Journal of Experimental Marine Biology and Ecology 185 (1995) 219-233 JOURNAL OF EXPERIMENTAL MARINE BIOLOQY AND ECOLOGY Compensation in resource use by foragers released from interspecific competition zyxwvutsrqponmlkjihgfedcbaZYXWV Sally J. Holbrook*, Russell J. Schmitt Department zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Biological Sciences and Coastal Research Center, Marine Science Institute, University of Calfomia. Santa Barbara, CA 93106, USA Received 28 June 1994; revision received 12 August 1994; accepted 29 August 1994 zyxwvutsrqponmlkjih Abstract On shallow reefs where their populations co-occur, black surfperch (Embiotocajacksoni Agazzi) and striped surfperch (Embiotoca later&is Agazzi) compete strongly for a single preferred re- source, dense patches of crustacean food located on the alga Gelidium robustum. Four-year-long competition experiments revealed a substantial degree of density compensation by each com- petitor; densities of each species increased on the order of 40% in the absence of the competi- tor. However, overall densities of surfperch on experimental reefs remained much lower at the end of the experiment than initial (combined) densities. Studies of behavioral compensation, following a reduction in competitor density, revealed that both black surfperch and striped surfperch were able to immediately utilize foraging opportunity on Gelidium, but the two species differed greatly in their ability to garner the freed resources. Striped surfperch compensated behaviorally for all of the new foraging opportunity, whereas black surfperch made use of only a small fraction of it. Although newly-available resources were not shared equitably among members of local populations of either species of surfperch, the unevenness in resource distri- bution during competitive release appeared to be more pronounced for black surfperch. An understanding of patterns of behavioral compensation sheds light on the determinants of the magnitude of density compensation by each competitor. The degree of density compensation realized by each species was influenced by different factors: the quantity of freed foraging opportunity for striped surfperch, and the ability of the forager to fully exploit the freed resource (black surfperch). Keywords: Density compensation; Embiotoca lateralis; Embiotocn jacksoni; Foraging behavior; Interspecific competition; Reef fish; Surfperch * Corresponding author. 0022-0981/95/$9.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0022-0981(94)00149-9