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  • 1
    Electronic Resource
    Electronic Resource
    Why don't predators have positive effects on prey populations? (1992)
    Springer
    Evolutionary ecology 6 (1992), S. 449-457 
    Details
    ISSN: 1573-8477
    Keywords: optimal foraging ; predation ; predator-prey interactions ; mathematical models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Three mechanisms by which increasing predation can increase prey population density are discussed: (1) Additional predation on species which have negative effects on the prey; (2) Predation on consumer species whose relationship with their own prey is characterized by a unimodal prey isocline; (3) Predation on species which adaptively balance predation risk and food intake while foraging. Possible reasons are discussed for the rarity of positive effects in previous predator-manipulation studies; these include the short-term nature of experiments, the large magnitudes of predator density manipulation, and various sources of bias in choice of system and interpretation of results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02270691
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  • 2
    Electronic Resource
    Electronic Resource
    Mixed responses to resource densities and their implications for character displacement (1990)
    Springer
    Evolutionary ecology 4 (1990), S. 93-102 
    Details
    ISSN: 1573-8477
    Keywords: character displacement ; competition ; consumer-resource system ; frequency dependence ; functional response ; predation ; resource
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary How should a consumer of two resource types adapt to changes in their abundances? This paper shows that many different biological circumstances produce mixed responses; i.e. increasing availability of one resource increases the consumer's efforts to obtain it, while increasing availability of the other resource decreases the consumer's efforts at exploitation. This implies that competition from a second consumer species may cause convergent or divergent character displacement of the first species. The signs and magnitudes of the second derivative of the fitness function are important in determining which outcome occurs. The degree of resource limitation of the consumer species also influences the nature of adaptive shifts in resource use.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02270907
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Avian daily foraging patterns: Effects of digestive constraints and variability (1994)
    Springer
    Evolutionary ecology 8 (1994), S. 36-52 
    Details
    ISSN: 1573-8477
    Keywords: foraging ; daily routine ; digestion ; starvation ; predation ; reserves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Birds show a typical daily pattern of heavy morning and secondary afternoon feeding. We investigate the pattern of foraging by a bird that results in the lowest long-term rate of mortality. We assume the following: mortality is the sum of starvation and predation. The bird is characterized by two state variables, its energy reserves and the amount of food in its stomach. Starvation occurs during the day if the bird's reserves fall to zero. The bird starves during the night if the total energy stored in reserves and the stomach is less than a critical amount. The probability that the bird is killed by a predator is higher if the bird is foraging than if it is resting. Furthermore, the predation risk while foraging increases with the bird's mass. From these assumptions, we use dynamic programming techniques to find the daily foraging routine that minimizes mortality. The principal results are (1) Variability in food finding leads to routines with feeding concentrated early in the day, (2) digestive constraints cause feeding to be spread more evenly through the day, (3) even under fairly severe digestive constraints, the stomach is generally not full and (4) optimal fat reserve levels are higher in more variable environments and under digestive constraints. This model suggests that the characteristic daily feeding pattern of small birds is not due to digestive constraints but is greatly influenced by environmental variability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01237664
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  • 4
    Electronic Resource
    Electronic Resource
    Fitness minimization and dynamic instability as a consequence of predator–prey coevolution (1997)
    Springer
    Evolutionary ecology 11 (1997), S. 1-20 
    Details
    ISSN: 1573-8477
    Keywords: coevolution ; fitness minimization ; mathematical model ; predation ; predator–prey interaction ; population cycles ; quantitative traits ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We analyse dynamic models of the coevolution of continuous traits that determine the capture rate of a prey species by a predator. The goal of the analysis is to determine conditions when the coevolutionary dynamics will be unstable and will generate population cycles. We use a simplified model of the evolutionary dynamics of quantitative traits in which the rate of change of the mean trait value is proportional to the rate of increase of individual fitness with trait value. Traits that increase ability in the predatory interaction are assumed to have negative effects on another component of fitness. We concentrate on the role of equilibrial fitness minima in producing cycles. In this case, the mean trait of a rapidly evolving species minimizes its fitness and it is ‘chased’ around this equilibrium by adaptive evolution in the other species. Such cases appear to be most likely if the capture rate of prey by predators is maximal when predator and prey phenotypes match each other. They are possible, but less likely when traits in each species determine a one-dimensional axis of ability related to the interaction. Population dynamics often increase the range of parameter values for which cycles occur, relative to purely evolutionary models, although strong prey self-regulation may stabilize an evolutionarily unstable subsystem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018445517101
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  • 5
    Electronic Resource
    Electronic Resource
    Fitness minimization and dynamic instability as a consequence of predator-prey coevolution (1996)
    Springer
    Evolutionary ecology 10 (1996), S. 167-186 
    Details
    ISSN: 1573-8477
    Keywords: coevolution ; fitness minimization ; mathematical model ; predation ; predator—prey interaction ; population cycles ; quantitative traits ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We analyse dynamic models of the coevolution of continuous traits that determine the capture rate of a prey species by a predator. The goal of the analysis is to determine conditions when the coevolutionary dynamics will be unstable and will generate population cycles. We use a simplified model of the evolutionary dynamics of quantitative traits in which the rate of change of the mean trait value is proportional to the rate of increase of individual fitness with trait value. Traits that increase ability in the predatory interaction are assumed to have negative effects on another component of fitness. We concentrate on the role of equilibrial fitness minima in producing cycles. In this case, the mean trait of a rapidly evolving species minimizes its fitness and it is ‘chased’ around this equilibrium by adaptive evolution in the other species. Such cases appear to be most likely if the capture rate of prey by predators is maximal when predator and prey phenotypes match each other. They are possible, but less likely when traits in each species determine a one-dimensional axis of ability related to the interaction. Population dynamics often increase the range of parameter values for which cycles occur, relative to purely evolutionary models, although strong prey self-regulation may stabilize an evolutionarily unstable subsystem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01241783
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Regulation of THI4(MOL1), a thiamine-biosynthetic gene of Saccharomyces cerevisiae (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 10 (1994), S. 481-490 
    Details
    ISSN: 0749-503X
    Keywords: THI4 (MOL1) ; thiamine biosynthesis ; thiamine uptake ; regulation ; molasses ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: THI4, a Saccharomyces cerevisiae gene originally identified as a result of transient expression in molasses medium and named MOL1 is regulated by thiamine. Using a THI4 promoter-lacZ fusion on a centromeric yeast vector, we have shown that the THI4 is completely repressed throughout batch culture by thiamine at a concentration around 1 μM, but shows high level constitutive expression in thiamine-free medium. The transient expression pattern observed in molasses medium can be mimicked by the addition of 0·15 μM-thiamine to defined minimal medium. Cells grown in thiamine-free medium have an intracellular thiamine concentration of around 9 pmol/107 cells. A low level (1 μM) of exogenous thiamine is completely sequestered from the medium within 30 min; intracellular thiamine concentrations rise rapidly, followed by a gradual decrease as a result of dilution during growth. A saturating extracellular level of thiamine leads to a maximal intracellular concentration of around 1600 pmol/107 cells, at which point the transport system is shut down. After transfer from repressing to non-repressing medium, THI4 becomes induced when the intracellular concentration of thiamine falls to 20 pmol/107 cells. A thi4::UARA3 disruption strain is auxotrophic for thiamine, but can grow in the presence of hydroxyethyl thiazole, indicating that the gene product is involved in the biosynthetic pathway leading to the formation of the thiazole precursor of thiamine.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320100407
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Kluyveromyces lactis killer plasmid pGKL2: Molecular analysis of an essential gene, ORF5 (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 11 (1995), S. 615-628 
    Details
    ISSN: 0749-503X
    Keywords: Kluyveromyces lactis ; killer plasmid ; gene disruption ; epitope-tagging ; baculovirus over-expression ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The ORF5 of Kluyveromyces lactis killer plasmid pGKL2 (k2) is capable of encoding a small neutral protein of 18 kDa of as yet unassigned function. Although this ORF is located between two larger ORFs, 4 and 6, which it overlaps, RNA analysis showed that it is transcribed monocistronically. One-step gene disruption of ORF5, via in vivo homologous recombination between native plasmid k2 and a transfer vector employing the Saccharomyces cerevisiae LEU2 gene fused to the k2 UCS5 element, yielded Leu+ transformants at high frequencies. The transformants were found to carry a new recombinant form of k2 with ORF5 replaced by the LEU2 marker, termed rk2, in addition to the wild-type plasmids k1 and k2. Northern analysis detected a plasmid-dependent LEU2 transcript distinct in size and regulation from its nuclear counterpart. Recombinant plasmid, rk2, was unable to displace native k2 during Leu+ selective growth; however rk2 was displaced by k2 during non-selective growth. Thus, ORF5 appears to be an essential gene for plasmid integrity and/or maintenance. The ORF5 product was detected by over-expression of an epitope-tagged allele in the baculovirus system. Western analysis using a monoclonal antibody specific for the epitope tag identified a protein band with apparent molecular weight of 20 kDa, corresponding in size to the predicted product.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320110703
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Temporal and tissue-specific expression of myosin heavy chain isoforms in developing and adult avian muscle (1989)
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 10 (1989), S. 372-385 
    Details
    ISSN: 0192-253X
    Keywords: Monoclonal antibodies ; Myogenesis ; Adult isoforms ; Quail ; Chicken ; Muscle development ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We have raised monoclonal antibodies (Mabs) to myosin heavy chain isoforms (MHCs) that have specific patterns of temporal expression during the development of quail pectoral muscle and that are expressed in very restricted, tissue-specific patterns in adult birds. We find that an early embryonic, a perinatal, and an adult-specific, fast myosin heavy chain a.e co-expressed at different levels in the pectoral muscle of 8-12 day quail embryos. The early embryonic MHC disappears from the pectoral muscle at approximately 14 days in ovo, whereas the perinatal MHC persists until 26 days post-hatching. The adult-specific MHC accumulates preferentially and eventually completely replaces the other isoforms. These Mabs cross-react with the homologous isoforms of the chick and detect a similar pattern of MHC expression in the pectoral muscle of developing chicks. Although the early embryonic and perinatal MHC isoforms recognized by our Mabs are expressed in the pectoral muscle only during distinct developmental stages, our Mabs also recognize MHC isoforms present in the heart and extraocular muscle of adult quail. Immunofingerprinting using Staphylococcus aureus protease V8 suggests that the early embryonic and perinatal MHC isoforms that we see are strongly homologous with the adult ventricular and extraocular muscle isoforms, respectively. These observations suggest that at least three distinct MHC isoforms, which are normally expressed in adult muscles, are co-expressed during the early development of the pectoral muscle in birds. In this respect, the pattern of expression of the MHCs recognized by our Mabs in developing, fast muscle is very similar to the patterns described for other muscle contractile proteins.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/dvg.1020100505
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  • 9
    Electronic Resource
    Electronic Resource
    Embryonic and fetal rat myoblasts express different phenotypes following differentiation in vitro (1993)
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 14 (1993), S. 356-368 
    Details
    ISSN: 0192-253X
    Keywords: Myogenesis ; myosin heavy chain ; rat primary muscle cultures ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Myosin heavy chain (MHC) is encoded by a multigene family containing members which are expressed in developmental and fiber type-specific patterns. In developing rats, primary (1°) and secondary (2°) myotjbes can be disfinguished by differences in MHC expression: 1° myotubes coexpress embryonic and slow MHC, while 2° myotubes initially express only embryonic MHC. We have used monoclonal antibodies which recognize the embryonic, slow, neonatal, and adult fast IIB/IIX MHCs to examine MHC accumulation in myoblasts obtained from hindlimbs of embryonic day (ED) 14 and ED 20 Sprague-Dawley rats during differentiation in vitro. Embryonic myoblasts (ED 14), which develop into 1° myotubes in vivo, differentiate as myocytes or small myotubes (i.e., 1-4 nuclei) which express both embryonic and slow MHC. They do not accumulate detectable levels of neonatal or adult fast IIB/IIX MHC. Fetal myoblasts, which develop into secondary myotubes in vivo, fuse to form large myotubes (i.e., 10-50 nuclei) and express predominantly embryonic MHC at 3 days in culture. These myotubes accumulate neonatal and adult fast IIB/IIX isoforms of MHC and eventually contract spontaneously. In contrast to embryonic myotubes, they do not accumulate slow MHC. Our results demonstrate that embryonic and fetal rat myoblasts express different phenotypes in vitro and suggest that they represent distinct myoblast lineages similar to those previously described in chickens and mice. These two lineages may be responsible for the generation of distinct populations of 1° and 2° myotubes in vivo. © 1993Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/dvg.1020140505
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