ScienceDaily (July 8, 2010) — Long before TV's campy Fantasy Island, the isolation of island communities has touched an exotic and magical core in us. Darwin's fascination with the Galapagos island chain and the evolution of its plant and animal life is just one example.
Think of the extensive lore surrounding island-bred creatures like Komodo dragons, dwarf elephants, and Hobbit-sized humans. Conventional wisdom has it that they -- and a horde of monster-sized insects -- are all products of island evolution.
But are they?
Dr. Shai Meiri of Tel Aviv University's Department of Zoology says "yes," they are a product of evolution, but nothing more than one would expect to see by "chance," citing research that shows there's nothing extraordinary about evolutionary processes on islands. He and his colleagues have conducted a number of scientific studies comparing evolutionary patterns of island and mainland ecosystems, and the results refute the idea that islands operate under different, "magical" rules.
Man bites evolutionary dog
"My findings are a bit controversial for some evolutionary biologists," says Dr. Meiri, the author of several papers and essays on island evolution. His research is based on statistical models he developed.
"There is a tendency to believe that big animals become very small on islands, and small animals become very big, due to limited resources or lack of competition. I've shown that this is just not true, at least not as a general rule. Evolution operates on islands no differently than anywhere else."
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Volume 19 Issue 4, Pages 475 - 484
Published Online: 16 Apr 2010
RESEARCH PAPER
One size does not fit all: no evidence for an optimal body size on islands
Pasquale Raia 1,2 *, Francesco Carotenuto 1 and Shai Meiri 3
1 Dipartimento di Scienze della Terra, Università Federico II, Largo San Marcellino 10, 80138 Naples, Italy, 2 Center for Evolutionary Ecology, Largo San Leonardo Murialdo 1, 00146 Roma, Italy, 3Department of Zoology, Tel Aviv University, Tel Aviv 69978, Israel
Correspondence to *Pasquale Raia, Dipartimento di Scienze della Terra, Università Federico II, Largo San Marcellino 10, 80138 Naples, Italy.
E-mail: pasquale.raia@libero.it
KEYWORDS
Body size evolution • Brownian motion model • island rule • mammalian phylogenetic tree • optimal body size theory • phylogenetic dispersion
ABSTRACT
Aim
Optimal body size theories predict that large clades have a single, optimal, body size that serves as an evolutionary attractor, with the full body size spectrum of a clade resulting from interspecific competition. Because interspecific competition is believed to be reduced on islands, such theories predict that insular animals should be closer to the optimal size than mainland animals. We test the resulting prediction that insular clade members should therefore have narrower body size ranges than their mainland relatives.
Location
Location
World-wide.
Methods
Methods
We used body sizes and a phylogenetic tree of 4004 mammal species, including more than 200 species that went extinct since the last ice age. We tested, in a phylogenetically explicit framework, whether insular taxa converge on an optimal size and whether insular clades have narrow size ranges.
Results
Results
We found no support for any of the predictions of the optimal size theory. No specific size serves as an evolutionary attractor. We did find consistent evidence that large (> 10 kg) mammals grow smaller on islands. Smaller species, however, show no consistent tendency to either dwarf or grow larger on islands. Size ranges of insular taxa are not narrower than expected by chance given the number of species in their clades, nor are they narrower than the size ranges of their mainland sister clades – despite insular clade members showing strong phylogenetic clustering.
Main conclusions
Main conclusions
The concept of a single optimal body size is not supported by the data that were thought most likely to show it. We reject the notion that inclusive clades evolve towards a body-plan-specific optimum.
DIGITAL OBJECT IDENTIFIER (DOI)10.1111/j.1466-8238.2010.00531.x About DOI
DIGITAL OBJECT IDENTIFIER (DOI)10.1111/j.1466-8238.2010.00531.x About DOI
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