BERKELEY, Calif., Dec. 29 (UPI) -- Finite space, limited food and competition for resources in the environment are limiting factors in the number of the world's species, U.S. researchers say.
The long-accepted assumption has been borne out by a study of lizard populations on the four Caribbean islands of Puerto Rico, Jamaica, Hispaniola and Cuba, ScienceDaily.com reported Wednesday.
Daniel Rabosky of the University of California, Berkeley, and Richard Glor of the University of Rochester studied patterns of species accumulation of lizards over millions of years on the islands.
Species diversity -- the number of distinct species of lizards -- correlated to available space, they found.
"Geographic size correlates to diversity," Glor said. "In general, the larger the area, the greater the number of species that can be supported.
"For example, there are 60 species of Anolis lizards on Cuba, but far fewer species on the much smaller islands of Jamaica and Puerto Rico."
There are only six species on Jamaica and 10 on Puerto Rico, he said.
Rabosky and Glor found that species diversification of lizards on the four islands reached a plateau millions of years ago and has essentially come to an end.
However, a state of equilibrium does not mean that the evolution of a species comes to an end, Glor says.
Lizards will continue to adapt to changes in their environment but they are not expected to develop in a way that increases the number of species within a habitat, he says.