Census Period Research Articles

Biodiversity and reduced extinction risks in spatially isolated rodent populations

Ecologists have rarely explored the potential influence of local (alpha) biodiversity on the stability and local extinction of spatially isolated populations. Twenty years of annual counts of a small, grazing rodent (Utah prairie dogs, Cynomys parvidens) from 20 different isolated local populations (colonies) in southern Utah, U.S.A. were analysed. These prairie dogs exhibited large fluctuations and repeated extinctions at individual colonies during the census period. Frequency of extinction at a colony declined dramatically as the number of locally occurring plant species increased. This pattern was not explained by differences among colonies in plant productivity, plant species composition, colony size, or variability in annual counts. Thus, lower extinction risk of consumer populations may be associated with greater resource diversity, and maintaining high local plant diversity may help sustain spatially isolated herbivore populations in fragmented habitats.

A Conveniept Method for Estimating the Breeding Density of a Threatened Passerine Bird Apalopteron familiare, Endemic to the Ogasawara (Bonin) Islands, Japan.

We investigated a convenient method for estimating the absolute density of breeding populations of a threatened subtropical passerine, Apalopteron familiare, which is endemic to the Ogasawara (Bonin) Islands. In order to estimate the number of breeding males or pairs, the method takes advantage of the brief dawn chorus period of the species. The number of vocalising males detected, using the method, was very stable during each census period. The detectability of resident males was nearly 90% of the total number of resident males known to be occupying the study area, based on territory mapping of marked birds. Only about 10% of resident, paired males did not sing, thus the method registered almost all males singing in the study site. As few unpaired, singing males were present, the number of males estimated by the method was approximately the same as that of paired males.

サンケイ式昆虫誘引器を改良したマツノマダラカミキリ生け捕り用トラップ

A trap for capturing Monochamus alternatus adults alive was devised by adding a plastic funnel to a commercial attraction trap. The funnel was set in a bucket to prevent collected adults from escaping. About 30% of collected beetles escaped from buckets with funnels per day on average under experimental conditions. Twenty-one traps were set in pine stands and captured beetles were collected every 3-4 days. The escape ratio during each census period was estimated at 34-56%, corresponding well to the value estimated from the laboratory experiment. On sunny summer days, the temperature in the buckets reached 45-49°C, which seemed to be lethal to the beetles. The maximum temperature in buckets covered with aluminum foil was about 6°C lower than in the uncovered bucket, but was still too hot to keep captured beetles alive.

A cross-sectional audit of benzodiazepine use among general practice patients.

In order to assess how many general practice patients take benzodiazepines for long periods, a cross-sectional audit of clinical practice was conducted. During a 3-day census period, 26 general practitioners in the area of Bergamo, Italy, entered into the study every patient who was taking benzodiazepines. The prevalence of use of this class of drugs was 14.0% (CI 12.5-15.7), while the prevalence of daily use for 12 months or more was 4.7% (CI 3.8-5.8). Finally, the prevalence of very long-term use of benzodiazepines, i.e. those taking these drugs for more than 10 years, was 0.65% (CI 0.34-1.14). Compared to non-long-term users, long-term users were older (OR 2.38, CI 1.39-4.08) and had a lower level of education (OR 2.40, CI 1.04-5.54). In addition, insomnia was associated with long-term use of this class of drugs (OR 1.82, CI 1.02-3.24). These findings provide evidence that the long-term use of benzodiazepines is an important issue in everyday general practice and that this calls for precise management tactics.

Changing Cultural Pattern and Demographic Scenario of the Mina and Bhil Tribes of Rajasthan India

This paper attempts to study the changing life structure of certain cultural and demographic characteristics of the Minas and Bhils of Rajasthan. Data were collected from the 1961 1971 and 1981 census returns for 10 districts in the arid region of India. Furthermore some additional information on cultural aspects was collected from the existing literature on the tribes under study. In general data analyses indicated that the Minas and Bhils are no more isolated but acculturated with the Sanskritic norms and values of Hinduism. The variation of growth rate among Minas and Bhils shows a significant change where most of the southern districts of Rajasthan are showing a declining growth rate whereas in the north-western districts an increasing trend is visible for both the tribal communities of Rajasthan. Sex ratio is found higher among Bhils compared to Minas over the census periods. In response to the different literacy missions the educational levels are in a dilapidated condition among the Bhils which prevents the developmental spurts in their stagnant socioeconomic and demographic conditions. In the context of the occupational patterns the crude work participation is slightly higher among the Bhils than the Minas. In spite of the ongoing Tribal Welfare Programs both the socioeconomic and demographic life of the Minas and Bhils is far below the desired level. It is suggested that special thrusts should be adopted to improve educational conditions with special emphasis on females.

Colonization and Saturation of Habitats by Lizards

We studied the colonization of habitats by four species of iguanid lizard (Urosaurus ornatus, Sceloporus graciosus, S. undulatus, and Uta stansburiana) to determine differences among the species in colonization, differences among habitat types in colonization, and the time trajectory of colonization. We surveyed lizards on eight study plots in three habitats after a density reduction experiment. We discovered no difference among lizard species in their recovery relative to numbers removed. However, there were significant differences in recovery among habitats, suggesting an important role of habitat type in the resilience of the lizards to the perturbation. Colonization by lizards was rapid and most study plots were colonized within 2 to 3 mo of the manipulation. One year after the experiment, all species were represented on all plots. Saturation (ratio of marked lizards to the number removed on each plot) was significantly different between the first and all other post-manipulation census periods. There was no significant difference in saturation among the second (1 yr), third (15 mo) and fourth (27 mo) census periods, suggesting asymptotic saturation within 1 yr of the perturbation. The pattern of colonization by resident lizards was similar to that of all lizards (residents and transients). There was no difference in saturation among species, but there were significant habitat and census period differences in saturation.

Response of a lizard species to the senescence of a dominant plant in the Sonoran desert

:Animal species often respond to changes in the plant community during ecological succession. I discovered such a response in the distribution of a lizard (Urosaurus ornatus, tree lizard) associated with different stages of senescence of saguaro cactus (Carnegiea gigantea). From 1986 through 1995, I periodically assessed the distribution and numbers of tree lizards in the mesquite (Prosopis juliflora), palo verde (Circidium microphylum), and saguaro association in the Saguaro National Park, Arizona. Many of the lizards use saguaro cactus as vantage points for territory defense, feeding and oviposition. Two study plots contained 137 sites which consisted of living, dead standing, and dead prone saguaro cactus. Plots were surveyed for tree lizards in 1986, 1987, 1988, 1992, and 1995. In each year, a site was counted as used by lizards if a resident lizard (captured during two or more census periods) was present. During the study, only 3/91 (3.3%) living cactus were ever used by lizards. In contrast, 73% (27/37) of dead standing saguaro and 12.5% (4/32) of dead prone cactus were used in at least one year of the study. Living saguaro comprised an average of 63% of all sites, dead standing was 19%, and dead prone was 18%. An average of 79% of all lizard records were from the use of dead standing cactus. Only 7% of lizard records were from living saguaro. Analysis of the pattern of use of the classes of cactus showed a highly significant saguaro effect, no significant differences in use among years, and no significant saguaro class by year interaction. Saguaro cactus provide opportunities for exploitation of a distinct microhabitat resource (primarily dead standing cactus) by tree lizards. It appears that dead saguaro are quickly recognized and exploited by tree lizards, which allows an expansion of the territory and home range boundaries of individual lizards.

Biological inventory for conservation evaluation III. Relationships between birds, vegetation and environmental attributes in southern Australia

Relationships between diurnal, terrestrial birds, vegetation and environmental attributes were investigated in the open Eucalyptus forests of south east Australia. Of the 83 bird species recorded, the probability of occurrence of the Yellow-faced Honeyeater, Superb Fairy-wren, Golden Whistler, Fan-tailed Cuckoo and Shining Bronze-Cuckoo was modelled. The Yellow-faced Honeyeater was the only taxon modelled whose distribution could be best explained using climatic variables. The other four species were related to habitat features at the site level. The models developed for these species were specific to each data set used and are unlikely to be appropriate for other data collected at other times of the year. Statistical modelling was used to investigate the response of bird assemblages to environmental and biological regimes. The models reflect differences in the bird species composition of sites in relation to elevation and soil moisture/nutrient gradients across the region. Birds favouring higher elevations were separated from birds favouring mid and lower elevations. Birds favouring wetter environments were separated from those using drier habitats although these species were also present in the wetter environments. Differences in the distribution of birds related to elevation were explained by the environmental attributes minimum temperature of the coldest month and mean precipitation of the driest quarter which also affect vegetation formations and associations across the study region. Vegetation floristics and topographic position, which can reflect the moisture and nutrient status of sites, were important in characterising the specific habitat requirements of a number of birds. Physical and biological regimes were significantly related to bird species richness. Species richness was found to be greatest in moist forests found at mid and low elevations throughout the year. A stratified field survey was successful in recording the majority of forest birds that can occur in the eucalypt forests of south east Australia but sufficient data for reliably modelling the distribution and habitat quality of birds were obtained for only about 10% of the birds recorded. Even when data from two census periods were aggregated, data were sufficient for only 27% of the total number of birds recorded to develop a habitat model. Suggested modifications to the survey design based on the data and analyses used in this study, are discussed in terms of the intended purpose of the field survey.

Mortality and Recruitment Rate Evaluations in Heterogeneous Tropical Forests

1 The methods commonly used to estimate stem turnover rates (i.e. mortality and recruitment) in species rich tropical forests suffer from a previously unrecognized artefact. The estimated rate is not independent of the census period. 2 An average rate estimate will decrease with time if the sample population cannot be characterized as homogeneous. This artefact may have considerable significance for comparisons between permanent plot studies that have used different census periods. 3 We present a theoretical consideration of this census effect. The artefact will be severe when a fraction of the population has a very much higher mortality rate than the average. 4 Using a simple formulation we provide a mathematical proof that rate estimates will decline with increasing census periods for all but perfectly uniform populations. 5 The phenomenon of apparent rate decrease may be used to provide ecologically significant information about the diversity and dynamics of the population as it is related to the variance of life expectancies within the sample. 6 Such an artefact complicates evaluation of change over nonstandard time intervals and requires careful and detailed attention. Similar problems will effect any estimation procedure which cannot account for all the rate variation within a study population. Recognition of the problem is a necessary first step.

Higher rates of SIDS persist in low income groups

To examine how changes in the rates of sudden infant death syndrome (SIDS) have varied in different income groups during a 25 year period. Census data were obtained for five census periods (1971, 1976, 1981, 1986 and 1991) on the number of SIDS cases and inevitable deaths. Census area units (CAU) were ranked according to the average income earned by adults over the age of 15 years for each census year. The CAU were then divided into three equal income groups: low, middle and high. The rates of SIDS differed significantly between the three income groups for the 1991 census period with the low income SIDS rate being 4.6/1000 births compared to 1.2/1000 live births for the higher income groups (Chi-squared = 18.3, P < 0.0001). There was no association between rates of inevitable deaths and income groups. Currently, low income groups have three times the rate of SIDS compared to those in higher income groups. The reason for this is probably because the disadvantaged groups carry an overall higher burden of risk factors for SIDS. This must be kept in mind as further SIDS educational programmes are developed and implemented.

A Likelihood Method for Estimating Pacific Salmon Escapement based on Fence Counts and Mark–Recapture Data

Pacific salmon escapements in natural streams are often determined by conducting fence counts in conjunction with mark–recapture operations. Typical field conditions are characterized by protracted floods, undetected immigration, variation in sampling rates, mortality during the census periods, small sample sizes, and few successive recaptures. Closed population models tend to overestimate escapement under such conditions, and traditional open population models cannot always be relied on due to the lack of sufficient data. A likelihood-based estimation method was specifically designed for such conditions. A distinguishing feature of this model is that individual recapture histories are not required for parameter estimation. The model is also structured to incorporate ancillary data in the estimation process to improve the precision and accuracy of the estimates. The model is described in detail, and suggestions are made to facilitate its application. Constructed data sets resembling those obtained under field conditions were used to evaluate the performance of the model. The estimates generated with simulated data and actual field data were compared with those based on visual foot surveys and other mark–recapture models.

Factors Affecting the Efficiency of the Area Search Method of Censusing Birds in Open Forests and Woodlands

SummaryThis paper examines factors that influence the ability of area searches to census the complete bird population at a site. Such factors included duration and repetition of census periods, density of vegetation, density of individuals of species, weather and time of day. Total time spent on the site was found to be more important than the duration or the number of repetitions of the census period, especially in sites with a dense understorey. In sites with a sparse under-storey, more repetitions of censuses of short duration were more effective. To obtain a complete species list, a total time of around 100 census minutes was required in sparse sites compared with 150 minutes in dense sites. Birds occurring at high density were not necessarily encountered early in the censusing, probably due to their mobility. Increasing wind strength, time after sunrise and minimum temperature adversely affected the number of species found.

Mortality and growth of a commercial hardwood ‘el cativo’, Prioria copaifera, in Panama

The demography of a valuable timber tree, Prioria copaifera, was studied in undisturbed forest on Barro Colorado Island (BCI) in central Panama using data from a permanent, 50 ha census plot. All individuals above 20 mm diameter at breast height (dbh) in the plot were mapped and dbh measures taken in 1982, 1985, and 1990. Although Prioria is mainly known from swamp forest, it was abundant in the upland forest of BCI, with a mean density of 27–29 stems ha −1 of 10 mm dbh or more. Mortality rates of Prioria were 0.5 and 0.6% year −1 during the two census intervals and did not depend on dbh. Mean growth of saplings was slow, less than 1 mm year −1, but larger trees grew rapidly, at 8–16 mm year −1. Growth rates of medium and large trees were higher during 1985–1990, probably because a severe drought in 1983 increased forest-wide mortality rates and opened the forest canopy, allowing more light to penetrate the forest. During both census intervals, growth was extremely variable, ranging from 0 to 40 mm year −1 in different individuals. The range of variability changed little with size: across dbh values from 100 to 1000 mm, maximum growth rates were 20–40 mm year −1. Unlike absolute growth rates, however, relative growth declined with size, from about 5% year −1 in saplings to 1% year −1 in large trees, and was much more variable among small stems than among larger. Information about variation in growth between individuals and between census periods will be important in forest management, as it indicates how and to what extent silvicultural treatment might enhance timber production in Prioria. In addition, rapid growth of some stems suggests that plantation forestry might be productive in Prioria. Our finding that population density and performance were good in upland soils suggests that plantations of this species could be attempted in drier soils than previously thought necessary.

Population Growth, Structure, and Seed Dispersal in the Understory herb Cynoglossum virginianum: a Population and Patch Dynamics Model

Abstract We use a combined model of forest canopy dynamics and patch‐specific demography to examine the response of a forest understory herb, Cynoglossum virginianum, to changes in rates of forest disturbance, rates of long distance seed dispersal, and patterns of seed dormancy. The matrix modelling approach followed that of Horvitz and Schemske (1986), in which empirically‐determined demographic parameters of a population experiencing open canopy conditions are modified depending upon demographic decay functions describing plant demography in a series of patch‐types undergoing succession toward fully closed canopy. In our analysis, demographic transition elements were estimated from 14 years of long‐term census data on three subpopulations at the Smithsonian Environmental Research Center, Anne Arundel County, Maryland. One of the three subpopulations was subjected to full canopy exposure in the second year of data collection, while the other two subpopulations remained in full understory conditions for the entire census period. Our results suggest small negative effects of a doubling of the rate of canopy disturbance (defined as the rate at which new treefall gaps appear in closed canopy) and only small positive effects of long distance dispersal on population growth rate, which predicts tittle selection for long distance dispersal. However, our analyses predict positive benefits of enhanced seed dormancy in this species, particularly if dormancy is higher in new gaps relative to understory conditions. These results are primarily a product of enhanced reproductive output in the years immediately following gap opening which is counterbalanced by increased seedling mortality in those years and a near complete suppression of reproductive output in later years (closing gaps). The suppression of reproduction in closing gaps may be a manifestation of a delayed effect of high costs of reproduction imposed in prior years. We discuss our results in terms of observed patterns of seed dispersal and in terms of the overall potential influence of forest gap dynamics on the demography of understory herbs similar to C. virginianum, in which demographic responses to changes in canopy conditions differ in strength and direction among life history stages.

The Continuing Population Decline of Torreya taxifolia Arn.

SCHWARTZ, M. W. (Illinois Natural History Survey, Champaign, IL 61820) AND S. M. HERmANN (Tall Timbers, Inc., Tallahassee, FL 32312). The continuing population decline of Torreya taxifolia Am. Bull. Torrey Bot. Club 120: 275-286. 1993.-Torreya taxifolia is a federally endangered dioecious conifer endemic to ravine bluffs along the east side of the Apalachicola River in Gadsden and Liberty Counties, Florida and Decatur County, Georgia (plus one outlying population in Jackson County, Florida). Torreya taxifolia experienced a catastrophic population decline, presumably fungal in origin, in the late 1950's. Within 10 years virtually no adults remained in the wild, a situation that persists to the present. Size measurements of trees indicate that the mean length of the longest stem is less than one meter. In a census population of over 100 trees, 10% died in four years, mostly from small size classes. Extension of terminal buds along the primary stem was infrequent, with only 47% of all trees experiencing any growth in length during the four year census period. With 32% of all trees losing their primary stem during the census interval, the mean size of individuals within the population is decreasing. Most individuals are multi-stemmed and continue to carry symptoms of disease. Although no causative agent for the decline has been identified, the most prevalent symptoms of disease are needle spots, needle necrosis and stem cankers. Growth fate does not appear to be strongly related to habitat or the incidence of disease symptoms, although stem mortality was higher among trees with heavy foliar pathogen loads. With no sexually mature trees and no seed production, this species faces continued decline.

セジロウンカ卵期の死亡要因の評価

Egg mortality factors of the whitebacked planthopper, Sogatella furcifera HORVATH were evaluated in paddy fields planted with a japonica variety, Hinohikari for 6 weeks from late-tillering to heading stage. The overall mortality rate was more than 80% throughout the census period with a peak of 92.7% at 7 weeks after transplanting. Physiological death caused by plant reaction against oviposition was responsible for 68.9-94.5% of the overall mortality. Mortality caused by this factor was highest at 7 weeks after transplanting and decreased as rice grew older. The parasitism rate by Anagrus sp. was estimated at 18.8-59.3% of eggs that escaped from the other mortality factors. The mortality rate due to predation and unknown factors was negligible except for the heading stage when it increased to 12.8%. Eggs laid in the central vein of leaves had a parasitism rate more than 3 times as high as those laid in leaf sheaths, while the physiological death rate was slightly higher in leaf sheaths than in leaves. The possible effect of each mortality factor on the population dynamics of S. furcifera was discussed with special reference to the role of physiological death.

General and Cause-Specific Adult Mortality Among Immigrants in Canada, 1971 and 1981

In this study we examine general and cause-specific mortality for American English Scottish Italian and other foreign-born immigrants in relation to the Canadian-born population for the census periods 1971 and 1981. Results from a Poisson regression analysis based on log-rate models for relative mortality risk reveal limited support for the hypothesis that the life stresses of the migration experience lead to an increased risk of death due to suicide homicide and accidents among immigrants. The prediction that discrepancies in socioeconomic status are of importance in explaining mortality differentials gained partial support....Overall the findings are consistent with the literature based on other immigrant societies that the foreign-born generally experience better survival probabilities than their host countries. (SUMMARY IN FRE) (EXCERPT)

A ten‐year study of population dynamics of citrus pests in the pesticide‐reduced orchard

SummaryTo determine the effectiveness of a pest management system that uses pesticides at a low level, we censused populations of seven insect pests and three plant diseases from 1980 to 1989 in a citrus orchard which was managed with a pesticide‐reduced and pesticide‐free protocols, in Wakayama Prefecture, Japan. In the orchard, we controlled the pests solely by spraying petroleum oil once a year from 1980 to 1985, by not spraying insecticide in 1986, and spraying only germicide in 1987. The arrowhead scale population remained much lower level at which citrus trees begin to wither when petroleum oil was sprayed, whereas it rapidly increased and began to wither trees during the years without spraying petroleum oil. The Indian wax scale population rapidly increased only during a 2‐year period and then declined. Although the infection level of the sooty mold was unusually high on the trees where the density of the scale was high, this pathogen did little damage to citrus trees. The population of the red wax scale gradually increased throughout the census period but did not reach the level at which citrus trees begin to be damaged. Other pests also caused negligible damages to citrus trees. The results indicated that the pesticide‐reduced pest management system which was proposed by Inoue and Ohgushi (1976, 1977) is valid for the prevention of the outbreak of the arrowhead scale, and that is has the sufficient control efficiency for the other pests in citrus orchards.

Violent criminal behavior: Is there a general and continuing influence of the South?

Historically, the South has been characterized by high homicide rates relative to other regions in the United States. The present study attempts to make sense of the disparate findings among extant studies of the Southern culture of violence thesis by correcting for their methodological problems and by examining violent crime rates at three levels of aggregation-cities, metropolitan areas, and states—and across three decennial census periods—1960, 1970, and 1980. Whereas most studies of the Southern culture of violence thesis use homicide rates as the focal measure of violent behavior, the present study investigates the generalizability of the Southern culture of violence thesis to other violent index crimes. In addition, the models are also compared over time to determine whether the Southern regional effects persist over time and, if so, whether there is a diminishing effect of region. The results provide evidence for the existence of a Southern culture which supports situation-specific types of violence (i.e., defensive acts) rather than violence in general. Furhermore, the findings provide mixed support that cultural effects diminish over time.

Autumn and Winter Bird Populations in Herbicide-treated Cross Timbers in Oklahoma

-Birds were counted during autumn and winter from October 1987 through February 1989 on sites in Cross Timbers in central Oklahoma 5 and 6 yr after herbicide treatments. We censused two replications of tebuthiuron-treated, triclopyr-treated, and untreated reference sites with a modification of the point-count method. Thirty-five species were documented during the entire census period; 16 species were observed only on herbicidetreated sites and two species only on reference sites. During autumn and winter, more birds and more species were found on sites treated with herbicides than on reference sites. Tebuthiuronand triclopyr-treated sites supported similar numbers of species during both seasons. Herbicide-treated sites had the highest species richness, but untreated areas were needed to maintain interior woodland species.