Effects of prey distribution on resource defense, foraging behavior, and growth in stream-dwelling Arctic char (Salvelinus alpinus)

Animals exhibit variable competitive strategies in response to the distribution of critical resources, ranging from indirect interactions during resource depletion (i.e., exploitative competition) to direct attacks and monopolization (i.e., interference competition). Spatial distribution of drifting prey provides a unique form of resource heterogeneity that may shape resource defense, foraging, and growth in stream salmonids. I conducted a field experiment on Arctic char Salvelinus alpinus in a small Icelandic stream to test different spatial distributions of drifting invertebrate prey. Specifically, ninety-six individually-tagged juvenile Arctic char, placed in twelve stream enclosures for one month, were subjected to upstream flow manipulations that yielded invertebrate drift either evenly distributed (dispersed) or unevenly distributed (clumped) in space. Observers recorded repeated individual estimates of activity, spatial location, aggression, and foraging behavior. Body size was measured to estimate growth rates and predict dominance status. Fish aggregated more in the clumped prey treatment, where larger, dominant individuals monopolized the concentrated resource patch and excluded subordinate fish. Aggression was more pronounced (attack rate ~60% higher) in the clumped versus dispersed prey scenario. Furthermore, in the clumped treatment, dominant fish exhibited a sedentary foraging tactic whereas subordinates searched more widely for prey. Mean growth rate did not differ between treatments, but surprisingly, larger fish grew slower in the clumped than in the dispersed treatment. Overall, the study extends resource defense theory to invertebrate drift, a rapidly renewing food resource, and shows that as flow alteration redistributes this resource, it may shift the competitive structure and growth patterns in drift-feeding fish.

Author dc:creator

• Kelsey Stansberry 2001-

Contributors dc:contributor

• Háskólinn á Hólum

• Fiskeldis- og fiskalíffræði
• Bleikja
• Fæðuöflun dýra
• Fæðuframboð
• Hryggleysingjar

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/1946/53362

OAI identifier oai:identifier

oai:skemman.is:1946/53362