Limited resources cap species diversity

U. ROCHESTER (US) — Finite space, limited food supplies, and competition for resources work together to limit species diversity and achieve equilibrium.

Researchers studied patterns of species accumulation of lizards over millions of years on the four Caribbean islands of Puerto Rico, Jamaica, Hispaniola, and Cuba, focusing on distinct species, rather than the number of individual lizards.

“Geographic size correlates to diversity,” says Richard Glor, assistant professor of biology at the University of Rochester.

“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 6 species on Jamaica and 10 on Puerto Rico.

The study is published in the journal, Proceedings of the National Academy of Sciences.

Ecologists Robert MacArthur of Princeton University and E.O. Wilson of Harvard University established the theory of island biogeography in the 1960s to explain the diversity and richness of species in restricted habitats, as well as the limits on the growth in number of species.

The MacArthur-Wilson theory was developed for ecological time-scales, which encompass thousands of years, while the current work extends the concepts over a million years, Glor says.

“MacArthur and Wilson recognized the macroevolutionary implications of their work but focused on ecological time-scales for simplicity.”

Historically, biologists needed fossil records to study patterns of species diversification of lizards on the Caribbean islands. But advances in molecular methodology allowed Glor and Daniel Rabosky at the University of California, Berkeley, to use DNA sequences to reconstruct evolutionary trees that show the relationships between species.

The scientists found that species diversification of lizards on the four islands reached a plateau millions of years ago and has essentially come to an end.

The extent and quality of the data used in the research showed that species diversification of lizards on the islands was not continuing and had indeed entered a state of equilibrium.

“When we look at other islands and continents that vary in species richness,” says Glor, “we can’t just consider rates of accumulation; we need to look at the plateau points.”

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 aren’t expected to develop in a way that increases the number of species within a habitat.

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