Covariates streamline age‐specific early life survival estimates of two chelonian species

Abstract

Delayed maturity and high survival rates of immatures and adults characterize long‐lived species’ life histories. Understanding how these traits interact in stochastic environments is essential to understand early life in long‐lived species and to assist conservation planning. Unfortunately, available information of demographic traits in immatures are often fragmentary and the logistical difficulties of capturing and recapturing this cohort leave little room for improvement. Published immature chelonian survival estimates vary broadly, are often not age‐specific, and lack precision. In an attempt to overcome this issue, we developed a novel modelling approach based on Capture‐Recapture data to obtain robust age‐specific survival probabilities in two chelonian species (the freshwater European pond turtle, Emys orbicularis, and the terrestrial Hermann's tortoise, Testudo hermanni). More specifically, we show that implementing a linear relationship between survival probabilities and age does not distort survival estimates and improves precision. Both species display a progressive increase in survival with age, reaching a plateau at the ages of four to five. As maturity occurs later in both species (8–12 years‐old), the survival plateau might be governed by the final hardening of the carapace, which brings obvious survival benefits. Taking advantage of the flexibility of multievent models we encourage a systematic field approach even when very large samples from immatures cannot be amassed. Only so can demographic traits in chelonians, and more generally in long‐lived species, be properly explored.

Landscape connectivity affects individual survival in unstable patch networks: The case of a freshwater turtle inhabiting temporary ponds

“…for turtles during drought periods; Roe & Georges, 2008b), our results did not indicate a decrease in survival during the dry period despite the differences found in movement rates between periods. Juveniles had consistently lower estimated survival rates than adults, which is consistent with the literature (Arsovski et al 2018;Hamer et al, 2018;Iverson, 2018). However, their survival increased far more drastically with pond connectivity, as measured by Eigenvector centrality, and was especially low in poorly connected ponds.…”

“…However, because freshwater turtles are long-lived and most studies report only annual survival, we also estimated annual survival using the delta method approximation for estimating sampling variances and deriving 95% confidence intervals (Powell 2007;Saumure, Herman, & Titman, 2007), thereby providing comparable estimates with those reported elsewhere (e.g. Arsovski et al 2018;Canessa et al, 2016;Congdon, Gotte, & McDiarmid, 2016). In addition, for complementary purposes, we provide in Appendix S2 the annual estimates of apparent survival derived from single-state CJS modelling applied to our data pooled into one record per year.…”

Tradeoffs with Growth and Behavior for Captive Box Turtles Head-Started with Environmental Enrichment

“…However, we did not find any treatment difference in turtles' propensity to emerge, perhaps because there was no potential cost associated with not emerging. Additionally, hiding in cover is likely innate for this species, as this is probably the most efficient antipredator behavior for juveniles which are smaller and have less rigid shells than adults [3,18,26]. As with our predator recognition assay, future experiments might show greater treatment differences if shelter emergence tests incorporate aspects of our other assays, such as determining if turtles will differ in emergence propensity based on whether food or predator cues are present.…”

“…Juvenile turtles (order Testudines) often have lower estimated survival rates than adults, with predation assumed to be the primary cause of mortality [16,17]. Older, larger animals are less vulnerable to predation, in part due to a larger and thicker shell that can be a successful deterrent for many predators [3,18]. Additionally, wild turtles often do not reach reproductive sizes for upwards of 1-2 decades, so increasing juvenile growth rates should allow individuals to be closer to reproductive size upon release [19].…”

Survival of Immature Gopher Tortoises Recruited into a Translocated Population

“…The wide range in immature apparent survival estimates among sites is likely due in part to site-specific factors such as habitat quality or predator abundance (Smith et al 2013) but may also be influenced by the size distribution of animals comprising the immature class. Predicted annual survival increases with increasing size in immature desert tortoises (from 54% at 60 mm MCL to 95% at 150 mm MCL; McGovern 2019) and age in other turtle species (Fernández-Chacón et al 2011, Arsovski et al 2018; however, few studies have investigated whether survival also increases over the immature period in gopher tortoises. Wright (2016) and McKee (2019) reported that annual apparent survival of subadult gopher tortoises is significantly higher than that of juveniles, although neither provided separate estimates for the hatchling stage.…”