Gigantism And Island Dwarfism: Do You Know What It’s All About?
These two mechanisms, known as gigantism and island dwarfism, manifest themselves in certain endemic species on islands across the planet. We’ll tell you everything you need to know about the topic in this article.
What factors favor island gigantism and dwarfism?
As a first measure, it is very important to define what we are referring to when we talk about island gigantism and dwarfism.
In both cases, it is an evolutionary response of animal species – and also of some plants – that live on islands separated from the continents.
In island gigantism, species outgrow their ancestors, and this may be due to three main causes:
1. Absence of predators
When an animal is small, it is more likely to be devoured by a larger one, but it is also easier to hide. If on the island where they live there is no one to hunt them, then there will be no problem in growing larger than normal.
2. Lack of competitors
Another cause of island gigantism is that there are no opposing species fighting for the same resources. By being “unique”, they can eat more and better and therefore grow.
3. Presence of large prey
When the food is too big, the animals have to adapt. One way is to grow too.
In turn, island dwarfism is the inverse evolutionary process of the previous one, and it is more common than we imagine. By being “stuck” in a small habitat like an island, the animals reduce their size to be able to adapt to the lack of resources.
Examples of insular gigantism
Rodents and birds are clear examples of island gigantism, but not the only ones. Although most species that grew more than usual as an evolutionary process are extinct, there are still some today, which are:
1. Galapagos Tortoise
In total, there are 10 species that fall under the name “Galapagos tortoise” – main photo of this article – and are related to each other. They live on this island in the Pacific Ocean that belongs to Ecuador, and they are the largest in the world.
The Chelonoidis nigra have copies that can measure more than two meters and weigh half a ton. Its life expectancy can reach 170 years!
They are among the largest and heaviest insects in the world, and their habitat is New Zealand. The giant weta can measure 10 centimeters and weigh about 30 grams.
Males are larger than females, and they are also more aggressive.
During the day they remain hidden in holes or trees, and at night they go out to hunt thanks to their powerful jaws that allow them to eat beetles and moths.
It is a carnivorous mammal endemic to the island of Madagascar, considered the only predator in its territory. Compared to ancient species, the current pit measures and weighs twice as much as before.
Today, there are male specimens with 80 centimeters in length – plus 90 centimeters of tail – that weigh about 10 kilos.
Examples of island dwarfism
The process known as island dwarfism is more common among mammals, although it also happens to some reptiles. Among them, we can highlight:
1. Fox of the islands
This is a small endangered canid inhabiting the Santa Barbara Islands off the coast of California. It is the smallest fox in North America, with a body similar to that of a domestic cat.
It’s 50 centimeters long – plus 20 centimeters of tail – and weighs about 2 kilos.
2. Cuban crocodile
This reptile is the smallest of the saurians family – no more than three meters long – and, as its name indicates, it lives on the island of Cuba (its habitat is very restricted).
It feeds on birds, fish and mammals and, despite its size, is one of the most dangerous in the world.
Gigantism and insular dwarfism, without a doubt, are forms of evolution that animals have to adapt to their habitat. Still, in many cases – considering also external factors such as the appearance of man – they cannot survive and are extinct.