https://phys.org/news/2021-04-island-gigantism-dwarfism-result-evolutionary.html Phys.org Topics * Week's top * Latest news * Unread news * Subscribe [ ] Science X Account [ ] [ ] [*] Remember me Sign In Click here to sign in with or Forget Password? Not a member? Sign up Learn more * Nanotechnology * Physics * Earth * Astronomy & Space * Technology * Chemistry * Biology * Other Sciences * * share this! * 68 * 18 * Share * Email 1. Home 2. Biology 3. Evolution 1. Home 2. Biology 3. Ecology * * * --------------------------------------------------------------------- April 15, 2021 Island gigantism and dwarfism the result of evolutionary island rule by Radboud University Nijmegen Confirmed: Island gigantism and dwarfism result of evolutionary island rule A juvenile Brookesia micra standing on a human finger tip Credit: Frank Glaw, Jorn Kohler, Ted M. Townsend, Miguel Vences, CC BY 2.5, via Wikimedia Commons It is an old-standing theory in evolutionary ecology: animal species on islands have the tendency to become either giants or dwarfs in comparison to mainland relatives. Since its formulation in the 1960s, however, the 'island rule' has been severely debated by scientists. In a new publication in Nature Ecology and Evolution on April 15, researchers solved this debate by analyzing thousands of vertebrate species. They show that the island rule effects are widespread in mammals, birds and reptiles, but less evident in amphibians. Dwarf hippos and elephants in the Mediterranean islands are examples of large species who exhibited dwarfism. On the other hand, small mainland species may have evolved into giants after colonizing islands, giving rise to such oddities as the St Kilda field mouse (twice the size of its mainland ancestor), the infamous dodo of Mauritius (a giant pigeon), and the Komodo dragon. In 1973, Leigh van Valen was the first to formulate the theory, based on the study by mammologist J. Bristol Foster in 1964, that animal species follow an evolutionary pattern when it comes to their body sizes. Species on islands have the tendency to become either giants or dwarfs in comparison to mainland relatives. "Species are limited to the environment on an island. The level of threat from predatory animals is much lower or non-existent," says Ana Benitez-Lopez, who carried out the research at Radboud University, now researcher at Donana Biological Station (EBD-CSIC, Spain). "But also limited resources are available." However, until now, many studies showed conflicting results which led to severe debate about this theory: is it really a pattern, or just an evolutionary coincidence? Island rule confirmed The team of scientists at Radboud University, Donana Biological Station, National Museum of Natural Sciences and Imperial College London has revisited the island rule, aiming to solve this debate by performing a meta-analysis of over a thousand vertebrate species. They show that island rule effects are widespread in mammals, birds and reptiles, but less evident in amphibians, which mostly tend towards gigantism. The study also indicates that the magnitude of insular dwarfism and gigantism is more pronounced in smaller, more remote islands for mammals and reptiles. Size is context-dependent They also found an effect of climate and seasonality on the island rule. Small mammal and bird species grew larger and large species stayed the same size to conserve heat in colder, harsher insular environments. Furthermore, when seasons are present, availability of resources become less predictable for reptiles, leading smaller reptile species to become larger. Benitez-Lopez concludes, "Using a wealth of data from museum and live specimens, we were able to rigorously demonstrate for the first time that insular gigantism and dwarfism across vertebrates is a generalized pattern and not just an evolutionary coincidence." --------------------------------------------------------------------- Explore further Miniature guttural toads on Mauritius and Reunion stun researchers --------------------------------------------------------------------- More information: The island rule explains consistent patterns of body size evolution in terrestrial vertebrates, Nature Ecology and Evolution (2021). DOI: 10.1038/s41559-021-01426-y Journal information: Nature Ecology & Evolution Provided by Radboud University Nijmegen Citation: Island gigantism and dwarfism the result of evolutionary island rule (2021, April 15) retrieved 16 April 2021 from https:// phys.org/news/ 2021-04-island-gigantism-dwarfism-result-evolutionary.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. 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