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Density-dependent costs of an inducible morphological defense in crucian carp

Publiceringsår: 1997
Språk: Engelska
Sidor: 1805-1815
Publikation/Tidskrift/Serie: Ecology
Volym: 78
Nummer: 6
Dokumenttyp: Artikel i tidskrift
Förlag: Ecological Society of America


Ere should be fitness costs associated with the defense, otherwise it should

be permanent. Thus, in the absence of predators and with limited resources, defended

individuals are expected to be outcompeted by individuals lacking the costly defense.

Crucian carp, Carassius carassius, increase in body depth in response to chemical stimuli

from piscivorous fish, and the deeper body constitutes a morphological defense against

gape-limited piscivores. Here, we have performed a field experiment investigating effects

of population density on the relative competitive performance of shallow-bodied and deepbodied

crucian carp. We assigned groups of six individually marked fish (the ‘‘focal’’

individuals) of either morph into enclosures with either low or high crucian carp density,

and monitored changes in body mass, length, and body depth of these fish for 4 mo. In

addition, we determined sex, and final liver and gonadal mass, of all focal fish.

At high population density, there was a reduction in food resources (zooplankters),

which resulted in reduced gonad mass, reduced gonadosomatic indices, and reduced growth

in fish of both morphs. Unexpectedly, the relative allocation to livers was higher at high

density. There was no difference in body mass gain between morphs at the low density,

whereas at the high density shallow-bodied fish gained twice as much body mass as deepbodied

fish. Hence, when predators were absent and food resources were limited, deepbodied

individuals suffered a substantial cost when competing with shallow-bodied conspecifics.

This study verifies the theoretical prediction that an inducible defense results in fitness

costs in the absence of predators. Further, as we found no measurable disadvantage of the

deep-bodied morphology at high food availability but a strong disadvantage under intense

competition for food, our results also demonstrate the importance of relating defense costs

to levels of intraspecific competition.


  • Ecology
  • antipredator
  • body size
  • Carassius carassius
  • competition
  • cost
  • density dependence
  • field-enclosure experiment
  • fish
  • inducible defense
  • phenotypic plasticity
  • resource allocation
  • Sweden.


  • ISSN: 0012-9658

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