Pelagic predators

Ryan, Peter G.; Bester, Marth�n

doi:10.18820/9781928357063/06

Cited by 47 publications

(37 citation statements)

References 119 publications

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“…The PEIs seasonally support up to five million land‐based predators that come to the islands to breed and molt (Williams et al. ; Condy ; Ryan and Bester ). Over the last three decades, there has been an overall decrease in the population sizes of predators that predominantly feed inshore such as gentoo penguins, Crozet shags, and rockhopper penguins (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The sub‐Antarctic Prince Edward Islands (PEIs) lie in the direct path of the ACC and provide a critical habitat for up to five million top predators (pinnipeds, flying seabirds, and penguins) that breed on land (Williams et al. ; Condy ; Ryan and Bester ). The abundance and diversity of organisms associated with these islands confers on them elevated ecological and conservation status (Ryan and Bester ) and makes the PEIs ideal laboratories to study the sensitivity and adaptation of sub‐polar ecosystems to long‐term natural and anthropogenic changes (Smith ).…”

Section: Introductionmentioning

confidence: 99%

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Critical indirect effects of climate change on sub‐Antarctic ecosystem functioning

Allan

Froneman

Durgadoo

et al. 2013

Ecology and Evolution

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Sub-Antarctic islands represent critical breeding habitats for land-based top predators that dominate Southern Ocean food webs. Reproduction and molting incur high energetic demands that are sustained at the sub-Antarctic Prince Edward Islands (PEIs) by both inshore (phytoplankton blooms; “island mass effect”; autochthonous) and offshore (allochthonous) productivity. As the relative contributions of these sustenance pathways are, in turn, affected by oceanographic conditions around the PEIs, we address the consequences of climatically driven changes in the physical environment on this island ecosystem. We show that there has been a measurable long-term shift in the carbon isotope signatures of the benthos inhabiting the shallow shelf region of the PEIs, most likely reflecting a long-term decline in enhanced phytoplankton productivity at the islands in response to a climate-driven shift in the position of the sub-Antarctic Front. Our results indicate that regional climate change has affected the balance between allochthonous and autochthonous productivity at the PEIs. Over the last three decades, inshore-feeding top predators at the islands have shown a marked decrease in their population sizes. Conversely, population sizes of offshore-feeding predators that forage over great distances from the islands have remained stable or increased, with one exception. Population decline of predators that rely heavily on organisms inhabiting the inshore region strongly suggest changes in prey availability, which are likely driven by factors such as fisheries impacts on some prey populations and shifts in competitive interactions among predators. In addition to these local factors, our analysis indicates that changes in prey availability may also result indirectly through regional climate change effects on the islands' marine ecosystem. Most importantly, our results indicate that a fundamental shift in the balance between allochthonous and autochthonous trophic pathways within this island ecosystem may be detected throughout the food web, demonstrating that the most powerful effects of climate change on marine systems may be indirect.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Critical indirect effects of climate change on sub‐Antarctic ecosystem functioning

Allan

Froneman

Durgadoo

et al. 2013

Ecology and Evolution

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“…Finally, most bird species nesting in the islands are either poor dispersers (e.g. Lesser Sheathbill Chionis minor ) or are intensely philopatric (albatrosses, petrels) (for a review see Ryan & Bester, 2008) making repeated dispersal events by that route also seem unlikely, or at least sufficiently unlikely to explain the complex phylogeographical patterns we document.…”

Section: Discussionmentioning

confidence: 99%

Phylogeography of a mite, Halozetes fulvus, reflects the landscape history of a young volcanic island in the sub-Antarctic

Mortimer

Vuuren

Meiklejohn

et al. 2011

Biological Journal of the Linnean Society

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Previous studies of the microarthropods of Marion Island, Southern Ocean, documented high mitochondrial COI (cytochrome c oxidase subunit I) haplotype diversity and significant genetic structure, which were ascribed to landscape subdivision. In this paper we revisit these ideas in light of new geomorphological evidence indicating a major lineament orientated along N26.5°E. Using the microarthropod Halozetes fulvus, we test the hypothesis that the eastern and western sides of the island show different population genetic patterns, corresponding to the previously unrecognized geological separation of these regions, and perhaps also with differences in climates across the island and further landscape complexity. Mitochondrial COI data were collected for 291 H. fulvus individuals from 30 localities across the island. Notwithstanding our sampling effort, haplotype diversity was under‐sampled as indicated by rarefaction analyses. Overall, significant genetic structure was found across the island as indicated by ΦST analyses. Nested clade phylogeographical analyses suggested that restricted gene flow (with isolation‐by‐distance) played a role in shaping current genetic patterns, as confirmed by Mantel tests. At the local scale, coalescent modelling revealed two different genetic patterns. The first, characterizing populations on the south‐western corner of the island, was that of low effective population size and high gene flow. The converse was found on the eastern side of Marion Island. Taken together, substantial differences in spatial genetic structure characterize H. fulvus populations across Marion Island, in keeping with the hypothesis that the complex history of the island, including the N26.5°E geological lineament, has influenced population genetic structure. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 131–145.

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“…Killer whale research in this sector has been mostly restricted to land‐based studies from these island groups. These small, isolated terrestrial refuges are the seasonal breeding sites for thousands of southern elephant seals Mirounga leonina , albatrosses and millions of fur seals and penguins (Goldsworthy et al ., ; Weimerskirch et al ., ; Ryan & Bester, ). These breeding colonies form high‐prey‐density foci for predators such as killer whales (e.g.…”

Section: Introductionmentioning

confidence: 99%