Buller's shearwater (Puffinus bulleri). the similarity between muscle δD values of hatch-year haw... more Buller's shearwater (Puffinus bulleri). the similarity between muscle δD values of hatch-year hawaiian petrels and their prey suggests that trophic fractionation does not influence δD values of muscle. We hypothesize that isotopic discrimination is associated with water loss during salt excretion through salt glands. salt load differs between seabirds that consume isosmotic squid and crustaceans and those that feed on hyposmotic teleost fish. In support of the salt gland hypothesis, we show an inverse relationship between δD and percent teleost fish in diet for three seabird species. Our results demonstrate the utility of δD in the study of oceanic consumers, while also contributing to a better understanding of δD systematics, the basis for one of the most commonly utilized isotope tools in avian ecology.
Foraging segregation may play an important role in the maintenance of animal diversity, and is a ... more Foraging segregation may play an important role in the maintenance of animal diversity, and is a proposed mechanism for promoting genetic divergence within seabird species. However, little information exists regarding its presence among seabird populations. We investigated genetic and foraging divergence between two colonies of endangered Hawaiian petrels (Pterodroma sandwichensis) nesting on the islands of Hawaii and Kauai using the mitochondrial Cytochrome b gene and carbon, nitrogen and hydrogen isotope values (d 13 C, d 15 N and dD, respectively) of feathers. Genetic analyses revealed strong differentiation between colonies on Hawaii and Kauai, with U ST = 0.50 (p \ 0.0001). Coalescent-based analyses gave estimates of \1 migration event per 1,000 generations.
In the Hawaiian Islands human colonization, which began approximately 1200 to 800 years ago, mark... more In the Hawaiian Islands human colonization, which began approximately 1200 to 800 years ago, marks the beginning of a period in which nearly 75% of the endemic avifauna became extinct and the population size and range of many additional species declined. It remains unclear why some species persisted while others did not. The endemic Hawaiian petrel (Pterodroma sandwichensis) has escaped extinction, but colonies on two islands have been extirpated and populations on remaining islands have contracted. We obtained mitochondrial DNA sequences from 100 subfossil bones, 28 museum specimens, and 289 modern samples to investigate patterns of gene flow and temporal changes in the genetic diversity of this endangered species over the last 3,000 years, as Polynesians and then Europeans colonized the Hawaiian Islands. Genetic differentiation was found to be high between both modern and ancient petrel populations. However, gene flow was substantial between the extirpated colonies on Oahu and Molokai and modern birds from the island of Lanai. No significant reductions in genetic diversity occurred over this period, despite fears in the mid-1900's that this species may have been extinct. Simulations show that even a decline to a stable effective population size of 100 individuals would result in the loss of only 5% of the expected heterozygosity. Simulations also show that high levels of genetic diversity may be retained due to the long generation time of this species. Such decoupling between population size and genetic diversity in long-lived species can have important conservation implications. It appears that a pattern of dispersal from declining colonies, in addition to long generation time, may have allowed the Hawaiian petrel to escape a severe genetic bottleneck, and the associated extinction vortex, and persist despite a large population decline after human colonization.
Resumen. En el futuro, deseamos usar análisis de isótopos estables de plumas de vuelo para entend... more Resumen. En el futuro, deseamos usar análisis de isótopos estables de plumas de vuelo para entender el comportamiento alimenticio de aves marinas pelágicas como Pterodroma sandwichensis y Puffinus auricularis newelli. El análisis de las rémiges es particularmente informativo porque generalmente se conoce la secuencia y el momento en que ocurre la muda. Nuestro primer paso, que reportamos aquí, es obtener valores de isótopos precisos a partir de plumas rémiges completas utilizando un protocolo poco invasivo apropiado para aves vivas o especímenes de museo. La alta variabilidad de los valores de 13 C y 15 N observada en las plumas no permite el uso de una pequeña sección de la pluma. Encontramos que el rango promedio observado en 42 plumas rémiges de P. sandwichensis es de 1.3‰ tanto para 13 C como para 15 N, mientras que en 10 plumas rémiges de P. auricularis newelli es de 1.3‰ y 0.7‰ para 13 C y 15 N, respectivamente. El 13 C para 52 plumas estudiadas aumentó desde la punta hacia la base, y la mayoría de las plumas de P. sandwichensis mostraron una tendencia similar para 15 N. Aunque el rango promedio en D para 21 rémiges de P. sandwichensis fue de 11‰, no encontramos una tendencia longitudinal. Discutimos la influencia del nivel trófico, de la localidad de forrajeo, del metabolismo y de la pigmentación sobre los valores de isótopos y comparamos tres métodos para obtener promedios de valores de isótopos para la pluma entera. Nuestro nuevo protocolo de muestreo de las barbas sólo requiere de 1.0 mg de pluma y un tiempo de preparación mínimo. Debido a que este protocolo deja las plumas casi intactas, éste podrá facilitar la obtención de valores de isótopos a partir de plumas rémiges de aves vivas y de especímenes de museo. Consecuentemente, ayudará a entender las tendencias históricas en el comportamiento de forrajeo.
Human exploitation of marine ecosystems is more recent in oceanic than near shore regions, yet ou... more Human exploitation of marine ecosystems is more recent in oceanic than near shore regions, yet our understanding of human impacts on oceanic food webs is comparatively poor. Few records of species that live beyond the continental shelves date back more than 60 y, and the sheer size of oceanic regions makes their food webs difficult to study, even in modern times. Here, we use stable carbon and nitrogen isotopes to study the foraging history of a generalist, oceanic predator, the Hawaiian petrel (Pterodroma sandwichensis), which ranges broadly in the Pacific from the equator to near the Aleutian Islands. Our isotope records from modern and ancient, radiocarbon-dated bones provide evidence of over 3,000 y of dietary stasis followed by a decline of ca. 1.8‰ in δ 15 N over the past 100 y. Fishery-induced trophic decline is the most likely explanation for this sudden shift, which occurs in genetically distinct populations with disparate foraging locations. Our isotope records also show that coincident with the apparent decline in trophic level, foraging segregation among petrel populations decreased markedly. Because variation in the diet of generalist predators can reflect changing availability of their prey, a foraging shift in wide-ranging Hawaiian petrel populations suggests a relatively rapid change in the composition of oceanic food webs in the Northeast Pacific. Understanding and mitigating widespread shifts in prey availability may be a critical step in the conservation of endangered marine predators such as the Hawaiian petrel.
Buller's shearwater (Puffinus bulleri). the similarity between muscle δD values of hatch-year haw... more Buller's shearwater (Puffinus bulleri). the similarity between muscle δD values of hatch-year hawaiian petrels and their prey suggests that trophic fractionation does not influence δD values of muscle. We hypothesize that isotopic discrimination is associated with water loss during salt excretion through salt glands. salt load differs between seabirds that consume isosmotic squid and crustaceans and those that feed on hyposmotic teleost fish. In support of the salt gland hypothesis, we show an inverse relationship between δD and percent teleost fish in diet for three seabird species. Our results demonstrate the utility of δD in the study of oceanic consumers, while also contributing to a better understanding of δD systematics, the basis for one of the most commonly utilized isotope tools in avian ecology.
Foraging segregation may play an important role in the maintenance of animal diversity, and is a ... more Foraging segregation may play an important role in the maintenance of animal diversity, and is a proposed mechanism for promoting genetic divergence within seabird species. However, little information exists regarding its presence among seabird populations. We investigated genetic and foraging divergence between two colonies of endangered Hawaiian petrels (Pterodroma sandwichensis) nesting on the islands of Hawaii and Kauai using the mitochondrial Cytochrome b gene and carbon, nitrogen and hydrogen isotope values (d 13 C, d 15 N and dD, respectively) of feathers. Genetic analyses revealed strong differentiation between colonies on Hawaii and Kauai, with U ST = 0.50 (p \ 0.0001). Coalescent-based analyses gave estimates of \1 migration event per 1,000 generations.
In the Hawaiian Islands human colonization, which began approximately 1200 to 800 years ago, mark... more In the Hawaiian Islands human colonization, which began approximately 1200 to 800 years ago, marks the beginning of a period in which nearly 75% of the endemic avifauna became extinct and the population size and range of many additional species declined. It remains unclear why some species persisted while others did not. The endemic Hawaiian petrel (Pterodroma sandwichensis) has escaped extinction, but colonies on two islands have been extirpated and populations on remaining islands have contracted. We obtained mitochondrial DNA sequences from 100 subfossil bones, 28 museum specimens, and 289 modern samples to investigate patterns of gene flow and temporal changes in the genetic diversity of this endangered species over the last 3,000 years, as Polynesians and then Europeans colonized the Hawaiian Islands. Genetic differentiation was found to be high between both modern and ancient petrel populations. However, gene flow was substantial between the extirpated colonies on Oahu and Molokai and modern birds from the island of Lanai. No significant reductions in genetic diversity occurred over this period, despite fears in the mid-1900's that this species may have been extinct. Simulations show that even a decline to a stable effective population size of 100 individuals would result in the loss of only 5% of the expected heterozygosity. Simulations also show that high levels of genetic diversity may be retained due to the long generation time of this species. Such decoupling between population size and genetic diversity in long-lived species can have important conservation implications. It appears that a pattern of dispersal from declining colonies, in addition to long generation time, may have allowed the Hawaiian petrel to escape a severe genetic bottleneck, and the associated extinction vortex, and persist despite a large population decline after human colonization.
Resumen. En el futuro, deseamos usar análisis de isótopos estables de plumas de vuelo para entend... more Resumen. En el futuro, deseamos usar análisis de isótopos estables de plumas de vuelo para entender el comportamiento alimenticio de aves marinas pelágicas como Pterodroma sandwichensis y Puffinus auricularis newelli. El análisis de las rémiges es particularmente informativo porque generalmente se conoce la secuencia y el momento en que ocurre la muda. Nuestro primer paso, que reportamos aquí, es obtener valores de isótopos precisos a partir de plumas rémiges completas utilizando un protocolo poco invasivo apropiado para aves vivas o especímenes de museo. La alta variabilidad de los valores de 13 C y 15 N observada en las plumas no permite el uso de una pequeña sección de la pluma. Encontramos que el rango promedio observado en 42 plumas rémiges de P. sandwichensis es de 1.3‰ tanto para 13 C como para 15 N, mientras que en 10 plumas rémiges de P. auricularis newelli es de 1.3‰ y 0.7‰ para 13 C y 15 N, respectivamente. El 13 C para 52 plumas estudiadas aumentó desde la punta hacia la base, y la mayoría de las plumas de P. sandwichensis mostraron una tendencia similar para 15 N. Aunque el rango promedio en D para 21 rémiges de P. sandwichensis fue de 11‰, no encontramos una tendencia longitudinal. Discutimos la influencia del nivel trófico, de la localidad de forrajeo, del metabolismo y de la pigmentación sobre los valores de isótopos y comparamos tres métodos para obtener promedios de valores de isótopos para la pluma entera. Nuestro nuevo protocolo de muestreo de las barbas sólo requiere de 1.0 mg de pluma y un tiempo de preparación mínimo. Debido a que este protocolo deja las plumas casi intactas, éste podrá facilitar la obtención de valores de isótopos a partir de plumas rémiges de aves vivas y de especímenes de museo. Consecuentemente, ayudará a entender las tendencias históricas en el comportamiento de forrajeo.
Human exploitation of marine ecosystems is more recent in oceanic than near shore regions, yet ou... more Human exploitation of marine ecosystems is more recent in oceanic than near shore regions, yet our understanding of human impacts on oceanic food webs is comparatively poor. Few records of species that live beyond the continental shelves date back more than 60 y, and the sheer size of oceanic regions makes their food webs difficult to study, even in modern times. Here, we use stable carbon and nitrogen isotopes to study the foraging history of a generalist, oceanic predator, the Hawaiian petrel (Pterodroma sandwichensis), which ranges broadly in the Pacific from the equator to near the Aleutian Islands. Our isotope records from modern and ancient, radiocarbon-dated bones provide evidence of over 3,000 y of dietary stasis followed by a decline of ca. 1.8‰ in δ 15 N over the past 100 y. Fishery-induced trophic decline is the most likely explanation for this sudden shift, which occurs in genetically distinct populations with disparate foraging locations. Our isotope records also show that coincident with the apparent decline in trophic level, foraging segregation among petrel populations decreased markedly. Because variation in the diet of generalist predators can reflect changing availability of their prey, a foraging shift in wide-ranging Hawaiian petrel populations suggests a relatively rapid change in the composition of oceanic food webs in the Northeast Pacific. Understanding and mitigating widespread shifts in prey availability may be a critical step in the conservation of endangered marine predators such as the Hawaiian petrel.
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