When animals evolve on islands, size doesn't matter

Nov 07, 2007
When animals evolve on islands, size doesn't matter

A theory explaining the evolution of giant rodents, miniature elephants, and even miniature humans on islands has been called into questions by new research published today in Proceedings of the Royal Society B: Biological Sciences.

The new study refutes the ‘island rule’ which says that in island environments small mammals such as rodents tend to evolve to be larger, and large mammals such as elephants tend to evolve to be smaller, with the original size of the species being the key determining factor in these changes.

The new research findings suggest that the tendency to either evolve larger or smaller on islands varies from one group of species to another, irrespective of original size. The research team, from Imperial College London, suspect instead that a number of external factors, including the physical environment of the particular island, the availability of prey, the presence of predators and the presence of competing species all play a role in determining the size evolution of island mammals.

Dr Shai Meiri from the NERC Centre for Population Biology at Imperial College London, lead author on the paper, explains: “If the island rule was correct, then most large mammals living on islands would be smaller than their continental relatives, and most small island mammals would be larger those living on continents. Our large dataset of mammal body sizes shows that this isn’t the case: there is evidence that most mammal groups show no tendency to consistently either grow larger or smaller, in contradiction to the island rule.”

Dr Meiri, who carried out the work with Professor Andy Purvis and Natalie Cooper from the College’s Department of Life Sciences, added: “The island rule suggests that the smallest mammals such as mice will exhibit the most evolutionary growth on islands, whilst the largest mammals like elephants will dwarf the most, with all mammals in between on a sliding-scale.

“Our analyses showed this isn’t the case, and the relationship between mammal size and evolutionary size change on islands is not that straightforward. Crucially, when we examined size change in light of the evolutionary relationship between different species, there was no connection between an evolution towards large size and greater degree of dwarfism on islands, or between evolution towards small size and island gigantism.”

The research team concluded that although there does appear to be a weak correlation between the size of a mammal and how its size then evolves in an island habitat, this reflects some groups’ specific tendencies towards gigantism or dwarfism, and not the general course of evolution. “The course of size evolution is dependent on a complex interplay of many other factors, that have led to the evolution of fascinating miniature and giant species of mammals on islands,” concludes Dr Meiri.

Source: Imperial College London

Explore further: Italian olive tree disease stumps EU

add to favorites email to friend print save as pdf

Related Stories

Who's your daddy? Hippo ancestry unveiled

Feb 24, 2015

A great-great grandfather of the hippopotamus likely swam from Asia to Africa some 35 million years ago, long before the arrival of the lion, rhino, zebra and giraffe, researchers said Tuesday.

Addressing feral cats' diet may help protect native species

Feb 02, 2015

Because reducing the impacts of feral cats—domestic cats that have returned to the wild—is a priority for conservation efforts across the globe, a research team recently reviewed the animals' diet across Australia and ...

Recommended for you

Italian olive tree disease stumps EU

18 hours ago

EU member states are divided on how to stop the spread of a disease affecting olive trees in Italy that could result in around a million being cut down, officials said Friday.

China starts relocating endangered porpoises: Xinhua

23 hours ago

Chinese authorities on Friday began relocating the country's rare finless porpoise population in a bid to revive a species threatened by pollution, overfishing and heavy traffic in their Yangtze River habitat, ...

A long-standing mystery in membrane traffic solved

Mar 27, 2015

In 2013, James E. Rothman, Randy W. Schekman, and Thomas C. Südhof won the Nobel Prize in Physiology or Medicine for their discoveries of molecular machineries for vesicle trafficking, a major transport ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.