Priority effects and habitat complexity affect the strength of competition
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Both habitat complexity and priority effects can influence the strength of competitive interactions; however, the independent and synergistic effects of these processes are not well understood. In Moorea, French Polynesia, we conducted a factorial field experiment to quantify the independent and combined effects of priority effects and habitat complexity on the strength of intraspecific competitive interactions among recently settled individuals of a coral reef fish (Thalassoma quinquevittatum: Labridae). Simultaneous arrival of focal individuals with competitors resulted in a 2.89-fold increase in survival relative to reefs where focal individuals arrived 5 days later than competitors (i.e., a priority effect). Increasing habitat complexity resulted in a 1.55-fold increase in survivorship when focal individuals arrived simultaneously with or before competitors. However, increasing habitat complexity did not affect the survivorship of focal individuals arriving 5 days later than competitors. Behavior observations showed that survivorship was negatively correlated with aggression. Aggression by prior residents towards focal individuals was significantly greater when focal individuals arrived 5 days later than competitors than when they arrived simultaneously. Increasing habitat complexity did not reduce aggression. Our results suggest that, when competitors arrive simultaneously, competitive interactions are weak and subordinates are not displaced from complex habitat; increasing habitat complexity increases survival by disrupting predation. Conversely, when competitors arrive at different times, aggression intensifies and increasing habitat complexity does not disrupt predation because competitive subordinates are excluded from habitat resources. This study demonstrates that the strength of competition can be context-dependent and may vary with the timing of competitive interactions and habitat complexity.
KeywordsCompetition Habitat complexity Interaction strengths Priority effects Reef fish
C. W. Osenberg, J. S. Shima, L. Liggins and two anonymous reviewers provided many helpful comments on versions of this manuscript. Staff of the Richard B. Gump South Pacific Research Station provided invaluable logistical support. This project was possible with financial support from NSF (OCE-0242312), a VUW PhD Scholarship awarded to S.W.G., a Fulbright-Ministry of Research, Science and Technology Graduate Student Award to S.W.G., a New Zealand Post Graduate Study Abroad Award to S.W.G., a Three Seas Fellowship and a French American Cultural Exchange Grant to A.C.S., and National Geographic International Ecostations Fellowships awarded to S.W.G. and A.C.S. This is a contribution from UC Berkeley’s Richard B. Gump South Pacific Research Station, Moorea, French Polynesia.
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