{"id":{"repo_id":"holar","oai_identifier":"oai:skemman.is:1946/53362"},"canonical_url":"https://search.dev.ndltd.org/etd/holar/oai:skemman.is:1946/53362","repository":{"repo_id":"holar","name":"Hólar University College","base_url":"https://skemman.is/oai/request"},"display":{"title":"Effects of prey distribution on resource defense, foraging behavior, and growth in stream-dwelling Arctic char (Salvelinus alpinus)","abstract":"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.","abstract_html":"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.","abstract_has_math":false,"creators":["Kelsey Stansberry 2001-"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Háskólinn á Hólum"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2026,"date_issued":"2026-05-26T12:10:56Z","date_published":"2026-05-26T12:10:56Z","updated_at":"2026-07-27T19:56:59Z","subjects":["Fiskeldis- og fiskalíffræði","Bleikja","Fæðuöflun dýra","Fæðuframboð","Hryggleysingjar"],"languages":["en"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/1946/53362","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Háskólinn á Hólum"]},{"key":"dc:creator","label":"Author","values":["Kelsey Stansberry 2001-"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-05-26T12:10:52Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-05-26T12:10:52Z"]},{"key":"dc:date.issued","label":"Date","values":["2026-05-26T12:10:56Z"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Fiskeldis- og fiskalíffræði","Bleikja","Fæðuöflun dýra","Fæðuframboð","Hryggleysingjar"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/1946/53362"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["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.","Dýr sýna breytileika þegar þau keppa um nauðsynlegar auðlindir; sum dýr reyna einfaldlega að nýta stærri hluta auðlindarinnar, en önnur dýr útiloka samkeppnisaðila frá auðlindum með beinum árásum. Dreifing hryggleysingja sem reka með vatnsstraumum er lítt rannsakað dæmi um dreifingu fæðuauðlindar, sem mótað getur félagsatferli, fæðunám og vöxt laxfiska í ám. Ég gerði vettvangstilraun í lítilli á á Íslandi og skoðaði viðbrögð bleikju (Salvelinus alpinus) við ólíkri svæðisdreifingu hryggleysingja á reki. Níutíu og sex bleikjuseiðum var haldið í tólf netbúrum í mánuð, og vatnsflæði var hagrætt til að fæða á reki bærist inn í netbúrin á jafndreifðan eða hnappdreifðan hátt. Í tilrauninni voru endurteknar einstaklingsmælingar gerðar á virkni, staðsetningu, árásum, og fæðuatferli seiðanna. Stærð fiska var mæld til að meta vaxtarhraða og stöðu í goggunarröð. Fiskar voru nær hverjum öðrum í hnappdreifðu fæðumeðferðinni, og stærri einstaklingar, ofar í goggunarröðinni, einokuðu þá svæði innan búrsins þar sem meira var af fæðu. Fiskarnir voru árásargjarnari þar sem fæða var hnappdreifð í samanburði við jafndreifðu meðferðina (tíðni árása ~60% hærri). Í hnappdreifðu meðferðinni voru stærri fiskar staðbundnari við fæðuleit en minni fiskar, sem leituðu að bráð yfir stærra svæði. Enginn munur var á meðalvaxtarhraða á milli meðferða, en stærri fiskar uxu hægar í hnappdreifðu en í jafndreifðu meðferðinni. Þessi rannsókn skilar nýrri þekkingu á því hvernig dýr verja auðlindir, með því að skoða fæðuauðlind sem berst með vatnsstraumum og endurnýjast hratt. Þá sýnir rannsóknin hvernig rennslisbreytingar geta mótað svæðisdreifingu hryggleysingja, og haft áhrif á samkeppni og vöxt hjá fiskum sem nýta þá auðlind."]},{"key":"dc:title","label":"Title","values":["Effects of prey distribution on resource defense, foraging behavior, and growth in stream-dwelling Arctic char (Salvelinus alpinus)"]}]}],"canonical_facts":{"dc:contributor":["Háskólinn á Hólum"],"dc:creator":["Kelsey Stansberry 2001-"],"dc:date.accessioned":["2026-05-26T12:10:52Z"],"dc:date.available":["2026-05-26T12:10:52Z"],"dc:date.issued":["2026-05-26T12:10:56Z"],"dc:description.abstract":["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.","Dýr sýna breytileika þegar þau keppa um nauðsynlegar auðlindir; sum dýr reyna einfaldlega að nýta stærri hluta auðlindarinnar, en önnur dýr útiloka samkeppnisaðila frá auðlindum með beinum árásum. Dreifing hryggleysingja sem reka með vatnsstraumum er lítt rannsakað dæmi um dreifingu fæðuauðlindar, sem mótað getur félagsatferli, fæðunám og vöxt laxfiska í ám. Ég gerði vettvangstilraun í lítilli á á Íslandi og skoðaði viðbrögð bleikju (Salvelinus alpinus) við ólíkri svæðisdreifingu hryggleysingja á reki. Níutíu og sex bleikjuseiðum var haldið í tólf netbúrum í mánuð, og vatnsflæði var hagrætt til að fæða á reki bærist inn í netbúrin á jafndreifðan eða hnappdreifðan hátt. Í tilrauninni voru endurteknar einstaklingsmælingar gerðar á virkni, staðsetningu, árásum, og fæðuatferli seiðanna. Stærð fiska var mæld til að meta vaxtarhraða og stöðu í goggunarröð. Fiskar voru nær hverjum öðrum í hnappdreifðu fæðumeðferðinni, og stærri einstaklingar, ofar í goggunarröðinni, einokuðu þá svæði innan búrsins þar sem meira var af fæðu. Fiskarnir voru árásargjarnari þar sem fæða var hnappdreifð í samanburði við jafndreifðu meðferðina (tíðni árása ~60% hærri). Í hnappdreifðu meðferðinni voru stærri fiskar staðbundnari við fæðuleit en minni fiskar, sem leituðu að bráð yfir stærra svæði. Enginn munur var á meðalvaxtarhraða á milli meðferða, en stærri fiskar uxu hægar í hnappdreifðu en í jafndreifðu meðferðinni. Þessi rannsókn skilar nýrri þekkingu á því hvernig dýr verja auðlindir, með því að skoða fæðuauðlind sem berst með vatnsstraumum og endurnýjast hratt. Þá sýnir rannsóknin hvernig rennslisbreytingar geta mótað svæðisdreifingu hryggleysingja, og haft áhrif á samkeppni og vöxt hjá fiskum sem nýta þá auðlind."],"dc:identifier.uri":["https://hdl.handle.net/1946/53362"],"dc:language.iso":["en"],"dc:subject":["Fiskeldis- og fiskalíffræði","Bleikja","Fæðuöflun dýra","Fæðuframboð","Hryggleysingjar"],"dc:title":["Effects of prey distribution on resource defense, foraging behavior, and growth in stream-dwelling Arctic char (Salvelinus alpinus)"],"dc:type":["Thesis"]},"updated_at":"2026-07-27T19:56:59Z"}