Solving the conundrum of intra-specific variation in metabolic rate: A multidisciplinary conceptual and methodological toolkit: New technical developments are opening the door to an understanding of why metabolic rate varies among individual animals of a species: New technical developments are opening the door to an understanding of why metabolic rate varies among individual animals of a species.

Researchers from diverse disciplines, including organismal and cellular physiology, sports science, human nutrition, evolution and ecology, have sought to understand the causes and consequences of the surprising variation in metabolic rate found among and within individual animals of the same species. Research in this area has been hampered by differences in approach, terminology and methodology, and the context in which measurements are made. Recent advances provide important opportunities to identify and address the key questions in the field. By bringing together researchers from different areas of biology and biomedicine, we describe and evaluate these developments and the insights they could yield, highlighting the need for more standardisation across disciplines. We conclude with a list of important questions that can now be addressed by developing a common conceptual and methodological toolkit for studies on metabolic variation in animals.

Island restoration to rebuild seabird populations and amplify coral reef functioning.

Mobile organisms like seabirds can provide important nutrient flows between ecosystems, but this connectivity has been interrupted by the degradation of island ecosystems. Island restoration (via invasive species eradications and the restoration of native vegetation) can reestablish seabird populations and their nutrient transfers between their foraging areas, breeding colonies, and adjacent nearshore habitats. Its diverse benefits are making island restoration increasingly common and scalable to larger islands and whole archipelagos. We identified the factors that influence breeding seabird abundances throughout the Chagos Archipelago in the Indian Ocean and conducted predictive modeling to estimate the abundances of seabirds that the archipelago could support under invasive predator eradication and native vegetation restoration scenarios. We explored whether the prey base exists to support restored seabird populations across the archipelago, calculated the nitrogen that restored populations of seabirds might produce via their guano, and modeled the cascading conservation gains that island restoration could provide. Restoration was predicted to increase breeding pairs of seabirds to over 280,000, and prey was predicted to be ample to support the revived seabird populations. Restored nutrient fluxes were predicted to result in increases in coral growth rates, reef fish biomasses, and parrotfish grazing and bioerosion rates. Given these potential cross-ecosystem benefits, our results support island restoration as a conservation priority that could enhance resilience to climatic change effects, such as sea-level rise and coral bleaching. We encourage the incorporation of our estimates of cross-ecosystem benefits in prioritization exercises for island restoration.

Restauración en islas para reconstruir las poblaciones de aves marinas y amplificar la funcionalidad de los arrecifes de coral Resumen Los organismos móviles como las aves marinas pueden proporcionar flujos importantes de nutrientes entre los ecosistemas, aunque esta conectividad ha sido interrumpida por la degradación de los ecosistemas isleñas. La restauración de islas (por medio de la erradicación de especies invasoras y la restauración de la vegetación nativa) puede reestablecer las poblaciones de aves marinas y su transferencia de nutrientes entre las áreas de forrajeo, las colonias reproductoras y los hábitats adyacentes a la costa. Los diferentes beneficios de la restauración de islas hacen que sea cada vez más común y escalable a islas más grandes y archipiélagos completos. Identificamos los factores que influyen sobre la abundancia de aves reproductoras en todo el archipiélago de Chagos en el Océano Índico y realizamos un modelo predictivo para estimar la abundancia de aves que podría soportar el archipiélago bajo escenarios de la erradicación de un depredador invasor y la restauración de la vegetación nativa. Exploramos si existe la base de presas para soportar las poblaciones restauradas de aves marinas en el archipiélago, calculamos el nitrógeno que las poblaciones restauradas podrían producir mediante el guano y modelamos la conservación en cascada que podría proporcionar la restauración de la isla. Se pronosticó que la restauración incrementaría las parejas reproductoras a más de 280,000 y que las presas serían las suficientes para soportar las poblaciones restauradas de aves marinas. También se pronosticó que los flujos restaurados de nutrientes resultarían en un incremento de la tasa de crecimiento de los corales, la biomasa de los peces del arrecife y las tasas de bio­erosión y de alimentación de los peces loro. Dados estos beneficios potenciales entre los ecosistemas, nuestros resultados respaldan a la restauración de islas como una prioridad de conservación que podría incrementar la resiliencia a los efectos del cambio climático, como el incremento en el nivel del mar y el blanqueamiento de los corales. Promovemos que se incorporen nuestras estimaciones de los beneficios transecosistémicos dentro de los ejercicios de priorización para la restauración de islas.

A framework to unlock marine bird energetics.

Energetics can provide novel insights into the roles of animals, but employing an energetics approach has traditionally required extensive empirical physiological data on the focal species, something that can be challenging for those that inhabit marine environments. There is therefore a demand for a framework through which to estimate energy expenditure from readily available data. We present the energetic costs associated with important time- and energy-intensive behaviours across nine families of marine bird (including seabirds, ducks, divers and grebes) and nine ecological guilds. We demonstrate a worked example, calculating the year-round energetic expenditure of the great auk, Pinguinus impennis, under three migration scenarios, thereby illustrating the capacity of this approach to make predictions for data-deficient species. We provide a comprehensive framework through which to model marine bird energetics and demonstrate the power of this approach to provide novel, quantitative insights into the influence of marine birds within their ecosystems.

A model to estimate seabird field metabolic rates.

For free-ranging animals, field metabolic rate (FMR) is the sum of their energy expenditure over a specified period. This quantity is a key component of ecological processes at every biological level. We applied a phylogenetically informed meta-analytical approach to identify the large-scale determinants of FMR in seabirds during the breeding season. Using data from 64 studies of energetics in 47 species, we created a model to estimate FMR for any seabird population. We found that FMR was positively influenced by body mass and colony latitude and that it increased throughout the breeding season from incubation to brood to crèche. FMR was not impacted by colony-relative predation pressure or species average brood size. Based on this model, we present an app through which users can generate estimates of FMR for any population of breeding seabird. We encourage the use of this app to complement behavioural studies and increase understanding of how energetic demands influence the role of seabirds as driving components of marine systems.

Seabirds boost coral reef resilience.

Global climate change threatens tropical coral reefs, yet local management can influence resilience. While increasing anthropogenic nutrients reduce coral resistance and recovery, it is unknown how the loss, or restoration, of natural nutrient flows affects reef recovery. Here, we test how natural seabird-derived nutrient subsidies, which are threatened by invasive rats, influence the mechanisms and patterns of reef recovery following an extreme marine heatwave using multiyear field experiments, repeated surveys, and Bayesian modeling. Corals transplanted from rat to seabird islands quickly assimilated seabird-derived nutrients, fully acclimating to new nutrient conditions within 3 years. Increased seabird-derived nutrients, in turn, caused a doubling of coral growth rates both within individuals and across entire reefs. Seabirds were also associated with faster recovery time of Acropora coral cover (<4 years) and more dynamic recovery trajectories of entire benthic communities. We conclude that restoring seabird populations and associated nutrient pathways may foster greater coral reef resilience through enhanced growth and recovery rates of corals.

Conservation implications of forage base requirements of a marine predator population at carrying capacity.

Prey depletion may contribute to marine predator declines, yet the forage base required to sustain an unfished population of predatory fish at carrying capacity is unknown. We integrated demographic and physiological data within a Bayesian bioenergetic model to estimate annual consumption of a gray reef shark (Carcharhinus amblyrhynchos) population at a remote Pacific atoll (Palmyra Atoll) that are at carrying capacity. Furthermore, we estimated the proportion of the atoll's reef fish biomass production consumed by the gray reef sharks, assuming sharks either partially foraged pelagically (mean 7%), or solely within the reef environment (mean 52%). We then predicted the gray reef shark population potential of other, less remote Pacific Ocean coral reef islands, illustrating that current populations are substantially smaller than could be supported by their forage base. Our research highlights the utility of modeling how far predator population sizes are from their expected carrying capacity in informing marine conservation.

A year in the life of a North Atlantic seabird: behavioural and energetic adjustments during the annual cycle.

During their annual cycles, animals face a series of energetic challenges as they prioritise different life history events by engaging in temporally and potentially spatially segregated reproductive and non-breeding periods. Investigating behaviour and energy use across these periods is fundamental to understanding how animals survive the changing conditions associated with annual cycles. We estimated year-round activity budgets, energy expenditure, location, colony attendance and foraging behaviour for surviving individuals from a population of common guillemots Uria aalge. Despite the potential constraints of reduced day lengths and sea surface temperatures in winter, guillemots managed their energy expenditure throughout the year. Values were high prior to and during the breeding season, driven by a combination of high thermoregulatory costs, diving activity, colony attendance and associated flight. Guillemots also exhibited partial colony attendance outside the breeding season, likely supported by local resources. Additionally, there was a mismatch in the timing of peaks in dive effort and a peak in nocturnal foraging activity, indicating that guillemots adapted their foraging behaviour to the availability of prey rather than daylight. Our study identifies adaptations in foraging behaviour and flexibility in activity budgets as mechanisms that enable guillemots to manage their energy expenditure and survive the annual cycle.