Probing the adaptive landscape using experimental islands: density-dependent natural selection on lizard body size

Area of Science:

• Ecology
• Evolutionary Biology
• Herpetology

Background:

• Anolis lizards in the Greater Antilles are models for studying diversification driven by natural selection.
• Body size and shape are key traits influenced by competition and locomotor performance.

Purpose of the Study:

• To quantify natural selection on body size in brown anoles (A. sagrei) over three years.
• To experimentally assess the role of population density in driving natural selection.

Main Methods:

• Field study across seven replicate populations of A. sagrei.
• Experimental manipulation of population density on small islands.
• Measurement of natural selection on body size and heritability in a laboratory setting.

Main Results:

• The strength of natural selection on body size was proportional to population density (r2 = 0.81).
• Larger body sizes were favored at higher population densities, suggesting competitive advantages.
• Smaller individuals were disproportionately selected against at higher densities, indicating density-dependent selection.

Conclusions:

• Population density is a significant factor affecting natural selection in Anolis lizards.
• Natural selection on body size can lead to evolutionary responses, as indicated by significant heritability.
• The study highlights the interplay between density, competition, and adaptation in lizard populations.