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1.
Summary Mean daily food consumption and total lifetime food consumption of the spider,Nephila clavata, were estimated in natural populations. Daily food consumption in the late adult stage was 27–150 mg wet weight, which was nearly equivalent or slightly larger than that in other large web-building spiders. Considerable variation in food consumption was found among habitats or years. The largest variation among habitats in the same year was 7 and 5 fold for daily and lifetime consumption, respectively, while that among years in the same habitat was 3.5 and 2.5 for daily and lifetime consumption, respectively. Feeding conditions evaluated from the food consumption per body weight of spiders declined during the period from mid-July to mid-September in almost all the populations, which suggested that they faced to severe food limitation in this period.  相似文献   

2.
Summary Field studies were conducted to clarify whether variation in food availability among habitats influences population density, and whether population density has a negative effect on foraging success in the orb-web spider,Nephila clavata. Lifetime food consumption per individual (i.e., foraging success) strongly correlated with mean body size of adult females and mean fecundity in populations. Also, there was a positive correlation between foraging success and population density. Since foraging success reflected potential prey availability in the habitat, food resource appeared to be a limiting factor for populations in this spider. Mean fecundity per individual correlated with population density of the following year, suggesting that decreased reproduction is a major component of food limitation on population density. Consistent defferences in mean body size between particular sites were observed over years, while such difference was less obvious in density. Thus, ranking of food abundance among habitats seems to be predictable between years. A field experiment revealed that an artificial increase in population density had no negative effect on the feeding rate of individuals, suggesting that intraspecific competition for food is not important in this species.  相似文献   

3.
Summary Dispersal rates were measured in lines selected for high and low response of egg production to conditioned media, and responsivness of egg production was measured in lines selected for high and low dispersal. A positive correlation was found between these two traits, each of which had previously been found to have a simple genetic basis. It is suggested that inTribolium castaneum the sensitivity to environmental conditions is mediated through a Sensor gene, which can activate either response, according to circumstances.  相似文献   

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Summary A detailed sensitivity analysis of a model of a predator-prey system comprised ofTetranychus urticae andPhytoseiulus persimilis was performed. The aim was to assess the relative importance of the life history parameters of both species, the functional response, and the components of the numerical response. In addition, the impact of the initial predator-prey ratio and the timing of predator introduction were tested. Results indicated that the most important factors in the system were relative rates of predator and prey development, the time of onset of predator oviposition, and the mode of the predator's oviposition curve. The total oviposition of the predator, the effect of prey consumption on predator oviposition, and predator searching were important under some conditions. Factors of moderate importance were the adult female predator's functional response, total prey oviposition, the mode of the prey's oviposition curve, abiotic mortality of the pre-adult predator, and the effect of prey consumption on predator development and on the immature predator's mortality. Factors of least importance were the variances of the predator's and prey's oviposition curves, the abiotic mortality of the adult predator, the abiotic mortality of the pre-adult and adult prey, the functional response of the nymphal and adult male predators, and the effect of prey consumption on adult predator mortality. The sex ratios had little effect, except when the proportion of female predators was very low. The initial predator-prey ratio and time of predator introduction had significant impacts on system behavior, though the patterns of impact were different.  相似文献   

6.
Plutella xylostella in the temperate zone shows a clear seasonal change in adult body size. In the laboratory, large and small moths were produced during immature stages at 15°C and 25°C, respectively. These moths were then used to evaluate longevity, age-specific flight ability, flight ability of mated and unmated females, and the influence of flight experience on the subsequent reproductive success. The large moths lived longer and displayed a greater flight ability over 3 weeks. Irrespective of body size, unmated females flew for a longer time than mated females, and flight experience affected their subsequent reproductive success. Females of both sizes mated and laid eggs soon after emergence, without any obvious pre-reproductive period. More flight experience did not delay oviposition, but did reduce egg production. It is likely that large moths with a longer adult life span and greater flight ability are better fitted for long-distance flight and more fecund than small ones. These experimental results may explain why long-distance migration ofP. xylostella is mostly seen during cool seasons, when relatively large moths with long forewing appear in the field.  相似文献   

7.
Summary The degree of feeding damage in the wild to the cruciferous perennialRorippa indica (L.) Hieron ranged from 0% (not damaged) to 100% (heavily damaged). However, “not damaged” and “heavily damaged” individuals did not differ in the relative suitability of their intrinsic traits forP. rapae, which caused the heaviest damage on the plant. Therefore, the different degrees of feeding damage may be due to variability in the extrinsic traits of the plant, that is, it may be determined by the habitat conditions where individual plants exist. Furthermore,R. indica allocated more resource to seed production at the expense of the roots when it was experimentally subjected to heavy leaf damage. The result suggested thatR. indica individuals may escape, by means of seed dispersal and seed dormancy, from unfavorable habitats where they are heavily damaged by herbivores.  相似文献   

8.
The wild crucifers,Rorippa indica andLepidium virginicum, are known to serve as host plants for the diamondback moth (DBM),Plutella xylostella, but they are less suitable than the preferred cultivated cruciferous plant, cabbage, in terms of adult body size and fecundity. The life history traits and flight activity of DBM adults grown on various host plants were investigated. The adults thus reared on each host plant were divided into three size groups (small, medium and large). In general, female adults grown on the wild crucifers were less fecund and lived longer than those reared on cabbage. Flight activity was higher in adults grown on wild crucifers than in those reared on cabbage. Male adults flew longer than females. Fecundity, longevity, flight activity and morphometrical characters of adults were positively correlated with pupal weight in individuals reared on the same host plant. A negative relationship was found between fecundity and flight activity in females of the same size group, but a positive one was observed in females reared on the same host plant.  相似文献   

9.
Reproductive behaviors related to habitat utilization were studied in males of the damsefly,Mnais nawai, which has two male forms, territorial orange-winged males (nawai) and non-territorial pale-orange-winged males (sahoi), at the upper part of a mountain stream where they partiallycoexist with a related species,Mnais pruinosa, which also has two male forms, territorial orange-winged males (esakii) and non-territorial hyaline-winged males (strigata). These two species showed parapatric distribution; the lower part of the stream was occupied byM. nawai, and the upper part byM. pruinosa. In the present study, cross-matings occurred between bothMnais species, although normal intraspecific matings occurred more frequently than cross-matings. Territorial males of both species copulated with conspecific females that entered their territory and guarded the ovipositing females, probably to avoid sperm displacement resulting from subsequent copulations. Severe competition for oviposition sites by territorial males even occurred between the two species. On the other hand, non-territorial males of both species have alternative mating strategies (including several tactics such as sneaking, takeover and interception). The possible benefits from conflict among territorial males of both species is discussed.  相似文献   

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Summary The postmetamorphic growth and survival of the salamanderHynobius nebulosus tokyoentis Tago were surveyed in the study site located in Habu village of Hinodemachi, a suburb of Tokyo City, during 1975–1981. A laboratory experiment on the growth rate of juveniles was conducted in parallel with the field survey. The result indicated that this salamander grew at the rate of 8,mm in s.v.l. per year during the juvenile stage, but its growth rate decreased markedly as low as 1.8 mm for males and 1.1 mm for females, once it had attained sexual maturity. According to the “capture-recapture” procedure the annual survival rate after metamorphosis was found to be quite high; that is, approximately 0.7. By using the growth rate of juveniles and the difference between the sizes at metamorphosis and sexual maturity, the age at first reproduction was estimated to be 4 year for males and 5 year for females. From the data obtained in this study, the intrinsic rates of increase (r) were calculated for various values of age at first reproduction under different survival schedules, and the relationship between the age at first reproduction and fitness as measured byr was examined. The result indicated that an optimal age maximizing fitness always existed under respective survival schedules, and the observed age at first reproduction of this salamandei was found to coincide well with the predicted optimal age.  相似文献   

13.
To examine density dependence in the survival, growth, and reproduction of Pomacea canaliculata, we conducted an experiment in which snail densities were manipulated in a paddy field. We released paint-marked snails of 15–20 mm shell height into 12 enclosures (pens) of 16 m2 at one of five densities – 8, 16, 32, 64, or 128 snails per pen. The survival rate of released snails was 95% and was independent of snail density. The snail density had a significant effect on the growth and egg production of individual snails. This density dependence may have been caused by reduced food availability. The females at high density deposited fewer and smaller egg masses than those at low density, and consequently produced fewer eggs. The females at densities 8 and 16 deposited more than 3000 eggs per female, while the females at density 128 oviposited only 414 eggs. The total egg production per pen was, however, higher at higher snail density. The survival rates of juvenile snails were 21%–37% and were independent of adult density. The juvenile density was positively correlated with the total egg production per pen and hence was higher at higher adult density. However, the density of juveniles larger than 5 mm in shell height, i.e., juveniles that can survive an overwintering period, was not significantly different among density treatments. These results suggest that snail density after the overwintering period is independent of the density in the previous year. Thus, density dependence in growth and reproduction might regulate the population of P. canaliculata in paddies. Received: October 23, 1998 / Accepted: July 16, 1999  相似文献   

14.
Summary A male fitness advantage to wing reduction was investigated for the oriental chinch bug,Cavelerius saccharivorus, which is wing dimorphic. Field surveys for the frequency of matings between wing morphs showed that the mating probability was much higher in brachypterous males than in macropterous males in the early breeding season. Brachypterous males copulated with not only brachypterous females but also macropterous females in this season. This led to a considerable rate (30%) of insemination of macropterous females just before emigration even in the early breeding season. A rearing experiment for the pre-reproductive period of females revealed that females mated with brachypterous males copulated and oviposited earlier than females mated with macropterous males. These results indicate that there is a fitness advantage to wing reduction in the males ofC. saccharivorus in terms of the earlier sexual maturation.  相似文献   

15.
One hundred and thirty carcasses of the red fox were collected in Tochigi Prefecture, by the Tochigi Prefectural Museum, from 1981 to 1991. The young/adult ratio of the sample was 1.60, which suggests that the hunting pressure has been relatively low in this area. Six percent of the animals were 5 years or older which compares to those taken in Hokkaido, but is higher than those in Europe and North America. The sex ratio for all specimens had a tendency towards male bias (0.587), but this bias was higher for the adult (0.605) than for the young (0.576). Among young (0 year-old) foxes, more individuals were killed on roads than by trapping or shooting (P<0.02, chisquare test). This mortality pattern was caused by high mortality of young males (P<0.02). The proportions of adults killed by the three mortality factors were similar, though only one of the 14 foxes older than 4 years old was shot, probably due to age-linked activity patterns. Most road-kills of young foxes occurred in May when juveniles began exploiting and in November when sub-adults began dispersal. The ratios of road-kills for the whole sample and for adults alone were 42% and 34%, respectively. These high rates of road-kills suggest that the mortality pattern in Tochigi has been affected by factors characteristic of urban environments.  相似文献   

16.
Summary Lifetime mating success of males in a natural population of the papilionid butterfly,Atrophaneura alcinous, was investigated and causes of the variation were examined. The most successful males mated with 5 females, whereas about 73% of the males failed to mate. Body size of males was not correlated with their eclosion date, longevity and lifetime mating success. There was no trade-off between mating success and longevity, and long-lived males had a disproportionately high mating success. Although number of available females per male per day was not variable among males with different longevities, long-lived males had higher mating efficiency. Time interval between matings by non-virgin males was shorter than that from eclosion to the first mating. High lifetime mating success of long-lived males was strongly related to their mating experience, not to their ageper se.  相似文献   

17.
Summary Reproduction and egg diapause of the oriental chinch bug,Cavelerius saccharivorus, in the subtropical winter season were investigated in relation to its wing polymorphism. Macropterous females collected from the southern part of Okinawa Is. in the autumn season delayed their oviposition and were less fecund early in the adult life period, but survived much longer than brachypterous females collected from the same locality. The total fecundity was not significantly different between wing morphs. The diapause of eggs laid by brachypters tended to be terminated more easily at a high temperature than that of eggs laid by macropters. This indicated that the eggs laid by macropters were more intense in their diapause than those laid by brachypters. However, irrespective of the parental wing form, diapause showed considerable variation in its intensity within and between clutches.  相似文献   

18.
A complete understanding of the evolution of sociality in aphids requires a detailed knowledge of the patterns of soldier investment in their ecology. The eusocial bamboo aphidPseudoregma bambucicola has a morphologically specialized first-instar soldier caste. The proportion of soldiers was positively correlated with colony size. Within a colony, soldiers were evenly distributed among subcolonies; within each subcolony, however, their distribution was biased toward peripheries which were exposed to many predators. Field experiments introducing natural enemies such asEupeodes confrater (Diptera: Syrphidae) andSynonycha grandis (Coleoptera: Coccinellidae) revealed that the survival rate of these predators was negatively correlated with the density of soldiers, suggesting that soldiers can more or less defend their colonies by killing or removing a range of natural enemies. Observations suggest that large mature colonies attract more predators than newly established small colonies and that, within a colony, the predators attack each subcolony regardless of its position on bamboo shoots. This implies the presence of a positive correlation between colony size and predation risk. Thus, the investment in soldiers seems to reflect the attacking pattern of predators within a colony. These results agree with the defence-optimization hypothesis in soldier investment ofP. bambucicola colonies.  相似文献   

19.
Summary The three year (1988–1990) life tables ofNephotettix cincticeps were constructed, and the daily survival rate and longevity of female adults were estimated by Hokyo and Kiritani’s (1967) method for the overwintering and the first-generations on the foxtail grass in Okayama, southwestern Japan. The life tables and the population parameter values estimated were compared with those in the other generations on rice. The FARMCOP suction sampler was employed to survey the population density. The durations of pre-ovarial maturation of female adults of the 1st generation on foxtail grass and rice seedling were similar. Longevity of adults of the overwintering and the first generations which emerged on the wild host was longer than that of the other generations (2nd and 3rd generations) on the rice plants. Fecundity of females decreased successively as the generation proceeded and it became lowest in the final 3rd generation. Only about 3.5 percent of first-instar nymphs of the 1st generation emerged as adults in the fallow field. The survival rate of nymphs on foxtail grass was always lower in comparison with that on rice plants. However, the survival rates of nymphs on foxtail grass and rice seedling were not significantly different from each other under laboratory conditions. In the fields, senescence of foxtail grass occurred in the midst of nymphal period of the 1st generation. The survival rate of nymphs on foxtail grass decreased with the increasing in the nymphal density. Abundance of spiders during the 1st generation was higher than that in the early stage of rice plants.  相似文献   

20.
Summary Spatial relationships of mate acquisition probability for individuals of both sexes of a gregariously-mating coreid bug,Colpula lativentris, were studied in relation to aggregation size. Operational sex ratio was always strongly male biased. Mate acquisition probability of females was rather constant and independent of aggregation size, as predicted by an ideal free distribution. Moreover laboratory experiments showed that both multiple mating and rearing density little affected female fecundity, suggesting ideal free distribution of females in terms of reproductive success. On the other hand, mate acquisition probability of males was higher in larger aggregations, where more receptive females were available. This male discrepancy from an ideal free distribution was similar to the patterns predicted by an ideal free distribution under perceptual constraints (Abrahams, 1986), but not by that under unequal competitive ability.  相似文献   

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