Is it possible for there to be more than one keystone species in an area, as well as foundation species?

Yes, there can be more than one keystones species and foundation species in an area. The densities will be similar for the species but one species can have reduced biomass than the other.

Explain why we would expect low species diversity when disturbance/predation occur with a high frequency.

If a lot of the spices are being eaten by predators and disturbances are stopping the species from surviving and reproducing then the species will die off and it will lead to low diversity

What does species richness mean?

The number of different species in a community

How does climate shape a biological community?

Climate is one of the abiotic factors that can introduce variation. According to the videos on niches and competition, no two species can coexist indefinitely if they use the same survival strategy. For example, both wolves and foxes may hunt rabbits, but wolves can run faster so they will eventually outcompete the foxes, driving them to extinction and reducing overall biodiversity. With temperature variation, the foxes' strategy might actually prove better in some years. For example, foxes might have better vision and find it easier to spot rabbits against snow, so they would do better in years with more snow, while wolves will do better in years with less snow. The constant change of climate allows both species to find a niche in otherwise identical conditions and therefore coexist. Another example would be tree populations - taller trees grow better because they get more sunlight, so if a single tree was to grow much taller than all the others and grow in an umbrella shape, blocking out sunlight and killing all the trees around it, giving other tress 0 chance of survival. If a tree would be much taller that all other trees, it would be more susceptible to breaking due to wind as it would have to take all the wind resistance by itself. A forest full of trees roughly the same height help each other break wind thus climate (wind intensity or lightning bolts) prevent one tree from pushing out all the others.

what are the factors that affect species diversity in an ecosystem

Several notable factors are listed in the article. I have copied/paraphrased them here. - Climate of the community's location. - Geography of the community's location. - Heterogeneity (patchiness) of the environment - Frequency of disturbances, or disruptive events. - Interactions between organisms Hope this helps!

Can you explain how, for example, an area with only 7 types of species and a total 27 individuals has greater biodiversity than an area with 10 different species and a total 48 individuals?

Because in the first case there is a smaller number of individuals. 7/27 = 0.25 10/48 = 0.20 Biodiversity is greater in the first case.

How does climate shape a biological community

The climate determines what sorts of organisms can inhabit any given area, and weather patterns create the need for the evolution/adaptation of these species, which shapes the biological community. Hope that helps!

Main content

Course: AP®︎/College Biology > Unit 8

Lesson 4: Community ecology

Community structure

Google Classroom

Species richness and species diversity. Why more diverse ecosystems may be more stable. Roles of foundation and keystone species.

Key points:

A community's structure can be described by its species richness, which is the number of species present, and species diversity, which is a measure of both species richness and species evenness (relative numbers).
Community structure is influenced by many factors, including abiotic factors, species interactions, level of disturbance, and chance events.
Some species, such as foundation species and keystone species, play particularly important roles in determining their communities' structure.

Introduction

Different ecological communities can be pretty different in terms of the types and numbers of species they contain. For instance, some Arctic communities include just a few species, while some tropical rainforest communities have huge numbers of species packed into each cubic meter.

One way to describe this difference is to say that the communities have different structures. Community structure is essentially the composition of a community, including the number of species in that community and their relative numbers

^{1}

. It can also be interpreted more broadly, to include all of the patterns of interaction between these different species

^{2}

Some ecologists also use the term "community structure" for the pattern of a community in space – how the populations that make it up are distributed in the physical environment

^{3, 4}

. For instance, a community may have sharp edges or may blend gradually into the neighboring community. Also, different populations may occupy different areas inside the community's boundaries.

In this article, we'll mostly focus on community structure as defined by species composition.

In this article, we'll look at some of the ways that community structure can be quantified (measured numerically). Then, we'll examine factors that shape community structure, focusing especially on foundation and keystone species.

How do we measure community structure?

Two important measures ecologists use to describe the composition of a community are species richness and species diversity.

Species richness

Species richness is the number of different species in a particular community. If we found

30

species in one community, and

300

species in another, the second community would have much higher species richness than the first.

Communities with the highest species richness tend to be found in areas near the equator, which have lots of solar energy (supporting high primary productivity), warm temperatures, large amounts of rainfall, and little seasonal change. Communities with the lowest species richness lie near the poles, which get less solar energy and are colder, drier, and less amenable to life. This pattern is illustrated below for mammalian species richness (species richness calculated only for mammal species, not for all species). Many other factors in addition to latitude can also affect a community's species-richness.

Global species richness as calculated for mammal species. Image credit: "Community ecology: Figure 14," by OpenStax College, Biology, CC BY 4.0. Modification of work by NASA, CIESIN, Columbia University.

Species diversity

Species diversity is a measure of community complexity. It is a function of both the number of different species in the community (species richness) and their relative abundances (species evenness). Larger numbers of species and more even abundances of species lead to higher species diversity. For example:

A forest community with $20$ ‍ different kinds of trees would have greater species diversity than a forest community with only $5$ ‍ kinds of trees (assuming that the tree species were even in abundance in both cases).
A forest community with $20$ ‍ different kinds of trees in even abundances would have greater species diversity than a forest community with the same number of species in very uneven abundances (for instance, with $90 %$ ‍ of the trees belonging to a single species).

In general, ecologists think that more diverse ecological communities are more stable (that is, more able to recover after a disturbance) than less diverse communities. You can explore why this is the case in the video on ecological networks. However, the diversity-stability relationship isn't a universal rule, and there are some cases where other factors (besides species diversity) are more important in determining community and ecosystem stability

^{5, 6}

What factors shape community structure?

The structure of a community is the result of many interacting factors, both abiotic (non-living) and biotic (living organism-related). Here are some important factors that influence community structure:

The climate patterns of the community's location.
As we saw above in the discussion of species richness, global climate patterns (variation in temperature, solar energy input, etc. with distance from the equator) can affect community structure. So can more local climate patterns, such effects created by mountain ranges, bodies of water, and even streams and valleys.
The predictability or variability of climate can also affect community structure – for instance, some species may be unable to survive in a region with sporadic droughts or sporadic drops below freezing.
The geography of the community's location.
The heterogeneity (patchiness) of the environment $^{7}$ ‍.
If there is more variation, or heterogeneity, in a community's environment, this may allow for greater species richness because there are more distinct habitats to be occupied.
For example, imagine a community occupying a field, and another occupying a field that is dotted with piles of rock. The second community may have greater species richness because species that can live in the rocks (but not in the open field) will be present, in addition to those species that can live in the field.
The frequency of disturbances, or disruptive events.
Interactions between organisms.
All of the interspecies interactions that can occur between organisms (competition, predation, and various forms of symbiosis) have the potential to shape a community. For instance, two species that compete intensively with one another may be unable to coexist in the same community, or a prey species may be unable to persist in a community that contains a highly effective predator.
We'll also see some examples of interspecies interactions with especially important effects on community structure below.

A community's structure can also be shaped by the chance events that happened during its history. For instance, suppose that a single seed blows into the dirt of a particular area. If it happens to take root, the species may establish itself and, after some period of time, become dominant (excluding similar species). If the seed fails to sprout, another similar species may instead be the lucky one to establish itself and become dominant.

Foundation and keystone species

Some species have unusually strong impacts on community structure, preserving the balance of the community or even making its existence possible. These "special" species include foundation and keystone species.

Foundation species

A foundation species plays a unique, essential role in creating and defining a community. Often, foundation species act by modifying the environment so that it can support the other organisms that form the community

^{9, 10, 11}

Kelp (brown algae) is a foundation species that forms the basis of the kelp forests off the coast of California. Kelps create environments that allow the survival of other organisms that make up the kelp forest community

^{9}

. The corals of a coral reef are another foundation species. The exoskeletons of living and dead coral make up most of the reef structure, which protects other species from waves and ocean currents. Beavers, which modify their environment by building dams, can also be seen as a foundation species

^{9, 11}

Keystone species

A keystone species is a species that has a disproportionately large effect on community structure relative to its biomass or abundance. Keystone species differ from foundation species in two main ways: they are more likely to belong to higher trophic levels (to be top predators), and they act in more diverse ways than foundation species, which tend to modify their environment

^{10, 11}

Ecology is sometimes a little bit messy when it comes to naming things. Different sources use different definitions for keystone and foundation species. If your class requires you to know these definitions, make sure to consult your book or teacher for the definition you should use. In some sources, foundation species are viewed as a subcategory of keystone species.

If you are just trying to understand basic concepts of community structure, the key point is not the definitions. It's simply that certain species exert unusually strong effects on the structure of their communities. In some cases, these species physically modify the environment or otherwise provide necessary conditions for the community's existence (a foundation species, as described in this article). In other cases, certain species control community composition by other means such as predation, and may have strong effects despite low abundance (a keystone species, as described in this article).

The intertidal sea star Pisaster ochraceus, which is found in the northwestern United States, is perhaps the most famous example of a keystone species. In a classic experiment of community ecology, the sea stars were experimentally removed from the intertidal zone where they lived. As a result, populations of their prey (mussels) increased, altering the species composition of the community and sharply reducing species diversity. When the sea stars were present, about

25

species of barnacles and algae were found in the lower part of the intertidal zone, but when they were missing, the mussel population expanded downward and almost entirely replaced these other species

^{12}

This type of sharp reduction in diversity or collapse of community structure commonly occurs when a keystone species is removed. In this case, the loss of diversity happened because the mussels crowded out other species, which could normally persist because the sea stars kept the mussels in check.

Explore outside of Khan Academy

Do you want to learn more about the classic keystone species experiment described above? Check out this scrollable interactive from LabXchange.

LabXchange is a free online science education platform created at Harvard’s Faculty of Arts and Sciences and supported by the Amgen Foundation.

Attribution:

This article is a modified derivative of "Community ecology," by Robert Bear and David Rintoul, CC BY 4.0. Download the original article for free at http://cnx.org/contents/db89c8f8-a27c-4685-ad2a-19d11a2a7e2e@24.18.

The modified article is licensed under a CC BY-NC-SA 4.0 license.

Works cited:

Cecie Starr and Ralph Taggart, "Which factors shape community structure?" in Biology: The Unity and Diversity of Life, 11th ed. (Belmont: Thomson/Brooks-Cole, 2006), 822.
The Editors of Encyclopedia Britannica, "Community," Encyclopedia Britannica, last modified February 15, 2016, http://www.britannica.com/science/community-biology.
Steve Roxburgh, "What Are Ecological Communities?" Ecological Systems Course, last modified March 4, 2001, http://www.steverox.info/Downloads/Teaching/Ecological%20communities.pdf.
Timothy Fridtjof Flannery, "The Process of Succession." Encyclopedia Britannica, last modified June 3, 2016, http://www.britannica.com/science/community-ecology/The-process-of-succession#toc70596
"Ecology/Community Succession and Stability," Wikibooks, last modified June 3, 2015, https://en.wikibooks.org/wiki/Ecology/Community_succession_and_stability.
Kent E. Holsinger, "Diversity, Stability, and Ecosystem Function," accessed June 4, 2016, http://darwin.eeb.uconn.edu/eeb310/lecture-notes/diversity-stability.pdf.
Peter H. Raven, George B. Johnson, Kenneth A. Mason, Jonathan B. Losos, and Susan R. Singer, "Dynamics of Ecosystems," in Biology, 10th ed., AP ed. (New York: McGraw-Hill, 2014), 1224-1225.
Charlene D'Avanza, "Ecology of Disturbance," Teaching Issues and Experiments in Ecology, accessed July 18, 2016, http://www.esa.org/tiee/vol/v1/figure_sets/disturb/disturb_back1.html.
"Foundation Species and Dominant Species," Saylor.org Academy, accessed June 4, 2016, http://www.saylor.org/site/wp-content/uploads/2011/07/BIO313-Foundation-Species-and-Dominant-Species-FINAL1.pdf.
Aaron M. Ellison, et al., "Loss of Foundation Species: Consequences for the Structure and Dynamics of Forested Ecosystems," Front. Ecol. Environ. 3, no. 9 (2005): 479-480.
G. Tyler Miller and Scott E. Spoolman, "Keystone and Foundation Species Help Determine the Structure and Functions of Their Ecosystems," in Essentials of Ecology, 5th ed. (Belmont: Cengage Learning, 2009), 95.
Tom Carefoot, "Keystone Predator," A Snail's Odyssey, accessed July 12, 2016, http://www.asnailsodyssey.com/LEARNABOUT/SEASTAR/seasKeys.php.

References:

"Assembly Rules." Wikipedia. Last modified August 21, 2015. https://en.wikipedia.org/wiki/Assembly_rules.

Carefoot, Tom. "Keystone Predator." A Snail's Odyssey Accessed July 12, 2016. http://www.asnailsodyssey.com/LEARNABOUT/SEASTAR/seasKeys.php.

D'Avanza, Charlene. "Ecology of Disturbance." Teaching Issues and Experiments in Ecology. Accessed July 18, 2016. http://www.esa.org/tiee/vol/v1/figure_sets/disturb/disturb_back1.html.

"Diversity index." Wikipedia. Last modified May 29, 2016. https://en.wikipedia.org/wiki/Diversity_index.

"Ecological Effects of Biodiversity." Wikipedia. Last modified May 27, 2016. https://en.wikipedia.org/wiki/Ecological_effects_of_biodiversity.

"Ecology/Community Succession and Stability." Wikibooks. Last modified June 3, 2015. https://en.wikibooks.org/wiki/Ecology/Community_succession_and_stability.

"Ecology/Species Richness and Diversity." Wikibooks. Last modified March 19, 2016. https://en.wikibooks.org/wiki/Ecology/Species_Richness_and_Diversity.

Ellison, Aaron M., Michael S. Bank, Barton D. Clinton, Elizabeth A. Colburn, Katherine Elliott, Chelcy R. Ford, David R. Foster, Brian D. Kloeppel, Jennifer D. Knoepp, Gary M. Lovett, Jacqueline Mohan, David A. Orwig, Nicholas L. Rodenhouse, William V. Sobczak, Kristina A. Stinson, Jeffrey K. Stone, Christopher M. Swan, Jill Thompson, Betsy Von Holle and Jackson R. Webster. "Loss of Foundation Species: Consequences for the Structure and Dynamics of Forested Ecosystems." Front. Ecol. Environ. 3, no. 9 (2005): 479-486.

Farabee, M. J. "Community and Ecosystem Dynamics." Online Biology Book. Accessed June 6, 2016. https://www2.estrellamountain.edu/faculty/farabee/biobk/BioBookcommecosys.html#Community%20Structure.

Flannery, Timothy Fridtjof. "The Process of Succession." Encyclopedia Britannica. Last modified June 3, 2016. http://www.britannica.com/science/community-ecology/The-process-of-succession#toc70596

"Foundation Species and Dominant Species." Saylor.org Academy. Accessed June 4, 2016. http://www.saylor.org/site/wp-content/uploads/2011/07/BIO313-Foundation-Species-and-Dominant-Species-FINAL1.pdf.

"Foundation Species." Wikipedia. Last modified June 1, 2016. https://en.wikipedia.org/wiki/Foundation_species.

Holsinger, Kent E. "Diversity, Stability, and Ecosystem Function." Accessed June 4, 2016. http://darwin.eeb.uconn.edu/eeb310/lecture-notes/diversity-stability.pdf.

"Intermediate Disturbance Hypothesis." Wikipedia. Last modified May 30, 2016. https://en.wikipedia.org/wiki/Intermediate_Disturbance_Hypothesis.

Miller, G. Tyler and Scott E. Spoolman. "Keystone and Foundation Species Help Determine the Structure and Functions of Their Ecosystems." In Essentials of Ecology, 5th ed., 95-96. Belmont: Cengage Learning, 2009.

"Overview." Island Biogeography. Accessed June 7, 2016. http://www.islandbiogeography.org.

Raven, Peter H., George B. Johnson, Kenneth A. Mason, Jonathan B. Losos, and Susan R. Singer. "Community Ecology." In Biology, 10th ed., AP ed., 1185-1206. New York: McGraw-Hill, 2014.

Raven, Peter H., George B. Johnson, Kenneth A. Mason, Jonathan B. Losos, and Susan R. Singer. "Dynamics of Ecosystems." In Biology, 10th ed., AP ed., 1207-1227. New York: McGraw-Hill, 2014.

Reece, Jane B., Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, and Robert B. Jackson. "Diversity and trophic structure characterize biological communities." In Campbell Biology, 10th ed., 1216-1220. San Francisco: Pearson, 2011.

"Relative Species Abundance." Wikipedia. Last modified April 22, 2016. https://en.wikipedia.org/wiki/Relative_species_abundance.

Roxburgh, Steve. "What Are Ecological Communities?" Ecological Systems Course. Last modified March 4, 2001. http://www.steverox.info/Downloads/Teaching/Ecological%20communities.pdf

Starr, Cecie and Ralph Taggart. "Which Factors Shape Community Structure?" In Biology: The Unity and Diversity of Life, 11th ed., 822. Belmont: Thomson/Brooks-Cole, 2006.

The Editors of Encyclopedia Britannica. "Community." Encyclopedia Britannica. Last modified February 15, 2016. http://www.britannica.com/science/community-biology.

Thompson, John N. "Keystone Species." Encyclopedia Britannica. Last modified March 19, 2015. http://www.britannica.com/science/keystone-species.

Roxburgh, Steve. "What Are Ecological Communities?" Ecological Systems Course. Last modified March 4, 2001. http://www.steverox.info/Downloads/Teaching/Ecological%20communities.pdf.

Want to join the conversation?

Sort by:

mario.rosales
Posted 7 years ago. Direct link to mario.rosales's post “Is it possible for there ...”
Is it possible for there to be more than one keystone species in an area, as well as foundation species?
Button navigates to signup pageComment on mario.rosales's post “Is it possible for there ...”
(9 votes)
Answer
- Garrett Rocco
  Posted 7 years ago. Direct link to Garrett Rocco's post “Yes, there can be more th...”
  Yes, there can be more than one keystones species and foundation species in an area. The densities will be similar for the species but one species can have reduced biomass than the other.
  Button navigates to signup page
  (13 votes)
manishve86
Posted 7 years ago. Direct link to manishve86's post “How does climate shape a ...”
How does climate shape a biological community?
Button navigates to signup pageButton navigates to signup page
(3 votes)
Answer
- Seolfor
  Posted 7 years ago. Direct link to Seolfor's post “Climate is one of the abi...”
  Climate is one of the abiotic factors that can introduce variation. According to the videos on niches and competition, no two species can coexist indefinitely if they use the same survival strategy. For example, both wolves and foxes may hunt rabbits, but wolves can run faster so they will eventually outcompete the foxes, driving them to extinction and reducing overall biodiversity. With temperature variation, the foxes' strategy might actually prove better in some years. For example, foxes might have better vision and find it easier to spot rabbits against snow, so they would do better in years with more snow, while wolves will do better in years with less snow. The constant change of climate allows both species to find a niche in otherwise identical conditions and therefore coexist.
  
  Another example would be tree populations - taller trees grow better because they get more sunlight, so if a single tree was to grow much taller than all the others and grow in an umbrella shape, blocking out sunlight and killing all the trees around it, giving other tress 0 chance of survival. If a tree would be much taller that all other trees, it would be more susceptible to breaking due to wind as it would have to take all the wind resistance by itself. A forest full of trees roughly the same height help each other break wind thus climate (wind intensity or lightning bolts) prevent one tree from pushing out all the others.
  Comment on Seolfor's post “Climate is one of the abi...”
  (11 votes)
maeganresuello
Posted 5 years ago. Direct link to maeganresuello's post “Explain why we would expe...”
Explain why we would expect low species diversity when disturbance/predation occur with a high frequency.
Button navigates to signup pageButton navigates to signup page
(5 votes)
Answer
- SofiyaMarkova
  Posted 5 years ago. Direct link to SofiyaMarkova's post “If a lot of the spices ar...”
  If a lot of the spices are being eaten by predators and disturbances are stopping the species from surviving and reproducing then the species will die off and it will lead to low diversity
  Button navigates to signup page
  (5 votes)
christina_potter26
Posted 3 years ago. Direct link to christina_potter26's post “Is it possible for there ...”
Is it possible for there to be more than one keystone species in an area, as well as foundation species?
Button navigates to signup pageButton navigates to signup page
(6 votes)
Answer
NavarraW
Posted 7 months ago. Direct link to NavarraW's post “What does species richnes...”
What does species richness mean?
Button navigates to signup pageComment on NavarraW's post “What does species richnes...”
(4 votes)
Answer
- jaz
  Posted 7 months ago. Direct link to jaz's post “The number of different s...”
  The number of different species in a community
  Button navigates to signup page
  (5 votes)
atakpajonah
Posted 7 years ago. Direct link to atakpajonah's post “what are the factors that...”
what are the factors that affect species diversity in an ecosystem
Button navigates to signup pageButton navigates to signup page
(3 votes)
Answer
- Scout Finch
  Posted 6 years ago. Direct link to Scout Finch's post “Several notable factors a...”
  Several notable factors are listed in the article. I have copied/paraphrased them here.
  - Climate of the community's location.
  - Geography of the community's location.
  - Heterogeneity (patchiness) of the environment
  - Frequency of disturbances, or disruptive events.
  - Interactions between organisms
  Hope this helps!
  Button navigates to signup page
  (4 votes)
Clara
Posted 5 years ago. Direct link to Clara's post “Can you explain how, for ...”
Can you explain how, for example, an area with only 7 types of species and a total 27 individuals has greater biodiversity than an area with 10 different species and a total 48 individuals?
Button navigates to signup pageButton navigates to signup page
(3 votes)
Answer
- Ivana - Science trainee
  Posted 4 years ago. Direct link to Ivana - Science trainee's post “Because in the first case...”
  Because in the first case there is a smaller number of individuals.
  
  7/27 = 0.25
  10/48 = 0.20
  
  Biodiversity is greater in the first case.
  Button navigates to signup page
  (4 votes)
Arvyn De
Posted 7 years ago. Direct link to Arvyn De's post “What about the other type...”
What about the other types of species like other than keystone and foundation species. Someone should add that.
Button navigates to signup pageButton navigates to signup page
(4 votes)
Answer
Jose Rosario
Posted 6 years ago. Direct link to Jose Rosario's post “How does climate shape a ...”
How does climate shape a biological community
Button navigates to signup pageButton navigates to signup page
(2 votes)
Answer
- Scout Finch
  Posted 6 years ago. Direct link to Scout Finch's post “The climate determines wh...”
  The climate determines what sorts of organisms can inhabit any given area, and weather patterns create the need for the evolution/adaptation of these species, which shapes the biological community. Hope that helps!
  Button navigates to signup page
  (4 votes)
Broski
Posted 7 months ago. Direct link to Broski's post “What would happen if you ...”
What would happen if you put 1 keystone species in every country?
Button navigates to signup pageComment on Broski's post “What would happen if you ...”
(3 votes)
Answer