Equilibrium Theory of Island Biogeography | Biogeography

Summary

The video explores the Equilibrium Theory of Island Biogeography, focusing on the balance between species immigration and extinction on islands. Factors like isolation and island size significantly influence species richness. More isolated or smaller islands tend to have lower species diversity due to reduced immigration and higher extinction rates. Conversely, less isolated, larger islands support a greater number of species, highlighting the dynamic equilibrium shaped by environmental conditions and ecological processes.

Takeaways

• 🌍 Island Biogeography studies factors that affect species richness in isolated communities like oceanic and continental islands.
• 🌋 Oceanic islands often form through volcanic activity, and their species composition increases over time through succession.
• 🌊 Continental islands are already populated before isolation and may experience a decrease in species based on their level of isolation.
• ⚖️ The Equilibrium Theory of Island Biogeography explains that the number of species on an island reaches a balance between immigration and extinction.
• 🛣️ Isolation level affects species equilibrium: more isolated islands have fewer species due to lower immigration rates.
• 🚢 Less isolated islands have higher immigration and lower extinction rates, as species can be replenished from nearby sources.
• 🏝️ Island size also impacts equilibrium: smaller islands have higher extinction rates and lower species diversity.
• 🌿 Larger islands support more species due to larger habitats and reduced chances of extinction from random events.
• 🐾 Immigration rates to smaller islands are lower, further limiting species diversity compared to larger islands.
• 🔄 Over time, the forces of immigration and extinction on all islands create a stable equilibrium in the number of species.

Q & A

What is Island Biogeography?

Island Biogeography is the study of factors that influence species richness in naturally isolated communities, such as oceanic islands formed by volcanic activity and continental islands formed due to rising water levels.

How does the species composition change on oceanic islands after their formation?

On oceanic islands, particularly those newly formed by volcanic eruptions, the species composition increases through the process of ecological succession until it reaches a similar level of diversity as the nearest mainland.

What is the initial state of species composition on continental islands?

Continental islands already possess a stable species composition before becoming isolated due to factors such as rising water levels.

What is the Equilibrium Theory of Island Biogeography?

The Equilibrium Theory of Island Biogeography suggests that islands reach a stable number of species over time, which is a balance between the immigration of species to the island and the extinction of species on the island.

How does the level of isolation affect the equilibrium number of species on an island?

More isolated islands, which are farther from the source of species, have a lower equilibrium number due to a lower immigration rate, while less isolated islands closer to the source have a higher equilibrium number.

Why is extinction higher on more isolated islands?

Extinction is higher on more isolated islands because they are further from the source of species, making it less likely for species on the brink of extinction to be replenished by new immigrants.

What is the role of island size in determining the equilibrium level of species?

Island size is a significant factor affecting the equilibrium level of species. Larger islands support more diverse habitats and have a lower risk of extinction due to chance events, leading to a higher equilibrium number of species.

How does island size influence extinction rates?

Extinction rates are higher on smaller islands compared to larger ones because smaller islands offer less habitat diversity and smaller habitat areas, increasing the chance of species extinction through random events.

What is the relationship between immigration rates and island size?

Immigration rates are generally lower on smaller islands due to the reduced likelihood of random dispersal to a smaller landmass.

What is the general trend in species numbers between near large islands and distant small islands?

The number of species is generally higher on near large islands compared to distant small islands, as larger islands can support more species and are less likely to experience species loss.

How does the dynamic between immigration and extinction affect species numbers on islands over time?

Over time, the counteracting forces of immigration and extinction create an equilibrium in the number of species on an island, with the specific equilibrium level being influenced by factors such as island isolation and size.

Outlines

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🌴 Equilibrium Theory of Island Biogeography

This paragraph introduces the Equilibrium Theory of Island Biogeography, which is the study of factors influencing species richness in isolated natural communities such as oceanic and continental islands. Oceanic islands, formed by volcanic activity, experience an increase in species diversity through succession until they reach a similar level as the mainland. In contrast, continental islands, which are formed due to rising water levels, start with a stable species composition and tend to lose species over time due to isolation. The theory posits that a stable number of species on an island is reached through a balance between immigration and extinction rates. The level of isolation and the size of the island are the two major factors affecting this equilibrium. More isolated islands have lower immigration and higher extinction rates, leading to a lower equilibrium number of species. Island size also plays a role, with larger islands supporting more species due to a greater diversity of habitats and reduced chance of extinction through chance events. Immigration rates are generally lower on smaller islands due to the reduced chance of random dispersion. The video concludes by summarizing that the equilibrium of species on islands is a result of the interplay between immigration and extinction over time.

Keywords

💡Island Biogeography

Island Biogeography is the study of factors that influence the diversity and distribution of species in isolated natural communities, such as islands. The video emphasizes that these communities can be oceanic islands formed by volcanic activity or continental islands formed due to rising water levels. Island Biogeography is central to understanding the dynamics of species richness and how it changes over time on these isolated landmasses.

💡Species Richness

Species richness refers to the total number of different species present in a given ecosystem. In the context of the video, species richness is a key aspect of island biogeography, as it discusses how the number of species on islands can fluctuate due to factors like isolation and island size.

💡Succession

Succession is the process by which the species composition of an ecosystem changes over time. The video mentions that in newly formed oceanic islands, species composition increases through succession until it reaches a level of diversity comparable to the closest mainland.

💡Isolation

Isolation in the video refers to the degree of separation between an island and the source of species, often the mainland or a larger nearby island. It is a critical factor in the Equilibrium Theory of Island Biogeography, as more isolated islands tend to have lower immigration rates and higher extinction rates, leading to a lower equilibrium number of species.

💡Equilibrium Theory

The Equilibrium Theory of Island Biogeography posits that the number of species on an island is a balance between immigration and extinction. The video explains that this equilibrium is dynamic and can vary between islands based on factors like isolation and size.

💡Immigration

Immigration, as discussed in the video, is the process by which new species arrive on an island. It is a key factor in the Equilibrium Theory, as the rate of immigration influences the species richness and the equilibrium level on islands. Islands closer to a species source tend to have higher immigration rates.

💡Extinction

Extinction in the context of the video refers to the disappearance of species from an island. It is one of the counteracting forces in the Equilibrium Theory, where the rate of extinction can affect the number of species present on an island. More isolated islands and smaller islands tend to have higher extinction rates.

💡Island Size

Island size is another significant factor in the Equilibrium Theory of Island Biogeography. Larger islands can support a greater number of species due to a higher potential for diverse habitats and larger habitat areas, which in turn reduces the chance of extinction through chance events. The video explains that smaller islands typically have lower equilibrium species numbers.

💡Habitat Diversity

Habitat diversity refers to the variety of environments that can support different species within an ecosystem. The video highlights that larger islands tend to have more diverse habitats, which can support a greater number of species and contribute to a higher equilibrium level of species richness.

💡Chance Events

Chance events in the video refer to random occurrences that can lead to the extinction of species. On smaller islands, the impact of chance events is more significant due to the limited habitat and resources, making species more vulnerable to extinction.

💡Random Dispersion

Random dispersion is the process by which species are distributed across the landscape by chance. The video notes that smaller islands have lower rates of random dispersion, which can result in lower immigration rates and, consequently, lower species richness.

Highlights

Island Biogeography is the study of species richness in naturally isolated communities.

Islands can be oceanic, formed by volcanic activity, or continental, formed by rising water levels.

Oceanic islands gain species diversity through succession until they match the nearest mainland.

Continental islands have a stable species composition before isolation and may lose species多样性 after.

The Equilibrium Theory of Island Biogeography describes a stable number of species on islands.

Species number on an island is a balance between immigration and extinction rates.

Isolation level is a major factor affecting species equilibrium, with more isolated islands having fewer species.

Islands closer to the mainland or other large islands have higher immigration rates and species equilibrium.

Extinction rates are higher on more isolated islands due to fewer immigration opportunities.

Island size is the second major factor influencing species equilibrium, with larger islands supporting more species.

Smaller islands have higher extinction rates and lower immigration rates, leading to fewer species.

Larger islands offer more diverse habitats and larger habitat areas, reducing the chance of extinction.

The chance of extinction through random events is reduced on larger islands.

Over time, the forces of immigration and extinction create an equilibrium in species number on islands.

Nearby large islands will have a higher number of species compared to distant small islands.

The video concludes by summarizing the factors influencing species equilibrium on islands.

Transcripts

In this video we are going to go over the Equilibrium Theory of Island Biogeography.

Island Biogeography refers to the study focusing on factors that affect species richness in

naturally isolated communities.

These communities include typical isolated oceanic islands, often formed by volcanic

activity.

It also includes continental islands which are formed for instance due to rising water

levels.

In oceanic islands, especially those newly formed through volcanic eruption, the species

composition will increase through the process of succession until reaching a similar level

of diversity as the closest mainland.

Continental islands already have a stable species composition before becoming isolated.

Now isolated, they will tend to decrease in the number of species present depending on

the level of isolation.

The Equilibrium theory of Island Biogeography refers to when these island have reached a

stable number of species.

It relates to the idea that the number of species found on an island over time is a

balance between immigration of species to the island and extinction of species, reaching

an equilibrium.

The level of this equilibrium is different on different islands, there are two major

factors that affect these differences: the first is the level of isolation, the second

is the size of the island.

Those islands that are more isolated are further from the source of species.

This source is often the mainland but can also be another larger island close by.

These more isolated islands have a lower equilibrium number due to a lower immigration rate.

Those that are closer and less isolated have easier immigration and the equilibrium number

is going to be higher.

Extinction is also higher on more isolated islands compared to less isolated islands.

This is due to the less isolated islands being closer to the source of the species.

Which means species that are about to go extinct are more likely to be saved by repeated immigration

to the island.

Island size is the second factor that affects the equilibrium level.

Extinction is higher on smaller islands compared to larger islands.

Because of this the equilibrium number of species is going to be smaller on small islands

and larger on large islands.

This occurs because there is more chance for diverse habitats in larger islands and habitat

areas are larger, on larger islands.

Because of this, the chance of extinction through chance events is reduced.

Immigration rates are also smaller on smaller islands, due to the reduced rate of random

dispersion to a smaller island.

In summary the number of species on near large islands are going to be higher than that on

distant small islands.

Over time on all islands the counteracting forces of immigration and extinction creates

an equilibrium in the number of species on an island.

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