Lizard species on large Caribbean islands are more numerous than those on smaller islands because there is more evolution going on.
The bigger the island, the faster species proliferate and diversify.
Jonathan B. Losos, Ph.D., associate professor of biology in Arts and Sciences at Washington University in St. Louis, proved this species-area relationship in a study of 143 species of Caribbean Anolis lizards on 147 islands. Focusing on the four largest islands, Cuba, Hispaniola, Jamaica and Puerto Rico, collectively known as the Greater Antilles, Losos showed that the diversity of lizard species is primarily a result of the evolutionary process of speciation, rather than the ecological processes of colonization and extinction.
Losos, and co-author Dolph Schluter, Ph.D., professor of biology at the University of British Columbia, published these results in the Dec. 14, 2000 issue of Nature. The study is an important and novel extension of a 33 year old theory on the genesis of biological diversity.
"When you focus on the larger islands, the rate of speciation is a function of island area," said Losos. "A large island equals more speciation events. At some level this is intuitive, but it has never been demonstrated before that differences in the rate of speciation, of evolution, can produce the species-area relationship."
Losos and Schluters results complement the well-known "Equilibrium Theory of Island Biogeography," proposed in 1967 by the late Robert MacArthur of Princeton University and E.O. Wilson of Harvard University. MacArthur and Wilsons ecological theory proposed that the number of species on any island reflects a balance between the rate at which new species colonize it and the rate at which populations of established species become extinct.
An "island" in this sense is not strictly an island in a stream or ocean, but any ecosystem, say a forest, surrounded by barriers. A major component of this theory i
Contact: Tony Fitzpatrick
Washington University in St. Louis