Competition for resources within a population can lead to niche partitioning between sexes, throughout ontogeny and among individuals, allowing con-specifics to co-exist. We aimed to quantify such partitioning in Antarctic fur seals, Arctocephalus gazella, breeding at South Georgia, which hosts ~95% of the world's population. Whiskers were collected from 20 adult males and 20 adult females and stable isotope ratios were quantified every 5 mm along the length of each whisker. Nitrogen isotope ratios (δ 15 N) were used as proxies for trophic position and carbon isotope ratios (δ 13 C) indicated foraging habitat. Sexual segregation was evident: δ 13 C values were significantly lower in males than females, indicating males spent more time foraging south of the Polar Front in maritime Antarctica. In males δ 13 C values declined with age, suggesting males spent more time foraging south throughout ontogeny. In females δ 13 C values revealed two main foraging strategies: 70% of females spent most time foraging south of the Polar Front and had similar δ 15 N values to males, while 30% of females spent most time foraging north of the Polar Front and had significantly higher δ 15 N values. This niche partitioning may relax competition and ultimately elevate population carrying capacity with implications for ecology, evolution and conservation. Competition for resources within a natural population can lead to diversification in resource use, ultimately allowing con-specifics to co-exist 1. The ecological niche is positioned within an n-dimensional hypervolume 2 , generally composed of spatial, temporal and trophic axes 3. Overlap in ecological niches causes competition for resources, which could lead to competitive exclusion 4,5 and consequent niche shifts, whereby the position of a niche alters along the spatial, temporal, and/or trophic axis 6,7. This niche partitioning commonly arises between sexes, but can also occur throughout ontogeny (hereby over an organism's lifespan) and among individuals within a species 8. The consequent reduction in intra-specific competition may lead to a greater carrying capacity for the population as a whole 9-11. Understanding the causes and consequences of intra-specific niche partitioning is therefore a major goal of research into the ecology, evolution and conservation of species 12,13. Niche partitioning between sexes has been explained by several interconnected hypotheses: (1) social roles: sexes segregating because they prefer to associate with the same class to benefit from social learning 14,15 ; (2) activity budgets: sexes segregating to synchronise activities (e.g. sex-specific behaviours) to enable spatial coherence of the social group 16,17 ; (3) life history strategies: including constraint of parental care; and (4) sexual size dimorphism (common in species with polgynous mating systems 18). The sexual size dimorphism hypothesis has received considerable attention as body size is a key trait influencing fitness 19. Indeed, males with larger body sizes could compete for mates mor...

No abstract

Many remote islands present barriers to effective wildlife monitoring in terms of challenging terrain and frequency of visits. The sub-Antarctic islands of South Georgia and the South Sandwich Islands are home to globally significant populations of seabirds and marine mammals. South Georgia hosts the largest breeding populations of Antarctic fur seals, southern elephant seals and king penguins as well as significant populations of wandering, black-browed and grey-headed albatross. The island also holds important populations of macaroni and gentoo penguins. The South Sandwich Islands host the world’s largest colony of chinstrap penguins in addition to major populations of Adélie and macaroni penguins. A marine protected area was created around these islands in 2012 but monitoring populations of marine predators remains a challenge, particularly as these species breed over large areas in remote and often inaccessible locations. During the 2019/20 austral summer, we trialled the use of an unoccupied aerial vehicle (UAV; drone) to monitor populations of seals, penguins and albatross and here we report our initial findings, including considerations about the advantages and limitations of the methodology. Three extensive southern elephant seal breeding sites were surveyed with complete counts made around the peak pupping date, two of these sites were last surveyed 24 years ago. A total of nine islands, historically recorded as breeding sites for wandering albatross, were surveyed with 144 fledglings and 48 adults identified from the aerial imagery. The UAV was effective at surveying populations of penguins that nest on flat, open terrain, such as Adélie and chinstrap penguin colonies at the South Sandwich Islands, and an extensive king penguin colony on South Georgia, but proved ineffective for monitoring macaroni penguins nesting in tussock habitat on South Georgia as individuals were obscured or hidden by vegetation. Overall, we show that UAV surveys can allow regular and accurate monitoring of these important wildlife populations.

No abstract