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131.
Steven L. Lima Patrick A. Zollner Peter A. Bednekoff 《Behavioral ecology and sociobiology》1999,46(2):110-116
In socially feeding birds and mammals, as group size increases, individuals devote less time to scanning their environment
and more time to feeding. This vigilance “group size effect” has long been attributed to the anti-predatory benefits of group
living, but many investigators have suggested that this effect may be driven by scramble competition for limited food. We
addressed this issue of causation by focusing on the way in which the scan durations of free-living dark-eyed juncos (Junco hyemalis) decrease with group size. We were particularly interested in vigilance scanning concomitant with the handling of food items,
since a decrease in food handling times (i.e. scan durations) with increasing group size could theoretically be driven by
scramble competition for limited food resources. However, we showed that food-handling scan durations decrease with group
size in an environment with an effectively unlimited food supply. Furthermore, this food-handling effect was qualitatively
similar to that observed in the duration of standard vigilance scans (scanning exclusive of food ingestion), and both responded
to changes in the risk of predation (proximity of a refuge) as one might expect based upon anti-predator considerations. The
group size effects in both food-handling and standard scan durations may reflect a lesser need for personal information about
risk as group size increases. Scramble competition may influence vigilance in some circumstances, but demonstrating an effect
of competition beyond that of predation may prove challenging.
Received: 22 September 1998 / Received in revised form: 1 February 1999 / Accepted: 14 February 1999 相似文献
132.
David J. Able 《Behavioral ecology and sociobiology》1999,46(6):423-428
Darwin predicted that scramble competition for access to reproductive females would result in sexual dimorphism of locomotory
structures, but direct evidence for this is extremely rare. I examined the relationship between variation in tailfin size
and mating success in a field and laboratory study of red-spotted newts, Notophthalmus viridescens. Over three breeding seasons, male tailfin size was positively correlated with variation in male amplexus frequency, and
indirectly correlated with male insemination frequency. In a laboratory study, I confirmed that males' ability to capture
females is affected by variation in tailfin size. This is the first study to show that naturally occurring variation in male
locomotory structures affects male mating success. It corroborates the prediction that scramble competition leads to sexual
selection on locomotory structures and, potentially, to dimorphism in these structures.
Received: 16 April 1999 / Received in revised form: 16 May 1999 / Accepted: 12 June 1999 相似文献
133.
Fertility signaling in queens of a North American ant 总被引:3,自引:0,他引:3
In most species of advanced eusocial insects, the partitioning of reproduction between nestmates is thought to be regulated
by means of primer pheromones or other chemical cues, which presumably influence the behavior of co-queens and workers such
that they maximize their own inclusive fitness. Here we show that in multi-queen colonies of the Nearctic ant, Leptothorax sp. A, physical dominance in concert with chemical cues, which signal the ovarian development of a queen, are used to control
reproduction of competing queens and to influence worker behavior. The analysis of ranks obtained during two fighting periods
in the annual colony cycle revealed a strong link between individual aggressiveness of a queen and her fertility. During the
adoption of newly mated queens in autumn, the resident, egg-laying α-queen was more likely to start aggression first and keep
her high rank position compared to the fighting period after hibernation. We suggest that this is proximately caused by the
α-queen having much stronger developed ovaries in autumn than the young queens, whereas after hibernation, the ovaries of
all queens are similarly inactive. Interactions during the first weeks after the end of hibernation and intrinsic, individual
differences in aggressiveness appear to be crucial for the dominance rank achieved later. Queens which were allowed to become
fertile when their nestmate queens still were kept under prolonged hibernation, were immediately socially dominant over the
latter when all queens were reunited, though no aggression occurred. In another experiment, queen antagonism was prevented
by spatial separation in different parts of the same nest and all queens began to lay eggs. Workers stayed preferentially
with queens with high actual fecundity rather than with those which had had high social status before separation. This and
further evidence suggest that ovarian status is communicated, most likely by a chemical cue perceived by co-queens and workers,
affects the direction of their aggressive behavior, and allows them to discriminate among queens.
Received: 5 May 1998 / Accepted after revision: 29 August 1998 相似文献
134.
Mark D. E. Fellowes Steve G. Compton James M. Cook 《Behavioral ecology and sociobiology》1999,46(2):95-102
The populations of many species are structured such that mating is not random and occurs between members of local patches.
When patches are founded by a single female and all matings occur between siblings, brothers may compete with each other for
matings with their sisters. This local mate competition (LMC) selects for a female-biased sex ratio, especially in species
where females have control over offspring sex, as in the parasitic Hymenoptera. Two factors are predicted to decrease the
degree of female bias: (1) an increase in the number of foundress females in the patch and (2) an increase in the fraction
of individuals mating after dispersal from the natal patch. Pollinating fig wasps are well known as classic examples of species
where all matings occur in the local patch. We studied non-pollinating fig wasps, which are more diverse than the pollinating
fig wasps and also provide natural experimental groups of species with different male morphologies that are linked to different
mating structures. In this group of wasps, species with wingless males mate in the local patch (i.e. the fig fruit) while
winged male species mate after dispersal. Species with both kinds of male have a mixture of local and non-local mating. Data
from 44 species show that sex ratios (defined as the proportion of males) are in accordance with theoretical predictions:
wingless male species<wing-dimorphic male species<winged male species. These results are also supported by a formal comparative
analysis that controls for phylogeny. The foundress number is difficult to estimate directly for non-pollinating fig wasps
but a robust indirect method leads to the prediction that foundress number, and hence sex ratio, should increase with the
proportion of patches occupied in a crop. This result is supported strongly across 19 species with wingless males, but not
across 8 species with winged males. The mean sex ratios for species with winged males are not significantly different from
0.5, and the absence of the correlation observed across species with wingless males may reflect weak selection to adjust the
sex ratio in species whose population mating structure tends not to be subdivided. The same relationship is also predicted
to occur within species if individual females adjust their sex ratios facultatively. This final prediction was not supported
by data from a wingless male species, a male wing-dimorphic species or a winged male species.
Received: 27 July 1998 / Received in revised form: 11 January 1999 / Accepted: 16 January 1999 相似文献
135.
A possibility of introducing alien cladoceran species into the pelagial zone of mesotrophic Lake Glubokoe has been estimated. For this purpose, observations have been performed on the cohorts of alien species (Daphnia magna and Simocephalus exspinosus) and aboriginal species (Daphnia hyalina and Diaphanosoma brachyurum). The results show that competition is a factor preventing the introduction of weak competitors, such as D. magna, but admitting stronger competitors, e.g., S. exspinosus. Competition in the lake may influence not only the species structure of the zooplanktonic community, but also its vertical distribution. 相似文献
136.
This study examines the effects of different risks of sperm competition upon ejaculate characteristics in the moth Plodia interpunctella. In this short-lived species, females will remate and thus generate sperm competition, while males have a limited sperm supply. We therefore predict males to have evolved prudence in ejaculate allocation and investigate the effects of (1) rival male presence, (2) female mating history and (3) female age, upon the ejaculation of eupyrene (fertilizing) and apyrene (non-fertile) sperm numbers. We found no effect of the presence of rival males upon ejaculate characteristics, and conclude, due to the mating system of P. interpunctella, that rival males do not represent a proximate risk of sperm competition. We controlled female mating history by allowing females to receive different and predictable numbers of sperm which they then store for at least 7 days. In subsequent matings (7 days later) we found that new males ejaculated significantly more eupyrene sperm to females that had previously received larger numbers of sperm. We conclude that males increase numbers of eupyrene sperm to maintain success in sperm competition with rival sperm already in storage in the female. We found no effect of female mating history upon the ejaculation of apyrene sperm. Female age, however, had a significant negative effect upon both sperm types. We discuss these results in relation to sperm competition theory and apyrene sperm function. 相似文献
137.
When endoparasitoid wasps oviposit into hosts which have already been parasitized (= superparasitism), this results in potentially
lethal interlarval competition. For solitary species, the decision to lay additional eggs should therefore be based on the
probability of superparasite survival in any superparasitized host. In this study, in vitro contests staged between three larval instars of Venturia canescens Grav. (Hymenoptera: Ichneumonidae) reveal that the age difference between competitors affects the outcome of interlarval
competition. Three parameters were used to assess parasitoid performance: the number of fights initiated, the number of bites
inflicted, and the duration of each bite. When fighting takes place between two first instars, then both competitors were
found to be evenly matched. However, at greater age differences, first-instar competitors appeared to win more fights than
their larger second instar rivals. The advantage shown by younger competitors is most pronounced in contests staged between
first and third instar larvae. These findings are consistent with the increasingly high levels of conspecific superparasitism
shown by V. canescens in the first 5 days after initial host attack, suggesting that this parasitoid can deploy her use of deliberate superparasitism
in an adaptive way.
Received: 13 December 1995/Accepted after revision: 5 March 1996 相似文献
138.
We tested the effect of different algal (Chlorella vulgaris) levels and inoculation densities on the outcome of competition between the rotifers Euchlanis dilatata and Brachionus patulus. The experiment was performed in 36 transparent jars, each with 20 ml of a test medium. We used three Chlorella levels: 0.75 × 106, 1.5 × 106, and 3.0 × 106 cells/ml. For each algal level, we used five different ratios of initial inoculation density. The population growth experiments were terminated after 19 days. Regardless of inoculation densities, an increase in food level resulted in an increased population abundance of both rotifer species. Regardless of food concentration,E. dilatatawas able to outcompete B. patulus at all inoculation densities when grown together. However, when Chlorella was offered in low concentration and there was a higher ratio of Brachionus to Euchlanis at the onset of the experiment, both rotifer species coexisted in more or less equal densities until the end of the experiments. When the food level was enhanced, E. dilatata totally eliminated B. patulus. The rate of population growth ranged from 0.002 to 0.578 for B. patulus and from 0.006 to 0.447 for E. dilatata. The results are discussed with respect to the factors influencing the outcome of competition between species. 相似文献
139.
Female ornaments in species with conventional sex roles often indicate individual quality, but the evolutionary forces maintaining
them are less clear. Sexual competition for breeding opportunities may represent an important role for female signals, especially
in polygynous species, but there is little experimental evidence for this. The wing patch size (WPS) of female collared flycatchers
indicates age and body condition and predicts social mating patterns. We challenged nest-building females with decoy females
of varying WPS and found that the aggressive response of residents increased with decoy WPS, suggesting a role for this female
ornament in territorial competition. Our results explain why female WPS predicts territorial distances when mated to a polygynous
male and indicate that the role of WPS in female competitive interactions is similar to that in males of the same population. 相似文献
140.
环境服务业对于减轻环境污染、改善生态环境、促进环境与经济、社会协调发展具有重要意义。研究建立了环境服务业核心竞争力评价指标体系.对11个污水处理厂开展调研研究.运用层次分析法评价污水处理服务业的核心竞争力,旨在为提高环境服务业的社会经济和环境综合效益提供理论借鉴。 相似文献