Researchers investigated the extent to which the founder effect and natural selection affected evolutionary change. Fig. 5.1 shows the brown anole lizard, Anolis sagrei. These lizards live on a number of Caribbean islands and feed on a variety of invertebrates and other small animals. [Figure 5.1] A. sagrei spends a lot of time perching (resting) on, or moving along, branches of shrubs and trees. The width of the branch that A. sagrei perches on is known as the perch diameter, as labelled in Fig. 5.1. There is a positive correlation between perch diameter and hind limb length of A. sagrei. Longer hind limbs allow A. sagrei to run faster on vegetation with a larger diameter. Shorter hind limbs are needed to provide stability on vegetation of a smaller diameter. In 2004, a hurricane caused the death of all the A. sagrei lizards on seven islands. In 2005, the researchers randomly collected seven male and seven female lizards from a source population on a nearby island. For each of the seven islands affected by the hurricane, a male and female lizard were mated and placed on each island. These islands formed the experimental founder islands where new populations of A. sagrei were successfully established from each founding pair. Fig. 5.2 shows the difference in vegetation between the source island and the seven experimental founder islands. [Figure 5.2] Many generations of A. sagrei were produced over the four years after the introduction of the founding pairs. Fig. 5.3 shows how the mean hind limb length of A. sagrei changed on the seven experimental islands and on the source island. [Figure 5.3]