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  • 1980-1984  (1,363)
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  • 1
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L (C4) on the one hand and of the grasses Avena sativa L (C3) and Panicum miliaceum L. (C4) on the other hand were maintained in a standard soil with different ground water tables. After 12 weeks the length, dry weight and nitrogen-content of the aboveground and belowground parts of the plants, and in addition the carbon-and ash-content and the δ13C value of the aboveground parts were determined. It turned out that the length and the dry weight of the shoots of the C3 species showed on increasing tendency with increased water supply, while the values of the C4 species were drastically diminished at the highest water level only. The roots showed in most cases an increased length and dry weight at drier conditions, more pronounced in the C4 than in the C3 species. The nitrogen content of the shoots was mostly higher in the shoots of the C3 plants and in the roots of the C4 plants; it changed in a non-regular manner with variations in water supply. Since the carbon content did not change markedly, the C/N ratio was variable. There was a slight tendency for a higher carbon content and mostly also for a higher C/N-ratio in the shoots of C4 plants. The δ13C values of both C3 as C4 plants were in general not at all influenced by the water supply; they were fixed genetically. The ash content of the analyzed species did not show a clear relationship to the type of photosynthetic CO2-fixation or to the water regime. The influence of light intensity was studied with mixed cultures of all four plant species, again with different water supply. There was a strong effect of light intensity on the competitive behaviour of the C3 and C4 plants under modified water conditions. The wild C3 plant Atriplex hortensis was most successful under conditions of relatively low light intensity and high water availability, while the cultivated ‘artificial’ species Avena sativa showed much less differences between full-light grown and shadow plants. The C4 plant Amaranthus retroflexus is most successful under competitive conditions at high water stress in full light. The C4 grass Panicum miliaceum showed maximum shoot growth in light, but was successful under competitive conditions especially also with good water supply. The light intensity had no effect on the δ13C values. — There was no indication that the soil-type as such has a distinct influence on the success of C3 or C4 plants in mixed cultures.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 50 (1981), S. 98-102 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cold resistance of twenty-seven species of Macaronesian Sempervivoideae uniformly cultivated under cool moderate but not hardening conditions was measured. The resistance limits of all the tested species ranged between-4 and-10°C. Cold stress response was principially different: Cold resistance of about half of the tested species was due to freezing point lowering. This response type, avoidance of freezing, in which any ice formation in the leaves leads to injury, was found in the most cold resistant species (Aeonium spathulatum, several Aichryson species). The other species developed tolerance to freezing, thus resembling the behaviour of the hardy Eurasian Sempervivum species. Several Aeonium and Monanthes species resist to reasonable lower temperatures than normally occur in their natural habitats. The species-specific differences in resisting cold stress may originate from different abilities to tolerate cellular freeze dehydration. The Sempervivum alliance illustrates well the two evolutionary strategies of cold tolerance: Avoidance mechanisms, like lowering the osmotic potential, are typical for species colonizing higher altitudes with moderate frosts. For species extending their distribution area into higher latitudes with more severe frosts, however, freezing tolerance is necessary.
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  • 3
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Multivariate analyses of 18 morphological variables recorded for amplectant males and females and non-amplectant males of Hyla marmorata and Triprion petasatus reveal that in both of these explosive breeding species, mating is significantly non-random. Females of H. marmorata from the relatively aseasonal environment of the Upper Amazon Basin average larger than males, and amplectant males average larger than non-amplectant males. Females of Triprion petasatus from the seasonal environment of the Yucatan Peninsula average larger than males, the sizes of males are significantly correlated with the sizes of the females with which they are paired in amplexus, and amplectant males have shorter internarial distances than non-amplectant males. For both species, non-random mating is interpretable in terms of sexual selection, but the relative importance of male-male competition and female choice cannot be assessed.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 50 (1981), S. 376-379 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nectar-foraging pollinators often exhibit a directional pattern of movement between plants when the energetic costs of revisiting previously utilized areas can significantly reduce foraging efficiency. However, bumblebees (Bombus spp.) foraging for pollen on flowers of Aquilegia caerulea rarely moved in a straight line among successively visited plants. Most flights from plants visited were either to closely neighboring plants or were longer and involved bypassing near neighbor plants. Bees biased their flights toward plants with relatively large numbers of flowers yet visited only a small fraction of the flowers on each plant. Such foraging tactics might result when the energetic costs of revisiting plants are minor. Alternatively we suggest that bumblebees foraging for pollen may not perceive revisitations and their associated costs because they do not assess pollen returns on a per plant basis. In this case energetic-efficiency arguments predicting the pattern of foraging movements among plants may be inappropriate. A better level of analysis would be where the bees assess net energy returns, perhaps between bouts of pollen-combing and corbiculae-packing.
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  • 5
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Empirical associations among co-adapted traits such as body size and patterns of reproduction, development, and behavior are unknown for most animal species, despite numerous theories suggesting otherwise. One way to study these complex relationships is first to consider closely related species and then to generalize findings to other groups. In the present study, relationships among body size, reproductive patterns, development, and sociality were examined in 17 members of the family Canidae (canids). Large canids are more social than smaller species, and offspring of large species achieve independence and tend to breed first at a later age. Large females give birth to absolutely larger young, but relative to their own body weight they allocate fewer resources to bringing a large pup to term. Overall, sexual dimorphism in size is small to moderate, and this is associated with monogamous mating habits and paternal care of young.
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  • 6
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. In an attempt to evaluate the importance of individual daily habits to a freeliving animal, foraging behaviour of kestrels was observed continuously for days in sequence in open country. Data obtained in 2,942 observation hours were used. Flight-hunting was the prominent foraging technique yielding 76% of all prey obtained. 2. Flight-hunting was impeded by rain, fog and wind speeds below 4 m/s and above 12 m/s (Fig. 3). Flight-hunting tended to be suppressed also in response to recent successful strikes and more generally by a high level of post-dawn accumulated prey (Figs. 4, 5). Flight-hunting had a tendency to be enhanced in response to recent unsuccessful strikes (Fig. 6). 3. Trapping results demonstrated a fine-grained daily pattern of common vole trap entries, with peaks at intervals of ca. 2 h (Figs. 7, 8). The interpretation of some of this pattern as representative of vole surface activity was supported by overall strike frequencies of kestrels hunting for voles (Fig. 9). 4. Detailed analysis of the behaviour of three individuals revealed significant peaks in hunting yield and frequency, coinciding with each other and with peaks in vole trapping (Fig. 11). It is suggested that the kestrels adjusted their flight-hunting sessions to times of high ‘expected’ yield. Vole activity peaks sometimes remained unexploited. 5. Meal frequencies culminated shortly before nightfall except in incubating females. The difference between the daily distributions of hunting and eating was due to some of the prey being cached in daytime and retrieved around dusk (Fig. 13). Caching behaviour is interpreted as a circadian strategy allowing separate optimization of hunting-adjusted to prey availability-and eating-adaptive by retaining minimum body weight in daytime flight and by thermo-regulatory savings at night. 6. Some kestrels showed remarkable constancy from day to day in the temporal distribution of specific behaviours (Fig. 16) and of spatial movements (Figs. 18, 19). In three 1–2 week sequences of observation analysed, flight-hunting frequency peaked 24 h after prey capture (Fig. 17). This is probably based on day to day correlations in flight-hunting frequency as well as on increased motivation for hunting in response to prey capture 24 h ago (Table 5). 7. In one individual with three distinct hunting areas, the tendency to return to an area again was maximal 24 h after prey capture in that area (Fig. 21, Table 6). A field experiment tested the effect of prey capture on the daily distributions of hunting and site choice in this individual (Fig. 22). A significant concentration of flight-hunting activity in the experimental feeding area was observed at the daily time of feeding (Fig. 23). Two alternative hypotheses are compatible with the result. Favoured is the one that the birds use “time memory” for the optimization of their daily patterns of flight-hunting and site choice. 8. By adjusting her daily flight-hunting to times of high yield, one kestrel saved 10–22% on her total time spent flight-hunting. Maximal efficiency, by concentration of all hunting activity in the hour of maximal yield, was not attained, presumably because of information constraints. The generality of the contribution of daily habits to survival is discussed.
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  • 7
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Stachys aegyptiaca Pers. is a desert calcicolous chasmophyte. Its growth in the Egyptian Desert is confined to the limestone formations of the Northern Arabian Desert, Sinai and the Isthmic Desert. The plant lives under harsh climatic conditions: high summer temperatures with mean maxima above 35°C and low rainfall ranging from 9.4 mm/annum at El-Tor to 87.3 mm/annum at Hemme. The vegetation dominated by Stachys aegyptiaca is a pioneer stage in the development of the wadi bed ecosystem. Other chasmophytes are the main associates of the Stachys community. The studied plant has been recorded among the associates of numerous plant communities. Runoff, accelerated by the rugged topography in areas where the plant grows, and the stoniness of the substratum contribute to securing ample water supply to the plant. The daily march of the transpiration rate was investigated in two seasons. It has been clear that there is an obvious regulation of transpiration in summer. The osmotic pressure of the plant sap was determined at regular monthly intervals throughout one year. The average osmotic value is 17 atm, ranging from 13.8 atm in April to 19.3 atm in November.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 46 (1980), S. 7-12 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Simulation model estimates of bioenergetics are coupled with observations of diet selection and arthropod prey abundances to assess (1) the role of bird populations in trophic energy fluxes in a temporally heterogeneous shrubsteppe ecosystem, and (2) the degree to which those populations may be limited by food. The model estimates a total annual energy demand of 2.91 kcal m-2 yr-1 by the entire passerine avifauna during 1974, with daily demands varying from 0.0025 to 0.0260 kcal m-2. Coupling energy requirements with estimates of arthropod availability implies that bird demands on the insect standing crop never exceeded 0.7% per day of that standing crop during the breeding season or summer. Overall, the bioenergetic estimates imply that these birds are unlikely to be important in ecosystem processes and, reciprocally, are unlikely to be limited by food resources even during peak energy demands. As a consequence, I suggest that biological interactions such as competition play a relatively minor role in structuring the bird community in this variable environment.
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  • 9
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Wyeomyia smithii Coq. (Diptera: Culicidae) completes its pre-adult development only within leaves of the purple pitcher-plant, Sarracenia purpurea. Between early June and mid-October in northern New York State, the daily temperature cycle in leaves lagged the photic cycle by 0–6 h and exhibited a mean daily amplitude of 14.5°C. Thermoperiod acts as a potent zeitgeber. At constant temperatures, W. smithii respond to the shorter dark period of a symmetric skeleton photoperiod as “day”. However, a superimposed thermoperiod having the thermophase coincident with the longer dark period overrides this tendancy. Thermoperiods may also perturb the photoperiodic clock but W. smithii compensate for the range of phase relationships between the photic and thermal cycles observed in nature. Compared with constant temperatures, W. smithii develop more slowly but exhibit a 7-fold increase in fecundity when reared under fluctuating temperatures. The net result is a 50% greater capacity for increase in the latter regimen. These results suggest that maximum fitness in W. smithii is achieved through the action of, and not despite, thermal heterogeneity.
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  • 10
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Leaf tissue preferences of monophagous, oligophagous, and polyphagous insect herbivores were determined using young and mature leaf tissue abundances and herbivore feeding observations. Larvae of monophagous and oligophagous herbivores preferred young leaf tissues while, overall, larvae of polyphagous species preferred mature leaves of their various host plants. Even though a species is often polyphagous over its geographical range, larvae from local populations may be very specialized in their diet. When this occurs these specialized larvae prefer the more nutritious and perhaps more toxic young leaves of some of their host plants. Resource abundance and plant chemistry are discussed as major factors influencing herbivore feeding patterns.
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