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| 2. |
- Nilsson, Erika, et al.
(författare)
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Facilitation and interference among three predators affect their consumption of a stream-dwelling mayfly
- 2006
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 51:8, s. 1507-1514
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Tidskriftsartikel (refereegranskat)abstract
- 1. We experimentally tested if a multiplicative risk model accurately predicted the consumption of a common mayfly at risk of predation from three predator species in New Zealand streams. Deviations between model predictions and experimental observations were interpreted as indicators of ecologically important interactions between predators. 2. The predators included a drift-feeding fish [brown trout (T), Salmo trutta], a benthivorous fish [galaxiid (G), koaro, Galaxias brevipennis] and a benthic predatory stonefly (S; Stenoperla sp.) with Deleatidium sp. mayflies as prey. Eight treatments with all predator species combinations and a predator-free control were used. Experiments were performed in aquaria with cobbles as predator refuges for mayflies and we measured the proportion of prey consumed after 6 h for both day and night trials. 3. Trout consumed a higher proportion of prey than other predators. For the two predator treatments we found less than expected prey consumption in the galaxiid + trout treatment (G + T) for both day and night trials, whereas a higher than expected proportion of prey was consumed during night time in the stonefly + trout (S + T) treatment. 4. The results indicate interference (G + T) and facilitation (S + T) between predators depending on predator identity and time of day. Thus, to make accurate predictions of interspecific interactions, it is necessary to consider the ecology of individual species and how differences influence the direction and magnitude of interactions.
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| 3. |
- Persson, Anders, et al.
(författare)
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Linking patch-use behavior, resource density, and growth expectations in fish
- 2006
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Ingår i: Ecology. - 0012-9658. ; 87:8, s. 1953-1959
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Tidskriftsartikel (refereegranskat)abstract
- Optimality theory rests on the assumptions that short-term foraging decisions are driven by variation in environmental quality, and that these decisions have important implications for long-term fitness. These assumptions, however, are rarely tested in a field setting. We linked behavioral foraging decisions in food patches with measures of environmental quality covering larger spatial (resource density) or temporal (growth parameters) scales. In 10 lakes, we measured the food density at which benthic fish give up foraging in experimental food patches (giving-up density, GUD), quantified the biomass of benthic invertebrates, and calculated the maximum individual size (L-infinity) of bream (Abramis brama L.), a typical benthivore in these lakes. We found positive relationships between resource density and both GUD and L-infinity, and a positive relationship between L-infinity and GUD. Prey characterized as vulnerable to predation contributed most to the relationships between resource density and either GUD or L-infinity. A path analysis showed that resource density and L-infinity directly explained 54% and 28%, respectively, of the variation in GUD, whereas 86% of the variation in L-infinity was explained by resource density, with mostly indirect contribution from GUD. We conclude that the short-term foraging behavior of benthivores matched our expectations based on optimality theory by being positively linked to variables on environmental quality operating at both a larger spatial scale and a longer temporal scale.
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| 4. |
- Stenberg, Marika
(författare)
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Foraging behaviour in benthivorous fish
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The foraging ability of an organism is essential since it affects various traits, e.g. growth, reproduction effort, social status and, ultimately, fitness. Foraging is often associated with food intake but includes more aspects such as searching for and assessing food patches and evaluating the patch as good or bad compared to the rest of the environment. On top of that, a forager also has to survive while foraging, and consequently, has to trade-off food and safety. Moreover, foragers are not always foraging alone but in groups. For individuals foraging in groups it may be a way of diluting the individual risk of predation and enhancing their information on predation risk and where to find food, but it may also lead to increased competition for resources. Hence, foraging decisions made in a food patch rely on estimations of several factors. In my thesis I have investigated the effect of resource distribution, resource density, predation risk and group size dynamics on foraging behaviour in benthivorous fish. I have used artificial food patches in all studies and measured giving-up density (GUD) of benthivorous fish in those food patches. In both pools and natural lakes I have shown that benthivorous fish are capable of assessing resources in their environment. I have found that benthivorous fish harvest and leave experimental patches at harvest rates (i.e. GUD) that correspond to both the quality of the surrounding environment and to their prior expectations of potential lifetime growth. My results also show that perceived risk of predation affect how, where and when benthivorous fish utilize resources. In my studies benthivorous fish mainly foraged in group, which may be a way to enhance information on predation risk and where to find food. Hence, patch use behaviour may be used successfully to gain insights about the ecology of benthivorous fish and ultimately to properties of different lake ecosystems (e.g. to reveal which mechanisms structure communities).
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| 5. |
- Stenberg, Marika, et al.
(författare)
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Patch use behaviour in benthic fish depends on their long-term growth prospects
- 2006
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 112:2, s. 332-341
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Tidskriftsartikel (refereegranskat)abstract
- Animals foraging in a heterogeneous environment may combine prior information on patch qualities and patch sample information to maximize intake rate. Prior information dictates the long-term expectations, whereas prior information in combination with patch sample information determines when to leave an individual food patch. We examined patch use behaviour of benthic feeding fish in their natural environment at different spatial scales to test if they could determine patch quality and if patch use behaviour was correlated with environmental quality. In seven lakes along a gradient of environmental quality (measured as maximum benthivore size), we made repeated measurements of giving-up density (GUD) in artificial food patches of different qualities. At the largest spatial scale, between lakes, we tested if giving-up densities revealed the long-term growth expectation of benthic fish. At the local scale of patches and micro patches we tested for the ability of benthic fish to assess patch quality, and how this ability depended on the patch exploitation levels between the different lakes. We found that GUD was positively related to maximum size of bream, suggesting that short-term behavioural decisions reflected long-term growth expectations. Benthic fish discriminated between nearby rich and poor patches, but not between rich and poor micropatches within a food patch. This suggests that the foraging scale of benthic fish lies between the patch and micro patch scale in our experiments. We conclude that patch use behaviour of benthic fish can provide a powerful measure of habitat quality that reveals how benthic fish perceive their environment.
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| 6. |
- Stenberg, Marika, et al.
(författare)
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The effects of spatial food distribution and group size on foraging behaviour in a benthic fish
- 2005
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Ingår i: Behavioural Processes. - : Elsevier BV. - 0376-6357. ; 70:1, s. 41-50
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Tidskriftsartikel (refereegranskat)abstract
- Animals foraging in heterogeneous environments benefit from information on local resource density because it allows allocation of foraging effort to rich patches. In foraging groups, this information may be obtained by individuals through sampling or by observing the foraging behaviour of group members. We studied the foraging behaviour of goldfish (Carassius auratus) groups feeding in pools on resources distributed in patches. First, we determined if goldfish use sampling information to distinguish between patches of different qualities, and if this allowed goldfish to benefit from a heterogeneous resource distribution. Then, we tested if group size affected the time dedicated to food searching and ultimately foraging success. The decision of goldfish to leave a patch was affected by whether or not they found food, indicating that goldfish use an assessment rule. Giving-up density was higher when resources were highly heterogeneous, but overall gain was not affected by resource distribution. We did not observe any foraging benefits of larger groups, which indicate that grouping behaviour was driven by risk dilution. In larger groups the proportion searching for food was lower, which suggests interactions among group members. We conclude that competition between group members affects individual investments in food searching by introducing the possibility for alternative strategies, such as scrounging or resource monopolisation. (c) 2005 Elsevier B.V. All rights reserved.
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| 7. |
- Stenberg, Marika, et al.
(författare)
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Utvärdering av projektstödsdammars betydelse för den större vattensalamandern
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Den större vattensalamandern (Triturus cristatus) är ett groddjur som minskat i stora delar av Europa. I Sverige finns ett åtgärdsprogram vars syfte är att få arten att uppnå en gynnsam bevarandestatus. En del i bevarandearbetet med arten är att anlägga nya lekvatten i lämpliga landmiljöer. I denna rapport utvärdas om dammar som anlagts inom ramen för främst jordbruksverkets andsbygdsutvecklingsstöd (LBU-stöd), s.k. projektstödsdammar, kan gynna den lokala förekomsten av större vattensalamander. Undersökning av den större vattensalamanderns förekomst (främst reproduktion i form av larver under sensommaren) utvärderades i 40 projektstödsdammar i Skåne under 2008. Detta var samtliga projektstödsdammar som låg inom 500 m från en lokal där arten konstaterats 2000-talet. Dammarna varierade i flera avseende såväl åldersmässigt som i deras fysikaliska, kemiska och biologiska karaktärer. Tre av dammarna var anlagda så att de hade förbindelse med vattendrag genom rör. Resultaten visade att dammarna kan, om de utformas på rätt sätt, gynna arter som den större vattensalamandern. I drygt 22 % av de 40 undersökta dammarna hade den större vattensalamandern reproducerat sig och i ytterligare 3 dammar (8 %) noterades vuxna salamandrar. En förutsättning för lyckad reproduktion är att dammarna inte torkar ut för tidigt (8 % i denna studie) och att det inte förekommer fisk i dammarna (ca 37 % i denna studie). Även förekomst av småspigg medför utebliven reproduktion hos den större vattensalamandern enligt denna undersökning. Förutom att de bör vara fiskfria och inte torka ut verkar projektstödsdammar kunna fungera som reproduktionslokaler för den större vattensalamandern så länge de inte är nyanlagda och därmed saknar undervattens- och flytbladsvegetation. Det är heller inte bra om de ligger i områden där det förekommer mycket asfalterade vägar. Om salamandrarna måste passera vägar under sin vandring mellan lekvatten och övervintringsplats finns risk att de blir överkörda. Reproduktion hos den större vattensalamandern verkar gynnas om det finns flera närbelägna vatten med arten. Baserat på de insamlade resultaten ges rekommendationer för hur projektstödsdammar bör utformas för att gynna hänsynskrävande arter som den större vattensalamandern.
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