DOI: 10.5061/dryad.9p8cz8wgv
title: Favoring recruitment as a conservation strategy to improve the resilience of long-lived reptile populations: insights from a population viability analysis

description: In long-lived species, although adult survival typically has the highest
 elasticity, temporal variations in less canalized demographic parameters
 are the main drivers of population dynamics. Targeting recruitment rates
 may thus be the most effective strategy to manage these species. We
 analyzed 1136 capture–recapture histories collected over 9 years in an
 isolated population of the critically endangered Lesser Antillean iguana,
 using a robust-design Pradel model to estimate adult survival and
 recruitment rates. From an adult population size estimated at 928 in 2013,
 we found a yearly decline of 4% over the 8-year period. As expected under
 the canalization hypothesis for a long-lived species, adult survival was
 high and constant, with little possibility for improvement, whereas the
 recruitment rate varied over time and likely drove the observed population
 decline. We then used a prospective perturbation analysis to explore
 whether managing the species’ immature cohorts would at least slow the
 population decline. The prospective perturbation analysis suggested that a
 significant and sustained conservation effort would be needed to achieve a
 recruitment rate high enough to slow the population decline. We posit that
 the high recruitment rate achieved in 2014 – likely due to the maintenance
 in 2012 of the main nesting sites used by this population – would be
 sufficient to slow this population’s decline if it was sustained each
 year. Based on the results of diverse pilot studies we conducted, we
 identified the most likely threats targeting the eggs and immature
 cohorts, stressing the need to improve reproductive success and survival
 of immature iguanas. The threats we identified are also involved in the
 decline of several reptile species, and species from other taxa such as
 ground-nesting birds. These findings on a little-studied taxon provide
 further evidence that focusing on the immature life stages of long-lived
 species can be key to their conservation.
description: Between 2012 and 2020, we conducted a yearly mark–recapture
 survey at the end of the males’ reproductive peak of activity (i.e. 9
 primary sessions). Each primary session consisted of five secondary
 sessions (i.e. 5 consecutive days of sampling for 7.5 hours per day). We
 thus sampled the population over 45 secondary sessions. The capture teams
 consisted of 10 to 12 people, at least half of whom were proficient at
 spotting and capturing iguanas. Field assistants were divided into
 two-person teams, with each inexperienced person partnered with someone
 experienced. To ensure comprehensive and uniform coverage of the islet, we
 divided it into five zones that could be covered in a similar duration.
 Consequently, zones with dense cover or high iguana density were smaller
 than open zones or with few iguanas. We minimized observer bias by
 randomly assigning a two-person team to a zone at the start of the
 five-day sample period. Each two-person team systematically searched for
 iguanas in their zone before moving to the next zone on the following day.
 Therefore, all teams had the opportunity to search each zone for a total
 of 7.5 hours. We captured iguanas by hand or with a noose and scanned them
 for an existing PIT tag (11.5 x 2.12 mm; 0.1g, Trovan®, Ltd., EID, U.S.);
 if they lacked a tag, we inserted a new one on the ventral side of the
 right thigh. We analyzed the capture–recapture data
 using a robust design Pradel model, which is based on two nested temporal
 scales of sampling: the year and the repeated intra-year sessions (Pradel,
 1996). Robust design schemes allow the population to be open between the
 primary sessions, but assume closure for the secondary sessions (Kendall,
 Nichols, & Hines, 1997). Recruitment is defined as the number of
 adults that recruit into the population in a given year for any adult
 present in the population the year before (Pradel, 1996). We analyzed only
 adult data because juvenile Lesser Antillean iguanas (SVL &lt; 18 cm)
 usually have substantially lower capture and recapture probabilities than
 adults. They represented only 0 to 0.7% of total captures per year and
 thus were too few to model age-specific parameters. Their inclusion could
 have generated strong recapture heterogeneity, leading to biased estimates
 of demographic parameters (Arsovski et al., 2018). We compared models
 using Akaike Information Criteria with correction for small sample size
 (AICc) (Hurvich & Tsai, 1989). All analyses were conducted using
 the MARK program (White & Burnham, 1999). (See Material and
 Methods - Statistical Analysis for more information).
description: This dataset contains the raw capture-recapture history of the
 Adult and Subadult iguanas (1156 individuals) captured between 2012 and
 2020 on Chancel Islet, Martinique. We provide this dataset as a csv (comma
 separated) file. Additional information is available in the ReadMe
 file.