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8.5 Community Ecology

5 min readjanuary 7, 2023

Caroline Koffke

Caroline Koffke

Jillian Holbrook

Jillian Holbrook

Caroline Koffke

Caroline Koffke

Jillian Holbrook

Jillian Holbrook

Species Diversity

A refers to a group of different populations living in the same area. An example of this would be humans, dogs, and rats living in the city of Chicago. 🐀

Communities can be large or small, and they can be found in a variety of environments, including terrestrial, aquatic, and even the air! In a , the various species interact with one another through a variety of processes, such as , , and , which have differential positive, negative, or neutral effects.

Understanding the dynamics of a can help scientists and researchers better understand how ecosystems function and how they can be managed and conserved.

When studying a , scientists often measure the and in that area, as dynamics inform ecosystem function, management, and conservation. refers to the number of unique species living in the area and the percentage of the population represented by each species.

The structure of a is described in terms of and . An environment with a large number of unique species whose populations are also equally distributed is considered highly diverse!

The diversity of a can be measured using , the following equation:

Diversity Index = 1 - Σ (n / N)^2

where:

n = the total number of organisms of a particular species N = total number of organisms of all species

Interactions between populations in a determine the health of that , changes in species and populations over time, and how energy and matter are transferred. These relationships consist of , competition, , , and , which we will further explore in terms through the lens of ecology!

Community Interactions

Predator and Prey (/-)

A predator/prey relationship refers to a relationship in which one organism eats another. The predator in one relationship may be the prey in another relationship. An example of a predator/prey relationship is a snake and a mouse. The snake is the predator and eats the mouse, which is the prey. 🐍

In another scenario, the snake may become the prey. A hawk serves as a potential predator for the snake. This relationship is the most common way of showing the transfer of energy in an ecosystem.

in ecosystems is a top-down control on other species, often making it an ecosystem service. By limiting prey populations, predators create that affect the population sizes or behaviors of species at other levels of an ecosystem.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F5BADEAA1-FD8B-8DEC-48339B69FA77B685.jpg?alt=media&token=2f47ebd0-f17f-4f53-ac30-9b9f443e1322

Image courtesy of NPS.


refers to relationships in which two species are competing for the same limited habitat, food, or water. Any time that two organisms share a common food source in , competition might result. As an example, hawks and badgers might be in competition for snakes as a source of food.

Competition can lead to a decrease in one population if another population is more fit to hunt prey. It may also lead to a stabilizing of both populations if both groups are equally fit.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fsource.gif?alt=media&token=75a624ce-dbb9-4c01-929a-4cd311bdf276

Image courtesy of Giphy.

is the process by which different species divide up resources and use them in different ways. To avoid , different species utilize different .

Mutualism (/)

refers to a relationship in which both species involved receive a fitness benefit from the relationship.

A classic example of this is the Acacia tree and the Acacia ant. The tree produces small leaves that possess large quantities of nutrients for the ants to eat. In return, the ants protect the Acacia tree from some predators and reduce the bacterial population on the leaves of the tree. Because both species are equally benefited from the relationship, this is considered an example of . 🐜

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F1024px-Ant_-_Pseudomyrmex_species%2C_on_Bull_Thorn_Acacia_(Acacia_cornigera)_with_Beltian_bodies%2C_Caves_Branch_Jungle_Lodge%2C_Belmopan%2C_Belize_-_8505045055.jpg?alt=media&token=7580c51a-564b-4aff-822a-677a819ae423

Image courtesy of Wikimedia Commons.

Commensalism (/0)

refers to a relationship in which one species benefits and the other species is neither harmed nor helped.

An example of this type of relationship is between a barnacle and a whale. A barnacle is a sea creature that bonds to a surface and waits for the water to carry particles of plankton and other food sources across their mouths.

Barnacles frequently bind to the thick skin of the whale. The barnacle benefits greatly from this because the whale’s frequent movement allows for an increased amount of plankton and other food particles to pass over the barnacle. The whale is neither harmed nor helped by the binding of the barnacle. 🐋

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FBalanus_improvisus_on_Mya_arenaria_shell.jpg?alt=media&token=5079bff3-88b3-4269-bd9a-ecc20dc3c1ea

Image courtesy of WikiMedia Commons.

Parasitism (/-)

is a type of interaction between species in which one species, the parasite, benefits at the expense of the other species, the host.

Parasites can be found in a wide range of species, including plants, animals, and even microorganisms. Many parasites are specialized to infect a particular host species, and they often have complex life cycles that involve multiple hosts. In some cases, the relationship between a parasite and its host can be relatively benign, with the host experiencing only minor effects from the parasite's presence. However, in other cases, the relationship can be much more harmful, with the parasite causing serious illness or even death in the host. Some parasites are able to manipulate the behavior or physiology of their hosts in ways that increase the parasite's chances of survival and reproduction.

and appear to be similar, as both relationships include one species experiencing a fitness benefit at the expense of the other. However, can be differentiated, as parasites are relatively small in comparison to the hosts they feed off of, and parasites tend to feed off part of other organisms rather than consume the entire organism, as is common in a predator/prey interaction.

For example, a tick and a dog represent . Relative to the dog, the tick is small. It bites the dog's skin to feed on nutrients in the dog's blood. In addition to the deprivation of nutrients, ticks carry diseases that may infect the dog. Ultimately, this relationship benefits the tick and harms the dog. 🐕

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F35317921432_3d3a1de77f_b.jpg?alt=media&token=5fe36f58-805b-4821-97b2-48b38325e6b3

Image courtesy of Flickr.


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Key Terms to Review (19)

Acacia Tree and Acacia Ant Mutualism

: This is a type of symbiotic relationship where both the acacia tree and the acacia ant benefit from each other. The acacia tree provides food and shelter for the ants, while the ants protect the tree from herbivores and help to spread its seeds.

Aquatic Environment

: An aquatic environment refers to a water-based ecosystem, which can be either saltwater (like oceans and seas) or freshwater (like lakes, rivers, and ponds).

Barnacle and Whale Commensalism

: This is a type of commensalism where barnacles attach themselves to the skin of whales. The barnacles benefit by getting transportation and more access to food sources, while the whale is neither harmed nor helped.

Commensalism

: Commensalism is a type of symbiotic relationship where one organism benefits without affecting the other organism positively or negatively.

Community

: In biology, a community refers to all the populations that live and interact within an area at a given time.

Community Interactions

: Community interactions refer to the ways in which different species within an ecosystem interact with each other. These interactions can be competitive, cooperative, or predatory.

Competition for Resources

: This is a biological concept where organisms vie for the same limited resources in an environment, such as food, water, light, space or mates.

Ecological Niches

: An ecological niche refers to the role a species plays in its ecosystem, including its interactions with other organisms and its environment.

Interspecies Competition

: Interspecies competition is a form of competition in which individuals of different species compete for the same resources in an ecosystem, such as food or living space.

Mutualism

: Mutualism is a type of symbiotic relationship where both organisms involved benefit from each other.

Niche Partitioning

: Niche partitioning involves dividing up a niche to avoid competition for resources. It allows multiple species to coexist in a single ecosystem by reducing direct competition for resources.

Parasitism

: Parasitism is a type of symbiotic relationship between two organisms where one organism (the parasite) benefits at the expense of the other (the host). The parasite derives nutrients from the host, often causing harm in the process.

Predation

: Predation is an interaction where one organism (the predator) kills another (the prey) for food.

Predator and Prey Relationship

: The predator-prey relationship is a biological interaction where one organism (the predator) hunts and kills another organism (the prey) for food.

Simpson’s Diversity Index

: Simpson's Diversity Index is a measure used by ecologists to quantify biodiversity in an area. It takes into account both richness (number) and evenness (distribution) among species present in an area.

Species Composition

: Species composition refers to the identity of all the different organisms that make up a community.

Species Diversity

: Species diversity refers to the variety of different species within a specific area or ecosystem.

Terrestrial Environment

: A terrestrial environment refers to land environments on Earth – including forests, grasslands, deserts, coastal areas etc., where organisms live and interact with each other and their surroundings.

Trophic Cascades

: Trophic cascades are ecological phenomena triggered by changes in top predators' population size that cause ripple effects down through lower levels of the food chain.

8.5 Community Ecology

5 min readjanuary 7, 2023

Caroline Koffke

Caroline Koffke

Jillian Holbrook

Jillian Holbrook

Caroline Koffke

Caroline Koffke

Jillian Holbrook

Jillian Holbrook

Species Diversity

A refers to a group of different populations living in the same area. An example of this would be humans, dogs, and rats living in the city of Chicago. 🐀

Communities can be large or small, and they can be found in a variety of environments, including terrestrial, aquatic, and even the air! In a , the various species interact with one another through a variety of processes, such as , , and , which have differential positive, negative, or neutral effects.

Understanding the dynamics of a can help scientists and researchers better understand how ecosystems function and how they can be managed and conserved.

When studying a , scientists often measure the and in that area, as dynamics inform ecosystem function, management, and conservation. refers to the number of unique species living in the area and the percentage of the population represented by each species.

The structure of a is described in terms of and . An environment with a large number of unique species whose populations are also equally distributed is considered highly diverse!

The diversity of a can be measured using , the following equation:

Diversity Index = 1 - Σ (n / N)^2

where:

n = the total number of organisms of a particular species N = total number of organisms of all species

Interactions between populations in a determine the health of that , changes in species and populations over time, and how energy and matter are transferred. These relationships consist of , competition, , , and , which we will further explore in terms through the lens of ecology!

Community Interactions

Predator and Prey (/-)

A predator/prey relationship refers to a relationship in which one organism eats another. The predator in one relationship may be the prey in another relationship. An example of a predator/prey relationship is a snake and a mouse. The snake is the predator and eats the mouse, which is the prey. 🐍

In another scenario, the snake may become the prey. A hawk serves as a potential predator for the snake. This relationship is the most common way of showing the transfer of energy in an ecosystem.

in ecosystems is a top-down control on other species, often making it an ecosystem service. By limiting prey populations, predators create that affect the population sizes or behaviors of species at other levels of an ecosystem.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F5BADEAA1-FD8B-8DEC-48339B69FA77B685.jpg?alt=media&token=2f47ebd0-f17f-4f53-ac30-9b9f443e1322

Image courtesy of NPS.


refers to relationships in which two species are competing for the same limited habitat, food, or water. Any time that two organisms share a common food source in , competition might result. As an example, hawks and badgers might be in competition for snakes as a source of food.

Competition can lead to a decrease in one population if another population is more fit to hunt prey. It may also lead to a stabilizing of both populations if both groups are equally fit.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fsource.gif?alt=media&token=75a624ce-dbb9-4c01-929a-4cd311bdf276

Image courtesy of Giphy.

is the process by which different species divide up resources and use them in different ways. To avoid , different species utilize different .

Mutualism (/)

refers to a relationship in which both species involved receive a fitness benefit from the relationship.

A classic example of this is the Acacia tree and the Acacia ant. The tree produces small leaves that possess large quantities of nutrients for the ants to eat. In return, the ants protect the Acacia tree from some predators and reduce the bacterial population on the leaves of the tree. Because both species are equally benefited from the relationship, this is considered an example of . 🐜

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F1024px-Ant_-_Pseudomyrmex_species%2C_on_Bull_Thorn_Acacia_(Acacia_cornigera)_with_Beltian_bodies%2C_Caves_Branch_Jungle_Lodge%2C_Belmopan%2C_Belize_-_8505045055.jpg?alt=media&token=7580c51a-564b-4aff-822a-677a819ae423

Image courtesy of Wikimedia Commons.

Commensalism (/0)

refers to a relationship in which one species benefits and the other species is neither harmed nor helped.

An example of this type of relationship is between a barnacle and a whale. A barnacle is a sea creature that bonds to a surface and waits for the water to carry particles of plankton and other food sources across their mouths.

Barnacles frequently bind to the thick skin of the whale. The barnacle benefits greatly from this because the whale’s frequent movement allows for an increased amount of plankton and other food particles to pass over the barnacle. The whale is neither harmed nor helped by the binding of the barnacle. 🐋

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FBalanus_improvisus_on_Mya_arenaria_shell.jpg?alt=media&token=5079bff3-88b3-4269-bd9a-ecc20dc3c1ea

Image courtesy of WikiMedia Commons.

Parasitism (/-)

is a type of interaction between species in which one species, the parasite, benefits at the expense of the other species, the host.

Parasites can be found in a wide range of species, including plants, animals, and even microorganisms. Many parasites are specialized to infect a particular host species, and they often have complex life cycles that involve multiple hosts. In some cases, the relationship between a parasite and its host can be relatively benign, with the host experiencing only minor effects from the parasite's presence. However, in other cases, the relationship can be much more harmful, with the parasite causing serious illness or even death in the host. Some parasites are able to manipulate the behavior or physiology of their hosts in ways that increase the parasite's chances of survival and reproduction.

and appear to be similar, as both relationships include one species experiencing a fitness benefit at the expense of the other. However, can be differentiated, as parasites are relatively small in comparison to the hosts they feed off of, and parasites tend to feed off part of other organisms rather than consume the entire organism, as is common in a predator/prey interaction.

For example, a tick and a dog represent . Relative to the dog, the tick is small. It bites the dog's skin to feed on nutrients in the dog's blood. In addition to the deprivation of nutrients, ticks carry diseases that may infect the dog. Ultimately, this relationship benefits the tick and harms the dog. 🐕

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F35317921432_3d3a1de77f_b.jpg?alt=media&token=5fe36f58-805b-4821-97b2-48b38325e6b3

Image courtesy of Flickr.


-----

Key Terms to Review (19)

Acacia Tree and Acacia Ant Mutualism

: This is a type of symbiotic relationship where both the acacia tree and the acacia ant benefit from each other. The acacia tree provides food and shelter for the ants, while the ants protect the tree from herbivores and help to spread its seeds.

Aquatic Environment

: An aquatic environment refers to a water-based ecosystem, which can be either saltwater (like oceans and seas) or freshwater (like lakes, rivers, and ponds).

Barnacle and Whale Commensalism

: This is a type of commensalism where barnacles attach themselves to the skin of whales. The barnacles benefit by getting transportation and more access to food sources, while the whale is neither harmed nor helped.

Commensalism

: Commensalism is a type of symbiotic relationship where one organism benefits without affecting the other organism positively or negatively.

Community

: In biology, a community refers to all the populations that live and interact within an area at a given time.

Community Interactions

: Community interactions refer to the ways in which different species within an ecosystem interact with each other. These interactions can be competitive, cooperative, or predatory.

Competition for Resources

: This is a biological concept where organisms vie for the same limited resources in an environment, such as food, water, light, space or mates.

Ecological Niches

: An ecological niche refers to the role a species plays in its ecosystem, including its interactions with other organisms and its environment.

Interspecies Competition

: Interspecies competition is a form of competition in which individuals of different species compete for the same resources in an ecosystem, such as food or living space.

Mutualism

: Mutualism is a type of symbiotic relationship where both organisms involved benefit from each other.

Niche Partitioning

: Niche partitioning involves dividing up a niche to avoid competition for resources. It allows multiple species to coexist in a single ecosystem by reducing direct competition for resources.

Parasitism

: Parasitism is a type of symbiotic relationship between two organisms where one organism (the parasite) benefits at the expense of the other (the host). The parasite derives nutrients from the host, often causing harm in the process.

Predation

: Predation is an interaction where one organism (the predator) kills another (the prey) for food.

Predator and Prey Relationship

: The predator-prey relationship is a biological interaction where one organism (the predator) hunts and kills another organism (the prey) for food.

Simpson’s Diversity Index

: Simpson's Diversity Index is a measure used by ecologists to quantify biodiversity in an area. It takes into account both richness (number) and evenness (distribution) among species present in an area.

Species Composition

: Species composition refers to the identity of all the different organisms that make up a community.

Species Diversity

: Species diversity refers to the variety of different species within a specific area or ecosystem.

Terrestrial Environment

: A terrestrial environment refers to land environments on Earth – including forests, grasslands, deserts, coastal areas etc., where organisms live and interact with each other and their surroundings.

Trophic Cascades

: Trophic cascades are ecological phenomena triggered by changes in top predators' population size that cause ripple effects down through lower levels of the food chain.


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AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.


© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.