20: Communities and Ecosystems - Biology

20: Communities and Ecosystems - Biology

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Populations typically do not live in isolation from other species. Populations that interact within a given area form a community. The organisms that form a community are found in habitats, physical environments where organisms live. However, only the biotic (living) components are considered part of a community. Scientists study ecology at the community level to understand how species interact with each other and compete for the same resources.


Multiple anthropogenic drivers are changing ecosystems globally, with a disproportionate and intensifying impact on freshwater habitats. A major impact of urbanization are inputs from wastewater treatment plants (WWTPs). Initially designed to reduce eutrophication and improve water quality, WWTPs increasingly release a multitude of micropollutants (MPs i.e., synthetic chemicals) and microbes (including antibiotic-resistant bacteria) to receiving environments. This pollution may have pervasive impacts on biodiversity and ecosystem services. Viewed through multiple lenses of macroecological and ecotoxicological theory, we combined field, flume, and laboratory experiments to determine the effects of wastewater (WW) on microbial communities and organic-matter processing using a standardized decomposition assay. First, we conducted a mensurative experiment sampling 60 locations above and below WWTP discharges in 20 Swiss streams. Microbial respiration and decomposition rates were positively influenced by WW inputs via warming and nutrient enrichment, but with a notable exception: WW decreased the activation energy of decomposition, indicating a “slowing” of this fundamental ecosystem process in response to temperature. Second, next-generation sequencing indicated that microbial community structure below WWTPs was altered, with significant compositional turnover, reduced richness, and evidence of negative MP influences. Third, a series of flume experiments confirmed that although diluted WW generally has positive influences on microbial-mediated processes, the negative effects of MPs are “masked” by nutrient enrichment. Finally, transplant experiments suggested that WW-borne microbes enhance decomposition rates. Taken together, our results affirm the multiple stressor paradigm by showing that different aspects of WW (warming, nutrients, microbes, and MPs) jointly influence ecosystem functioning in complex ways. Increased respiration rates below WWTPs potentially generate ecosystem “disservices” via greater carbon evasion from streams and rivers. However, toxic MP effects may fundamentally alter ecological scaling relationships, indicating the need for a rapprochement between ecotoxicological and macroecological perspectives.

Community Relations

The relationships between populations in a community are varied and may include both positive, negative, and mutually beneficial interactions. Examples of community-level relationships include competition (for food, nesting habitat, or environmental resources), parasitism (organisms that survive by feeding off a host organism), and herbivory (species that depend upon consuming local plant life to survive). These relationships often lead to changes in the genetic makeup of the population. For example, one or another genotype may be more successful due to certain community processes.

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What is Community?

Definition of a Community:

A community is a group of plants and animals that are found in a particular area that all interact in some way. The numbers and size of each population of each species of plant or animal strongly influence the community, and can cause it to change. Community ecologists focus on biotic interactions of fauna and flora. Humans can impact the community by removing or adding species.

Community Size:

A community is smaller in size than an ecosystem since it excludes abiotic factors. Therefore, a smaller entity is involved and the substrate that animals and plants live on or within is ignored.

Animal life:

Animals interact within the community either through predation or competition, which helps to determine the structure of the community. In other words, animals may compete to feed on plants, or for space. Different species also prey on other animals and help to regulate population sizes. For example, an owl can help control the number of rodents in an area by feeding on them. If there were no predators for the rodents, then there would be too many in the area.

Community Trophic levels:

The community also contains trophic levels and food webs with a flow of energy from producers up to consumers until a top predator is reached. Similar to an ecosystem, a community contains organisms that have different feeding modes such as herbivory, omnivory, and carnivory.

Examples of Community:

There may be a different macroinvertebrate community in one stream compared with another. Further examples would be, for instance, a community of birds, cypress trees, and all other organisms found living in a Louisiana swamp.

Difference Between Ecosystem and Community

Two of the most important entities in Ecology are the ecosystem and community, as those play significant roles in maintaining the composure of the environment. In order to make it convenient to study ecosystems, communities are important. However, when the components are observed in both these entities, it appears that they are similar hence, the difference between those are important to consider as in this article.

Ecosystem is the whole unit of biological and physical entities of a certain defined area or a volume. The size of an ecosystem could vary from a bark of a dead tree up to a great rain forest or the ocean. A small fish tank is an ecosystem, but it is an artificial ecosystem. That means an ecosystem could be either natural or manmade. However, the natural ecosystems last forever as there are self-sustaining mechanisms. Ecosystem is mainly composed of communities, which are combinations of populations.

Usually, a typical ecosystem contains producers, primary consumers (herbivores), secondary and tertiary consumers (mostly omnivores and carnivores), scavengers, and decomposers. Ecosystem is formed if these components, which encompass the energy cycling, are present in a particular place. Organisms will fit into the available niches by finding proper habitats and living in a preferred environment, and if that particular place could sustain the life without being diminished, the place eventually becomes an ecosystem. A collection of ecosystems makes a biome, and all the biomes collectively form the biosphere of the Earth.

According to the definition, community is the ecological unit that is composed of a group of organisms in different populations of different species that occupy a particular place at a particular period while interacting with both biotic and abiotic environment. It would be easy to understand when it is introduced as a collection of populations living in a particular place at a given time. A community may consist of different species of animals, plants, and microorganisms. The composition of species in a community differs in different ecosystems a particular community in a tropical rainforest has much more species than in a desert. Since it consists of many different populations, there are many habitats as well as many ecological niches.

One particular community is composed of thousands of interactions and relationships within and among populations. When two populations live together in a relationship, it could be mutualism, commensalism, parasitism, or synergism. Those basic ecological relationships or associations result in many ways such as both populations are benefitted, one benefitted and other suffered, or one benefits while other has no effect. Predation is another very important ecological relationship taken place in a community that results in a death for one party (prey) while the other party (predator) gets food. There are many food chains functioning inside a community those are important for the energy flow inside the entire ecosystem, which is formed as a collection of communities.

What is the difference between Ecosystem and Community?

• Ecosystem is a collection of communities, but community is a collection of populations.

• Ecosystems could be either manmade or natural, but communities are always natural or at least, communities are mended naturally inside a manmade ecosystem.

• Ecosystem is larger in all parameters than the community is.

• Community is not defined with particular characteristics, whereas a particular ecosystem is defined for its characteristics based on environmental and biological parameters.

• Communities are subjected to change with the affecting conditions, but a particular ecosystem does not change with those factors as it becomes another ecosystem with varying conditions.

What is an Ecosystem

The term ecosystem refers to both biotic factors and abiotic factors in a particular geographical area. Biotic factors include plants, animals, and microorganisms in a particular environment. The biotic factors interact with each other. At the same time, they interact with their physical environment. These interactions occur based on fulfilling two requirements in the environment. The first requirement is the flow of energy through different levels of factors in an ecosystem, which can be explained by food chains in an ecosystem. Most ecosystems get their energy from the sun. The radiation energy in the sunlight is trapped by autotrophs in a process called photosynthesis. Autotrophs produce simple sugars by trapping the energy of sunlight. Therefore, autotrophs are considered as the primary producers in an ecosystem. The organic compounds in autotrophs are used by heterotrophs as their food. Heterotrophs are considered as the primary or secondary consumers. A part of the energy is released to the environment as heat by the cellular functions in both autotrophs and heterotrophs. The death of both autotrophs and heterotrophs leaves the organic matter to decomposers to use as their energy sources. The final part of the energy is released to the environment by the cellular functions in the decomposers.

Figure 1: An Ecosystem

The second requirement is the recycling of nutrients in an ecosystem. Different living organisms require different types of nutrients from their environment. Moreover, different living organisms produce different forms of compounds. Therefore, mechanisms should exist to recycle the compounds in an ecosystem in such a way to continuously use them in an ecosystem. Different cycles are possessed by the environment to recycle the materials in an ecosystem such as carbon cycle, nitrogen cycle, phosphorus cycle, and water cycle. These cycles ensure the continuous supply of different forms of nutrients to organisms in an ecosystem. A hypothetical ecosystem is shown in figure 1.

Marine Communities

Download and print these marine community illustrations to learn about the organisms that live in different ocean environments.

Biology, Earth Science, Oceanography

This set of marine community illustrations can be used as visual aids during formal or informal instruction while teaching about the marine realm. There are three versions of each illustration:

  • unlabeled illustration
  • titled, unlabeled illustration
  • titled, labeled illustration

The three different versions were created in order to provide materials that best suit the needs of any educational situation.

Different areas of the ocean can be classified as different types of marine ecosystems. An ecosystem is defined as "a community and the interactions of living and nonliving things in an area." Marine ecosystems have distinct organisms and characteristics that result from the unique combination of physical factors that create them. Marine ecosystems include: the abyssal plain (areas like deep sea coral, whale falls, and brine pools), polar regions such as the Antarctic and Arctic, coral reefs, the deep sea (such as the community found in the abyssal water column), hydrothermal vents, kelp forests, mangroves, the open ocean, rocky shores, salt marshes and mudflats, and sandy shores.

The hydrosphere connects all freshwater and saltwater systems. Salinity, or high salt content, and global circulation make marine ecosystems different from other aquatic ecosystems. Other physical factors that determine the distribution of marine ecosystems are geology, temperature, tides, light availability, and geography.

Some marine ecosystems are very productive. Near-shore regions, including estuaries, salt marshes, and mangrove forests, teem with life. Others, like the abyssal plain at the bottom of the ocean, contain pockets of life that are spread far apart from one another. Some marine ecosystems, like the deep sea, are in constant darkness where photosynthesis cannot occur. Other ecosystems, like rocky shores, go through extreme changes in temperature, light availability, oxygen levels, and other factors on a daily basis. The organisms that inhabit various marine ecosystems are as diverse as the ecosystems themselves. They must be highly adapted to the physical conditions of the ecosystem in which they live. For example, organisms that live in the deep sea have adapted to the darkness by creating their own light source—photophores are cells on their bodies that light up to attract prey or potential mates. Many parts of the ocean remain unexplored and much still remains to be learned about marine ecosystems.

Building Off Known Genomes to Advance Systems and Ecosystems Biology

Jesse Poland of Kansas State University proposed sequencing intermediate wheatgrass (Thinopyrum intermedium, alternately known as Agropyron intermedium), shown on the left. Intermiedate wheatgrass has a biomass yield equivalent to that of the candidate bioenergy feedstock switchgrass. The right-hand specimen is of Agropyron repens, which co-occurs with Agropyron intermedium. (Matt Lavin, CC BY-SA 2.0 Wikimedia Commons)

The U.S. Department of Energy Joint Genome Institute (DOE JGI), a DOE Office of Science User Facility, has announced that 27 new projects have been selected for the 2016 Community Science Program (CSP).

“These new CSP projects, selected through our external review process, exploit DOE JGI’s cutting-edge capabilities in nucleic acid sequencing and analysis and build our portfolio in key focus areas including sustainable bioenergy production, plant microbiomes and terrestrial biogeochemistry,” said Susannah Tringe, DOE JGI User Programs Deputy.

The CSP 2016 projects were selected from 74 full proposals received, resulting from 98 letters of intent submitted. The total allocation for the CSP 2016 portfolio is estimated to tap nearly 40 trillion bases (terabases or Tb) of the DOE JGI’s plant, fungal and microbial genome sequencing capacity. The full list of projects may be found at

One reference genome, many applications

Several projects highlight how a single reference genome can be applied to advance previously supported studies, while others focus on plant-microbial interactions. Two, in particular, leverage recent DOE Office of Biological and Environmental Research (BER) Sustainable Bioenergy awards.

Daniel Schachtman from the University of Nebraska, Lincoln proposed a project focusing on a systems analysis of Sorghum bicolor, a potential bioenergy feedstock sequenced by the DOE JGI and published in the journal Nature in 2009. The project seeks to understand how genotype—its underlying genetic makeup—microbiome composition, and the environment influence sorghum’s phenotype—the plant’s observable traits. This work is also supported by a Sustainable Bioenergy grant to Schachtman as well as colleagues at the Donald Danforth Plant Science Center and the University of North Carolina.

Another project aimed at improving bioenergy crop yields comes from Tom Juenger at University of Texas at Austin. By sequencing several hundred switchgrass genotypes, the team hopes to identify genetic variations that contribute to high yields and high quality plant biomass that can be used for biofuel production. Juenger’s project dovetails with his Sustainable Bioenergy Crop Development grant through BER. For this funding opportunity, BER solicited applications for systems-biology driven basic research focused on understanding the roles of microbes and microbial communities in contributing to the health of bioenergy crop feedstocks and their associated ecosystems.

There are four projects utilizing the Chlamydomonas reinhardtii genome resource generated by the DOE JGI in 2007, for example. One project from University of California, Berkeley’s Kris Niyogi involves resequencing algal mutants to identify genes related to photosynthesis. Another comes from Sabeeha Merchant at the University of California, Los Angeles investigating algae that colonize snow in the Arctic as potential feedstocks in algal farms for biofuel.

The CSP project led by Clark University’s David Hibbett focuses on an in-depth genomic survey of the Lentinula genus. Lentinula is a group of white-rot, wood-decaying fungi perhaps best known as the genus of shiitake mushrooms, Lentinula edodes. (Image by dominik18s via Flickr CC BY 2.0)

From Jesse Poland of Kansas State University is a proposal to sequence intermediate wheatgrass (Thinopyrum intermedium), a perennial distantly related to wheat and with a biomass yield equivalent to switchgrass. By producing a whole-genome assembly of intermediate wheatgrass, and then conducting comparative analyses with the DOE JGI Flagship and grass model species Brachypodium distachyon, and with wheat, the team hopes to develop genomic resources that can be applied toward methods for improving the productivity of candidate bioenergy feedstock grasses.

Inter-organismal interactions

In addition to the Juenger project noted above, a project from J. Chris Pires at the University of Missouri focuses on the symbiotic relationship between orchids and fungi. Orchids are found around the world and their seeds rely on carbon solely provided by mycorrhizal fungi to germinate and develop into seedlings. Studying these relationships may provide researchers with insights into the evolution of plant-fungal interactions for DOE-relevant biomass feedstocks.

A proposal from Matteo Lorito at the University of Naples in Italy focuses on a similar symbiotic association between soil fungi and feedstock crops. His project specifically targets secondary metabolites, compounds that help the organism thrive and communicate, produced by Trichoderma fungal species interacting with the grass B. distachyon.

Other projects highlight the importance of microbial interactions within an ecosystem. One such project comes from Christopher Francis of Stanford University, who is studying the role of nitrogen-cycling microbial communities at uranium-contaminated groundwater sites within the upper Colorado River Basin. The goal is to determine the role that nitrification may play in the release of uranium into the aquifer.

Christopher Francis of Stanford University is interested in the floodplains in the upper Colorado River Basin, which are generally nutrient-poor but abundant in iron sulfide minerals, leading to the descriptor “naturally reduced zones” (NRZs). There are concerns that NRZs are slow-release sources of uranium to the aquifer that could persist for hundreds of years. (Photo by Roy Kaltschmidt, Berkeley Lab)

Two more plant microbiome projects focus on fungal interactions involving potential sustainable bioenergy feedstocks such as poplar and eucalyptus. One from Richard Hamelin at the University of British Columbia in Canada aims to develop a database of pathogens that could harm pine and poplar trees and thus prevent outbreaks through early detection, while the other from Ian Anderson at the University of Western Sydney in Australia looks at functional gene expression from the mutualistic Pisolithus genus, several species of which have symbiotic relationships with pine and eucalyptus.

Focusing on fungi

Several other projects have a fungal component, highlighting the breadth of this particular branch on the Tree of Life. Three of the selected projects extend the 1000 Fungal Genome Project, which aims to have at least two reference genomes from the more than 500 recognized families of fungi. Still other projects focus on harnessing fungal enzymes for bioenergy applications. One of the latter comes from Veronika Dollhofer at the Bavarian State Research Center for Agriculture in Germany. She proposed the study of anaerobic fungi from ruminant guts to better understand how they break down ingested plant matter. The enzymes in anaerobic fungi allow them to both degrade plant mass and convert it into sugars, a combination that could be useful in production-scale biogas plants.

Watch the video: Ecological Communities. Biology (January 2023).