Name: island biogeography and species richness
Uploaded: 2019-01-29T11:04:46.000Z
Duration: 4 min 4 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Systems

ESS.EES.4.1

Species Distribution and Biogeography

Biogeography is the study of the distribution of organisms across geographic space, and the processes that shape these distributions. Broadly speaking, the theory of biogeography states that any species present in a specific location either evolved there or moved there from a different location. If the latter is true, when these colonizers arrive at their new location, characteristics of the environment like food availability, and interactions with other species will decide whether they establish a new population or perish. 

The theory of Island Biogeography was formulated in 1967, by Edward O. Wilson and Robert MacArthur. It&#39;s based on the assumption that the number of species at any given site, is determined by the colonization and extinction rates. The theory is called Island Biogeography, because it was first used to explain the variations in a number of species on oceanic islands. But Island Biogeography theory can also be applied to city species distribution in many other non-continuous habitat types, such as forests fragmented by agriculture. 

One major prediction of Island Biogeography theory is that islands closer to the mainland will have a greater colonization rate, than islands that are further away. This makes a lot of sense. If an island is far away from the mainland, it&#39;s hard for organisms to physically travel there. Secondly, larger islands will typically be able to support more species than smaller islands. Additionally, with the increasing size of islands the extinction risk of a species would decrease, because larger islands can support larger, more robust populations of any individual species, like this booming colony of bunnies. On the other hand, the extinction rate increases as more and more distinct species coexist on an island, and in terms of statistics, this is simply because there are more opportunities for extinction events to occur. Ecologically speaking, more species inhabiting the same island, also leads to an increased chance of antagonistic interactions, like predator-prey interactions or territory fights. Furthermore, as more species inhabit the island, the colonization rate decreases, because there are fewer resources to go around, and niche space is occupied, so new arrivals are less likely to be able to establish. 

Overall the theory of Island Biogeography predicts that there will be a dynamic equilibrium on any given island - meaning that the number of species should remain stable at the point where colonization and extinction rates meet. Note that this also means that the composition of species on the island can still change as some species go extinct, and new immigrants become established. Additionally, the actual values at equilibrium will always be particular to the characteristics of the individual island, such as its size or proximity to the mainland. 

In this laboratory, you will test the theory of Island Biogeography through a simulation with artificial islands of different sizes.

species distribution and biogeography

<h4>Species Distribution</h4>

Biogeography is the study of species distribution across geographic space and the processes that shape these distributions. This discipline is based on the assumption that each species within a location must have immigrated from another geographic area or evolved from a local species. Within each habitat, a variety of biotic and abiotic factors act on individual species to shape birth, death, immigration, and emigration rates. To avoid local extinction, the combined birth and immigration rates of a species must equal or surpass the death and emigration rates. These factors and others act in a dynamic fashion to determine the location and persistence of species across the globe.

<h4>Island Biogeography Theory</h4>

In 1967, Edward O. Wilson and Robert MacArthur studied and characterized species distribution on isolated oceanic islands to better understand these phenomena. Such islands provided a simple framework to carve out early theories of biogeography, which continue to inform current understanding of population dynamics today. Furthermore, these theories have been applied not only to island ecosystems, but also to more complex isolated or semi-isolated landscapes, including inland lakes and forests fragmented by agriculture. The original theories established by Wilson and MacArthur were based on assumptions about island habitats; namely, that the number of species on each island is determined by the overall colonization and extinction rates and that island size and proximity to the mainland will affect these factors.

One tenet of island biogeography states that an island closer to the mainland will have a greater colonization rate than sites further away. This is predicted based on the assumption that the mainland (or larger, populated areas) will serve as a source of emigrating individuals that may populate nearby uncolonized locations. The process of colonization is more likely to occur over shorter distances, as it depends on the dispersal of organisms. For example, birds will fly from one location to another or seeds can drift passively on the wind. The biological limitations of most emigrating organisms, however, do not allow them to disperse to sites at great distance.

Early biogeographers also found that larger islands tend to support a greater number of species than smaller islands. This is because of the greater amount of resources and niches, as well as the larger population sizes that bigger areas can sustain. With more individuals, the risk of extinction for each species decreases. Generally, larger populations are less likely to be irreversibly affected by threats like natural disasters, disease, or genetic drift. However, as the number of species within a habitat increases, so do the overall extinction rates. This effect is largely due to the increased potential for antagonistic interactions, like competition or predation, with increasing diversity of organisms. Furthermore, species abundance generally results in a decrease in available resources and niches for new colonizers. Accordingly, each geographic area will support a limited number of individuals and species.

<h4>Dynamic Equilibrium</h4>

These findings predict the establishment of a dynamic equilibrium at which the number of species on an island stabilizes due to balanced immigration and extinction rates. This balance is influenced by the individual factors of each location, including the size, resources, and species present. While the overall number of species may remain relatively constant due to this equilibrium, the specific species composition of a habitat is expected to change as new immigrants arrive and old resident species become extinct. Since large islands near the mainland have the highest immigration rate and the lowest extinction rate, they are predicted to support the greatest number of species. The opposite is observed for smaller, more isolated islands. To reach equilibrium, extinction risk increases and colonization rate decreases as the number of species on an island increases. The point at which dynamic equilibrium is reached can be plotted as the intersection between the colonization rate and extinction rate. These factors together determine the diversity of species that can be supported by each habitat.

<h4>Broad Applications of Island Biogeography Theory</h4>

Though these theories were established based on island habitats, they have been tested and supported across a wide range of ecosystems and organisms1-2. For example, &#8220;sky islands&#8221; are individual peaks of high-altitude mountains that contain a distinct species composition. Many species in these locations are unable to survive in low-altitude climates, making dispersal between mountain peaks difficult. For organisms like amphibians, plants, and terrestrial insects with limited mobility, these &#8220;sky islands&#8221; are as isolated as true oceanic islands and behave according to the theories of island biogeography. Importantly, many of the species found in oceanic islands, sky islands, and other segregated habitats are endemic, meaning they are found only in that location and nowhere else. The specific evolutionary pressures of these local environments coupled with their isolation from outside populations often leads to speciation, or the evolution of new species. For instance, komodo dragons and Galapagos tortoises speciated from mainland ancestors to form distinct endemic populations. However, these endemic species are at a greater risk of extinction than their mainland counterparts due to smaller population sizes and more limited habitat areas. Conservation of such species requires an understanding of the tenets of biogeography, habitat dynamics, and the requirements of individual populations3-4.

Often, human activity reduces the amount of suitable habitat or causes fragmentation of habitats into smaller and further apart sections. In an effort to prevent species extinction, conservation biologists may attempt to artificially promote balanced immigration and extinction rates. To achieve this, man-made connections between habitats, called corridors, can be built to increase the movement of species between fragmented sites and increase overall habitat area. Species may also be preserved and protected in man-made nature reserves. These corrective measures require a deep understanding of biogeography, which continues to shape species survival, location, and conservation to this day.

<h4>References</h4>

<ol class="references">
	<li>Lavelle, A., et al. (2016). 'Colonic biogeography in health and ulcerative colitis.' Gut Microbes 7(5): 435-442.</li>
	<li>Lachance, M. A., et al. (2001). 'Biogeography of the yeasts of ephemeral flowers and their insects.' FEMS Yeast Res 1(1): 1-8.</li>
	<li>Burns, K. C. (2015). 'A Theory of Island Biogeography for Exotic Species.' Am Nat 186(4): 441-451.</li>
	<li>Spatz, D. R., et al. (2014). 'The biogeography of globally threatened seabirds and island conservation opportunities.' Conserv Biol 28(5): 1282-1290.</li>
</ol>

Species Distribution

Biogeography is the study of species distribution across geographic space and the processes that shape these distributions. This ...

Education

JoVE Lab Manual

Biology

Ecology

island biogeography and species richness

Island biogeography explains why species are found in some places and not others. It looks at how biotic factors, like competition and predation, and abiotic factors, like habitat size and distance, shape birth, death, immigration, and emigration rates. For a species to avoid local extinction, births and immigration must match or exceed deaths and emigration.

Edward O. Wilson and Robert MacArthur helped define this field in 1967 by studying isolated oceanic islands. Islands gave early biologists a simple way to test ideas about colonization and extinction. These ideas later proved useful in other isolated or semi-isolated habitats, including inland lakes and forests broken into fragments by agriculture.

A key idea in island biogeography is that islands closer to the mainland usually receive more immigrants. The mainland acts as a source of individuals, and shorter distances make dispersal more likely. Birds can fly between places, and seeds can drift on the wind, but many organisms cannot travel far. Larger islands also tend to hold more species because they offer more resources, more niches, and larger populations. Bigger populations are less likely to be wiped out by natural disasters, disease, or genetic drift.

As species numbers rise, extinction rates can also rise. More species can mean more competition and predation, and fewer open resources and niches for new colonizers. Because each habitat has limited space and support, the number of species it can hold is not unlimited. These patterns lead to a dynamic equilibrium, or a balance, where immigration and extinction rates become equal. At that point, the total number of species stays fairly stable, even though the exact species present may change over time as newcomers arrive and resident species disappear.

The theory predicts that large islands near the mainland should support the most species. They have the highest immigration rates and the lowest extinction rates. Small, isolated islands should support fewer species because colonization is harder and extinction risk is higher. The point of dynamic equilibrium can be shown where the colonization and extinction curves intersect.

Island biogeography also applies to other isolated habitats. &quot;Sky islands&quot; are high mountain peaks with distinct species communities. Many of the organisms there cannot survive in low-altitude climates, so movement between peaks is difficult. This makes them behave much like true oceanic islands, especially for amphibians, plants, and terrestrial insects with limited mobility.

Many species in these isolated places are endemic, which means they live only in one location. Isolation and local environmental pressures can also drive speciation, the evolution of new species. Komodo dragons and Galapagos tortoises are examples of populations that speciated from mainland ancestors. However, endemic species often face a higher risk of extinction because their populations are small and their habitats are limited.

Biogeography is important for conservation. Human activity often reduces suitable habitat or breaks it into smaller, farther apart pieces. Conservation biologists may build corridors, which are man-made connections between habitats, to increase movement between fragmented sites and raise the effective habitat area. They may also protect species in nature reserves. These actions depend on biogeography because species survival depends on balancing immigration, extinction, and habitat needs.

Island Biogeography and Species Richness

animal behavior

Drosophila Taxis in Animal Behavior

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energy dynamics

Food Chain Energy Flow and Biomass

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measuring biodiversity

Why Biodiversity Matters in Ecosystems

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extinction

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Island biogeography explains why species are found in some places and not others. It looks at how biotic factors, like competition and predation, and abiotic factors, like habitat size and distance, shape birth, death, immigration, and emigration rates. For a species to avoid local extinction, births and immigration must match or exceed deaths and emigration. Edward O. Wilson and Robert MacArthur helped define this field in 1967 by studying isolated oceanic islands. Islands gave early...

population growth

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community diversity

Measuring Ecosystem Health

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climate change

Climate Change Effects on Sea Level and Species

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group behavior

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optimal foraging

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sexual selection and mate choice

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eusociality and division of labor

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ecology

Learn how island size, distance, and migration shape species richness, extinction risk, endemic species, and conservation in island biogeography.

Island Biogeography and Species Richness | JoVE K12

Pennsylvania State Academic Standards

Earth and Space Science

3.3.9-12.N

Louisiana Student Standards for Science

High School

Environmental Science

Environmental Awareness And Protection

HS-EVS2-3

ecosystems-interactions-energy-and-dynamics

Ecosystems: Interactions, Energy And Dynamics

HS-LS2-6

HS-LS2-7

Arizona Science Standards

Life Science

HS+B.L2

HS+B.L2U1.1

Next Generation Science Standards

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Heredity: Inheritance and Variation of Traits

HS-LS4-5

Earth’s Systems

HS-ESS2-6

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New York State Science Learning Standards

interdependent-relationships-in-ecosystems

Interdependent Relationships in Ecosystems

HS-LS2-2.

Natural Selection and Evolution

HS-LS4-5.

Earth and Space Sciences

HS-ESS2-7.

Georgia Standards of Excellence

Entomology

SEN1.

SEN1.c

SEC5.

SEC5.c

Model island colonization and extinction with cups, Ping-Pong balls, and dice. Compare near and far, large and small island trials in this high school lab.

Island Colonization and Extinction Lab | JoVE K12

Model colonization and extinction on near and far islands with large and small cup setups. Calculate rates, graph results, and compare dynamic equilibrium.

Island Equilibrium Lab: Colonization and Extinction | JoVE K12

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Analyze how the geosphere is shaped by plate tectonics and the rock cycle.

Island Biogeography and Species Richness

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