| 1. |
- Berglund, Olof, et al.
(författare)
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The effect of lake trophy on lipid content and PCB concentrations in planktonic food webs
- 2001
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Ingår i: Ecology. - 0012-9658. ; 82:4, s. 1078-1088
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the influence of trophic status on the lipid content and polychlorinated biphenyl (PCB) concentrations in planktonic food webs from 19 lakes in southern Sweden. The lipid content in phytoplankton (10-45 mum), microzooplankton (45-150 mum) and large macrozooplankton (>500 mum) was negatively related to the total phosphorus (Tot-P) concentration in lakes. The lipid content in macrozooplankton (>150 Gem) and young-of-the-year roach (Rutilus rutilus) was not related to Tot-P in lakes. On a dry mass basis (ng/g dry mass), the sum of PCB concentrations in phytoplankton and microzooplankton was negatively related to Tot-P in lakes. Thus, the PCB concentrations in phytoplankton and microzooplankton were explained by the decreasing lipid content of these fractions with increasing trophic status of lakes; and when normalized to lipid content (ng/g extractable lipid) we found no differences in PCB concentrations among lakes. We conclude that the lipid content of phytoplankton increased with increased nutrient stress, explaining the negative relationship between lake trophy and phytoplankton organochlorine (OC) concentrations on a dry mass basis. The relationship found between lipids and lake trophy in producers was not transferred in the food chain.
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| 2. |
- Dahl, Jonas, et al.
(författare)
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Induced morphological defenses in the wild: Predator effects on a mayfly, Drunella coloradensis
- 2002
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Ingår i: Ecology. - 0012-9658. ; 83:6, s. 1620-1634
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Tidskriftsartikel (refereegranskat)abstract
- Phenotypic plasticity may enable organisms to optimize their phenotypes in environments that are heterogeneous over time or space. For example, inducible defenses are favored for prey populations faced with variable predation risk. We studied the impact of brook trout (Salvelinus fontinalis) on the development of defensive morphological characters in larvae of the mayfly, Drunella coloradensis, both in natural streams and in a series of experiments carried out in streamside, circular, flow-through chambers. Drunella larvae in natural streams with trout had Ion-er caudal filaments per unit body size and relatively heavier exoskeletons than Drunella in fishless streams. Female larvae that developed in fish streams were also significantly smaller and less fecund at metamorphosis than those living in fishless streams, suggesting a possible fitness cost associated with development of morphological defenses. However, timing of metamorphosis of Drunella larvae to the adult stage did not differ between fish and fishless streams. Larvae originating from fish and fishless streams were reared and exposed to water with fish cues or fishless control water for three weeks (1998) or until they developed black wing pads, i.e., just before emergence (1999). In both experiments waterborne fish cues induced the development of relatively longer caudal filaments, but only in Drunella originating from sites without fish. Waterborne fish cues had no effect oil Drunella growth rates, behavior, or size at emergence. Drunella originating from fish streams had significantly lower mortality when exposed to predation by trout than Drunella originating from fishless streams. Caudal filament length appears to enhance survival, as Drunella with intact caudal filaments had lower predation rates than Drunella with their tails artificially shortened. This study provides evidence of chemically induced morphological plasticity that could reduce predation rates of these mayflies in natural stream environments.
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| 3. |
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| 4. |
- Peckarsky, BL, et al.
(författare)
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Predator chemicals induce changes in mayfly life history traits: A whole-stream manipulation
- 2002
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Ingår i: Ecology. - 0012-9658. ; 83:3, s. 612-618
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Tidskriftsartikel (refereegranskat)abstract
- In high-elevation streams of western Colorado, mayflies (Baetis bicaudatus) develop taster, but mature at a smaller size where trout are present compared to streams where fish are absent. These life history traits reduce the time of larval exposure to trout predation, but Cost reduced fecundity. We designed a field experiment involving manipulation of whole streams to determine whether these changes were caused by the presence of brook trout, and specifically, whether they could be triggered by trout chemical cues, fit 1999 and 2000. We introduced water from containers with brook trout (Salvelinus fontinalis) into five naturally fishless streams, and fishless stream water into live adjacent control streams to determine whether these cues alone could induce the mayfly life history traits we have observed in natural trout streams. As in previous small-scale experiments, the size at which mayflies matured declined significantly, in streams with added trout chemicals but did not change in streams with fishless water only. Thus, life history traits similar to those observed in the field were induced within the natural variability inherent ill streams. These results demonstrate the strength of this predator-prey interaction and indicate that brook trout are an important agent of natural selection oil mayfly life history traits.
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| 5. |
- Pettersson, Lars, et al.
(författare)
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Density-dependent costs of an inducible morphological defense in crucian carp
- 1997
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Ingår i: Ecology. - 0012-9658. ; 78:6, s. 1805-1815
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Tidskriftsartikel (refereegranskat)abstract
- ere should be fitness costs associated with the defense, otherwise it should be permanent. Thus, in the absence of predators and with limited resources, defended individuals are expected to be outcompeted by individuals lacking the costly defense. Crucian carp, Carassius carassius, increase in body depth in response to chemical stimuli from piscivorous fish, and the deeper body constitutes a morphological defense against gape-limited piscivores. Here, we have performed a field experiment investigating effects of population density on the relative competitive performance of shallow-bodied and deepbodied crucian carp. We assigned groups of six individually marked fish (the ‘‘focal’’ individuals) of either morph into enclosures with either low or high crucian carp density, and monitored changes in body mass, length, and body depth of these fish for 4 mo. In addition, we determined sex, and final liver and gonadal mass, of all focal fish. At high population density, there was a reduction in food resources (zooplankters), which resulted in reduced gonad mass, reduced gonadosomatic indices, and reduced growth in fish of both morphs. Unexpectedly, the relative allocation to livers was higher at high density. There was no difference in body mass gain between morphs at the low density, whereas at the high density shallow-bodied fish gained twice as much body mass as deepbodied fish. Hence, when predators were absent and food resources were limited, deepbodied individuals suffered a substantial cost when competing with shallow-bodied conspecifics. This study verifies the theoretical prediction that an inducible defense results in fitness costs in the absence of predators. Further, as we found no measurable disadvantage of the deep-bodied morphology at high food availability but a strong disadvantage under intense competition for food, our results also demonstrate the importance of relating defense costs to levels of intraspecific competition.
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| 6. |
- Spiegelberger, T, et al.
(författare)
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Long-term effects of short-term perturbation in a subalpine grassland
- 2006
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Ingår i: Ecology. - 0012-9658. ; 87:8, s. 1939-1944
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical advances and short-term experimental studies have furthered our understanding of how ecosystems respond to perturbation. However, there are few well-replicated experimental studies that allow an assessment of long-term responses. Results from a controlled, large-scale field experiment in a subalpine grassland near Interlaken, Switzerland, show that 2-4 years of liming (Ca: 40 g center dot m(-2)center dot yr(-1)) still significantly affected the composition of the vegetation and the soil microbial community nearly 70 years after the treatments were imposed, whereas NPK fertilization (8 g center dot m(-2)center dot yr(-1)) only marginally affected vegetation composition. The exchangeable content of Ca ions and soil pH were higher in limed plots but were unaffected in fertilized plots. Plant species and PLFAs (phospholipid fatty acids) indicating low pH values were found in higher abundance in the unlimed plots, suggesting that the long-lasting effects of liming on the above- and belowground communities were mediated through changes in soil pH. The results of this long-term study indicate that the resilience of mountain ecosystems may be particularly low in response to perturbations that substantially alter soil pH or other key determinants of belowground processes.
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| 7. |
- Bastviken, David, 1971-, et al.
(författare)
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Methane as a source of carbon and energy for lake pelagic food webs
- 2003
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 84:4, s. 969-981
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Tidskriftsartikel (refereegranskat)abstract
- Water-column methane oxidation can represent a substantial carbon transformation pathway in lakes, and circumstantial evidence indicates that methane may be a potentially important source of carbon for pelagic food webs. We estimated methanotrophic bacterial production (MBP), methanotrophic bacterial growth efficiency (MBGE), heterotrophic bacterial production (HBP), primary production (PP), and the relative contribution of methanotrophic bacteria to overall bacterial biomass in three very different lakes during summer and winter. In addition, we measured stable carbon isotope ratios in particulate organic matter (POM), surface sediments, zooplankton, and methane. MBP corresponded to 0.3-7% of the organic C production by primary producers, and 0.5-17% of HBP during summer. During winter, MBP was 3-120% of HBP. MBP generally dominated the heterotrophic bacterial production at greater depths. Methanotrophic biomass was 3-11% of total bacterial biomass on a depth-integrated basis. Zooplankton were generally more depleted in 13C than POM. If phytoplankton d13C signatures were -35 to -30ë, such as the POM signals, observed zooplankton signatures could be explained by a fraction of 5-15% methanotrophic bacteria in their diet. The results indicate that methanotrophic bacteria can provide a significant food source for zooplankton, and that methane oxidation represents a potentially important benthic-pelagic carbon and energy link in many lakes, particularly during winter.
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| 8. |
- Brose, Ulrich, et al.
(författare)
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Consumer-resource body-size relationships in natural food webs
- 2006
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Ingår i: Ecology. - : Ecological Society of America esa. - 0012-9658 .- 1939-9170. ; 87:10, s. 2411-2417
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-'resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator-prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator-prey body-size ratios are on average significantly higher (1) in freshwater habitats than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer-resource interaction strengths may vary systematically across different habitat categories and consumer types.
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| 9. |
- Ehrlén, Johan, et al.
(författare)
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Dispersal limitation and patch occupancy in forest herbs
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81, s. 1667-1674
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of species depends on the availability of suitable habitats, the capacity to disperse to these habitats, and the capacity of populations to persist after establishment. Dispersal limitation implies that not all suitable habitat patches will be occupied by a species. However, the extent to which dispersal limits local distribution is poorly known. In this study, we transplanted seeds, bulbils, and juvenile plants to examine patterns of dispersal limitation and patch occupancy in seven temperate-forest herbs. Recruitment was recorded during four years in 48 patches. The investigated species varied considerably in their natural abundance in the patches. Patterns of seedling emergence and establishment among patches were not related to any of nine investigated abiotic factors. In contrast, the availability of seeds or bulbils was found to limit recruitment in six of the investigated species. Establishment was also successful in many patches where the species did not occur naturally. Estimated patch occupancy in the investigated species ranged from 17.2% to 94.6%. Seed size was positively correlated with the probability of successful establishment of seeds and negatively correlated with patch occupancy. The results suggest that dispersal limitation is an important structuring factor in temperate-forest herb communities. The distribution of species can be perceived as the result of processes operating both among and within patches. Seed size is a key trait in these processes.
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| 10. |
- Eklöv, Peter, et al.
(författare)
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Facilitation among piscivorous predators: effects of prey habitat use
- 2001
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Ingår i: Ecology. - 0012-9658. ; 82:9, s. 2486-2494
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Tidskriftsartikel (refereegranskat)abstract
- The combined effects of predators on prey may substantially differ from thatof each predator species alone because of alterations in prey behavior. Using enclosures within a pond, we examined experimentally the effects of two piscivorous predators on prey mortality and prey resource levels in two habitats. The two predators use two different foraging modes, which also allowed us to examine the behaviorally induced indirect effects of prey on predator growth and prey food resources. Both perch (Perca fluviatilis) and pike (Esox lucius) caused significant mortality of roach (Rutilus rutilus), and the combined predator mortality was higher than predicted from a multiplicative prey consumption model. Growth rates of perch were similar when enclosures contained only perch and when they contained perch combined with pike. The growth rate of pike was higher when they were together with perch compared to when alone. Growth of roach was similar among treatments. The invertebrate food resources of roach increased by a factor 10 in the open water but remained at similar levels throughout the experiment in the vegetation. Biomass of Daphnia longispina, the dominant zooplankton species in the open water, was strongly correlated with mortality of roach, indicating a density-mediated indirect effect of predators on prey resources. There was no indirect effect on D. longispina in the vegetation caused by habitat restriction of roach and only a weak relationship in the open water. There was a strong indirect effect of pike predation on macroinvertebrates induced by a habitat shift of roach. Our results suggest that there was facilitation between predators caused by conflicting antipredator behavior of roach, which resulted in density-mediated indirect effects on prey resources. The behavioral response of roach to the two predators also induced indirect effects on invertebrate prey.
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