Population dynamics of a damselfish: Effects of a competitor that also is an indirect mutualist

  • Holbrook S
  • Schmitt R
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We estimated the population consequences to an inferior competitor from interactions with a superior competitor that also is an indirect mutualist. The competitors are two damselfishes, three-spot dascyllus (Dascyllus trimaculatus) and orange-fin ane- monefish (Amphiprion chrysopterus), that vie for shelter space on a sea anemone (Heteractis magnifica). Anemonefish have an indirect positive effect on dascyllus populations due to the faster growth that anemones experience when they are occupied by Amphiprion.A long-term experiment revealed that anemonefish depressed dascyllus density (number of individuals per area of anemone per area of reef) more than abundance (number of indi- viduals per reef area) because anemonefish caused a greater net increase in anemone surface area.We calculated that the effect of competition alone would depress dascyllus populations to near zero. The indirect positive interaction compensated for ?67% of the direct negative effect. Failure to consider the indirect positive interaction in this system would lead to a gross underestimate of the strength of competition, and would not reveal the critical im- portance of the indirect mutualism in maintaining local populations of the inferior com- petitor. Indirect mutualisms are common in nature, and assessing how they mediate effects of other processes is crucial to a more accurate understanding of natural communities

Author-supplied keywords

  • Abundance
  • Amphiprion
  • Competition
  • Damselfish
  • Dascyllus
  • Indirect effects
  • Interaction strength
  • Mutualism
  • Population dynamics
  • Sea anemone

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  • Sally J. Holbrook

  • Russell J. Schmitt

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