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.