| 1. |
- Brönmark, Christer, et al.
(författare)
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Costs of inducible defence along a resource gradient.
- 2012
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Ingår i: PloS one. - : Public Library of Science (PLoS). - 1932-6203. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- In addition to having constitutive defence traits, many organisms also respond to predation by phenotypic plasticity. In order for plasticity to be adaptive, induced defences should incur a benefit to the organism in, for example, decreased risk of predation. However, the production of defence traits may include costs in fitness components such as growth, time to reproduction, or fecundity. To test the hypothesis that the expression of phenotypic plasticity incurs costs, we performed a common garden experiment with a freshwater snail, Radix balthica, a species known to change morphology in the presence of molluscivorous fish. We measured a number of predator-induced morphological and behavioural defence traits in snails that we reared in the presence or absence of chemical cues from fish. Further, we quantified the costs of plasticity in fitness characters related to fecundity and growth. Since plastic responses may be inhibited under limited resource conditions, we reared snails in different densities and thereby levels of competition. Snails exposed to predator cues grew rounder and thicker shells, traits confirmed to be adaptive in environments with fish. Defence traits were consistently expressed independent of density, suggesting strong selection from predatory molluscivorous fish. However, the expression of defence traits resulted in reduced growth rate and fecundity, particularly with limited resources. Our results suggest full defence in predator related traits regardless of resource availability, and costs of defence consequently paid in traits related to fitness.
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| 2. |
- Brönmark, Christer, et al.
(författare)
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Predator induced morphological plasticity across local populations of a fresh water snail
- 2011
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:7
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Tidskriftsartikel (refereegranskat)abstract
- The expression of anti-predator adaptations may vary on a spatial scale, favouring traits that are advantageous in a given predation regime. Besides, evolution of different developmental strategies depends to a large extent on the grain of the environment and may result in locally canalized adaptations or, alternatively, the evolution of phenotypic plasticity as different predation regimes may vary across habitats. We investigated the potential for predator-driven variability in shell morphology in a freshwater snail, Radix balthica, and whether found differences were a specialized ecotype adaptation or a result of phenotypic plasticity. Shell shape was quantified in snails from geographically separated pond populations with and without molluscivorous fish. Subsequently, in a common garden experiment we investigated reaction norms of snails from populations' with/without fish when exposed to chemical cues from tench (Tinca tinca), a molluscivorous fish. We found that snails from fish-free ponds had a narrow shell with a well developed spire, whereas snails that coexisted with fish had more rotund shells with a low spire, a shell morphology known to increase survival rate from shell-crushing predators. The common garden experiment mirrored the results from the field survey and showed that snails had similar reaction norms in response to chemical predator cues, i.e. the expression of shell shape was independent of population origin. Finally, we found significant differences for the trait means among populations, within each pond category (fish/fish free), suggesting a genetic component in the determination of shell morphology that has evolved independently across ponds.
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| 3. |
- Gyllström, Mikael, et al.
(författare)
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Bioturbation as Driver of Zooplankton Recruitment, Biodiversity and Community Composition in Aquatic Ecosystems
- 2008
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 11:7, s. 1120-1132
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Tidskriftsartikel (refereegranskat)abstract
- In an experimental study we assessed if benthic bioturbating invertebrates affect the recruitment (hatching) of zooplankton from the sediment, and if this effect persists as differences in the zooplankton community in the water column, that is, if bioturbation quantitatively stimulates benthic-pelagic coupling. We investigated the effects of four different benthic invertebrates (Asellus aquaticus, Chironomus plumosus, Tubifex tubifex in the presence or absence of the predator Sialis lutaria). In total, 45 zooplankton taxa hatched from the sediment and the hatching success of some of these was dependent on the species identity of the bioturbating invertebrate. The predator Sialis reduced the abundance of all three invertebrate species, but tended to positively influence the zooplankton recruitment rates, possibly through increasing the activity of the bioturbating invertebrates. The most striking effect of bioturbation on the hatching and pelagic zooplankton community properties was that, on average, 11% more species hatched in the Asellus treatment than in any other treatment. This was also mirrored in the zooplankton water column community where, on average, 7% more species established a viable population in treatments with Asellus as bioturbator. In a complementary field survey, Asellus was more common in littoral than in profundal sediments. Because Asellus strongly affected recruitment of zooplankton in our experiment, we argue that bioturbation may partly explain why recruitment of resting stages of both phyto- and zooplankton is generally higher in littoral than in profundal areas.
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| 4. |
- Lakowitz, Thomas
(författare)
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Predator induced phenotypic plasticity in a freshwater snail
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis I examined a phenotypically plastic defence in a common freshwater snail, Radix balthica. Adaptive prey defences may involve behavioural, life-history or morphological changes. Snails are important species in freshwater systems. Their role as grazers on periphytic algae makes them particularly important as they have a positive impact on macrophyte growth in lakes and ponds. The structuring role of predators, especially fish, on snails may therefore have a great impact on lake ecosystems. I have studied the occurrence of different shell shapes in this snail in nature. In laboratory studies, I have determined the degree of shell plasticity over many populations, the morphological reaction to multiple predators, costs of expressing plastic traits and the role of plasticity in a community context with other snails. My results show this snail to have different shell shapes in nature that can be attributed to the presence or absence of molluscivorous fish. In the laboratory, I established it to be a phenotypically plastic species with identical reaction norms irrespective if the population originated from a fish or fish free pond. In a test with multiple predators, fish and crayfish that differs in foraging strategies, I showed that this species produces different shell shapes, but that the main defensive change was directed to defend against fish predation and that shape determined the crushing resistance of the shell. I also showed it to be able to compensate differences in shell shape with shell thickness to maintain crushing forces of the shell that are an important factor for defence against fish. The costs for adaptive trait changes like morphology, shell thickness or behaviour seems to be relatively low in this species. Instead, costs mainly emerge from reduced growth rates and lower fecundity. In the competition with other snail species, R. balthica is a strong competitor that dominates the system with or without the presence of predator cues only. Under direct predation from fish, it depends on the higher crush resistance of a morphologically altered shell shape and persists together with another hard shelled species in this environment. The main conclusions from my thesis is that this species is plastic over a large geographical range, probably through high gene flow and that fish has been a key predator in the evolution of a plastic defence. It shows great versatility in many traits in the presence of fish and at relatively low costs. It is a strong competitor and due to the morphologically plastic shell, persistent in many environments.
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| 5. |
- Lakowitz, Thomas, et al.
(författare)
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Tuning in to multiple predators: conflicting demands for shell morphology in a freshwater snail.
- 2008
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 53:11, s. 2184-2191
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Tidskriftsartikel (refereegranskat)abstract
- 1. We examined the response to chemical cues from fish and crayfish, two predators with contrasting feeding modes, and their single and combined effect on shell morphology in the freshwater snail Radix balthica. 2. Snails were subjected to four treatments: tench (Tinca tinca), signal crayfish (Pacifastacus leniusculus), a combination of tench and signal crayfish and no predators (control). Shell shape, crushing resistance and shell thickness were quantified. We also analyzed whether shape or shell thickness contributes most to crushing resistance. 3. Chemical cues from the fish induced a rounder shell shape in R. balthica, a thicker shell and a higher crushing resistance, whereas crayfish chemical cues had no effect on shell morphology, shell thickness or crushing resistance. Shell shape contributed more to crushing resistance than shell thickness. 4. The combined predator treatment showed an intermediate response between the fish and crayfish treatments. Shell roundness was reduced compared to the fish treatment, but the reduced crushing resistance that comes with a less rounded shell was compensated by an increased investment in extra shell material, exceeding that of the fish treatment. 5. Our study extends previous studies of multipredator effects on phenotypically plastic freshwater snails by showing that the snails are able to fine tune different elements of morphology to counter predator specific foraging modes.
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| 6. |
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| 7. |
- 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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