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1.
Clear diel periodicity in the timing of egg laying was observedin the tropical cyclopoid cope-pods Oithona plumifera, Oithonanana, Oithona simplex and Corycaeus amazomcus, and the harpacti-coidEuterpina acutifrons in waters surrounding Jamaica, West Indies.Individual females incubated under ambient food conditions formultiple clutches displayed remarkable constancy in their clutchdurations (= egg or embryonic development time). All speciesexhibited clutch durations of 20–23 h and cycle durations(= sum of clutch and inter-clutch durations) of 24 h, exceptfor the offshore species O.plumifera where the clutch durationwas 36 h and the cycle duration 48 or 72 h. Egg laying appearedto be synchronized by photoperiod, occurring around dawn formost species. In order to avoid biases, diel periodicity mustbe accounted for in estimates of egg production rates, and futureefforts should concentrate on the responses of clutch size andinterclutch durations to natural food climates.  相似文献   

2.
Modeling patterns of zooplankton diel vertical migration   总被引:4,自引:0,他引:4  
Realized predation pressure, defined as the product of predationpressure and light intensity, expresses the mortality pressuredue to visual predation. The part of realized predation pressurewhich is sensed by organisms is here considered to be relatedto food level and temperature. This partly realized predationpressure is referred to as sensed predation pressure. We proposea possible control mechanism of diel vertical migration (DVM):organisms move vertically following the minimum change in sensedpredation pressure. To investigate this assumption, we presenta math ematical model of DVM. We assume that when predatorsare present, the food level is above a minimal level, and temperatureis higher than the tolerance of organisms to growth, prey organismsundertake DVM following the minimum change in sensed predationpressure. We examine how patterns of migration may be affectedby changes in water clarity, predation pressure, food leveland temperature. This work supports the assumption that minimizingchanges in sensed predation pressure can explain the wide variationin the vertical profile of zooplankton.  相似文献   

3.
The diel emergence patterns of 16 chironomid species from a Berkshire lake are characterized. A study of these patterns and those described previously in the literature indicate that the diel pattern for any chironomid species can often be predicted on the basis of the Tribe to which it belongs. Chironomini spp. usually emerge at dusk or at night. Macropelopiini spp. and Metrioenemini spp. characteristically emerge during daylight but the former peak in the morning and the latter peak in the afternoon. Orthocladiini and Tanytarsini spp. exhibit more varied patterns although bimodalism is a frequent feature. The phylogenetic conservatism in the diel patterns displayed implies that these patterns became established early during chironomid evolution, and are, therefore, plesiomorphic.  相似文献   

4.
5.
ABSTRACT. An electronic timer and fraction collector consisting of CMOS integrated circuits is described. It converts 50- or 60-Hz AC to real-time pulses in programmable whole-number increments (1, 10 or 60s) from 3 to 16659, producing timing periods from 3 s to more than 11 days. The fraction collector contains a leaf-switch feedback circuit that automatically adjusts to various gear motor speeds and sample tube spacings so that proper positioning results. Hourly collections by the device of the bark beetles Ips typographus L. and Pityogenes chalcographus L. (Scolytidae) emerging from logs of Norway spruce, Picea abies , indicated that both species emerged with a diel periodicity. A unimodal emergence peak for both sexes of both species occurred at midday in LD 20:4 at a constant 25°C and 80% r.h.  相似文献   

6.
Vertical distributions and swimming behaviors of 7 species ofhydromedusae (Aequorea victoria, Bougainvillia principis, Gonionemusvertens, Mitrocoma cellularia, Phialidium gregarium, Polyorchispenicillatus, and Stomotoca atra) were observed over 24-h periodsin a 2 m high, 1500 1 transparent tank. In this tank, most speciesperformed well-marked diel vertical migrations that were mediatedby swimming. Manipulation of the light regime showed the didswimming behaviors to be light-dependent rather than intrinsic,even in species that do not possess recognized photoreceptors.Correlations between vertical migration and spawning times forseveral species of medusae suggest that in cases when verticalmigration reduces the distances between individuals (e.g., inmass movements to the surface) just prior to spawning, enhancedfertilization success may result from such movements. 1Present address: Friday Harbor Laboratories, Friday Harbor,WA 98250, USA.  相似文献   

7.
Zooplankton and ichthyoplankton assemblages were studied fromJanuary 2003 to June 2004 in a temperate shallow estuary (Mondegoestuary, Portugal). Monthly sampling was performed at five stationsat high and low tides, with subsurface tows with 335 and 500µm mesh Bongo nets. Analysis of variance (ANOVA) showeda significant effect (P < 0.05) of the mesh size of the neton the abundance of main zooplankton groups. On average, theabundance of the 500 µm taxocenosis was 67 and 102 timeslower than the 335 µm taxocenosis at high and low tidesrespectively, especially in the south arm. More than 80 specieswere identified in the zooplankton samples. The upper reachesof northern arm are dominated by freshwater crustacean mesozooplanktonlike Acanthocyclops robustus and Diaptomus spp. and the cladoceransDaphnia, Ceriodaphnia and Bosmina, often being codominant. Inthe southern arm, the resident estuarine copepod Acartia tonsawas dominant, eventually being the most abundant taxon. Marinereaches of estuary are usually dominated by the marine calanoidcopepods Acartia clausi and Temora longicornis and the siphonophoresMuggiaea atlantica. Concerning the ichthyoplankton, this wasdominated by the larvae of estuarine resident species, mainlyPomatoschistus sp., and eggs of Engraulis encrasicolus. Theabundance of Pomatoschistus sp. larvae was positively correlatedwith water temperature. Statistical analysis (canonical correspondenceanalysis) used to determine the spatiotemporal structure ofthe zooplankton assemblages and its correlation with environmentalvariables showed that salinity and temperature were the mainfactors influencing the distribution of zooplankton. The resultsobtained also showed that abundance was strongly influencedby the hydrological circulation pattern and direct or indirecthuman impacts that occur in each arm of the estuary. This article was presented at Plankton Symposium III, held atFiguera da Foz, portugal, between 17 and 20 March 2005, underthe auspices of the University of Coimbra and the Universityof Aveiro, and coordinated by Mário Jorge Pereira andUlisses M. Azeiteiro.  相似文献   

8.
Phenotypic plasticity itself evolves, as does any other quantitative trait. A very different question is whether phenotypic plasticity causes evolution or is a major evolutionary mechanism. Existing models of the evolution of phenotypic plasticity cover many of the proposals in the literature about the role of phenotypic plasticity in evolution. I will extend existing models to cover adaptation to a novel environment, the appearance of ecotypes and possible covariation between phenotypic plasticity and mean trait value of ecotypes. Genetic assimilation does not sufficiently explain details of observed patterns. Phenotypic plasticity as a major mechanism for evolution--such as, invading new niches, speciation or macroevolution--has, at present, neither empirical nor model support.  相似文献   

9.
SUMMARY. Six channels were constructed in various parts of two riffles from which chironomid exuviae were collected every 3 h for three 24-h periods in July 1974. Diel emergence patterns were calculated for twelve abundant species and six different patterns were observed.
Krenosmittia cf. camptopheleps and Cordites had their major emergence pulse during peak light periods and it is proposed that high or increasing light intensity is a cue for their emergence. Stempellinella cf. brevis begins its emergence in the morning and continues until after darkness. Increasing and high water temperatures are suggested as the emergence cue since emergence tracks water temperatures with little apparent effect of light. Parametriocnemus sp. and Polypedilum ( Tripodura ) sp. begin emerging in late evening and continue into early daylight hours. These patterns indicate low and decreasing water temperatures as the emergence cue with little apparent effect of light. Corynoneura sp. and Thienemanniella sp. emerged primarily during daylight hours with a minor pulse in the morning and the major pulse in late afternoon. It is proposed that the emergence cue is simply the presence of light and that water temperature determines how many individuals are able to prepare for emergence and respond to the cue. Rheotanytarsus cf. exiguus and Tanytarsus ( Sublettea ) coffmani have major emergence peaks just after sunset and minor pulses in the morning hours. Changes in light are proposed as their emergence cue with water temperatures determining the number of individuals able to respond to that cue. Eukiefferiella discoforipes gr. sp. and Nilotanypus sp. emerge continuously throughout daylight and darkness hours, showing no obvious pattern.  相似文献   

10.
1. The hypothesis under test was that larvae of Dinocras cephalotes (Curtis), Perla bipunctata Pictet, Isoperla grammatica (Poda), and Perlodes microcephalus (Pictet) differed markedly in their diel activity and feeding patterns. Mature larvae collected about 1 month prior to adult emergence were used either for gut analyses or for observations of their activity and feeding patterns in three stream tanks with natural substrata and glass bottoms, so that activity could be observed above and below the substratum. A dull red light was used for observations in the dark. Food (larvae of Ephemeroptera, Simuliidae, and Chironomidae) was provided in excess. 2. Larvae for gut analyses were taken 1 h before dusk or dawn (n = 30 larvae per species for each day or night sample). The only species with food in the gut for the day samples was P. microcephalus. All species fed at night, the mean number of prey per larva being very similar for D. cephalotes, P. bipunctata, and I. grammatica but significantly higher for P. microcephalus. Most prey were insect larvae, especially Simuliidae and Chironomidae. 3. Diel activity patterns of single larvae differed interspecifically but not intraspecifically. Larvae of D. cephalotes and P. bipunctata were rarely active during the day; their activity increased at dusk and decreased at dawn, and was highest during the night; their success at prey capture was highest at dusk and dawn, with an ambush rather than a search strategy. Isoperla grammatica was rarely active during the day, most active at dusk and dawn when prey capture was highest, using a search strategy, and less active for the rest of the night. Perlodes microcephalus was active during the day, but only below the substratum, and very active from dusk to dawn with a high prey‐capture success, using a search strategy. These experiments provided support for the hypothesis under test. The discussion concludes that the results could also help to explain known differences in growth rate and the length of the life‐cycle in these four species.  相似文献   

11.
1. We examined the seasonal and diel patterns of invertebrate drift in relation to seston and various habitat characteristics in two each of four different kinds of alpine streams [rhithral (snow‐fed) lake outlets, rhithral streams, kryal (glacial‐fed) lake outlets and kryal streams]. Samples were collected at four times of the day (dawn, midday, dusk and midnight) during three seasons (spring, summer and autumn). 2. Habitat characteristics differed mainly between rhithral and kryal sites, with the latter having higher discharge and turbidity, lower water temperature, and higher concentrations of ammonium, and particulate and soluble reactive phosphorus. Seasonality in habitat characteristics was most pronounced for kryal streams with autumn samples being more similar to rhithral sites. 3. The concentration of seston was lowest in the glacial‐influenced lake outlets and slightly higher in the stream sites; no seasonal or diel patterns were evident. 4. The density of drifting invertebrates averaged less than 100 m?3 and was lowest (<10 m?3) at three of the four kryal sites. Taxon richness and diversity were lowest at rhithral lake outlets. Chironomidae dominated the drift as well as benthic communities and <30% of benthic taxa identified were found in the drift. 5. Drifting invertebrates showed no consistent seasonal pattern. However, density tended to be highest in spring at rhithral sites and in autumn at kryal sites. No diel periodicity in drift density was found at any site and the lack of diel pattern may be a general feature of high altitude streams. 6. Glacially influenced habitat parameters were a major factor affecting drift in these alpine streams, whereas no clear differences were observed between streams and lake outlets. Our findings indicate that invertebrate drift in alpine streams is primarily influenced by abiotic factors, and therefore, substantially differs from patterns observed at lower altitude.  相似文献   

12.
Hydrobiologia - Detailed seasonal analyses of phytoplankton assemblages’ composition were performed on long-term datasets (20&nbsp;years) of two oligotrophic Mediterranean lagoons (Diana...  相似文献   

13.
Sheep epizoochory has often been proposed as an important vector which can help to overcome the dispersal limitation of plants in fragmented landscapes. In order to evaluate the contribution of herbivores to recruitment especially of target species, the dispersal and post-dispersal fate of such seeds must be known. In a field experiment sheep with seeds of mainly target species (experimentally attached to their coats) were present at three sand plots for 24 h. Natural epizoochorous dispersal was already shown for most of the species in our study area. Seed detachment, trampling intensity and seed shadow were measured; seedling emergence and survival were recorded over an 8-month period. In addition, the effect of sheep trampling on seedling emergence and survival of two threatened species, Jurinea cyanoides and Koeleria glauca, were studied.  相似文献   

14.
15.
The process of biological growth and the associated generation of residual stress has previously been considered as a driving mechanism for tissue buckling and pattern selection in numerous areas of biology. Here, we develop a two-dimensional thin plate theory to simulate the growth of cultured intestinal epithelial cells on a deformable substrate, with the goal of elucidating how a tissue engineer might best recreate the regular array of invaginations (crypts of Lieberkühn) found in the wall of the mammalian intestine. We extend the standard von Kármán equations to incorporate inhomogeneity in the plate’s mechanical properties and surface stresses applied to the substrate by cell proliferation. We determine numerically the configurations of a homogeneous plate under uniform cell growth, and show how tethering to an underlying elastic foundation can be used to promote higher-order buckled configurations. We then examine the independent effects of localised softening of the substrate and spatial patterning of cellular growth, demonstrating that (within a two-dimensional framework, and contrary to the predictions of one-dimensional models) growth patterning constitutes a more viable mechanism for control of crypt distribution than does material inhomogeneity.  相似文献   

16.
A method is described for measurement of the in situ feeding rate of planktonic herbivores. Freshly caught Zooplankton are washed with filtered sea water and frozen. The gut contents are later analysed using acetone extracts of the entire sample. Fluorescence peaks due to ingested chlorophyll are easy to quantify for sample sizes of 20–200 animals. This method obviates some of the problems, such as confinement and previous feeding history, associated with extrapolation from laboratory experiments to field conditions. The method is illustrated by an investigation of diel feeding patterns of marine copepods. Initial results indicate the complexity of these patterns, with either a single night peak or dawn and dusk peaks for adult copepods. Diel variations in feeding activity appear to occur in addition to, but closely interacting with, the diel vertical migrations of the animals.  相似文献   

17.
A comparative experimental study of the rhythmic shedding of two geographic strains of Schistosoma bovis cercariae by Bulinus truncatus and Planorbarius metidjensis did not show any differences in emergence patterns. In our opinion, the results support the hypothesis that cercarial emission rhythms are determined primarily by the parasite in these snail/parasite associations.  相似文献   

18.
1. Aquatic predators may influence drift periodicity either directly or indirectly (by non‐consumptive effects involving chemical cues). We took drift samples (eight successive 3‐h sampling intervals over a 24‐h period) on five dates (September 2007, March, April, June and August 2008). Samples were taken at three sites (one site with trout throughout the year, two sites without trout but with fire salamander larvae as top predators from April to August, but without vertebrate predators during the rest of the year) in a stream near Vienna, Austria, to examine the effects of predators on drift periodicity. 2. Of 45 331 specimens caught, the most abundant taxa were Ephemeroptera (32.3%; mainly Baetidae), Diptera (21.5%; mainly Chironomidae), Amphipoda (17.4%; all Gammarus fossarum), Plecoptera (5.4%), Coleoptera (3.5%) and Trichoptera (1.2%). For more detailed analyses, we chose Ephemeroptera (Baetidae; n = 13 457) and Amphipoda (G. fossarum; n = 7888), which were numerous on all sampling dates. 3. The number of drifting baetids and amphipods, as well as total drift density, was generally higher at night than by day, although without predators these differences were significant for Gammaridae but not for Baetidae. 4. When broken down to size classes, night–day drift ratios generally were not significantly different from equality in all size classes of baetids when larval fire salamanders and trout were absent. When predators were present, however, baetid drift density was usually higher at night, except in the smallest and largest size classes. In all size classes of G. fossarum, drift density was usually higher at night, whether with or without the top predators. 5. Although we could study predator effects on drift periodicity at three sites on only a single stream, it seems that non‐consumptive effects may affect Baetidae. Salamander larvae, most probably via kairomones, induced a shift towards mainly nocturnal drift, which could be interpreted as predator avoidance.  相似文献   

19.
Modelling field emergence patterns in arable weeds   总被引:3,自引:0,他引:3  
A model was developed to simulate weed emergence patterns after soil cultivation. In the model, the consecutive processes of dormancy release, germination and pre-emergence growth were modelled in separate modules. Input variables of the model were: date of soil cultivation, soil temperature and soil penetration resistance. Output variables of the model were: seedling density and timing of seedling emergence. The model was parameterized for Polygonum persicaria , Chenopodium album and Spergula arvensis with data from previous field and laboratory experiments. The model was evaluated with data from an experiment, in which emergence of P. persicaria , C. album and S. arvensis was monitored in field plots that were cultivated once only, at one of five dates in the spring. At the same time as the field observations on seedling emergence, seasonal changes in seed dormancy of the buried weed seeds were assessed by testing the germination of seed lots that were buried in envelopes. From a comparison between field observations and simulated data, it appeared that the model overestimated the rate of dormancy release in spring, whereas germination and pre-emergence growth were simulated well. In general, therefore, both the numbers of emerging seedlings and the timing of emergence could be predicted accurately, when dormancy was not simulated but introduced from experimental data. Improvement of predictions of field emergence of weeds should mainly focus on increasing the precision of the simulation of dormancy release. Close correlations were found between seedbed temperature and both the extent and rate of seedling emergence, but analysis with the simulation model revealed that they were only partly based on causal relationships, so that they have limited predictive value.  相似文献   

20.
In ectothermic organisms, it is hypothesized that metabolic rates mediate influences of temperature on the ecological and evolutionary processes governing biodiversity. However, it is unclear how and to what extent the influence of temperature on metabolism scales up to shape large-scale diversity patterns. In order to clarify the roles of temperature and metabolism, new theory is needed. Here, we establish such theory and model eco-evolutionary dynamics of trophic networks along a broad temperature gradient. In the model temperature can influence, via metabolism, resource supply, consumers' vital rates and mutation rate. Mutation causes heritable variation in consumer body size, which diversifies and governs consumer function in the ecological network. The model predicts diversity to increase with temperature if resource supply is temperature-dependent, whereas temperature-dependent consumer vital rates cause diversity to decrease with increasing temperature. When combining both thermal dependencies, a unimodal temperature-diversity pattern evolves, which is reinforced by temperature-dependent mutation rate. Studying coexistence criteria for two consumers showed that these outcomes are owing to temperature effects on mutual invasibility and facilitation. Our theory shows how and why metabolism can influence diversity, generates predictions useful for understanding biodiversity gradients and represents an extendable framework that could include factors such as colonization history and niche conservatism.  相似文献   

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