The Influence of Landscape Heterogeneity and Dispersal on Survival of Neonate Insular Iguanas

The relationship between dispersal and predator–prey interactions in heterogeneous landscapes is an underappreciated factor influencing species persistence. This relationship, however, is critical for understanding population dynamics and for implementing management strategies for species. We investigated the influence of habitat heterogeneity and dispersal patterns on neonate survival for the iguana Cyclura cychlura cychlura inhabiting Andros Island in the Bahamas. Contrary to our hypothesis, there was a clear survival advantage for neonates that spent more time in open mangrove habitat than relatively more closed-canopy habitats, most likely because of fewer primary predators in mangroves relative to other habitats. Snake predation was the most significant cause of mortality for neonates dispersing away from nest sites and was highest during the first week after release. The probability of survival to 28 days ranged from 16.7 to 28.4%. Most neonates displayed rapid, nearly linear movements away from nests for a minimum of 14 to 21 days. Mean straight-line distance away from nest sites for surviving neonates was 601 m. There was a significant positive relationship between mean daily movement rates away from nests and days survived. We suspect that the initial and rapid movements away from nests reduce relative predation by dispersing neonates from a zone where predators learn to exploit them. Our results have implications for translocation programs targeting endangered insular iguanas throughout the Neotropics because historically only the presence of non-native mammalian predators was used as a metric to evaluate potential translocation sites.

Fig. 1

Example of P-value distributions from 20 iterations, each using different combinations of randomly selected siblings from single clutches. See Massot et al. (1994) for details. The distributions are from the regression analysis of mean daily dispersal distance versus number of days survived. The vertical dashed line represents the cut-off point for statistical significance (P ≤ 0.05). The solid arrow represents the P-values from analyses that treated each sibling independently. The dashed arrow represents the P-values averaged across all 20 iterations, which ensured independence of data points.

Fig. 2

Kaplan-Meier survival curves with 95% confidence intervals for Andros Iguana hatchlings using combined 2003 and 2004 data. Solid lines represent the pessimistic estimate where all censored hatchlings were assumed dead. Hatched lines represent the optimistic estimate where every censored observation was assumed not a death and that the hatchlings survived to the end of the study.

Fig. 3

Weekly fates of Andros Iguana hatchlings with number of hatchlings confirmed killed per week by snake genera (see text for species) and unknown avian species.

Fig. 4

Median survival time as a function of proportional time spent in each of three habitats. Shown are the fitted curves from each habitat-specific regression model (solid line: pine woodland; dashed line: shrubland; dotted line: mangrove). See Table 1 for parameter values.

Fig. 5

Mean straight-line distance (m) ± 1 S.E. from nests for Andros Iguana hatchlings surviving a minimum of 14 days (n = 18).

Contributor Notes

Associate Editor: G. Haenel.

¹ Conservation Department, John G. Shedd Aquarium, 1200 South Lake Shore Drive, Chicago, Illinois 60605; and San Diego Zoo's Institute for Conservation Research, Escondido, California 92027; E-mail: cknapp@ufl.edu. Send reprint requests to this address.

² School of Natural Resources and the Environment, University of Florida, Gainesville, Florida 32611; E-mail: silviacr@ufl.edu.

³ Department of Infectious Diseases and Pathology, University of Florida, Gainesville, Florida 32611; E-mail: caroph@ufl.edu.

Received: 16 Jan 2009

Accepted: 01 Oct 2009