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Foster’s Rule

What is Foster’s Rule?

The Foster Rule is also known as the Island Rule. It refers to a theory about changes in the body size of species influenced by the availability of natural resources.

Foster's Rule

In short, it states that small animals can become large animals over time when isolated on a resource-rich island in the absence of animal predators.

Similarly, the idea is widespread that, large mammals begin to shrink to a small size when isolated from an island with very few or available resources Bristol Foster proposed this law published in 1964 in his article entitled “Evolution Of Mammals On Islands”. . . . . . . . . .

Foster compared 116 species on land with their island counterparts. He suggested that some creatures become smaller versions of themselves (island dwarfism), while others are smaller and become larger versions of themselves (island gigantism). This proposal was dominated by two factors – .

Insular Dwarfism

Over time, larger animals tend to decline. Also known as island dwarfism, it can occur on land, as seen in dwarf tamarisks. One of the main reasons is the low population density, which is characteristic of the islands.

This process has been present in some species of elephants and dinosaurs throughout history. It can occur in isolated ecosystems, away from reproduction, and away from external influences such as deserts, caves and mountains.

It is often found in terrestrial animals that live on islands. Smaller areas have fewer inhabitants because it means less food and the demand for this food is met by fewer animals so they survive in such areas and life flourishes once food is plentiful.

Smaller animals have shorter gestation periods and shorter gestation periods. Not the competition between carnivores, but the availability of food (prey) and their size contribute as the main factor.

Insular Gigantism

The extent of an island or island is a process in which the main squares are equally included in an isolated island, and the fruit size is one side of Foster’s rule.

Large carnivores do not succeed in inhabiting the islands due to marine spreading, because in their absence they are overrun by other small carnivores, reptiles and birds which eventually become larger and grow when predatory pressure on the smaller animals decreases and there is no less competition for them.

The increased size of such animals reduces risk in situations of food scarcity because they can survive and move for long periods without food.

Key Points

  • The Foster rule is an environmental law. It is told how the members of a tribe become smaller or larger depending on the resources available in nature.
  • Island dwarfism explains the decline of animals over time due to limited food and intense competition between species.
  • Island size is seen in animals migrating from continent to island. This is largely due to reduced prey availability and less competition.
  • Due to their increased size, they can survive for long periods without food.

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