ALBERT

Description: Individual foraging niche specialisation is recognised as an important determinant of ecological structure and function, particularly for species with high per-capita trophic influence like marine apex predators. Stable isotopes provide a powerful approach to understand the mechanisms and consequences of niche specialisation, especially in cryptic predators, yet have poor resolution for incorporating nutrition, which is a critical aspect of foraging interactions. Multidimensional nutritional ecology compartmentalises foods and diets as mixtures of nutrients (e.g. proteins, lipids, carbohydrates) to draw mechanistic links between individual nutrition, physiology, behaviour and fitness, the drivers of foraging decisions and their trophic implications. Yet difficulties in establishing time-integrated nutrient intakes has hampered progress in predator nutritional ecology. We employed a novel approach integrating stable isotopes and a multidimensional nutritional niche framework to investigate individual diet specialisation across multiple niche realisations in juvenile white sharks (Carcharodon carcharias). We sampled tooth files to generate individual isotopic profiles (δ13C, δ15N, δ34S) and characterise individual isotopic niches (δ-space). We then contextualised isotopic specialisation patterns by estimating individual prey use (p-space) using Bayesian mixing models, and further combined this with nutritional geometry framework models to quantify the nutritional dimension (N-space) of individual specialisation. Isotopic analyses indicated that juvenile white sharks mostly foraged as individual specialists within a broader, generalist, population niche. Mixing models showed individual differences in the consumption of dolphin, shark and batoid prey (rays), which comprised much of the overall diet. Despite δ-space and p-space variance, modelled nutrient intakes were similar for most sharks, which may suggest complementary feeding on nutritionally disparate prey among individual sharks towards a particular nutritional goal. Our approach helps to address the challenges of estimating time-integrated nutrient intakes in cryptic species, expanding our knowledge of individual diet specialisation into a nutritional dimension and revealing how specialisations may differ across niche realisations (prey use and nutritional niches). We argue that this can facilitate stronger links between individual diet specialisation, its intrinsic (e.g. nutritional goals, fitness) and extrinsic (e.g. trophic dynamics) outcomes.

Description: Territorial protandry, or early season male-biased settlement at breeding sites, is a widespread phenomenon in a range of animal breeding systems. While protandry is common across several avian lineages and has been linked with increased reproductive success of earlier breeding males in terrestrial species, the selective advantage of breeding protandry has only rarely been studied in seabirds. We assessed the seasonal changes in the sex ratio at the breeding site and sexspecific correlates of arrival date with reproductive success during 2 breeding seasons of a colonial seabird, the Australasian Gannet (Morus serrator), at Cape Kidnappers, New Zealand.We found no biases in overall sex ratios of adults and fledglings but detected a male sex bias during nest site establishment, and a significantly higher probability of reproductive success for earlier-settling males. In contrast, the reproductive success of females did not correlate with the timing of arrival. Our findings provide an assessment of the sex differences in reproductive correlates of the timing of breeding settlement in gannets and are consistent with selective advantages as suggested by indirect selection hypotheses. This study contributes to our understanding of the fitness benefits of protandry, and its linkages with sex differences in breeding philopatry and mate fidelity, in a long-lived seabird species with obligate and extended biparental care.