Lorenzo Garizio

Migration is a widespread phenomenon across taxa, yet the ecological mechanisms underlying its evolution and maintenance, particularly whether migratory behaviors are primarily driven by access to spatially restricted breeding sites or by seasonal tracking of trophic resources, remain poorly documented outside birds and large mammals. Despite increasing evidence that reptiles perform seasonal migrations, the ecological mechanisms underlying these movements have rarely been formally tested. The critically endangered Galápagos pink land iguana ( Conolophus marthae ), endemic to Wolf Volcano, Isabela Island, exhibits partial migration along a steep altitudinal gradient, providing an opportunity to disentangle the relative roles of breeding-site availability, trophic resource dynamics, and thermoregulatory conditions as drivers of migration. We used GPS tracking data from 22 individuals (7 males, 15 females) monitored between 2019 and 2023, combined with high-resolution spatio-temporal models of vegetation productivity and air temperature across the species’ altitudinal range, to characterize population-level movement patterns and evaluate competing hypotheses explaining the evolution of this migratory behavior. Movement models revealed a clear pattern of partial migration: 16 out of 22 tracked individuals performed seasonal altitudinal movements between a restricted high-elevation mating area and a larger dispersal area at lower elevation, with males reaching the mating area approximately 48 days earlier than females. The dispersal area remained consistently more productive than the mating area throughout the year, rejecting the prediction that individuals should track the shifting trophic resource peaks. Instead, the mating season coincided with the local productivity peak within the mating area, whereas temperature differences between areas were small ( ca. 2°C) and did not explain migration timing. These results support a site-dependent hypothesis of partial migration over a resource-tracking hypothesis, indicating that access to spatially restricted breeding sites is the primary driver of migration in this species, with local trophic resource dynamics fine-tuning reproductive timing. Providing empirical evidence for the ecological mechanisms underlying migration in a large terrestrial reptile, our results extend site-dependent theories of migration beyond birds and mammals and identify breeding-site availability as a key ecological driver of migratory behaviors across taxa.

Aim: This study aimed to test the effectiveness of a hierarchical, spatially explicit, Bayesian modelling framework combining Integrated Nested Laplace Approximation (INLA) with Stochastic Partial Differential Equation (SPDE) as an alternative to traditional Species Distribution Models (SDMs), particularly in cases where standard assumptions are violated, such as for small‐ranged, data‐limited species. Using the critically endangered Galápagos Pink Land Iguana ( Conolophus marthae ) as a case study, we also aimed to produce spatially explicit predictions to inform conservation strategies for this species. Location: The Galápagos Archipelago, Ecuador. Methods: We applied the INLA‐SPDE model to address spatial autocorrelation in occurrence data, which is common when most observations originate from a limited number of surveys, as frequently happens with isolated, small‐ranged species of high conservation priority. The model was used to identify environmental drivers of occurrence and to map both the current and potential distribution of C. marthae . We evaluated the predictive performance of the model through spatial cross‐validation. Results: The model revealed that trophic resource availability, presence of open areas and terrain roughness are key factors limiting the distribution of C. marthae . Its current range was estimated at approximately 27 km ² , while around 330 km ² of suitable areas were identified across three main sites outside its known distribution. The model showed good predictive performance (Cohen's K = 0.68; TSS = 0.70), with consistent predictor effects across model runs. Main Conclusions: Our findings demonstrated the utility of the INLA‐SPDE approach in modelling distributions of small‐ranged species, overcoming limitations of classical SDMs. The results obtained provided the first formal estimate of the range of C. marthae and identified new suitable areas, constituting an essential starting point to evaluate a species translocation, a key conservation strategy outlined in the Conservation and Management Plan for this species.

Thermoregulation in reptiles depends on the interplay between environmental conditions, genetic adaptation and phenotypic plasticity. Behavioral strategies and skin pigmentation are among the main factors influencing the ability of reptiles to modulate heat transfer with the environment. The critically endangered Galápagos pink land iguana ( Conolophus marthae ) displays a unique coloration, due to the absence of pigments across large portions of its body. In this study, we compared thermoregulatory strategies of C. marthae and the syntopic population of yellow iguana ( C. subcristatus ) on Wolf Volcano (Isabela Island, Galápagos). While the two species display similar body temperatures, C. marthae tends to expose itself to lower levels of ultraviolet B (UVB) irradiance. This difference reflects contrasting microhabitat use, with pink iguanas occupying shaded areas more frequently than yellow iguanas. The lack of photoprotective pigments in the pink iguana’s dermis may explain this behavior, as prolonged exposure to UV irradiance can be detrimental to iguana health. The avoidance of high solar radiation highlights the role of microhabitat features in meeting the thermoregulatory requirements of the pink iguana, which may preferentially select areas with denser vegetation that provides shelters and shade. Thus, the distinctive partial skin depigmentation of the pink iguana, which is otherwise interpretable as detrimental, may instead shape microhabitat selection, reduce competition, and ultimately facilitate coexistence with C. subcristatus .

Invasive alien species control is recognized worldwide as a priority action to preserve global biodiversity. However, a lack of general life history knowledge for threatened species can impede the effectiveness of conservation actions. Galápagos pink land iguanas (Conolophus marthae) are endemic to Wolf Volcano, Galápagos, Ecuador. These iguanas are threatened by invasive alien species, particularly feral cats, that may affect their small population size. To guarantee the long-term survival of C. marthae, the Galápagos National Park Directorate is considering, along with an ongoing campaign of feral cat control, the implementation of a head-start program. However, the success of this management strategy necessarily relies on the identification of pink iguana nesting grounds, which were still unknown at the onset of this study. We modeled the movement patterns of male and female iguanas during the reproductive season, using location data collected from custom-made remote tracking devices installed on adult pink iguanas in April 2021. We first calculated for each individual the vector of distances from its starting location, which was defined as net displacement. We then used net displacement as the response variable in a generalized additive mixed model with day of the year as the predictor. Based on the hypothesis that males and females may behaviorally differ after mating, we looked for female-specific migratory behavior suggesting females were moving toward nesting areas. The results obtained confirmed our hypothesis, as females exhibited a distinct migratory behavior, reaching a small plateau area inside of Wolf Volcano’s caldera and ca. 400 m below the volcano’s northern rim. Moreover, once inside the caldera, females displayed a more aggregated distribution pattern. The movement data obtained allowed Galápagos National Park rangers to locate individual pink iguana nests and subsequently to sight and collect the first observed hatchlings of the species. This work constitutes a necessary baseline to perform dedicated studies of pink iguana nests and emerging hatchling iguanas, which is an essential step toward the development of an effective head-start program.

We present the first estimate of population dynamics parameters for critically endangered Galápagos pink land iguanas, Conolophus marthae , leveraging mark‐recapture data collected between 2006 and 2021. Demographic parameters were estimated using the POPAN formulation of the Jolly–Seber model. This approach provided a solid and robust estimate, consolidating the results obtained from previous estimates based on the Lincoln–Petersen method evaluating only two sampling occasions. Our results suggest that the abundance of males was higher than that of females at each sampling occasion, probably due to differences in sex‐specific behavior during the reproductive season. Our analyses also provide no evidence of a change in population size during the sampling period, estimated at 150–270 adult individuals, while suggesting positive entry rates. Finally, by comparing the biometric features of first‐captured versus recaptured iguanas, we found that the former have more juvenile‐like characteristics (i.e., they are, on average, smaller) than the latter. Although juvenile pink iguanas have rarely been recorded (only four sampled juvenile‐like individuals in over 16 years of field work), our combined results provide the first clear indication that the only known C. marthae population actively recruits new members from younger age classes. Such recruitment may have prevented any measurable population decline in the last 16 years, but it was also not sufficient to clearly increase the population size. These results are of the utmost importance for the conservation of this species. They will guide future high‐priority actions: (i) aiming at increasing population size by removing or mitigating threats and (ii) increasing the number of individuals by implementing a headstart program and/or founding a second viable population, as identified in the recently published IUCN Conservation and Management Plan.