Mercury and stable isotopes portray colony-specific foraging grounds in southern rockhopper penguins over the Patagonian Shelf.

Mercury pollution is a serious global environmental issue and the characterization of its distribution and its driving forces should be urgently included in research agendas. We report unusually high mercury (Hg) concentrations (>5 µg/g) along with stable isotopes values in feathers of southern rockhopper penguins (Eudyptes chrysocome) from colonies in the Southwest Atlantic Ocean. We found a highly heterogenous prevalence of Hg throughout the study area and over a three-fold higher mean Hg concentration in southernmost colonies. Variation in Hg concentrations among colonies is primarily explained by site, rather than by trophic position. We provide further support to the existence of a Hg hotspot in the food web of the Patagonian Shelf and spatially restrict it to the southern tip of South America. Our findings highlight the need for regional and colony-based seabird conservation management when high local variability and plasticity in foraging habits is evident.

The dynamic trophic niche of an island bird of prey.

Optimal foraging theory predicts an inverse relationship between the availability of preferred prey and niche width in animals. Moreover, when individuals within a population have identical prey preferences and preferred prey is scarce, a nested pattern of trophic niche is expected if opportunistic and selective individuals can be identified. Here, we examined intraspecific variation in the trophic niche of a resident population of striated caracara (Phalcoboenus australis) on Isla de los Estados (Staten Island), Argentina, using pellet and stable isotope analyses. While this raptor specializes on seabird prey, we assessed this population's potential to forage on terrestrial prey, especially invasive herbivores as carrion, when seabirds are less accessible. We found that the isotopic niche of this species varies with season, age, breeding status, and, to a lesser extent, year. Our results were in general consistent with classic predictions of the optimal foraging theory, but we also explore other possible explanations for the observed pattern. Isotopic niche was broader for groups identified a priori as opportunistic (i.e., nonbreeding adults during the breeding season and the whole population during the nonbreeding season) than it was for individuals identified a priori as selective. Results suggested that terrestrial input was relatively low, and invasive mammals accounted for no more than 5% of the input. The seasonal pulse of rockhopper penguins likely interacts with caracara's reproductive status by constraining the spatial scale on which individuals forage. Niche expansion in spatially flexible individuals did not reflect an increase in terrestrial prey input; rather, it may be driven by a greater variation in the types of marine prey items consumed.

Metapopulation dynamics and foraging plasticity in a highly vagile seabird, the southern rockhopper penguin.

Population connectivity is driven by individual dispersal potential and modulated by natal philopatry. In seabirds, high vagility facilitates dispersal yet philopatry is also common, with foraging area overlap often correlated with population connectivity. We assess the interplay between these processes by studying past and current connectivity and foraging niche overlap among southern rockhopper penguin colonies of the coast of southern South America using genomic and stable isotope analyses. We found two distinct genetic clusters and detected low admixture between northern and southern colonies. Stable isotope analysis indicated niche variability between colonies, with Malvinas/Falklands colonies encompassing the species entire isotopic foraging niche, while the remaining colonies had smaller, nonoverlapping niches. A recently founded colony in continental Patagonia differed in isotopic niche width and position with Malvinas/Falklands colonies, its genetically identified founder population, suggesting the exploitation of novel foraging areas and/or prey items. Additionally, dispersing individuals found dead across the Patagonian shore in an unusual mortality event were also assigned to the northern cluster, suggesting northern individuals reach southern localities, but do not breed in these colonies. Facilitated by variability in foraging strategies, and especially during unfavorable conditions, the number of dispersing individuals may increase and enhance the probability of founding new colonies. Metapopulation demographic dynamics in seabirds should account for interannual variability in dispersal behavior and pay special attention to extreme climatic events, classically related to negative effects on population trends.

Evaluación de veinte años de Lignum-vitae (Guaiacum sanctum, Zygophyllaceae) en el Parque Nacional Palo Verde de Costa Rica

Introducción: El guayacán real (Guaiacum sanctum; Zygophyllaceae) de Mesoamérica y las Antillas está amenazado en gran parte de su área de distribución. Evaluamos si una población de G. sanctum en el Parque Nacional Palo Verde en Costa Rica es viable a largo plazo. Métodos Usando dos estudios demográficos, uno en 1997 y otro en 2017, estimamos las tasas de supervivencia y fecundidad para cada clase de edad, la tasa de crecimiento poblacional (lambda), y las elasticidades para cada tasa vital, y usamos un modelo determinístico denso-independiente para proyectar la trayectoria a largo plazo de la población. Resultados: Las tasas vitales estimadas durante los últimos 20 años sugieren que esta población está disminuyendo rápidamente, con un lambda estimado de 0.62. Aunque algunas clases de edad aumentaron en abundancias, los renovales son raros y los individuos reclutados en 1997 aún no alcanzaron la madurez reproductiva. Nuestros resultados sugieren que la abundancia actual de G. sanctum dentro del Parque Nacional podría no ser un buen indicador del estado de conservación a largo plazo, y por nuestro análisis de viabilidad poblacional, estimamos que la población estudiada disminuiría a menos del 1 % de su actual abundancia en los próximos 200 años. Conclusiones: El deterioro ecosistémico a escala de paisaje esta afectando la región del Parque Nacional Palo Verde, como la pérdida de dispersores de semillas y la supresión de alteraciones, podría compensar la protección pasiva de G. sanctum dentro de los límites del Parque Nacional. Confiar en la estricta protección dada por la locación de la población dentro del parque podría no ser suficiente para conservar esta población de G. sanctum. Recomendamos incorporar, dentro de un programa de investigación, una protección experimental más proactiva y/o medidas de restauración, posiblemente incluyendo tratamientos de alteraciones.

Introduction: The Lignum-vitae (Guaiacum sanctum; Zygophyllaceae) of Mesoamerica and the Greater Antilles, is threatened over much of its range. We evaluated whether a G. sanctum population in the Palo Verde National Park of Costa Rica is viable in the long term. Methods: Using two demographic studies, one in 1997 and the other in 2017, we estimated survival and fecundity rates for each tree age class, population growth rate (lambda), and vital rates elasticity, and we used a density-independent deterministic population model to project the long-term trend of that population. Results: The estimated vital rates during the last 20 years suggested that this population is rapidly decreasing. Although some age classes increased in abundance, seedlings are rare and the plants that recruited in 1997 have not yet reached reproductive maturity. Our results suggest that the current abundance of G. sanctum within the national park may not be a good indicator of its long-term conservation status, and from our population viability analysis, we estimated that the population we studied would decrease to less than 1 % of its current size within the next 200 years. Conclusions: Landscape-scale ecosystem deterioration affecting the greater PVNP region, such as loss of seed dispersers and suppression of disturbances, may offset the passive protection of G. sanctum within park boundaries. Relying on the overall strict protection afforded by the location of the population within the Palo Verde National Park may not be sufficient to conserve this population of G. sanctum. We recommend that more proactive experimental protection and/or restoration measures, possibly including disturbance treatments, be implemented within a research program.