Bushar, L.M.

The island of Aruba is home to several endemic species, and has been colonized recently by the invasive boa, Boa constrictor. We present data for a multiple-year sampling effort on one of Aruba's endemic species, the Aruban Whiptail Lizard (Cnemidophorus arubensis). Our sampling began before the invasion of B. constrictor and ended after their firm establishment, thus affording us the unique opportunity to document the potential effects of this invasive snake on the endemic lizard. Additionally, we compare our data with earlier studies with an average lizard density of 235.1/ha (SE = 73.42, n = 11). After the invasion of the B. constrictor we calculated densities of C. arubensis as high as 2,185/ha. Although B. constrictor regularly preys upon C. arubensis, the relationship between B. constrictor and C. arubensis likely represents ecological facilitation of the lizard species. Herein, we further develop a hypothesis that may explain how the invasive B. constrictor has caused an increase in the population of this endemic lizard. Additionally, we suggest and discuss a few alternative hypotheses that may also account for this observed pattern of increased density. This study identifies a need for continued monitoring of Aruba's native fauna, as well as the need for further experimental approaches to understand the mechanism by which invasive predators ecologically interact with native prey.

Boa constrictor was first documented on the Caribbean island of Aruba in 1999. Despite intensive efforts to eradicate the snake from the island, B. constrictor has established a stable, reproductively successful population on Aruba. We generated mitochondrial sequence and multilocus microsatellite data for individuals from this population to characterize the origins and means of introduction to the island. Phylogenetic analyses and measures of genetic diversity for this population were compared with those for invasive B. constrictor imperator from Cozumel and B. constrictor constrictor from Puerto Rico. Cozumel populations of B. c. imperator had significantly higher number of alleles and significantly higher values for FIS than the Puerto Rico and Aruba populations. Observed, expected, and Nei's unbiased heterozygosities, as well as effective number of alleles, were not significantly different. The effective population sizes from Aruba and Puerto Rico were generally lower than those for either of the Cozumel populations; however, there were broad confidence intervals associated with published estimates. We conclude that the present B. constrictor population on Aruba probably was not established from the introduction of a single gravid or parthenogenic female but instead most likely resulted from the release or escape of a small number of unrelated captive snakes. This study adds to the growing body of evidence suggesting the ease with which a small number of relatively slow-maturing B. constrictor can quickly invade, become established, and avoid eradication efforts in a new location with suitable habitat.