What is discrete diffusion? Causes and types of isolated spread

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The pattern or nature of animal distribution is not consistent across the globe. Specifically, four types of diffusion can be observed. Fauna families of the same or closely related species often spread across distinct geographical regions of the world over long distances, rather than continuously expanding into adjacent regions. Such proliferation of animals is known as discrete proliferation. The three genera of Dipnoi shelling fish currently exhibit isolated distributions restricted to three continents of the world. The three continents are Australia, Africa, and South America.

Causes of Dispersal Distribution: Dispersal distribution of animals can be due to two reasons. The two reasons are as follows:

1. Fossil evidence indicates in most cases that animals that today exhibit isolated distributions were widespread over large areas in the distant past. But the barriers between populations have not been overcome, either by geological causes or by changes in climate or by the arrival of different animals, by wear and tear between the original animal community, or by disruption of open association. In this situation, the animals are separated into different subgroups. Even the animals from the intermediate region are destroyed. Thus, living organisms exhibit discrete distributions by occupying different geographic regions over long distances.

2. Another possible explanation for isolated dispersal is the occurrence of the same group of animals over long distances that were once connected by land. Animals were able to migrate easily through such connectors. With the extinction of congeners over time, migratory species became isolated from each other and now exhibit isolated distributions. In the past, North America and Eurasia were connected along the Bering Strait and played a significant role in the distribution of fauna.

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Types of discrete diffusion: Discrete diffusion can be of two types. namely- (a) intercontinental diffusion and (b) local diffusion.

(a) Intercontinental diffusion: Such a discrete spread occurs from one continent to another at the genus or tribe level (sometimes species). For example, tapir is found in South America and Southeast Asia. There is no tapir anywhere between these two continents. Another classic example is lungfish. In South America, there is a lungfish called Lepidosiren. And in Australia, there is a lungfish called Neoceratodus. There are no lungfish in the intercontinental zone.

(b) Local diffusion: This is the nature of the same fauna being confined to different zoogeographical regions over wide distances or concentrated in particular limited areas. For example, the lion (Panthera leo) is now restricted to the Gir forests of India and Africa. But in the past, lions were found in different parts of Asia and Africa.

^{I am a student of zoology and credit for this article goes to Madam Rita Parvin, Sir Shamol Shordar, Sir MD Rafikul Islam, Sir Shafiullah Shopon}

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