Appendix C. Study species and behavioral metrics.
Prey excursion distances or areas reflect the dominant movement types of each of the four focal prey species. The bullethead parrotfish (Chlorurus sordidus) and the whitecheek surgeonfish (Acanthurus nigricans) move continuously over the reef throughout the day, primarily to forage for benthic algae but occasionally in order to travel to spawning aggregations and/or nighttime sleeping areas. For these species, excursion area reflects the approximate area of reef covered by an individual during a five-minute observation period. The blackbar damselfish (Plectroglyphidodon dickii) is a central place forager (Orians and Pearson 1979) whose excursions radiate outwards from a home coral colony that provides shelter within the excursion area (at the study sites, usually Pocillopora spp. or Acropora spp.). Excursion area for P. dickii is therefore quantified as the ratio of total excursion area to refuge area provided by their home coral colony. This metric provides an estimate of the excursion area in which the individual is exposed to risk, thereby accounting for the unique behavioral characteristic of this focal species, i.e., they continuously move in and out of the shelter of their home coral colony. The bicolor chromis (Chromis margaritifer), also a central place forager, hovers continuously above or adjacent to its home coral colony in order to pluck zooplankton from the water passing over the reef. Excursion distance for this species reflects the mean distance from this shelter that individuals ventured in order to capture food or engage in other activities during the observation period. The magnitude of excursions for all four species therefore represents a trade-off for each species between necessary benefits (e.g., foraging, mating) and high-stakes costs (predation).
Orians, G. H., and N. E. Pearson. 1979. On the theory of central place foraging. Pages 155–177 in D. J. Horn, G. R. Stairs, and R. D. Mitchell, editors. Analysis of ecological systems. Ohio State University Press, Columbus, Ohio, USA.