摘要:

ABSTRACT.1The hypothesis that wing dimorphism reflects dimorphism for dispersal ability is tested in two populations of stream‐dwelling waterstriders,Gerris remigisSay, in southern Quebec, Canada.2Movements were assessed directly by recaptures of marked adults, and indirectly by comparisons of residence times and patterns of disappearance of macropterous and apterous morphs. Sampling was done weekly, over a period of 26 months, and 4828 adultG.remigiswere individually marked during this time.3Movements of>100 m were very rare for both morphs. The movement patterns of the two morphs were very similar, and differed only over the winter, when no macropters moved upstream. This latter observation suggests that macropters may be less successful than apterous individuals at moving overland, or rowing against a current at this time of year.4Residence times and patterns of disappearance of the two morphs were very similar during all seasons.5These results suggest that macropterousG.remigisdo not, in general, disperse using any means unavailable to the apterous morph, and that macropters in this species should not be simply categorized as long‐distance dispers

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00314.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1This paper investigates the behaviour, in the laboratory, of a forager simultaneously confronted with the conflicting needs to feed and to avoid predators. The foragers were larvae of the damselflyIschnura elegansVan der Linden, feeding onDaphnia magnaStrauss. The predators were adult females ofNotonecta glaucaL.2Patch choice byIschnuralarvae was significantly modified by the presence of predators. Larvae moved to feed in patches of high prey density when predators were absent but preferred dense cover, even though virtually no prey were available, when predators were present. This behaviour was not altered by hunger, up to 12 days without food. In other words,Ischnuralarvae were risk averse in their foraging behaviour.3In experiments with abundant prey available, the feeding rates ofIschnuralarvae confined to a single patch were also significantly reduced by the presence of hydrodynamically and chemically detectable predators. Predators detectable only by vision had little effect.4Calculations made from published data show that reduced larval feeding rates can lead to slower growth and development and prolonged instar durations inIschnura eleganslarvae. This may have important consequences for larval survival and adult reproductive fitness.

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00315.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1Temporal constancy in the structure of grasshopper assemblies (about forty‐five species each) from two types of North American grasslands was assessed; one site was followed 25 years and the other 7 years.2Densities and relative abundances varied but composition of assemblies based on ranks suggested significant structure when three or more species were included in the analysis.3Results compared favourably with other insect herbivore assemblies which have been examined; variability in population change was intermediate along the spectrum of organisms which have been studie

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00316.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1A novel technique for tracing the movements of insects in the field is described.2The detection system is based on radar technology originally developed for locating avalanche victims. The key of the system is a tiny electronic diode that, glued to the insect, can reflect microwave beams emitted by portable detection equipment.3The technique has been successfully tested in a field‐tracing experiment with carabid beetles. The results show that these insects are capable of dispersing surprisingly long distances in a relatively short period of tim

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00317.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1The effects of food resources on populations of larvae ofSitona hispidulus(F.), a root and nodule herbivore ofMedicago sativaL., were investigated in 1983 and 1984.2Density‐dependent mortality among first‐instar larvae indicated that a lack of available root nodules, the primary resource for first instars, contributed to the 66.2±5.2% and 80.7±4.1% mortalities of first‐instar larvae in 1983 and 1984, respectively. Initial densities of larvae entering the soil were 31.7±2.4 and 15.6±1.3 per soil sample (10.5 cm diam. ×15 cm deep) in 1983 and 1984, respectively (±SEM).3Survivorship and number of first‐instar larvae per soil core sample were significantly related to number and biomass of nodules per soil sample. Percentage soil moisture was not consistently correlated with survivorship and number of larvae per soil sample.4Numbers of second‐ and third‐instar larvae were not consistently correlated with either nodule or taproot biomass.5Numbers of fourth‐instar larvae were associated with taproot biomass, suggesting that taproot surface area may also limit population levels ofS.hispidulus.No correlations were found between taproot and nodule biomass on any sampling date indicating that high numbers of fourth‐instar larvae associated with larger taproots were not merely due to a greater survival of first instars associated with larger taproots.6The study suggests that population levels of nodule‐herbivores are controlled by the availability of root nodules. A sparse distribution of nodules results in high levels of mortality among nodule‐her

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00318.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1Velocity of load‐carryingAtta cephalotes(L.) foragers increases with increasing ant size and decreasing load size.2Foragers are selective in the sizes of loads they carry, but heavier loads would apparently increase their rate of leaf transport to the nest (mg of leaf m s−1).3Even for very thin leaves, leaf diameter is not correlated with ant body size despite the method of cutting (rotating around a fixed point on the leaf edge).4When cutting leaves of different densities, load mass is more closely matched to ant size than is load surface area. This implies that ants choose loads based on mass rather than surface area, and thus the several possible disadvantages associated with carrying loads of large surface area (e.g. increased disturbance by wind or rain) are unlikely explanations of why ants do not select larger loads.5The relationship beween forager size and load size is made more complex by further selectivity at the level of colony recruitment: larger ants recruit to higher‐density (thicker) leaf types.6Gross leaf transport rate is not maximized by foragingA.cephalotes, but net rate of energy intake cannot be assumed to follow the same pattern. If costs/time (not measured) are constant with changing load size, then the net rate of energy intake is not maximized. An alternative hypothesis is that costs/time increase with larger loads, thereby decreasing net rate of gain for larger

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00319.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1Patterns of vertical habitat use of ten species of cockroaches are examined. Three assemblages of cockroaches are recognized on the basis of morphology, foraging behaviour, foraging heights, and overlaps and breadths of vertical distributions.2Three apterous and brachypterous species occur near the ground and comprise one assemblage. They feed mainly on material in the leaf‐litter.3Species that perch higher either migrate into the leaf‐litter on a diel basis and feed on both leaf‐litter and epiphyllic materials, or some are strictly arboreal and forage on algae, liverworts, lichens, spores, pollen and trichomes on the surfaces of leaves.4Trophic and behavioural correlations with perch height are described and the functions of perching are examined.5We conclude that studies of interactions among species are confounded by our lack of understanding of stage‐ and sex‐specific interactions of coexisting species. A simplistic ‘species’approach to such interactions is inadequate because it does not recognize intraspeci

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00320.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1Repeated counts were made of the number of adultAphytis melinus(DeBach) wasps per fruit on Valencia oranges in an orchard over two successive periods. Resulting rates of parasitism per fruit were measured at the end of each period.2For both periods, corresponding to high and low mean numbers of adult parasites, there was a significant positive regresssion of adult wasps per fruit on the number of available hosts per fruit. However, there was a high level of variability about the regression, and the overall aggregative response appears to be weak.3For both periods, rates of parasitism per fruit were independent of host density per fruit and they showed a high level of variability at all densities. Similar patterns were found in another, commercial, orchard over a wide range of mean host densities.4There was no evidence for aggregation of parasites or density dependence of parasitism at a patch size corresponding to the whole tree.5Suggestions based on some host‐parasitoid models, that aggregations of parasite attack in areas of high host density are necessary for effective biological control, are rejected. However, the model of Hassell (1982), incorporating aggregation of parasites and limitations on the effectiveness of the parasite, seems to fit the data quite wel

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00321.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1Horvathiolus gibbicollis(Costa), a ground‐living seed‐feeding bug of the mediterranean region, has two wing morphs. In macrop‐terous bugs both pairs of wings are fully developed. In brachypterous ones forewings are reduced to about two‐thirds and hindwings to less than a third of their length in macropters.2Each morph bred true with regard to wing length when reared under variable density, food and temperature conditions for several generations.3All F1offspring between crosses of the two morphs were brachypterous. In F2approximately 25% were macropters and 75% brachypters implying monogenic control of wingform.4Flight muscles in macropters vary from fully developed to totally reduced. This variation is determined by environmental conditions during adult life. Most young adult bugs have flight muscles, and totally starved or unmated bugs retain their flight muscles. Fed and mated females histolyse flight muscles as they start laying eggs, while most males of the same group retain their muscles.5Brachypterous bugs have a smaller thorax and larger abdomen than macropterous ones.6Brachypterous bugs reach adulthood slightly before macropterous ones, and they have a distinctly shorter adult preoviposition period.7Lifetime egg production does not differ significantly between the two wing morphs. However, the temporal pattern of egg laying is different in the two morphs. The mx‐curve of macropters starts later, then attains a higher peak and finally decreases faster than that of brachypters.8Initially, macropters lay smaller eggs than brachypters, but egg volume increases with age in macropters and eventually approaches that of brachypters.9The initial increase in reproductive effort (egg volumexegg number) of macropters is concomitant with wing muscle histolysis and the mobilization of thorax space for reproduction.10Adult survival rate does not differ between t

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00322.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACT.1The patterns of mortality in laboratory populations of the grasshopperChorthippus brunneusThunberg are examined at a range of densities and at different stages of nymphal development with particular reference to the phenotypes of nymphs that die or survive.2Total mortality during nymphal development rises from density‐independence at the lowest densities to approximately compensating density‐dependence at the highest densities.3The greatest proportion of total mortality occurs in the first two instars. The stage broadly covering the second instar is the ‘key‐stage’ determining adult density. The mortality during these stages is largely density‐independent. There is relatively little mortality during stages broadly covering the final instar, but it is density‐dependent and also plays a significant part in determining final adult density.4As the mortality becomes more density‐dependent, either with density itself or with cohort age, the smallest individuals become increasingly disproportionately prone to mortality.5Males, which are smaller, are more susceptible to mortality than females, but their susceptibility relative to their size is less than

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1986.tb00323.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY