Abstract: Sexual competition is increasingly recognized as an important selective pressure driving species distributions. However, few studies have investigated the relative importance of interpopulation versus intrapopulation competition in relation to habitat availability and selection. To explain spatial segregation between sexes that often occurs in non-territorial and central place foragers, such as seabirds, two hypotheses are commonly used. The ‘competitive exclusion’ hypothesis states that dominant individuals should exclude subordinate individuals through direct competition, whereas the ‘niche divergence’ hypothesis states that segregation occurs due to past competition and habitat specialization. We tested these hypotheses in two populations of an extreme wide-ranging and sexually dimorphic seabird, investigating the relative role of intrapopulation and interpopulation competition in influencing sex-specific distribution and habitat preferences. Using GPS loggers, we tracked 192 wandering albatrosses Diomedea exulans during four consecutive years (2016–2019), from two neighbouring populations in the Southern Ocean (Prince Edward and Crozet archipelagos). We simulated pseudo-tracks to create a null spatial distribution and used Kernel Density Estimates (KDE) and Resource Selection Functions (RSF) to distinguish the relative importance of within- versus between-population competition. Kernel Density Estimates showed that only intrapopulation sexual segregation was significant for each monitoring year, and that tracks between the two colonies resulted in greater overlap than expected from the null distribution, especially for the females. RSF confirmed these results and highlighted key at-sea foraging areas, even if the estimated of at-sea densities were extremely low. These differences in selected areas between sites and sexes were, however, associated with high interannual variability in habitat preferences, with no clear specific preferences per site and sex. Our results suggest that even with low at-sea population densities, historic intrapopulation competition in wide-ranging seabirds may have led to sexual dimorphism and niche specialization, favouring the ‘niche divergence’ hypothesis. In this study, we provide a protocol to study competition within as well as between populations of central place foragers. This is relevant for understanding their distribution patterns and population regulation, which could potentially improve management of threatened populations.

Abstract: A good overlap between offspring energetic requirements and availability of resources is required for successful reproduction. Accordingly, individuals from numerous species fine-tune their timing of breeding by integrating cues that predict environmental conditions during the offspring period. Besides acquiring information from their direct interaction with the environment (personal information), individuals can integrate information by observing the behaviours or performance of others (social information). The use of social information is often beneficial because the accumulated knowledge of conspecifics may represent a source of information more reliable than the intrinsically more limited personal information. However, although social information constitutes the major source of information in a wide range of contexts, studies investigating its use in the context of timing of breeding are scarce. We investigated whether black-legged kittiwakes (Rissa tridactyla) used social information to adjust the timing of egg-laying. We manipulated social information using a food-supplementation experiment, known to advance kittiwakes' reproductive phenology. We expected food-supplemented and unsupplemented pairs to delay and advance, respectively, their timing of laying when surrounded by a majority of neighbours from the opposite food-treatment. However, both unsupplemented and food-supplemented kittiwakes delayed egg-laying when surrounded by a higher proportion of neighbours from the opposite food-treatment. This result shows that kittiwakes use social information to time egg-laying, but that it is not used to match the seasonal peak of food availability. We suggest that when social and personal cues give contradictory environmental information, individuals may benefit from delaying laying to gather more information to make better decisions about investment into eggs. Further, we explored a potential proximate mechanism for the pattern we report. We show that baseline corticosterone, known to mediate reproductive decisions, was lower in unsupplemented females facing a higher proportion of food-supplemented neighbours. Altogether, our results suggest that to fine-tune their timing of laying, kittiwakes use complex decision-making processes in which social and personal information interplay.

Abstract: We analyze mantle structure under South America in the DETOX-P1 seismic tomography model, a global-scale, multifrequency inversion of teleseismic P waves. DETOX-P1 inverts the most extensive data set of broadband, waveform-based traveltime measurements to date, complemented by analyst-picked traveltimes from the ISC-EHB catalog. The mantle under South America is sampled by ∼665,000 cross-correlation traveltimes measured on 529 South American broadband stations and on 5,389 stations elsewhere. By their locations, depths, and geometries, we distinguish four high-velocity provinces under South America, interpreted as subducted lithosphere (“slabs”). The deepest (∼1,800–1,200 km depth) and shallowest (<600 km) slab provinces are observed beneath the Andean Cordillera near the continent’s northwest coast. At intermediate depths (1,200–900 km, 900–600 km), two slab provinces are observed farther east, under Brazil, Bolivia and Venezuela, with links to the Caribbean. We interpret the slabs relative to South America’s paleo-position over time, exploring the hypothesis that slabs sank essentially vertically after widening by viscous deformation in the mantle transition zone. The shallowest slab province carries the geometric imprint of the continental margin and represents ocean-beneath-continent subduction during Cenozoic times. The deepest, farthest west slab complex formed under intra-oceanic trenches during late Jurassic and Cretaceous times, far west of South America’s paleo-position adjoined to Africa. The two intermediate slab complexes record the Cretaceous transition from westward intra-oceanic subduction to eastward subduction beneath South America. This geophysical inference matches geologic records of the transition from Jura-Cretaceous, extensional “intra-arc” basins to basin inversion and onset of the modern Andean arc ∼85 Ma.

Abstract: One pathway by which the oceans influence climate is via the emission of sea spray that may subsequently influence cloud properties. Sea spray emissions are known to be dependent on atmospheric and oceanic physicochemical parameters, but the potential role of ocean biology on sea spray fluxes remains poorly characterized. Here we show a consistent significant relationship between seawater nanophytoplankton cell abundances and sea-spray derived Cloud Condensation Nuclei (CCN) number fluxes, generated using water from three different oceanic regions. This sensitivity of CCN number fluxes to ocean biology is currently unaccounted for in climate models yet our measurements indicate that it influences fluxes by more than one order of magnitude over the range of phytoplankton investigated.