Multiyear Sampling Reveals an Increased Population Density of an Endemic Lizard after the Establishment of an Invasive Snake on Aruba
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.Abstract
Map of Aruba showing Arikok National Park shaded in gray. The general locality where lizard mark–recapture studies were conducted within the National Park is identified by an open square.
We used cheese balls (a) as an effective bait to capture lizards. This bait is visually similar to Acacia tortuosa flowers (b), which are readily eaten by Cnemidophorus arubensis.
Among-year comparisons of Cnemidophorus arubensis density indicate that lizards per hectare significantly increased after the introduction of Boa constrictor on Aruba. Estimated densities of lizards for 1971 (black circles) were obtained from the literature (Schall, 1974, 1975). Mean estimated densities in 1994 and 2010 (open circles) were based on mark–recapture analyses of data presented in this study. The 95% confidence limits for each mean population density estimate are also shown. Note that confidence limits for mark–recapture analyses are not symmetrical around the mean as there is greater confidence in the lower limit. Lizards were also sampled in 2006 (Table 1) but density estimates were not possible because of inadequate recaptures.
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