. The organisms that make up the base level of the pyramid vary from community to community.

In terrestrial communities, multicellular plants generally form the base of the pyramid, whereas in freshwater lakes a combination of multicellular plants and single-celled algae constitute the first trophic level. The trophic structure of the ocean is built on the plankton known as krill.

What can ecosystems learn? Expanding evolutionary ecology with learning theory

There are some exceptions to this general plan. Many freshwater streams have detritus rather than living plants as their energy base. Detritus is composed of leaves and other plant parts that fall into the water from surrounding terrestrial communities.

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It is broken down by microorganisms, and the microorganism-rich detritus is eaten by aquatic invertebrates, which are in turn eaten by vertebrates. The most unusual biological communities of all are those surrounding hydrothermal vents on the ocean floor. These vents result from volcanic activity and the movement of continental plates that create cracks in the seafloor.

Sulfur-oxidizing bacteria chemoautotrophs thrive in the warm, sulfur-rich water surrounding these cracks. The bacteria use reduced sulfur as an energy source for the fixation of carbon dioxide. Unlike all other known biological communities on Earth, the energy that forms the base of these deep-sea communities comes from chemosynthesis rather than from photosynthesis; the ecosystem is thus supported by geothermal rather than solar energy. Some species surrounding these vents feed on these bacteria, but other species have formed long-term, reciprocally beneficial relationships mutualistic symbioses with sulfur bacteria.


These species harbour the chemoautotrophic bacteria within their bodies and derive nutrition directly from them. The biological communities surrounding these vents are so different from those in the rest of the ocean that since the s, when biological research of these vents began, about new species have been described, and there are many more that remain undescribed—i. Among the described species there are at least 75 new genera, 15 new families, one new order, one new class, and even one new phylum.

Because all species are specialized in their diets, each trophic pyramid is made up of a series of interconnected feeding relationships called food chains.

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