| 1. |
- Ahlgren, Johan, et al.
(författare)
-
The influence of predator regime on the behaviour and mortality of a freshwater amphipod, Gammarus pulex
- 2011
-
Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 671:1, s. 39-49
-
Tidskriftsartikel (refereegranskat)abstract
- In species with restricted dispersal, traits may become genetically fixed leading to local adaptations. Therefore, predator avoidance in a prey species may differ between populations experiencing different predator regimes, but also between sexes within a population due to different vulnerability to predators. In this study we used male and female Gammarus pulex from two different predator regimes: fishless ponds, where invertebrates are the dominant predators and ponds with predatory fish. In the laboratory we examined refuge use, mortality, leaf decomposition rate and pair-formation in G. pulex when exposed to predator cues from either invertebrate predators or fish. Individuals from fish ponds spent more time in refuge and had a higher mortality than those from fishless ponds independent of predator cues. There was no effect of pond predator regime or predator cues on leaf decomposition rates. Further, fewer individuals formed pairs in G. pulex from fish ponds than from fishless ponds. Male G. pulex had a higher mortality and a higher decomposition rate than females independent of predator cues. However, there was no difference in refuge use between sexes. Our study shows that there are general differences in behaviour traits, both between predator regimes and sexes in G. pulex.
|
|
| 2. |
- Hansson, Lars-Anders, et al.
(författare)
-
Conflicting demands on wetland ecosystem services: nutrient retention, biodiversity or both?
- 2005
-
Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 50:4, s. 705-714
-
Tidskriftsartikel (refereegranskat)abstract
- 1. Wetland ecosystems may, besides having considerable economical value, increase landscape biodiversity and function as traps for nutrients from land to freshwater- and marine systems. As a result of these features, wetlands are nowadays often protected and restored, and many countries have even initiated wetland construction programmes. 2. In the present study, we aim at increasing the knowledge on how to improve the design of a wetland with respect to both biodiversity and nutrient retention, by analysing physical, chemical and biological features of a large set of constructed wetlands. 3. Our results show that a combination of the wetland features, namely shallow depth, large surface area and high shoreline complexity are likely to provide a high biodiversity of birds, benthic invertebrates and macrophytes and to have high nitrogen retention, whereas a small, deep wetland is likely to be more efficient in phosphorus retention, but less valuable in terms of biodiversity. 4. Hence, among the features used to design new wetlands, area, depth and shoreline complexity have fundamental, and sometimes conflicting, effects on nutrient retention and biodiversity. This means that there are, within limits, possibilities to direct the ecosystem function of a specific wetland in desired directions.
|
|
| 3. |
- Hertonsson, Pia, et al.
(författare)
-
Competition and facilitation within and between a snail and a mayfly larva and the effect on the grazing process
- 2008
-
Ingår i: Aquatic Ecology. - : Springer Science and Business Media LLC. - 1386-2588 .- 1573-5125. ; 42:4, s. 669-677
-
Tidskriftsartikel (refereegranskat)abstract
- We studied the competitive effects within and between two taxonomically distant freshwater herbivores, a snail and a mayfly, common in Swedish lakes, Lymnaea peregra and Cloeon dipterum, respectively, and their effect on grazing in a laboratory experiment. The experimental set-up consisted of 2-l aquaria, each containing a periphyton covered tile. Intra- and interspecific effects were tested by increasing the density of one species at a time in four different treatments, (1) snails (intraspecific treatment), (2) mayflies (intraspecific treatment), (3) mixed-snails (interspecific treatments, snails kept constant) and (4) mixed-mayflies (interspecific treatments, mayflies kept constant). Intraspecific competition affected both snails and mayflies negatively, i.e. increasing mortality with increasing con-specific density. Furthermore, there was a decrease in snail growth with increasing snail density. In the mixed-species treatments both species changed their microhabitat use indicating interspecific competition. Despite this, we also found a positive effect of mayfly density on snail growth, most likely due to indirect commensalism. No density-dependent effect of grazing on periphyton was found, probably due to interference competition between grazers. However, there was a significant difference in periphyton biomass, due to species composition of grazers. Irrespective of their densities, if they co-existed, the two grazer species decreased the periphyton biomass significantly compared with both single-species treatments. We considered this as a joint action of facilitation and interaction. Our results suggest that competition can be an important structuring factor in macroinvertebrate communities and that species composition can be significant for ecosystem processes within lentic environments.
|
|
| 4. |
- Åbjörnsson, Kajsa, et al.
(författare)
-
Influence of predator and dietary chemical cues on the behaviour and shredding efficiency of Gammarus pulex
- 2000
-
Ingår i: Aquatic Ecology. - 1386-2588. ; 34:4, s. 379-387
-
Tidskriftsartikel (refereegranskat)abstract
- In two laboratory experiments, we examined short- and long-term responses of the detritivorous amphipod Gammarus pulex to chemical cues from potential predators fed various diets. In the first experiment we studied the short-term effect on G. pulex (locomotory activity) when exposed to chemical cues from three co-existing predators; sculpin (Cottus gobio), trout (Salmo trutta), and signal crayfish (Pacifastacus leniusculus). Chemicals from sculpins and trout induced a short-term decrease in locomotory activity in G. pulex, whereas crayfish did not. There was no difference in activity between G. pulex exposed to water scented by trout or sculpin, and these responses were independent of predator diet (G. pulex, Asellus aquaticus and starved). In the second experiment we examined whether longer-term exposure (4 week) to chemical cues from sculpins affects rates of leaf processing by G. pulex. During the first week, G. pulex consumed significantly more leaves in the control (i.e., no fish cue) than in the fish cue treatment. After 4 weeks, however, there was no difference in total leaf processing rate between treatments indicating an adaptation to the cue.
|
|
| 5. |
- Åbjörnsson, Kajsa, et al.
(författare)
-
Responses of prey from habitats with different predator regimes: local adaptation and heritability
- 2004
-
Ingår i: Ecology. - 0012-9658. ; 85:7, s. 1859-1866
-
Tidskriftsartikel (refereegranskat)abstract
- We aimed to assess whether prey organisms with limited large-scale dispersal abilities are locally adapted to prevailing predator regimes by studying how chemical cues from predatory fish affected the behavior of Gammarus pulex (Amphipoda) from ponds with and without fish. We also examined, in the laboratory, the F1 generation from each pond by incubating them with or without cues from predatory fish. The potential benefits of a behavioral avoidance response were also assessed in an experiment in which G. pulex from the different ponds and incubations were exposed to fish predation. G. pulex from fish ponds increased their refuge use when exposed to fish cues, whereas populations from fishless ponds reduced their refuge use. The F1 generation responded similarly to their parents. Only the F1 generation from fish pond populations responded with more pronounced antipredatory behavior when raised in fish water. Moreover, both the original and the F1 generation of fish pond G. pulex survived longer when exposed to fish predation than those from fishless ponds, independent of whether they were raised in fish water or not (F1). Our results suggest that the behavioral response to predator cues in G. pulex is an inherited trait, i.e., a local adaptation to prevailing predator regimes.
|
|
| 6. |
- Åbjörnsson, Kajsa, et al.
(författare)
-
The influence of predator regime on reproductive traits in Gammarus pulex populations
- 2009
-
Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 635:1, s. 215-225
-
Tidskriftsartikel (refereegranskat)abstract
- Selection on traits conferring reduced predation may be opposed by selection on other traits associated with reproduction. Here, we examined the hypothesis that traits associated with reproduction in Gammarus pulex are driven by predation. We studied G. pulex originating from ponds with two different kinds of predator regimes: (1) ponds with fish-often large, non-gap-limited predators and (2) ponds without fish where invertebrates are the dominant predators-often small, gap-limited predators with a much more restricted prey size range. We examined the body size of males and females in G. pulex amplexus pairs originating from fish and fishless ponds. We also examined, in the laboratory, their mating success, the number of offspring per female and offspring mortality under different rearing conditions, with or without fish cue. Mating success, defined as the percentage of amplexus pairs that produced live offspring, was higher for G. pulex from fishless ponds independent of rearing condition. Individuals from fish ponds were larger and they produced a higher number of offspring which tended to be related to female body size. Offspring mortality was higher in populations from fish ponds compared to populations from fishless ponds. Despite the higher offspring mortality, females from fish ponds had a higher number of offspring alive after 13 weeks, which is the approximate time it takes for G. pulex to reach maturity. Our data imply that no trade-off between reducing body size to reduce mortality caused by fish and maximising reproductive success exist in G. pulex from fish ponds. The strategy with many offspring may be the correct strategy in fishponds where predation pressure generally is higher than in fishless ponds.
|
|
| 7. |
- Åbjörnsson, Kajsa, et al.
(författare)
-
The relative importance of lethal and non-lethal effects of fish on insect colonisation of ponds
- 2002
-
Ingår i: Freshwater Biology. - : Wiley. - 0046-5070. ; 47:8, s. 1489-1495
-
Tidskriftsartikel (refereegranskat)abstract
- 1. We hypothesised that adult insects actively monitor potential habitats for the presence of fish by means of chemical cues and avoid sites that pose significant risks. This was examined by quantifying colonisation of insects in outdoor pools with no fish (controls), fish (direct predation effect) or caged fish (chemical predator cues). 2. A significant direct effect of predation was found, but no indirect effect (avoidance of chemical cue pools), on the total biomass of colonising insects. However, predatory insects avoided fish-cue pools, thus releasing non-predatory insects from predation. This resulted in significantly greater biomass of non-predatory insects in fish-cue pools than control pools. 3. Fish reduced the number of species of colonising insects in pools through predation. This negative influence of fish implies that caution is necessary when stocking wetlands and ponds with fish if the goal is to maximise biodiversity. 4. Our data suggest that although predatory aquatic insects may use chemical signals to assess the quality of potential habitats with respect to predation risk, direct predation is the main method by which fish affect insect assemblages in ponds. Because fish and invertebrate predators may both have strong effects on prey mortality, behavioural adjustment by insects to the actual predator regime within a habitat should be more important than avoiding colonisation of habitats with fish.
|
|
