Final answer:
The increase in lizard population after predator removal is mainly due to the absence of predation pressure, serving as a limiting factor, leading to fewer deaths and allowing more individuals to reach reproductive age.
Step-by-step explanation:
The initial change that accounts for the increase in the population size of lizards after a predator is removed from the ecosystem is likely due to the absence of predation pressure. When the predator which preys on the lizards is no longer present, the lizard population can grow exponentially because more individuals survive to reproduce. Aside from the potential increase in reproductive rate, the main reason for the population increase is the removal of the predator, which acts as a limiting factor on the population size.
In the scenario described, on the island without predators, we would expect the lizards there to not evolve the same defensive adaptations that the lizards on the other island with predators might. These could include traits like camouflaged coloration, sharp spines, or toxins. The lack of predator pressure on the first island means that these traits would not confer as much of a survival advantage, and therefore, the selective pressure to develop such adaptations would be minimal.