Contrasting Patterns of Movement across Life Stages in an Insular Iguana Population
West Indian rock iguanas (genus Cyclura) represent the most endangered group of lizards in the world, with most taxa restricted to few or single islands. In addition to distribution and availability of resources, factors influencing optimal use of insular space in these large vertebrates may include a combination of social, ontogenetic, and long-term demographic factors. Life stage-specific dispersal and habitat use patterns have previously been characterized in Cyclura, but assessments across the lifespan are lacking. This study evaluates shifting patterns of movement in a single taxon, Cyclura nubila caymanensis. We used mark–recapture and radio tracking simultaneously to assess age- and sex-dependent variation in spatial ecology. Evidence for prolonged site fidelity among adults was consistent with territoriality-modulating space use in this long-lived taxon. Over 5–10 yr, some females were never resighted or recaptured outside of an 80-m perimeter. A notable exception was that gravid females migrated 1.17 ± 0.91 km to utilize coastal areas during the nesting season. In contrast, neonates dispersed farther (2.32 ± 2.26 km) and their trajectories were often nonlinear. Radio-tracked brother–sister pairs exhibited no tendency to disperse together during their first 4 wk, settling into final known locations at pairwise distances of 2.16 ± 1.74 km. Annual net displacement remained high over the first 1–3 yr of life. Our data are consistent with studies of related taxa wherein individual spatial requirements vary with population density and island size. Notably, panmixis of small island iguana populations appears largely driven by pre-reproductive movements.ABSTRACT
Overview of landcover classifications on Little Cayman. Modified habitat, grasslands, coastal habitat, mangrove (seasonally and tidally flooded mangrove shrubland, forest, and woodland, and pools, ponds, and mangrove lagoons), dry shrubland (<4.5 m), and dry forest and woodland (4.5 m < canopy < 16 m) habitat types are indicated (DaCosta-Cottam et al., 2009). Nesting sites 1–8 were monitored consistently between 2015 and 2017 and Sites 9–11 were monitored only in 2017. Nest sites are described in detail in Appendix 1.
Distribution of retreats utilized by nesting female Cyclura nubila caymanensis at major West End nest sites on Little Cayman. Colors distinguish nest sites of origin.
Visual summaries of nine representative radio tracking paths collected from hatchling Cyclura nubila caymanensis on Little Cayman. Blue triangles represent natal sites and red squares represent final known locations.
(A) Distribution of initial dispersal angles among 11 brother–sister pairs of Cyclura nubila caymanensis on Little Cayman, where members of the same pair share the same color, number, and ring. (B) Comparisons of total dispersal distances among eight brother–sister pairs that were tracked for at least 1 wk, where brown bars represent females and turquoise bars represent males.
Annual recapture rates of Cyclura nubila caymanensis in various age and sex classes between the survey years of 2016 and 2017 on Little Cayman. Numbers of animals first captured in each age class in 2015 and 2016 are indicated in the numbers above bars for 2016 and 2017, respectively. AM = Adult Males; AF = Adult Females; SA = Subadults; Y = Yearlings; H = Hatchlings.
Relationship between linear relocation distance and body size, in snout–vent length (SVL), of Cyclura nubila caymanensis at the start of a between-year or within-year life history transition on Little Cayman. The distribution of linear relocation distances is summarized in boxplots for each of five life history transition states, hatchling-yearling (H-Y; mean = 3,052 ± 3,935 m), yearling-subadult (Y-SA; mean = 1,103 ± 1,693 m), subadult-adult (SA-A; mean = 404 ± 776 m), adult-adult female (A-AF; mean = 46 ± 70 m) and adult-adult male (A-AM; mean = 281 ± 660 m), and two short-term dispersal phases; neonate dispersal within the first 4 wk (H4wk; mean = 1,261 ± 1,334 m) and female nesting migrations (Nest; mean = 1,149 ± 884 m). Short-term dispersal phases (e.g., first 4 wk post-hatching and female nesting) are indicated in red. All other relocation distances were obtained via long-term (>1 yr) monitoring.
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