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Marine Ecology Progress Series

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MEPS 607:155-169 (2018)  -  DOI:

Support for the trophic theory of island biogeography across submarine banks in a predator-depleted large marine ecosystem

C. H. Stortini1,*, K. T. Frank1,2, W. C. Leggett1, N. L. Shackell2, D. G. Boyce3

1Department of Biology, Biosciences Complex, Queen’s University, 116 Barrie St., Kingston, ON K7L 3N6, Canada
2Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Dr., Dartmouth, NS B2Y 4A2, Canada
3Ocean Frontier Institute, Steele Ocean Sciences Building, Dalhousie University, 1355 Oxford St., PO Box 15000, Halifax, NS B3H 4R2, Canada
*Corresponding author:

ABSTRACT: The trophic theory of island biogeography (TTIB) predicts that when predators are depleted, prey extinction rates decrease, leading to increases in prey alpha diversity and an increase in the slope of the species-area relationship (SAR). The TTIB has been tested and supported in a restricted set of systems at small spatial scales (0.25 m3 [reef patches] to 29500 m2 [terrestrial]). Across semi-insular fish communities on 10 offshore banks ranging in size from 534 to 10537 km2 on the Scotian Shelf (northwest Atlantic Ocean), we found support for the predictions of the TTIB. The prey SAR slope was significantly higher after the collapse of large predator populations than before the collapse, due largely to the immigration (or colonization) of many new prey species, principally on the largest banks. Coincident increases in core (resident) prey species densities, primarily on the largest banks, suggests that extinction risk decreased. The appearance of a strong SAR within the mesopredator trophic group in the post-predator collapse era (r2 = 0.55 relative to 0.12 in the pre-collapse era) suggests that the TTIB may also apply to mesopredator release in insular marine communities. Increases in mesopredator densities coincident with the colonization of previously unoccupied banks by core mesopredator species suggests that range expansions contributed to the increased strength of the SAR. Our study contributes to our evolving understanding of island biogeography theory and suggests that TTIB may provide a useful framework for evaluating trophic alterations in large marine (and non-marine) ecosystems.

KEY WORDS: Alpha diversity · Marine · Fish · Predator-prey · Species-area relationship · Diversity · Trophic theory · Island biogeography · Mesopredator release

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Cite this article as: Stortini CH, Frank KT, Leggett WC, Shackell NL, Boyce DG (2018) Support for the trophic theory of island biogeography across submarine banks in a predator-depleted large marine ecosystem. Mar Ecol Prog Ser 607:155-169.

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