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Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a major polyphagous pest with the potential to seriously damage various crops. A better understanding of FAW's performance on different hosts may help to predict which plants will be attacked when the preferred host is absent, and facilitate the development of effective pest management practices. We compared the larval performance of FAW fed on maize with that of FAW fed on potato and tobacco, which are important crops in China, using an age-stage two-sex life table and adult female oviposition preference experiments. In cage experiments with potato, tobacco, or maize as the host, FAW reared on maize exhibited the strongest performance with shorter developmental time in the larval stage, longer longevity, and a higher reproductive rate in adults. Females oviposited on maize in preference to potato or tobacco. Compared with larvae fed on maize, those fed on potato and tobacco exhibited significantly lower survival, with only 31.61% and 8.13% developing to the adult stage, respectively. Several life table parameters, including the mean generation time (T), net reproductive rate (R0 ), finite rate of increase (λ), and intrinsic rate of natural increase (r) were negatively affected in FAW fed on potato and tobacco. Our results support the preference-performance hypothesis, that is, that herbivore females maximize fitness by choosing host plants associated with strong larval performance. Although larvae and adults performed poorly on potato and tobacco, their offspring will be capable of establishing populations on them, posing a potential threat to these crops in China.

The life table of the indigenous Neoseiulus californicus was studied at different temperatures and 65 ± 5% relative humidity under conditions of 16 h light : 8 h dark (LD 16:8). The total developmental period from egg to adult varied from 3.0 to 14.0 days at 15 to 35°C. Survival to adulthood ranges from 86.21 to 93.94%, with the highest rate at 25°C. The lower threshold temperature from egg to adult stages of females and males was 10.84 and 10.72°C, respectively, and the thermal constant was 57.14 degree-days (DD) for females and 56.18 DD for males. Total number of eggs laid by each female was the highest (70.38 eggs) at 25°C, whereas average daily fecundity was the highest (3.69 eggs/female/day) at 30°C. The net reproductive rate was the highest (48.49) at 25°C and lowest (26.18) at 30°C. Mean generation time decreased from 19.04 to 11.47 days with increasing temperature from 20 to 30°C. Both intrinsic rate of natural increase (0.284) and finite rate of increase (1.32) were maximum at 30°C. Adult longevity was the highest (42.75 days for females and 32.60 days for males) at 20°C and lowest (22.70 days for females and 15.30 days for males) at 30°C. Sex ratio was female biased and was the highest (78.08) at 25°C and lowest (70.24) at 30°C. Developmental data of five constant temperatures, temperature thresholds and thermal requirements may be used to predict the occurrence, number of generations and population dynamics of N. californicus as an important biocontrol agent of Tetranychus urticae.

We used data on number of carcasses of wildlife species sold in 79 bushmeat markets in a region of Nigeria and Cameroon to assess whether species composition of a market could be explained by anthropogenic pressures and environmental variables around each market. More than 45 mammal species from 9 orders were traded across all markets; mostly ungulates and rodents. For each market, we determined median body mass, species diversity (game diversity), and taxa that were principal contributors to the total number of carcasses for sale (game dominance). Human population density in surrounding areas was significantly and negatively related to the percentage ungulates and primates sold in markets and significantly and positively related to the proportion of rodents. The proportion of carnivores sold was higher in markets with high human population densities. Proportion of small-bodied mammals ( 10 kg) decreased as human population density increased. We calculated an index of game depletion (GDI) for each market from the sum of the total number of carcasses traded per annum and species, weighted by the intrinsic rate of natural increase (rmax ) of each species, divided by individuals traded in a market. The GDI of a market increased as the proportion of fast-reproducing species (highest rmax ) increased and as the representation of species with lowest rmax (slow-reproducing) decreased. The best explanatory factor for a market's GDI was anthropogenic pressure-road density, human settlements with >3000 inhabitants, and nonforest vegetation. High and low GDI were significantly differentiated by human density and human settlements with >3000 inhabitants. Our results provided empirical evidence that human activity is correlated with more depleted bushmeat faunas and can be used as a proxy to determine areas in need of conservation action.

a volume of essays on topics in demography honoring Paul demeny would be incomplete without asking why large parts of the european civilization that produced Paul, a gentleman and a scholar in the finest sense of both words, have decided, through the aggregate decisions of women and men, to commit gradual “demographic suicide.” one would think that potential mothers and fathers, facing the promise of peace and relative prosperity, would choose to have children. But, puzzlingly, many people across europe are choosing to have fewer children than will produce stable, much less growing, populations. demography is destiny. the consequences of shifts in fertility (even as moderated or even partially reversed in the future) will have substantial consequences on many aspects of life: aging, health care costs, marital and family relationships, labor markets, immigration, the fiscal sustainability of social insurance programs, and schooling. if anything like the current fertility trends persists, the outcome will have profound consequences for what it means to be a “nation” and what are acceptable social relationships within a nation-state. Current projections of the rate of natural increase imply either unsustainably large reductions in the working-age population or substantially higher levels of the influx of “non-nationals” (or a little of both). the fact that women and men are making choices that result in lifetime childlessness must be symptomatic of a revolution in human affairs. leaving a posterity has, for thousands of years of human history, been an integral part of the very definition of prosperity and happiness for the typical person. those who remained childless—priests and nuns, monks and eunuchs—were recognized as choosing radically different paths to human meaning and happiness or were regarded as unfortunate.

To test the hypothesis of bottom-up regulation of appendicularians under high food conditions that occur during blooms, an experiment including measurements of fecundity, hatching success, and mortality at different quantity and quality of food was performed on Oikopleura dioica. Food level and fecundity were positively correlated. There was little effect of food on adult mortality, although higher food levels significantly decreased successful juvenile development. The positive effect of increased food concentration on fecundity was offset by a negative effect on hatching success; hence, the variance in quality and quantity of food explored in this study had little effect on the intrinsic rate of natural increase.

The maize orange leafhopper, Cicadulina bipunctata is a serious pest of forage maize in East and Southeast Asia. In temperate Japan, the occurrence of this leafhopper fluctuates widely among years. Here, we examined effects of climatic factors (temperature, precipitation and sunlight) on the occurrence of C. bipunctata. Seasonal occurrence of adult C. bipunctata in a census field from July to August, when forage maize was most susceptible to the pest, could be described by a simple exponential function with two parameter: estimated density of C. bipunctata on 1 July (N 0) and intrinsic rate of natural increase (r) for each year. Forward stepwise multiple regression analysis using seasonal occurrence data from 2004 to 2009 detected positive contributions of average temperatures in the previous December and February and a negative contribution of total precipitation during the previous winter to N 0. The analysis also indicated that average temperature in July of the current year and N 0 contributed positively and negatively to r, respectively. These results indicated that high temperature and little precipitation during winter and high temperature in early summer induced high occurrence of C. bipunctata in summer. A prediction model based on these factors supported the actual seasonal occurrence in 2010, suggesting that this prediction model is applicable to C. bipunctata forecasting. The prediction model indicated that further global warming in the future is likely to cause further outbreaks of C. bipunctata.

It has been argued that cities grow mostly by net in-migration and it has also been argued that they grow mostly by their own natural increase. Kingsley Davis finds that cities in the European industrial revolution grew mostly by in-migration but cities of the contemporary less-developed countries are growing mostly by their own natural increase. The case for their growth by migration was expressed as far back as Sussmilch who showed that deaths exceeded births in the principal cities of Europe so that without in-migrants cities would decline. The same view has been developed by Fischer and Wrigley. Most recently Sharlin finds the contrary for the cities of Europe. He adduces evidence that the population native to the city did replace itself and that the excess of deaths over births that appeared in the overall statistics was due to temporary residents especially tradesmen and servants who had no chance to marry but whose deaths would be counted as urban if they died in the city. This paper studies the contributions of the two components of city growth under various hypothetical conditions. It starts from the simple notion that when there is no city population there can be no natural increase and during the time after a city is established but still small its births cannot be numerous. At the other extreme when the country is mostly urbanized there is little rural population left to migrate to cities. Between these two extremes there must be a moment in the course of urban evolution when natural increase begins to exceed in-migration. The model that follows establishes this moment in terms of three parameters: urban rate of natural increase u rural rate of natural increase r and rate of net out-migration from the countryside m. The discussion starts with a special case in which u = r then goes on to arbitrary fixed values of u r and m and finally presents a result for arbitrary functions of time u(t) r(t) and m(t). The first case with u = r can be solved in commonsense terms; distinguishing u from r the urban rate of population increase from the rural requires a pair of differential equations. (excerpt)

The chronic effect of p-nonylphenol on survival and reproduction for two generations of the freshwater cladoceran Daphnia galeata was examined by life table experiments. The effects on survival and reproduction were used as the intrinsic rate of natural increase, r, with the Euler-Lotka equation and were analyzed with a simple mathematical model (a power function). The population-level EC(50), the concentration of a substance that reduces the intrinsic rate of natural increase by 50%, was estimated as 65.2 microg/L for the first generation and 81.5 microg/L for the second generation. No transgenerational effect that reinforces adverse responses in the offspring generation has been detected. From a 48-h immobility test an acute LC(50) was estimated to be 60.8 microg/L. The acute LC(50) is a good indicator of the chronic population-level effects of this chemical to this species.

In order to evaluate population-level effects of p-nonylphenol on a cladoceran zooplankton (Daphnia galeata), the chronic effects on survival and reproduction were estimated with partial life table tests, which examined responses in life history characters until 3 weeks after birth. The observed responses in survival and reproduction were converted to reductions of the intrinsic rate of natural increase r. The population level EC50, which is defined as the exposure concentration that reduces r by 50%, was estimated as 16.1 μg l−1. In order to examine the extent to which the population-level effect in terms of r is influenced by extra mortality in nature, which is induced by predation, starvation, etc., sensitivity (elasticity) measures of the intrinsic rate of natural increase to reductions in age-specific survival and reproduction were calculated under hypothetical predation schemes. The sensitivities of the intrinsic rate to changes in survival and reproduction invariably decline rapidly after the onset of reproduction irrespective of predation schemes. This implies that partial life cycle tests until 21 days after birth can provide reliable estimates of the population-level effects.

Effects of temperature on population parameters and the intrinsic rate of natural increase of the leafminer, Liriomyza sativae Blanchard, were studied at constant temperatures, 15, 20, 25, 30 and 3593 80% RH and a photoperiod of 12:12 (L:D) in the laboratory with Phaseolus vulgaris as the host plant. Developmental time of the immature stage decreased from 38 d at 15C to lld at 3593 Regression equations relating temperature (t) to development rates (y) for egg, larval and pupal stages, were y = 1.7862t - 13.841, y = 1.162t - 4.946 and y= 0.634t - 5.146, respectively. Longevity of female adult decreased from 20 d at 15°C to 9 d with temperature up to 35C The most favorable temperature range for reproduction was 20°C - 30oC in which the fecundity ranged from 158 to 282 eggs per female. The lowest total mortality was 9% at 25oC and the highest was 49% at 35 93 High intrinsic rate of natural increase (rm) was 0.27 and high net reproductive rate (R0) was 116.8 at temperature range between 25 t and 30 t indicating that this range was optimal for population growth and that population density might increase 117 times per generation under this temperature condition. Mean generation time (T) and time for population to double (t) decreased as temperature increased, showing a negative linear trend with temperature. The relationship between finite rate of increase (A) and temperature, however, was a positive linear regression.

Inbreeding depression may induce rapid extinction due to positive feedbacks between inbreeding depression and reduction of population size, which is often referred to as extinction vortex by inbreeding depression. The present analysis has demonstrated that the extinction vortex is likely to happen with realistic parameter values of genomic mutation rate of lethals or semilethals, equilibrium population size, intrinsic rate of natural increase, and rate of population decline caused by nongenetic extrinsic factors. Simulation models incorporating stochastic fluctuations of population size further indicated that extinction by inbreeding depression is facilitated by environmental fluctuations in population size. The results suggest that there is a positive interaction between genetic stochasticity and environmental stochasticity for extinction of populations by inbreeding depression.

An animal's life history can be summarized by key variables that account for its life course from conception to death. Biological parameters that are of interest relate to reproductive effort and developmental rates (e.g., gestation length, neonatal weight, prenatal and postnatal growth rates, weaning age, and weaning weight) and the rate of reproduction (e.g., age at first and last reproduction, interbirth interval, the number of offspring per litter, birth rate, and the intrinsic rate of natural increase [rmax]). The rather obvious fact that such variables differ from species to species and from individual to individual has been the subject of much interest since the late 1960s, following the observation that species seem to be arranged in a spectrum that ranges from small animals that breed rapidly and develop early, have many young per litter, and have short lives, to large animals that breed slowly and develop late, have few young per litter, and have long lives. © 1998 Wiley-Liss, Inc.

Six monitoring plots were established in the northern part of West Java, Indonesia, to clarify the factors that influence population fluctuations of the whitefly,Bemisia tabaci. Yellow sticky traps were used to monitor adult populations. To examine the relationship between the population fluctuations and the quantity of food resources, the quantity of food resources ofB. tabaci (i.e. soybean and mung bean) was also investigated routinely in each subdistrict where the experimental plot was located. The maximum number of adults per trap in each sowing season showed a similar noticeable seasonal trend in all experimental plots. Climatic factors did not have a major role to play in population fluctuations. The number of adults per trap in each experimental plot tended to increase when the quantity of food resources in each subdistrict increased. The changes of the quantity of food resources seemed to influence the population fluctuations. It is suggested that the operation of regulatory processes in population density is influenced largely by both the distance between habitat patches and the amplitude of temporal fluctuations of the quantity of food resources. An explanation for why the time lag between fluctuations of the quantity of food resources and the number of individuals ofB. tabaci occurred is discussed. Based on their flight ability and intrinsic rate of natural increase,B. tabaci is considered not to be a serious pest in the environment where the host plants are grown discontinuously in time and space.

In a study of the performance of Aphis fabae Scop. on 6 British and 3 Polish cultivars of Vicia faba L., the aphid showed a poor mean relative growth rate (MRGR) on the Polish cultivar Hangdown Bialy (p = < 0.05). Measurements of fecundity, the intrinsic rate of natural increase (r m ) and MRGR were obtained on a large number of individual plants. Correlations between MRGR and both r m or fecundity for individual plants across cultivars were not significant. Although within cultivars, individual plants of Aquadulce and Relon showed significant positive correlations of aphid MRGR on fecundity and r m respectively, the two correlations accounted for less than 20% of the variation in MRGR and no such correlations were found for the other seven cultivars. Although MRGR showed the highest residual variance (in relation to the mean) of the three performance indicators assessed, it nonetheless proved to provide the best discrimination between the cultivars tested. It is suggested that this is because MRGR is less subject to 'maternal influence' than fecundity or r m .

Cohorts of the epiphytic marine copepod Tisbe furcata were chronically exposed to copper in life-table experiments to test whether ecologically relevant impacts can occur at sublethal concentrations. Data on fecundity, longevity, and rate of development were used to calculate rm – the intrinsic rate of natural increase. Acute toxicity tests (96-h LC50 tests) were done to compare the concentrations of copper affecting individual lethality and population biology. The LC50 value for Tisbe furcata nauplii was 2.8 μM copper (178 μg/L). The results from the life-table experiments show that 0.9 μM copper (32% of LC50) can cause significant negative effects on demographic parameters (total production of nauplii, life span, and reproductive period for fertile females) and reduce the percentage of fertile females leading to a 61% reduction of rm. However, rm was still positive at 0.9 μM copper, and the net reproductive rate (Ro) indicated a fivefold increase in population size from one generation to the next. Although there were no significant effects of copper at 0.5 μM (18% of LC50), there was a negative trend in almost all the demographic parameters, indicating that the observed 10% reduction of rm at this concentration was an effect of copper. For the substances tested so far with both acute LC50 tests and life-table experiments, rm was not reduced at concentrations below LC50/10. When life-table experiments are used as part of environmental hazard assessments, concentrations below LC50/10 should be tested to detect substances that are potentially harmful to the environment at sublethal concentrations, rather than testing concentrations close to LC50.

In less than 3 years (1986-1988) Frankliniella occidentalis, imported from USA, had spread throughout Europe. It is a polyphagous Thysanoptera which causes important yield loss in greenhouses, in both vegetable and ornamental crops. Ho Never, insufficient data are available on its basic biology. The purpose of this work was thus to establish its life table. A cohort of 95 individuals were observed day during their whole lifetime. The development time is short, 14.2 days, and no significant difference has been observed between males and females. The mean fecundity is high, as 43.17 larvae were produced by a single female. The intrinsic rate of natural increase is 0.140, meaning that the theoretical population may double in 4.94 days.

The temporal stability of estimates of demographic behaviour for a sample population of the tropical rainforest gymnosperm Araucaria cunninghamii was analysed using a stage-classified (Lefkovitch) matrix model. Previously published life-table analyses, which used only 2 years of held data (1975–77), were compared with life-table analysis based on a further 5 years of field data for growth and survival (1977–82). The new analysis calculated the finite rate of natural increase, λ, as 1.009 ± 0.077. This value is closer to the theoretical value of 1.0 for a stable population than is the value calculated on the basis of only 2 years of field data (1.021 ± 0.093). However, the two estimates are not significantly different from each other or from a value of 1.0. Despite the similarity of estimates for λ, the life-table analysis based on 5 years of data showed some marked differences from the earlier analysis. Revised growth and survival rates imply a slower progression to reproductive maturity and shorter reproductive life for A. cunninghamii. The predicted stable stage distribution (SSD) showed a better fit to the initial stage distribution (ISD), and bulges in the frequency distribution for large trees can be explained by the varying rates at which individuals grow from one stage to the next. The relative contributions of survival, growth and fecundity to the observed population growth rate (elasticity) remained similar for both analyses. Survival rate contributes most significantly to the achieved population growth rate, and this appears typical of long-lived plant species. However, the pattern of elasticities across size-classes changed for the new analysis and identified different critical life history stages from those recorded previously. Elasticity is proposed as a measure for classifying species using the competitive (C), stress-tolerant (S) and ruderal (R) model of plant strategies.

The stream-dwelling harpacticoid copepod Bryocamptus zschokkei was reared in the laboratory at 3.5”, lo”, 15”, 18”, and 20°C with naturally conditioned leaf disks as a food source. Egg and naupliar development rates were fastest at 18°C. A complete life table experiment was conducted at 18°C. Females were longer-lived than other copepods and produced eggs continuously until death. The intrinsic rate of natural increase (r) and the net reproductive rate (R,) were found to be lower than those of most copepods. Reproduction is probably continuous throughout the year in the stream, since animals reproduced in the laboratory at the extreme temperatures experienced by the natural population. Since most copepods reproduce seasonally, the annual intrinsic rate of increase of B. zschokkei may be comparable to those of other copepods.

1. Life tables were constructed for natural populations of a cicada. Mogannia minuta, during an outbreak in sugarcane fields at Okinawa to determine possible reasons for the outbreak. 2. The highest mortality during the life cycle was during the beginning of the nymphal stage, and was mainly due to predation by ants. 3. The estimated rate of natural increase based on a survivorship—fecundity schedule in sugarcane fields was near unity, but during the increasing period the rate was estimated to be substantially higher than unity. 4. The rate of natural increase in Miscanthus-grassland was slightly negative, suggesting that the grassland population was maintained by immigration of adults from sugarcane fields. 5. Escape from predation may be the main cause of the special distribution pattern and the maintenance of extraordinarily high densities for many years.

The reproduction of an undescribed species of the genus Chiloplacus from the Canadian High Arctic was studied at 10°C. The mean number of eggs laid per female was 317.8±89.2, of which 46.8±7.8% hatched, resulting in net reproduction of 148.8 juveniles per female. Beginning as new-laid eggs the observed maximum age attained was 99 d, and the calculated generation time was 52.6 d. Egg-laying began 26 d after hatching and the reproductive period spanned 56 d. The intrinsic rate of increase was 0.095, and the first 12 reproductive days contributed 80.587% of the value of r. When r = 0.095 the stable age distribution was calculated to be 91.5% immatures and 8.5% adults. Chiloplacus sp. is intermediate in fecundity for free-living soil nematodes. lying between the generally highly fecund Rhabditidae on the one hand, and the much less fecund Dorylaimidae on the other. Chiloplacus sp. lays a larger portion of its eggs early in the reproductive period at 10°C than do species from warmer environments, suggesting that reproduction of Chiloplacus sp. is low-temperature compensated.

A Spanish language family planning education program utilizing the dynamics of values clarification has been designed and implemented in the state of Oaxaca, Mexico. The design of the program features three basic personality identification activities to help individuals identify other dimensions of adult life expression than child rearing. In addition, a series of simple and precise scenarios specifically related to family planning are presented. Each scenario is accompanied by a set of valuing questions that direct the learner to respond to the scenario. The activity booklet is entitled, "Clarification De Valores En La Planificacion Familar." The booklet requires the learner to make responses to the learning materials. Responses are then used as a basis for inferring that people are comprehending and above all personalizing knowledge about themselves and their culture and family planning. The program is cross cultural and can be used in Spanish speaking communities in the U.S. Its English language form can be used with English speaking target populations. Statistical analysis of seven critical categories of the program indicated that the shifts in attitudes from pre-to post-values, whether positive or negative (desirable or undesirable), were not significant at the .05 level of confidence. It should, however, be noted that small shifts in the rate of natural increase, or rate of natural decrease for population growth can have a dramatic effect on population growth when multiplied by time.A Spanish language family planning education program utilizing the dynamics of values clarification has been designed and implemented in the state of Oaxaca, Mexico. The program design features 3 basic personality identification activities to help individuals identify other dimensions of adult life expression than childrearing. In addition, a series of simple and precise scenarios specifically related to family planning are presented. Each scenario is accompanied by a set of valuing questions which direct the learner to respond to the scenario. The activity booklet is entitled "Clarificacion De Valores En La Planificacion Familiar." The booklet requires the learner to make responses to the learning materials. Responses are then used as a basis for inferring that people are comprehending and above all personalizing knowledge about themselves and their culture and family planning. The program is cross-cultural and can be used in Spanish-speaking communities in the US. Its English language form can be used with English-speaking target populations. Statistical analysis of 7 critical categories of the program indicated that the shifts in attitudes from pre- to post-values, whether positive or negative (desirable or undesirable) were not significant at the .05 level of confidence. It should, however, be noted that small shifts in the rate of natural increase, or rate of natural decrease for population growth can have a dramatic effect on population growth when multiplied by time.

The author investigates the possible role of future immigration on Canadas demographic processes. It is suggested that immigration will have an important role in light of declines in the rate of natural increase as well as trends in demographic aging. The implications of future immigration for both migration and social policy are considered with a focus on changes in the cultural and ethnic composition of the population resulting from immigration. (SUMMARY IN FRE AND SPA) (ANNOTATION)

The sex ratio changes in Sand martin populations, described in Persson (19876), will by definition act as a control loop to the ‘reproduction amplifier’ of the population. Age structure integrates the effect over a couple of years, thereby creating the specific time-lag of three to four years. One hypothesis of this paper suggests that these changes are intentional, a true feedback from the population level or the overall sex ratio. The main advantage of a feedback is to stabilize a system against parameter variations, in the present case primarily ‘catastrophic’ winter mortality and/or reproduction failure. In consequence the observed cycle is at least the by-product of an adaptation. If numerical values of r (the intrinsic rate of natural increase) and Tare introduced into the equations defining limit values of an age-structured model, its dynamic behaviour will be confined between diverging and damped oscillations, leaving a stable limit cycle as a very probable outcome. The disturbance creating a need for regulation may be epitomized as a variation of equilibrium levels. This variation must be dependent on African drought, and perhaps ultimately on the sunspot cycle (the second hypothesis of the paper). Regulation as an adaptation is created (and probably maintained) by means of group-selection; it has earlier been shown (Persson, 1978) that one prerequisite for group selection is at hand; the study population is virtually confined within the census area. The ‘vulnerability’ (Persson, 19873) of maximum populations complicates the picture. Additional vulnerability may result from a conflict between individual selection and group selection-young birds with high breeding fitness attempting double broods when they should not-that is injurious to perfect regulation.

The intrinsic rate of natural increase (rmax) is calculated for 58 primate species. It is found that this parameter is negatively correlated with body weight, so that larger primate species consistently have a lower rmax than do smaller species. Although there is no apparent link between the raw value of rmax and environmental predictability, a relationship between a high rmax, relative to body weight, and an unpredictable environment is found to exist. However, there is no relationship between a predictable environment and either the raw value of rmax, or the relative rmax. After body size effects are removed, rmax is not correlated with basal metabolic rate (BMR). Pre-natal maternal investment (MI) is found to correlate highly with BMR, even after the removal of body weight effects. MI does not correlate either with rmax or with environmental predictability. Diet appears to have little influence either on rmax on MI, but there is some indication that folivores have both a high relative rmax and a high relative MI. These results are discussed in the light of theories of life-history strategy evolution.

IN a recent article in this Review, Roger Price investigates the "onset of labour shortage" in French agriculture in the mid-nineteenth century.1 His main source of evidence regarding the existence and causes of the shortage consists of two inquiries conducted by government commissions in i866 and I870, respectively. This comment will review, and if possible clarify, the issues raised by Price. It will attempt to show that while the economic conditions of rural labour supply did indeed change around the middle of the century, neither the term "shortage" nor Price's analysis does them full justice. A significant part of the problem arises, it will also be argued, from uncritical use of evidence from one of the enqudtes.2 Price's argument, in brief, is that the years of the Second Empire witnessed a strong deterioration in agricultural profitability, at least in the commercial sector. Decades of easy profits gave way to a crisis. Although the period was one of movement towards freer international trade, the root of the problem can be traced to the markets for labour rather than those for output. Increasingly inadequate supplies of labour resulted, in turn, from what we can sum up as effects of modernization, a process which first drew substantial numbers of rural workers into urban employment and then aggravated the problem by lowering the rate of natural increase of the rural population itself. Although timing is not precisely specified in Price's argument, it may be inferred that the changes, which got under way in the i 850s, had their main impact on profit and rental incomes in the i 86os after agricultural prices stabilized. Landlords and operators of large commercial farms could respond to labour shortages in a number of ways. The former could reduce their direct involvement in farming, breaking up large holdings into a number of small tenancies or selling off the land piecemeal. The latter could modify their choice of techniques, their product mix, or both. It is somewhat difficult to tell whether, in Price's view, progressive responses outweighed passive ones or the other way round. Did regional disparities widen or narrow ? Was growth stimulated or slowed ? We are presented with alternative viewpoints and, presumably, left to choose. Before considering the nature of Price's evidence, it is necessary to set out a few specific points of clear-cut difference with him, because these matters have a direct bearing on the issues raised. First, while it is clear that the unfavourable

Simulation of the sterile insect release process was carried out based on a system which consisted of a logistic population model and Poisson-binomial model for normal, sterile and combined matings. From the results, relationship between the intrinsic rate of natural increase and the sterile vs. normal ratio necessary to attain eradication of the target pest species were presented. The effects of weakened sperm competitiveness and the increased number of matings per female were not so strong. On the other hand, a given rate of immigration could be a cause of failure of the eradication. A simple method to calculate relationship between hatchability and sterile vs. normal ratio was presented.

ummary Allometric laws which scale numerous biomechanical and physiological processes to size in mammals have long been recognized and widely used in biology. There is now sufficient evidence to suggest that those life history parameters such as growth and maximum rates of reproduction, which depend in part on metabolic rate, are also scaled to size. Data are presented which, coupled with a literature review, show that gestation time, growth rates, age at first reproduction, lifespan, the intrinsic rate of natural increase, birth rate, net reproductive rate and litter weight are allometrically scaled to size and are, in consequence, inter-related. The exponents of the scaling functions are similar in all mammalian orders but in some taxa such as the primates, the species grow slower, live longer and reproduce at a lower rate. For these taxa the differences in life history parameters can be explained by differences in brain size and an existing hypothesis that the maximum rate of neural tissue growth constrains the maximum rate of growth and development of the entire organism. It is then argued that because size scales the main life history parameters of mammals it should also be a central theme in ecology from the individual to the community level of organisation. Examples are presented to show that size is ubiquitous in ecology and accounts for most of the variation in life history parameters between species. Size scaling offers a method of reducing species of varying size to similar dimensions of time, space and rates of action. It is therefore fundamental in distinguishing those life history parameters which arise as a consequence of size, the first order strategies, from those that vary between populations and according to environmental circumstances, the second order strategies. From this approach should develop a broader biological synthesis in which genetic and physiological determinants will inevitably feature more centrally than they do in ecological and behavioural theory. Resume Les lois allometriques unissant les processus biomecaniques et physiologiques avec la taille chez les mammiferes ont ete reconnues depuis longtemps et largement utilisees en biologic Il y a maintenant assez de certitude pour suggerer que les parametres biologiques tels que croissance et taux maximal de reproduction, qui dependent partiellement du rendement metabolique, sont aussi fonctions de la taille. Les donnees presentees ici, couplees avec une revue de la litterature, montrent que la duree de gestation, le taux de croissance, l'âge a la premiere reproduction, la duree de vie, le taux intrinseque d'accroissement naturel, le taux de natalite, le taux de reproduction net et le poids de la portee sont en relation allometrique avec la taille et, par consequent, sont en interrelation.

The effects of continuous sublethal Co/sup 60/ radiation on the intrinsic rate of natural increase, r, was studied. An analysis was also made of the effects of radiation on the population attributes underlying r, namely, birth rate, b, death rate, d, and stable age-distribution. Each of 18 experimental populations was exposed to a different, continuous dose rate, ranging from 25 to 75 r/hr. The results showed that r decreased continuously as a nonlinear function of the dose rate (although st run. Concent a linear function of the square of the dose rate). The effects of increasing dose rate on the stable age- distribution were mainly a decrease in the proportion of individuals in the youngest age groups and an increase in the proportion of older individuals. The overall results indicate that the reduction of fecundity and fertility was due to direct effects of the radiation on the ovaries rather than to indirect, physiological effects. It was considered likely that dominant lethal chromosome aberrations were uitlmately responsible. Individual life expectancy at birth, or average life-span, was not greatly shortened by any of the dose rates employed. Furthermore, age-specific survival rates were not affected until late in reproductive life. Individual growth inmore » length increased with increasing dose rate. (TCO)« less

The primitive (single oviposition period) method for determining the finite rate of natural increase (Λ) of an insect species which lays all its eggs quickly is described, together with a summary of a more accurate method introduced by P. H. Leslie and L, C. Birch of calculating the infinite (infinitesimal) rate of increase (r) of any species. The parameter r is the natural logarithm of the parameter Λ. Two methods of simplifying this more accurate method are discussed and illustrated by six examples which are used to compare the results given by all four methods. The first modification of the Leslie-Birch method provides a means of representing a long oviposition cycle by a single figure so that the final calculation resembles the primitive single period method. The oviposition period is divided into a number of convenient unit periods, and using a table of weighting factors provided, the number of eggs laid in each of these unit periods is converted into the number of eggs required to be laid in the first of these unit periods of oviposition to make an equivalent contribution to the rate of increase. The equivalent oviposition figures for all the unit periods are summed to provide one figure which represents the observed egg number and pattern. The second modification provides a means of representing the observed egg pattern by a constant rate of oviposition. This requires the same table of weighting factors but also needs a series of charts which are provided. This method usually gives a good answer at the first attempt, whereas the first modification usually requires two trial and error solutions to give an accurate estimate of r and hence of Λ. Two of the examples show how the methods may be used for species for which information is scattered in the published literature. The minimum requirements for estimation of r are information on the length of the developmental cycle, the rate of egg output of adults, mortality of all stages and the sex ratio.

UP TO THIS POINT we have been considering the growth of population in the United States, but have not discussed its redistribution. For some parts of the country are growing while others are declining in population. Let us first review the main trends with respect to redistribution as revealed by the decennial census taken last year. I shall approach the subject by trying to identify those parts of the country which appear to be slated for growth, and those which evidence little growth potential, whatever happens to be their rate of natural increase. For, by and large, the place to invest in for many purposes is the place where population is growing. Because of the pressure for capital arising from foreign sources and because of our heavy taxation, I would expect interest rates to remain firm and probably to feel some upward pressure for several decades at least. I do not believe that profit rates will be affected by the slowing down of population growth in so far as profit depends upon risks and uncertainties. The slowing down of the rate of population growth should, however, reduce the significance of the growth factor for many industries unless they can devise new products and so start up on a new growth curve which is largely independent of population for a while. Perhaps television is a case in point. Even so, the profitinterest ratio should favor investment in equities, and this in turn should strengthen interest rates.

This study was undertaken to determine the effect of continuous low—level exposure to gamma radiation on a population of small mammals (Peromyscus maniculatus sonoriensis) in the laboratory. The average dose rate was slightly greater than 1 roentgen/day. One group was exposed as adults, with irradiation beginning when they were weaned (age 3 to 4 weeks); another group was the offspring of the irradiated adults, hence these animals were irradiated since conception. Descendants from 3 separate field populations were present in each group. The intrinsic rate of natural increase, r, was increased in animals irradiated as adults (r = .3574), as a result of an elevation of the instantaneous rate of birth, b, and a reduction of the instantaneous death rate, d. Animals irradiated since conception showed a lower intrinsic rate of natural increase (r = .1897) than the controls (r = .3134) due to a lower b and an increased d. Life span was shortened by irradiation. The average life expectance at birth, eo, was 22.18 ± 1.54 months for control females, 19.61 ± 1.99 for the females irradiated as adults, and 15.62 ± 1.58 for females irradiated some conception. Male life expectancy was greater in each group. The animals that survived irradiation during the pre— and postnatal stages had greater further life expectancy than individuals of equivalent age groups that had been irradiated only as adults. Age specific natality, mx, was reduced by radiation, both by lowering the maximum number of young per female and by shortening the reproductive life spans of females. Reduction was greatest in the animals since conception. There was evidence of hyperovulation in the group irradiated as adults. There was variation among the 3 field populations represented, both in reproductive capacity of control animals and in sensitivity to radiation. Among controls, the population from the lowest field elevation had the greatest intrinsic rate of natural increase. This population showed the least sensitivity to radiation, judged by the change in r. The greatest sensitivity to radiation was in the population from intermediate elevations. Field populations of Peromyscus living in favorable environments might withstand the degree of reduction induced by this level of radiation exposure. Field populations living under less favorable conditions possibly could not.

It is evident that the methods employed in human demography have much to offer for modern population ecology. The early work of Raymond Pearl and his associates on the computation of life tables for other forms of life besides man is well known, and it may be said that these pioneer studies did much to initiate all the later work in this field. Recently, Deevey ('47), impressed by the demonstrated value of life tables in human and laboratory population research, extended this technique by applying it to field observations and expressed the hope that students working in the field would, in the future, collect their data in such a way that they could be subjected to mortalitytable treatment. The studies to which we have thus briefly referred deal in the main with the construction of life tables, which summarize in a convenient form the degree of mortality according to age. If, in addition, it is possible to measure the degree of fertility, our information in regard to a particular species or population is greatly increased and we can apply the methods of analysis which are now commonly employed in the case of human populations. The development of this branch of population mathematics is principally due to A. J. Lotka, and the biologist will find convenient summaries of the theoretical