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| 2. |
- Diehl, S., et al.
(författare)
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EFFECTS OF PISCIVORE-MEDIATED HABITAT USE ON RESOURCES, DIET, AND GROWTH OF PERCH
- 1995
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Ingår i: Ecology. - UMEA UNIV,DEPT ANIM ECOL,S-90187 UMEA,SWEDEN. : Wiley. - 0012-9658 .- 1939-9170. ; 76:6, s. 1712-1726
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Tidskriftsartikel (refereegranskat)abstract
- We investigated experimentally how presence or absence of different piscivores influenced habitat use, diet, and individual growth of two size classes of juvenile perch (Perca fluviatilis) and abundances of juvenile perch resources in different habitats. Pond enclosures encompassed 3 X 6 m of dense vegetation and 9 X 6 m of open habitat, and were stocked with 75 young-of-year and 30 1-yr-old perch and with either three piscivorous perch, three northern pike (Esox lucius), or no piscivores. Northern pike were both larger and possessed a larger gape than piscivorous perch. To isolate behavioral responses of juvenile perch to piscivores, we replaced consumed young-of-year perch. Prey fish mortality was lowest without piscivores and highest with northern pike. Young-of-year perch increased their use of vegetation in the presence of both piscivores, whereas 1-yr-old perch increased their use of vegetation only with northern pike. For both age classes of prey fish, increased use of the vegetation led to reduced individual growth, owing to two complementary mechanisms. First, the physical complexity of submerged macrophytes likely interfered with the benthic feeding of perch, Second, increased use of the (relatively small) vegetated habitat increased the mean density experienced by prey fish. Piscivore-induced changes of prey fish densities in the two habitats had substantial effects on the biomass of prey fish resources in the open habitat, but only minor effects in the vegetation. Sialis lutaria, the major predatory macroinvertebrate (approximate to 50% of total macroinvertebrate biomass in the open habitat), and total predatory macroinvertebrates were positively affected by piscivores in the open habitat, but not in the vegetation. Chironomids (<3% of total macroinvertebrate biomass in the vegetation) and the sizes of nonpredatory macroinvertebrates were negatively affected by piscivores in the vegetation, but not in the open habitat. Biomass of nonpredatory macroinvertebrates, Cladocera, and Copepoda did not differ among treatments in either habitat. From our review of field experiments, vulnerable prey fish always change their habitat use in the presence of piscivores. Behaviorally mediated indirect effects of piscivores on individual growth rates and prey fish resources were just as frequently observed as direct effects of piscivores on prey fish survival.
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| 3. |
- Persson, Lennart, et al.
(författare)
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PREY REFUGES AFFECTING INTERACTIONS BETWEEN PISCIVOROUS PERCH AND JUVENILE PERCH AND ROACH
- 1995
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 76:1, s. 70-81
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Tidskriftsartikel (refereegranskat)abstract
- In size-structured populations, interactions are strongly dependent on size-specific foraging and anti-predator capacities of the organism. Conflicting size-specific selection pressures over the ontogeny often have different effects on different species leading to asymmetries in competitive and predator-prey interactions. Habitat complexity is likely to affect such asymmetric interactions due to species/size-specific competitive abilities in different habitats and due to the fact that habitat structural complexity may act differently as a prey refuge for different species. We experimentally analyzed the impact of a piscivorous predator (adult perch, Perca fluviatilis) on performance of juvenile perch and roach (rutilus rutilus) at different levels of structural complexity (no structure, structure forming a partial refuge, and structure forming a complete refuge) in enclosures in an experimental pond. We measured predator diet and growth, prey fish habitat use, survival, diet and growth, and prey resource levels in different habitats. Prey fish (perch and roach) were found in the diet of piscivorous perch in no refuge and partial refuge treatments. Growth rate of the piscivorous perch decreased with increased refuge efficiency. Juvenile perch increased their proportional use of the structurally complex refuges in the presence of piscivorous perch and the survival increased with increased refuge efficiency (from partial to complete refuge). The diet of juvenile perch changed from predominantly cyclopoid copepods in the absence of predators to predominantly macroinvertebrates in the presence of predators. There was no effect of predator-induced habitat restriction on growth of juvenile perch. Roach survival also increased with increased refuge efficiency in the presence of predators, and roach survival in the refuge treatments did not differ from each other or from the treatments with predators absent. Predator-induced habitat restriction in roach was associated with a decreased growth of roach. Our results suggest that, compared to juvenile roach, juvenile perch may compensate more for lost foraging opportunity in the open water via increased exploitation of structure-associated prey in refuges. As a result, predator-induced habitat shifts by juvenile perch and roach may alter competitive interactions between the species. On the other hand, structural complexity may form an almost complete refuge for juvenile roach from predators and thereby affect the predator-prey relationships between piscivorous perch and juvenile perch and roach to the advantage of juvenile roach. The demonstrated effects of structural complexity on competitive and predator-prey interactions between perch and roach can be related to the two species' distributions in lakes with different degrees of structural complexity.
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| 4. |
- Persson, L, et al.
(författare)
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Size-specific interactions in lake systems : Predator gape limitation and prey growth rate and mortality
- 1996
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 77:3, s. 900-911
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Tidskriftsartikel (refereegranskat)abstract
- To study the effects of different predators on the behavior and dynamics of their prey, we compared the performance of perch (Perca fluviatilis) and the abundance of their prey resource in four lakes with two different types of piscivory. In two of the lakes, perch were the only fish species present and piscivory was restricted to cannibalism. In the other two lakes, perch co-occurred with piscivorous pike (Esox lucius). Pike grow to larger sizes and can capture larger prey than piscivorous perch. Therefore, perch reach a size refuge earlier in the lakes without pike. Perch in the lakes lacking pike used both the epilimnion and hypolimnion habitats of the lakes, and a high proportion of the perch occurred below the thermocline. In contrast, perch in the lakes with pike were mainly captured along the littoral zone and were never captured below the thermocline. This difference in habitat use was reflected in different diets of perch in the different lakes. Perch in the lakes with pike were also less abundant than those in the lakes lacking pike and the growth rates of individual perch and the densities of predator-sensitive prey (pelagic and littoral) were higher, indicating that the presence of pike resulted in decreased intraspecific competition in perch. Evidence for a behavioral response to predation risk was found in 1+ (1 yr old) perch, which was suggested to be due to predation risk from both larger perch and pike. It is hypothesized that the use of the cold-water hypolimnion habitat by perch in the lakes lacking pike was a response of perch to reduce metabolic demands under conditions of severe resource limitation. Differences in gape limitation between predators species are suggested to have major effects on size-dependent mortalities and growth rates in prey and thereby on overall community dynamics. Evidence for this latter effect was observed in differences in zooplankton size structure between the lakes with and without pike.
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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. |
- Firle, S, et al.
(författare)
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The influence of movement and resting behavior on the range of three carabid beetles
- 1998
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Ingår i: ECOLOGY. - 0012-9658. ; 79:6, s. 2113-2122
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The need to study movement in specific ecosystems in order to understand population dynamics in space is appreciated among ecologists. Ecological data is, however, often collected at small scales making large-scale predictions dubious at best. To examine
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| 7. |
- Johnson, SD, et al.
(författare)
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Pollen carryover, geitonogamy, and the evolution of deceptive pollination systems in orchids
- 1999
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Ingår i: ECOLOGY. - : ECOLOGICAL SOC AMER. - 0012-9658. ; 80:8, s. 2607-2619
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Geitonogamy (transfer of pollen among flowers on the same plant) may lead to reduced outcrossing and interfere with sex function. Orchids with pollen packaged into pollinaria would be expected to be particularly vulnerable to the loss of cross-mating oppo
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| 8. |
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| 9. |
- Sheldon, BC, et al.
(författare)
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Gender and environmental sensitivity in nestling collared flycatchers
- 1998
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Ingår i: ECOLOGY. - : ECOLOGICAL SOC AMER. - 0012-9658. ; 79:6, s. 1939-1948
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In many vertebrates, males are apparently more affected by adverse environmental conditions, particularly during early stages of development, than are females. Three explanations have been proposed for this pattern. First, sexual size dimorphism (SSD) may
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| 10. |
- Smith, Henrik G., et al.
(författare)
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Adaptive significance of egg size in the European Starling: experimental tests
- 1995
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Ingår i: Ecology. - : Wiley. - 0012-9658. ; 76, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Reproductive success in relation to egg size was studied in European Starlings (Sturnus vulgaris) by swapping whole clutches between nests at the start of the incubation period. Egg size did not reflect parental quality as no measure of reproductive success was correlated with the foster mothers' mean egg size. There was a significant positive relationship between the mean size of the cross-fostered eggs and the subsequent mean size of hatchlings. The mean size of cross-fostered eggs did not affect hatching success or nestling growth rates, and initial nestling size differences between broods with large and small eggs persisted for <1 wk. No effect of mean egg size on mean nestling survival could be detected. Furthermore, a partial cross-fostering experiment, where nestlings were swapped between nests the day after hatching, failed to demonstrate any lasting effect of egg size on nestling size. It is suggested that mean egg size may only influence reproductive success during particularly inferior environmental conditions
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