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Reading 4. Almany_Oecologia_2004

Reading 4. Almany_Oecologia_2004 - Oecologia(2004 141...

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Oecologia (2004) 141: 105 113 DOI 10.1007/s00442-004-1617-0 COMMUNITY ECOLOGY Glenn R. Almany Differential effects of habitat complexity, predators and competitors on abundance of juvenile and adult coral reef fishes Received: 2 December 2003 / Accepted: 12 May 2004 / Published online: 12 June 2004 # Springer-Verlag 2004 Abstract Greater structural complexity is often associated with greater abundance and diversity, perhaps because high complexity habitats reduce predation and competi- tion. Using 16 spatially isolated live-coral reefs in the Bahamas, I examined how abundance of juvenile (recruit) and adult (non-recruit) fishes was affected by two factors: (1) structural habitat complexity and (2) the presence of predators and interference competitors. Manipulating the abundance of low and high complexity corals created two levels of habitat complexity, which was cross-factored with the presence or absence of resident predators (sea basses and moray eels) plus interference competitors (territorial damselfishes). Over 60 days, predators and competitors greatly reduced recruit abundance regardless of habitat complexity, but did not affect adult abundance. In contrast, increased habitat complexity had a strong positive effect on adult abundance and a weak positive effect on recruit abundance. Differential responses of recruits and adults may be related to the differential effects of habitat complexity on their primary predators. Seden- tary recruits are likely most preyed upon by small resident predators that ambush prey, while larger adult fishes that forage widely and use reefs primarily for shelter are likely most preyed upon by large transient predators that chase prey. Increased habitat complexity may have inhibited foraging by transient predators but not resident predators. Results demonstrate the importance of habitat complexity to community dynamics, which is of concern given the accelerated degradation of habitats worldwide. Keywords Competition . Habitat shift . Marine reserves . Predation . Recruitment Introduction The structural complexity of a habitat is a major determi- nant of local abundance and diversity (Bell et al. 1991 ), perhaps because habitat complexity influences the out- comes of competition and predation (Hixon and Menge 1991 ). High complexity habitats may reduce competition by providing more competitive refuges and/or a greater spectrum of resources (MacArthur and Levins 1967 ), and reduce predation by providing more prey refuges and/or reducing encounter rates between predators and prey (Murdoch and Oaten 1975 ). High complexity habitats can reduce predation for a wide range of taxa (Schneider 1984 ; Pierce 1988 ; Dickman 1992 ; Babbitt and Tanner 1998 ), and prey may increase their use of such habitats in the presence of predators (Holbrook and Schmitt 1988 ; Sih et al. 1992 ). While previous studies suggest that habitat complexity may be an important factor in population and community dynamics, we still know relatively little about the mechanisms underlying such effects. Understanding how habitat complexity influences demography will
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