Effects of density on foraging success and aggression in age-structured groups of brown trout

Publication: Research - peer-reviewJournal article – Annual report year: 2010

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Effects of density on foraging success and aggression in age-structured groups of brown trout. / Kaspersson, Rasmus; Höjesjö, Johan; Pedersen, Stig.

In: Animal Behaviour, Vol. 79, No. 3, 2010, p. 709-715.

Publication: Research - peer-reviewJournal article – Annual report year: 2010

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Kaspersson, Rasmus; Höjesjö, Johan; Pedersen, Stig / Effects of density on foraging success and aggression in age-structured groups of brown trout.

In: Animal Behaviour, Vol. 79, No. 3, 2010, p. 709-715.

Publication: Research - peer-reviewJournal article – Annual report year: 2010

Bibtex

@article{7151a13970294b05a1d28d9cff7ab663,
title = "Effects of density on foraging success and aggression in age-structured groups of brown trout",
keywords = "Salmo trutta, aggression, density, defence, fish, trout, foraging, body colour, intercohort, competition",
publisher = "Academic Press",
author = "Rasmus Kaspersson and Johan Höjesjö and Stig Pedersen",
year = "2010",
doi = "10.1016/j.anbehav.2009.12.025",
volume = "79",
number = "3",
pages = "709--715",
journal = "Animal Behaviour",
issn = "0003-3472",

}

RIS

TY - JOUR

T1 - Effects of density on foraging success and aggression in age-structured groups of brown trout

A1 - Kaspersson,Rasmus

A1 - Höjesjö,Johan

A1 - Pedersen,Stig

AU - Kaspersson,Rasmus

AU - Höjesjö,Johan

AU - Pedersen,Stig

PB - Academic Press

PY - 2010

Y1 - 2010

N2 - The benefit of monopolizing a limited resource is influenced by competitor density and by the relative competitive ability of defenders and intruders. Nevertheless, few studies have investigated the effect of density on resource defence in groups with large asymmetries in competitive ability, as a consequence of, for example, age and/or body size. We used two age classes (i.e. size groups) of stream-living brown trout, Salmo trutta, to investigate this issue. While old (and large) trout are assumed to be superior during interference competition, younger individuals may be both numerically dominant and constitute more than half of the total population biomass. In this experiment, the ability of one yearling to monopolize a concentrated food source was observed at four densities of under-yearlings (zero, two, six and 12) in an indoor seminatural stream. We predicted that the success of defence would decrease with increasing under-yearling density and that the frequency of defence (i.e. aggression) would peak at an intermediate density. As predicted, yearlings made significantly more unsuccessful foraging attempts and adopted darker body coloration at high density of under-yearlings, suggesting increased stress levels. However, in contrast to our second prediction, the number of aggressive interactions increased progressively with density. These novel findings suggest that the cost of defence increases with under-yearling density, probably as a consequence of stress from interference with under-yearlings employing alternative competitive strategies. However, the difference in size seems to enable yearlings to defend the food resource at higher density of competitors than predicted from the resource defence theory.

AB - The benefit of monopolizing a limited resource is influenced by competitor density and by the relative competitive ability of defenders and intruders. Nevertheless, few studies have investigated the effect of density on resource defence in groups with large asymmetries in competitive ability, as a consequence of, for example, age and/or body size. We used two age classes (i.e. size groups) of stream-living brown trout, Salmo trutta, to investigate this issue. While old (and large) trout are assumed to be superior during interference competition, younger individuals may be both numerically dominant and constitute more than half of the total population biomass. In this experiment, the ability of one yearling to monopolize a concentrated food source was observed at four densities of under-yearlings (zero, two, six and 12) in an indoor seminatural stream. We predicted that the success of defence would decrease with increasing under-yearling density and that the frequency of defence (i.e. aggression) would peak at an intermediate density. As predicted, yearlings made significantly more unsuccessful foraging attempts and adopted darker body coloration at high density of under-yearlings, suggesting increased stress levels. However, in contrast to our second prediction, the number of aggressive interactions increased progressively with density. These novel findings suggest that the cost of defence increases with under-yearling density, probably as a consequence of stress from interference with under-yearlings employing alternative competitive strategies. However, the difference in size seems to enable yearlings to defend the food resource at higher density of competitors than predicted from the resource defence theory.

KW - Salmo trutta

KW - aggression

KW - density

KW - defence

KW - fish

KW - trout

KW - foraging

KW - body colour

KW - intercohort

KW - competition

U2 - 10.1016/j.anbehav.2009.12.025

DO - 10.1016/j.anbehav.2009.12.025

JO - Animal Behaviour

JF - Animal Behaviour

SN - 0003-3472

IS - 3

VL - 79

SP - 709

EP - 715

ER -