Predation risk influences feeding rates but competition structures space use for a common Pacific parrotfish
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In terrestrial systems it is well known that the spatial patterns of grazing by herbivores can influence the structure of primary producer communities. On coral reefs, the consequences of varied space use by herbivores on benthic community structure are not well understood, nor are the relative influences of bottom-up (resource abundance and quality), horizontal (competition), and top-down (predation risk) factors in affecting spatial foraging behaviors of mobile herbivorous fishes. In the current study we quantified space use and feeding rates of the parrotfish, Chlorurus spilurus, across a strong gradient of food resources and predator and competitor abundance across two islands with drastically different fisheries management schemes. We found evidence that while feeding rates of this species are affected by direct interference competition and chronic predation risk, space use appears to be primarily related to exploitative competition with the surrounding herbivore community. We found no evidence that predation risk influences diurnal foraging space use in this small bodied parrotfish species. Additionally, we found the influence of chronic predation risk on feeding rates of this species to be less dramatic than the results of recent studies that used model predators to measure acute behavioral responses of other species of herbivorous fishes. Our results indicate that the non-consumptive effects of predators on the foraging behaviors of coral reef herbivores may be less dramatic than previously thought.
KeywordsHerbivory Coral reef Territory size Foraging behavior Chronic risk
This work was made possible by The Nature Conservancy, US Fish and Wildlife Service, the Palmyra Atoll Research Consortium, Richard B. Gump South Pacific Research Station, and the Mo’orea Coral Reef Long Term Ecological Research Program (National Science Foundation Grant OCE1637396). Funding was provided by the Gordon and Betty Moore Foundation as a part of the Reefs Tomorrow Initiative, The Marisla Foundation, and the American Academy of Underwater Sciences. We thank J. Schem and J. Eurich for field assistance; staff at Palmyra Station and Gump Station; C. Lowe, D. McCauley, and S. Hamilton for valuable discussion and comments on the manuscript; and the three reviewers and handling editor for advice and insight on improvements to the original manuscript. This is Contribution Number PARC-0134 from the Palmyra Atoll Research Consortium.
Author contribution statement
KD, PMC, and JEC conceived of and designed the study. All authors performed fieldwork. KD performed analysis and wrote the manuscript. All authors provided editorial advice.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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