中小城市污水处理厂设计中应注意的几个问题

针对当前中小城市污水处理厂设计中存在的厂址选择不合理、处理工艺盲目求新求变、设备选择不切合实际等问题进行探讨，结合已建成污水处理厂运行实际进行分析，提出优化厂址选择、结合当地实际选择处理工艺、根据需要选择设备等解决问题的办法。     

The Time Invariance Principle,the absence of ecological chaos,and a fundamental pitfall of discrete modeling

This paper is to show that most discrete models used for population dynamics in ecology are inherently pathological that their predications cannot be independently verified by experiments because they violate a fundamental principle of physics. The result is used to tackle an on-going controversy regarding ecological chaos. Another implication of the result is that all dynamical systems must be modeled by differential equations. As a result it suggests that researches based on discrete modeling must be closely scrutinized and the teaching of calculus and differential equations must be emphasized for students of biology.     

Male lagoon gobies, <Emphasis Type="Italic">Knipowitschia panizzae</Emphasis>, prefer more ornamented to larger females

Female ornamentation may be directly sexually selected, by male choice or female competition, or occurs as the result of a genetic correlation, arising from sexual selection on males. However, increasing evidence supports the former hypothesis, suggesting that males actively choose their partner preferring traits indicative of female quality. In the lagoon goby, Knipowitschia panizzae, a polygynous species whose males perform parental care to eggs, body length and the size of a sex-specific yellow patch on the belly are known to be reliable indicators of female fecundity. In this paper, we tested, using dummies, the male’s mating preferences for female body and yellow belly patch sizes. The two experimental trials in which a single female trait was variable showed that males prefer a larger belly patch and a larger body size, indicating that both these characters are selected by male mate choice. However, when faced with dummies exhibiting an inverse combination of body and belly patch sizes (experiment 3), males significantly preferred the smaller ones with larger yellow belly patches. A calculation of dummy theoretical fecundity reveals that in the first two experiments, males would have received an immediate benefit from their choice in terms of egg number, whereas in the third one, males chose partners that would have provided them with fewer eggs. The male lagoon goby preference for females with larger belly patches, regardless of their size, suggests that this trait, in addition to indicating fecundity, conveys information about other aspects of female and/or egg quality.     

Females reward courtship by competing males in a cannibalistic spider

Despite widespread recognition that intersexual interactions shape reproductive strategies, studies of male competition do not typically include effects imposed by females. In cannibalistic redback spiders, escalated fighting between rival suitors is predicted, as males are unlikely to mate with more than one female, and strong first-male sperm precedence favours mating with virgins. In staged competitions for matings between size mismatched rivals, smaller males adopted an alternative sneaking strategy. However, despite initial agonistic interactions, larger males did not pursue or incapacitate smaller males. When inter-male competition occurred, females struck at males frequently, although strikes were rarely seen when males courted in the absence of a rival. After minimal fighting, larger males engaged in significant courtship (3 h) rather than killing inferior rivals. Prolonged courtship was favoured by female behaviour, as males that attempted rapid copulation (smaller, sneaking males) were cannibalised before mating was completed. This premature cannibalism significantly decreases paternity in redback spiders. Thus, significant features of male competitive behaviour (i.e. prolonged courtship by larger males) may be predicted with consideration of the female’s response to male reproductive strategies. Although the effect of females may be more subtle in systems without the extreme reversed size-dimorphism of redbacks, these results suggest that female interests should be explicitly considered when studying inter-male interactions.     

Phenotypic correlates and survival consequences of male mating success in lek-mating greater prairie-chickens (<Emphasis Type="Italic">Tympanuchus cupido</Emphasis>)

Female choice and male–male aggression are two modes of sexual selection that can lead to elaboration of male morphological and behavioral traits. In lek-mating species, male mating success is often strongly skewed, and it is puzzling why variation in male traits is still observed given directional female choice. If male traits correlated with reproductive success are honest signals of male quality, there may be survival costs associated with the expression of those traits. In this study, we examined whether morphological, behavioral, and territorial traits are correlated with male mating success and survival in the lek-mating greater prairie-chicken (Tympanuchus cupido). We introduce a novel application of multinomial discrete choice models for analysis of female mate choice behavior. We found that behavioral and territorial attributes showed 6.5 times more variability among males than morphological traits. Both display and aggressive behaviors were strong predictors of male mating success, suggesting that both female choice and male–male aggression were important in determining mating success among male greater prairie-chickens. Moreover, annual survival of male prairie-chickens was independent of mating success and male traits. Females appear to be choosing males based on behavioral traits where large variation exists between males (coefficient of variation >30%). Behavioral traits were the most important factor in determining mating success of male prairie-chickens, but the mechanism underlying this relationship is unknown. In the future, experimental manipulations of male hormones or parasite loads could bridge the proximate mechanisms and ultimate consequences of factors mediating male mating success in lek-mating grouse.     

Sex-specific reproductive behaviours and paternity in free-ranging Barbary macaques (Macaca sylvanus)

In a wide variety of species, male reproductive success is determined by contest for access to females. Among multi-male primate groups, however, factors in addition to male competitive ability may also influence paternity outcome, although their exact nature and force is still largely unclear. Here, we have investigated in a group of free-ranging Barbary macaques whether paternity is determined on the pre- or postcopulatory level and how male competitive ability and female direct mate choice during the female fertile phase are related to male reproductive success. Behavioural observations were combined with faecal hormone analysis for timing of the fertile phase (13 cycles, 8 females) and genetic paternity analysis (n = 12). During the fertile phase, complete monopolisation of females did not occur. Females were consorted for only 49% of observation time, and all females had ejaculatory copulations with several males. Thus, in all cases, paternity was determined on the postcopulatory level. More than 80% of infants were sired by high-ranking males, and this reproductive skew was related to both, male competitive ability and female direct mate choice as high-ranking males spent more time in consort with females than low-ranking males, and females solicited copulations mainly from dominant males. As most ejaculatory copulations were female-initiated, female direct mate choice appeared to have the highest impact on male reproductive success. However, female preference was not directly translated into paternity, as fathers were not preferred over non-fathers in terms of solicitation, consortship and mating behaviour. Collectively, our data show that in the Barbary macaque, both sexes significantly influence male mating success, but that sperm of several males generally compete within the female reproductive tract and that therefore paternity is determined by mechanisms operating at the postcopulatory level.     

Current analyses do not resolve whether extra-pair paternity is male or female driven

Recent studies question the importance of indirect genetic effects in explaining female benefits of extra-pair matings in socially monogamous species. Compiling data on 14 wild bird species, Arnqvist and Kirkpatrick (Am Nat 165:S26–S37, 2005) estimated the average direct cost in terms or reduced parental care to be an order of magnitude larger than the potential effect of genetic benefits. This study has sparked a debate regarding potential confounding factors but no consensus appears to have been reached. Here we focus on the implicit assumption that all individuals face the same selective pressures and argue that this assumption is probably too strong in most cases. Using a theoretical model we show that when the amount of resources that a male provides depends on territory quality, his physical condition or prospects for alternative breeding opportunities, a female may respond to such differences by altering her mating behaviour. Such confounding factors may lead to direct fitness effects that result in negative correlations between paternal care and paternity even if females that produce extra-pair young experience a net benefit. Negative correlations can also result when males forcefully seek copulations and females resist them. We discuss the studies included in the analysis in this light, and conclude that current analyses on the net selective pressures remain uninformative. In addition to considering average effects across individuals and species we suggest giving attention to individual differences and the influence of ecological factors such as territory quality and predation pressures on female mating behaviour.     

Supply and demand: causes and consequences of assortative mating in common terns <Emphasis Type="Italic">Sterna hirundo</Emphasis>

Although assortative mating is widespread among long-lived monogamous birds, the underlying mechanisms still remain unclear in many species. In this study, we analysed assortative mating by age and body mass in the common tern Sterna hirundo with special regard to mate choice decisions of newly paired birds. To assess whether assortative mating by age is an active decision involving either homotypic or directional preferences or rather a passive process due to restricted availability of potential mates, we analysed the influence of age-dependent arrival date and cohort size. Furthermore, we looked for direct benefits in terms of reproductive success. Common terns mated assortatively by age and arrival date but not by body mass at arrival. Assortative mating by age was age dependent and was detected mainly in younger birds, whereas birds older than 8 years rather re-paired with younger ones. The availability of same-aged mates was restricted by cohort size and arrival date. We found no general evidence for better reproductive performance of same-aged pairs. Instead, relative reproductive success was related to own age and the relative age of mate: It should be advantageous for any bird to acquire an old mate; hence, assortative mating by age seems to be beneficial only for old terns but not for young ones. Age-assortative mating in common terns occurred by both passive and active processes, which are not mutually exclusive. Our results do not indicate a homotypic but a directional preference and support the theory that high-quality (older/experienced) individuals tend to mate assortatively if same-aged mates are available, which leaves low-quality (young/inexperienced) individuals to mate among themselves.     

Male-male association patterns and female proximity in the guppy,Poecilia reticulata

If males differ in their ability to attract potential mates, and are able to perceive such differences, theory predicts they should distribute themselves in a manner that increases their probability of obtaining potential matings. The relationship between male-male association patterns and the proximity of females in social groups, however, remains virtually unexplored. Experimental analysis of this relationship in the guppy, Poecilia reticulata, demonstrates that in preference tests males showed a strong tendency to associate with other males that were further away from potential mates than they were themselves. Male guppies pursue a behavioral strategy that involves categorizing other males based on their proximity (and possibly relative attractiveness) to females, remembering the identity of such individuals, and using this information when choosing between other males as associates. Such a strategy may increase a male's chances of being the individual chosen by a female assessing nearby males.     

Copying and the repeatability of mate choice

Models of sexual selection by female choice require heritable variation in female mating preferences in order for sexual selection to operate. However, recent theoretical work shows that female preferences which are transmitted non-genetically can result in exaggeration of male ornamentation. Guppies exhibit both mate copying and considerable heritable variation in female preferences. I studied the importance of these phenomena by measuring repeatability of female mate choice, which acts as an estimate of the upper limit to which a feature may be heritable, and the incidence of mate choice reversal in paired-trial binary mate choice experiments. Mate choice was significantly repeatable except in the treatment where females were given the opportunity to copy a female that contradicted their original choice. Apart from this, I found no evidence that females copy the mate choice of others. The differences between males in ornamentation had no effect on the consistency of female mate choice or the probability that they would reverse their original choice decision (in both controls and the copying experiment). The interval between choice trials did not influence repeatability significantly, indicating that the independence of choice decisions is not related to the time interval between them. Received: 9 February 1996/Accepted after revision: 6 July 1996