1. Immigration Rate: This refers to the rate at which new species arrive on the island from the mainland or other islands. It's influenced by the distance from the mainland (further islands have lower immigration rates) and the size of the island (larger islands attract more species).
2. Extinction Rate: This refers to the rate at which species disappear from the island, primarily due to factors like limited resources, competition, and random events. Smaller islands have higher extinction rates due to smaller population sizes and less habitat diversity.
Wilson's theory proposes a balance between these two pressures, leading to an equilibrium point where the number of species on an island remains relatively stable over time. This equilibrium is influenced by the island's size and distance from the mainland, with larger, closer islands supporting a greater diversity of species.
While Wilson's theory doesn't explicitly mention a third pressure, other factors can influence biodiversity on islands, such as:
* Habitat heterogeneity: Islands with diverse habitats can support more species.
* Past geological history: Islands with a long history of isolation may have unique endemic species.
* Human impact: Human activities like deforestation and introduced species can have significant effects on island biodiversity.
It's important to remember that Wilson's theory is a foundational concept, and other factors contribute to the complex interplay of species on islands.
