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Community Structure and Attributes for Successful Outcomes

Grade 7
Jun 6, 2023

Community Structure and Attributes

Interdependence of Living Organisms in Community and Energy Pyramid

With the exception of autotrophs, most organisms in a community rely on other organisms for food. A food chain can be used to symbolize this interdependence on other organisms, with each organism occupying a certain trophic level in the food chain.

In a given food chain, the grasshopper (primary consumer) feeds on autotrophs like grass. Secondary consumers like frogs feed on primary consumers. Tertiary consumers such as snakes eat secondary consumers. Finally, snakes are eaten by predators, such as eagles or hawks. Vultures and other scavengers feed on dead animals.

Energy pyramid

Some tropical rainforest communities have huge numbers of species crowded into each cubic meter, whereas Arctic communities have only a few species.

For most of the year, the Arctic region is extremely cold, whilst the tropical rainforest is hot and humid. Rainforests are found in areas with tropical climates. Because it is hot and rainy all year, they have a humid environment. Hence, organisms can survive better in tropical rainforests compared to the Arctic region.


As the environment changes, so do the result of interactions. Some of these interactions will likely boost diversity, while others will likely decrease it. One of the most important characteristics of a community is its diversity.



Explanation of Community Structure

The number of species present and their relative proportions is referred to as community structure.

The richness of a species in a community determines its structure. The types of species and the number of species that make up a community can vary greatly.


Communities can be small, with only a few species populations in a limited area, or large, with many species’ populations spread out across a large area.

The biotic composition of a community is referred to as community structure. It includes species diversity and abundance, as well as the trophic interactions established by community members.

Species richness, or the number of species present, and species diversity, which is a measure of both species richness and species evenness (relative numbers), can be used to define the structure of a community.

Measurement of Community Structure

Species richness and diversity are two essential measurements ecologists use to define the structure of a community.

Species Richness:

The number of different species in a community is referred to as species richness. If we identified 30 species in one community and 300 species in another, the second community would have significantly more species diversity than the first.

The communities with the highest species richness are found around the equator, where there is ample solar energy (supporting high primary productivity), mild temperatures, abundant rainfall, and little seasonal variation. The communities with the lowest species richness are found in the poles, which receive less solar energy and are colder, drier, and less conducive to life.

Rich communities can be found in places with a lot of solar energy, warm temperatures, a lot of rain, and little seasonal variation.

Species richness is represented as S. Here, the total variety of species seen is five. Hence S=5.


Species Diversity:

The species diversity in a community is a measure of its complexity. It is determined by the number of different species in the community (species richness) as well as the relative abundances of those species (species evenness).

Species diversity is a measure of species richness and species evenness, which means it considers not only the number of species present but also how evenly distributed their numbers are.

Species diversity is increased when there are more species and their abundances are more uniformly distributed.

Because the distribution of species is more even in community 1, there would be more species diversity compared to species diversity in community 2, which is shown in image 7.

Species Diversity

Example 1

For example, if two communities each have five species, the species richness for both communities will equal five. This would not be a community with a very even distribution if the initial community had 100 members and 80 of them were all of the same species. The second community would be more evenly distributed if it contained 100 members, with 20 individuals belonging to each of the five species. Community 2 would have more species variety because it was more uniformly dispersed.

Example 2

A forest community with 20 distinct kinds of trees, for example, would have more species diversity than one with only 5 different kinds of trees (assuming that the tree species were even in abundance in both cases).

A forest community with 20 distinct kinds of trees in even abundances has more species variety than one with the same number of species in very uneven abundances (for instance, with 90 percent of the trees belonging to a single species).

Ecologists believe that ecological groups with greater diversity are more stable (i.e., better able to recover after a disruption) than those with less diversity.

Factors Affecting Community Structure

A community’s structure is the result of several interacting factors, both abiotic (non-living) and biotic (living). Here are a few major characteristics that affect community structure:

1. The Climate Patterns in the Community’s Area:

Global climatic patterns (differences in temperature, solar energy input, and other factors as a function of distance from the equator) can have an impact on community structure.

Climate predictability or variability can have an impact on community structure; for example, some species may be unable to thrive in a place with periodic droughts or below-freezing temperatures.

2. The Geographical Location of the Community:

The geographical qualities of the community’s location can have an impact on its structure. For example, island communities that are farther away from the mainland have fewer species than those that are closer to the mainland. This reflects the fact that when the island is farther away, the possibility of a species arriving from the mainland is lower.

3. The Environment’s Heterogeneity (Patchiness):

Because there are more unique habitats to be occupied when there is more diversity or heterogeneity in a community’s environment, it may allow for increased species richness.

Consider two communities, one occupying a field and the other inhabiting a field littered with rock piles. Because species that can live in the rocks (but not in the open field) will be present in addition to those that can live in the field, the second community may have a higher species richness.

The number of disruptions or disruptive occurrences that occur on a regular basis:

The frequency of disruptive occurrences (such as hurricanes, wildfires, and landslides) might have an impact on the community’s structure. According to the intermediate disturbance theory, communities with a medium (middle) level of disturbance may have more species variety than those with highly frequent or very infrequent disturbances.

4. Organism-to-organism Interactions:

Competition, predation, and various forms of symbiosis are just a few of the interspecies interactions that can occur between organisms, and they all have the ability to influence a community. For example, two species that are very competitive may be unable to live in the same community, or a prey species may be unable to survive in a community with a powerful predator.

Effects of Species on Community: Foundation Species and Keystone Species

Some species have extremely powerful effects on community structure, keeping the community’s balance or even allowing it to exist. Foundation and keystone species are among the “special” species.

Foundation Species

A foundation species plays a crucial role in the formation and development of a community. Foundation species frequently operate by altering the environment in order to support the community’s other organisms.

Kelp (brown algae), for example, is a foundation species that creates habitats for other animals in the kelp forest ecosystem to survive.

Foundation Species

ecosystem to survive

One more foundation species is the corals of a coral reef. The majority of the reef structure is made up of living and dead coral exoskeletons, which protect other species from waves and ocean currents. Beavers are considered a foundation species because they alter their environment by constructing dams.

Keystone Species

Keystone species: A keystone species is one that, in relation to its biomass or abundance, has a disproportionately large impact on community structure.

Keystone species differ from foundation species in two respects: they are more likely to belong to higher trophic levels (to be top predators), and they behave in a wider range of ways than foundation species, which have a tendency to impact their environment.

The intertidal sea star Pisaster ochraceus, which can be found in the northwest United States, is the most well-known example of a keystone species.

The sea stars were taken from the intertidal zone, where they lived in a typical community ecology experiment.

As a result, their prey (mussels) population increased, changing the community’s species composition and drastically lowering species diversity. After sea stars were abundant, many species of barnacles and algae were found in the lower intertidal zone, but when they disappeared, the mussel population expanded downward and nearly completely replaced these other species.

keystone species

When a keystone species is lost, a significant reduction in diversity or breakdown of community structure is common. The loss of diversity occurred in this case because the mussels crowded out other species that could have survived if the sea stars had kept the mussels in check.

Invasive species are invaders who are not native to the habitat and create disruption to the ecosystem. Many invasive species, such as the Zebra Mussel, cause problems for native species. Invasive species spread quickly and reduce biodiversity, causing the total animal and plant community in that area to degrade.

keystone species

Community Function

Energy flow, resilience, and resistance are all features of community function.

The flow of energy, for example, as it passes through the various trophic levels of a food chain, is part of the energy flow in a community.

Two crucial attributes are resilience and resistance. Because biotic and abiotic changes can affect organism assemblages, they must be able to withstand these changes in order to achieve stability.

A stable community is one that can withstand, or at the very least rebound from, these changes. Resilience is defined as the ability to come back from a perturbation or disturbance, whereas resistance is defined as the ability to resist the effects of the perturbation or disturbance.

The ability of an ecosystem, such as a coral reef, to retain key functions and processes in the face of stresses or pressures by resisting and adapting to change is referred to as ecological resilience.

A reef system’s ecological resilience is mostly governed by two factors:

  • Coral resistance is the ability of corals to tolerate challenges. (e.g., sea surface temperature variations, genetic identity of corals, severity of local threats).
  • Recovery refers to a coral community’s ability to recover after a period of high mortality. (e.g., with favorable recruitment conditions, grazing by herbivores)

reef system's ecological resilience

After being harmed by an ecological disturbance, an ecosystem must be able to return to its usual patterns and processes in order to remain resilient. The Mulga forests in Australia, for example, can tolerate changes in their environment, such as forest fires, herbivory, and rainfall.

Community structure and attributes


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