Island Biogeography, Ecological Tolerance, & Natural Disruptions

2.3 Island Biogeography

The highest species richness is found in large islands near to mainland. The lowest species richness would be found on small islands far from mainland.

Very isolated islands also have lower genetic diversity because of a founder effect. Species living on the smaller islands will evolve to be specialists (surviving only within a specific set of conditions) because of the limited resources.

Founder Effect

Trivia: The founder effect is a phenomenon where a small group of individuals establish a new population, leading to reduced genetic diversity. This occurs on isolated islands due to limited gene flow from the mainland. The Galapagos Islands are a famous example, where unique species evolved due to founder effects.

Wildlife corridors

Island biogeography explores the effects of habitat fragmentation on species. Building roads can simulate islands, with the mainland being the old growth forest and small patches as islands. To overcome fragmentation, wildlife corridors are being built.

Overcoming Habitat Fragmentation

Trivia: Wildlife corridors are essential for maintaining biodiversity and allowing species to move between fragmented habitats. They act as green highways that connect isolated populations, promoting gene flow and reducing the risk of extinction. Without these corridors, species would be trapped in small, isolated patches of habitat, leading to loss of genetic diversity and increased vulnerability to environmental changes.

2.4 Ecological Tolerance

Ecological tolerance refers to the range of conditions that an organism can endure before injury or death. Conditions such as:

Temperature

Salinity

Dissolved oxygen

Sunlight

pH

Each individual or species has a range of abiotic conditions that it has adapted to.

2.5 Natural Disturbances

Natural disturbances like volcanic eruptions and hurricanes can disrupt ecosystems, but some can recover through resistance and resilience.

Ecosystem Resistance - when the disturbance does not diminish the net primary productivity of the ecosystem (some plants may have been destroyed but others grew in their place that were more suited to the new conditions)

Ecosystem Resilience - The RATE at which an ecosystem can go back to its original state after a disturbance

Island Disruptions

Trivia: Volcanic eruptions and hurricanes are natural disturbances that can disrupt ecosystems on islands. These events can cause significant damage to the environment and can lead to the loss of biodiversity. Islands are particularly vulnerable to these disturbances due to their isolated nature and limited resources for recovery.

Intermediate Disturbance Hypothesis

Ecosystems with medium levels of disturbance have HIGHER biodiversity than those with low or high disturbance. Examples include intertidal zones, seasonal changes in temperate zones, and frequent small wildfires. Low disturbance leads to intense competition, while high disturbance favors fast-growing species or extinction.

Ecosystems with high disturbance

Trivia: In ecosystems with high disturbance, fast-growing species have an advantage as they can quickly adapt and reproduce. However, this also increases the risk of extinction for slower-growing species that cannot keep up with the rapid changes.