Zooplankton and their relationships with water quality and fisheries

Zooplankton population structure in Rutland Water changed over the first five years of the reservoir's existence. Daphnia pulex, initially dominant was replaced by D. hyalina in late 1975 and since 1979 this latter cladoceran has coexisted for part of each year with Bosmina longirostris. Population fluctuations of all the main crustacean zooplankton — D. hyalina, Cyclops spp. and Diaptomus gracilis — were erratic in the first three years (1975–1977) but have since become more regular. The relationships of the zooplankton with their potential algal food supply and with their potential predators, the fish population, are discussed.     

Mammal Society dormouse survey, January 1975-April 1979

The dormouse survey was initiated by the Mammal Society and ran from January 1975 to April 1979. The dormouse is very much a southern mammal in Britain with a reduced range compared to that found 100 years ago. There seems to have been a decline in population and possible reasons for this are discussed. The habitat favoured by dormice is considered; a thick secondary layer is very important with bramble forming a major component. Dormouse nests are most often found in bramble at an average height of just over a metre from the ground. Dormouse requirements, particularly for scrub, should be considered when areas for wildlife conservation are being managed.     

The population ecology of a natural population of the pierid butterfly Colias alexandra

Summary Key factor analysis techniques were used to examine factors determining the abundance of a population of non-pest Colias. The number of individuals entering each successive life stage in the sample population are summarized in life tables for 1975 to 1979. Survivorship to the adult is a relatively consistent proportionality (-x=1.2%, S.D.=1.14; 1975–1979). Factors resulting in reduced natality and, less importantly, mortality during larval diapause determine the population trends for C. alexandra. Egg mortality, pre-diapause larval mortality and postdiapause mortality contribute little to these trends. Possible key sources contributing to reduced natality are examined. Mortality of adults (including removal by collectors), poor weather conditions during the oviposition period, unseasonal snow or drought which affect nectar sources or oviposition sites are among the factors which cause reduced natality and result in population depression.     

Clan Lethals and Inter-Year Allelism in Death Valley DROSOPHILA PSEUDOOBSCURA

A chromosome 2 lethal allelism rate of about 3% was found in the 1974 population of D. pseudoobscura in Death Valley, California. This rate was significantly higher than allelism rates in other Southern California populations. The Death Valley population was sampled again in 1975 and 1977, with allelism rates of 1% and 0.5%, respectively. In 1974, several lethals were in high frequencies (about 1%), a pattern that reappeared in 1975 and 1977. However, none of the lethals in high frequency one year were in high frequency another year; the particular lethal alleles present in this ephemeral population appear to be due to their random presence in the flies which refound the population every winter. The results for the Death Valley population are compared with a Japanese population of D. melanogaster in which lethals in high frequency one year are also in high frequency in succeeding years and with earlier work on chromosome 3 of D. pseudoobscura, which showed a lower lethal frequency and higher allelism rate.     

Investigations into the soil mycoecology of Chambal ravines of India

Summary The present investigation deals with the seasonal succession of fungal communities in wheat fields. The studies were performed during the year 1975–76 and involved four study seasons,viz. winter (1975), summer (1975), rainy (1975) and winter (1976). The observations during two winter seasons were done to find out whether or not fungal communities exhibit definite cyclic pattern. Of the 69 isolated species, 25 showed wider ecological amplitude whereas some species were specific of a particular season. Each season was marked by different fungal mycoflora. The population ofAspergillus terreus, a dominant member of the community, along with many other autochthonous species, exhibited a definite periodicity during various seasons. Seasonal variations in the fungal communities, variations in the extent of similarity among the fungal communities during various seasons and the impact of climatic conditions on the components of fungal communities are discussed.     

Kin selection in density regulated populations.

The process of kin selection has both intra- and inter-group components (Hamilton, 1975, in: Biosocial Anthropology Wade, 1980). Group advantageous characteristics can evolve when inter-group differences in fertility are sufficiently great to overcome any within-group disadvantage of the trait. The potential magnitude of inter-group differences in fertility is determined largely by the way a population is regulated. Inter-group differences decrease as the spatial scale over which a population is regulated becomes increasingly localized. The present paper extends previous work by Boyd (1982, Anim. Behav. 30, 972-982) on the quantitative relation between kin selection and density regulation. A simple genetic model is employed to examine the conditions under which the interaction of local density regulation and kin selection can maintain a stable polymorphism. The ecological factors determining the spatial and temporal scale of density regulation are discussed. Finally, the results are applied to two biological cases in which local density regulation may be influencing the direction of phenotypic plasticity in group advantageous characters.     

Parameters of cell competition in the compartments of the wing disc of Drosophila.

When compartments in the wing disc of Drosophila are mosaic for two populations of cells, one of which is dividing more slowly, then the slower-growing population tends to be eliminated. The phenomenon leading to the disappearance of nonlethal, slowly dividing Minute cells was termed cell competition by Morata and Ripoll (1975) [Morata, G., and Ripoll, P. (1975). Develop. Biol.427, 211–221]. In this paper the different parameters of cell competition are explored. Starvation of the larvae rescued the Minute clones and permitted the following observations: The Minute clones grow to some extent before being out-competed. Prior to their disappearance, they become fragmented into small patches. Cell competition is greater in the centre of compartments than in the boundary regions. Possible causes of cell competition are discussed, as well as the hypothesis that the phenomenon may be related to the control of growth.     

Aerial census of ringed seals Pusa hispida basking on the ice of the Bothnian Bay, Baltic

The censuses are based on six surveys (1590 km total) carried out between 13 April and 17 May 1975 and two surveys (560 km) on 13 and 15 May 1978. The material consists of 716 observations in 1975 and 214 observations in 1978, involving 1960 and 572 ringed seal specimens respectively. The transect width was determined in retrospect on the basis of the sighting angle and sighting distance, the latter being estimated and corrected by a factor typical for each separate flight. The mean sighting distances varied from 720 to 1140 m with a range from 160 to 2450 m. On average over 3000 ringed seats were basking on the ice of the Bothnian Bay in 1975 and 1978, promising at least 4000 specimens living in the area in total. Sources of methodological bias, factors affecting the observability of the seals, and the estimation of the total population based on the numbers of basking seals are discussed.     

Population biology of the rare military orchid (Orchis militaris L.) at an established site in Suffolk, England

In Britain, where it reaches the north-westerly limit of its European distribution, Orchis militaris L. is extremely rare. Well-established and persistent populations of O. militaris are known to exist at only two sites. The largest extant population of O. militaris occurs in a disused chalk pit in Suffolk. A preliminary demographic analysis of this population, covering the period 1975 to 1991, along with estimates of key life stage transition probabilities are presented here. From 1975 to 1986 the number of separate identifiable plants in the population declined substantially. Until 1986 recruitment of rosettes was poor. The largest cohort of new plants, recorded in 1976, was 35. Approximately 48% of new individuals recruited between 1976 and 1985 failed to flower. Of those flowering, approximately 55% flowered during their first year above ground. Of the original population recorded in 1975, 67.8% flowered at least once during the study. The reproductive performance, i.e. the frequency of flowering and the period between episodes of flowering, varied considerably between individuals. Some plants flowered every year while others only flowered once during the study. Few plants remained below ground for more than one year, while several apparently persisted below ground for more than 6 successive years. Although the number of plants that can be identified as separate individuals has declined, the total number of rosettes in the population has, from 1986, increased dramatically. Because of the dense clumping of these recruits it is not possible to determine whether they are derived from seed or vegetative propagation. When post 1986 recruitment is combined with the number of plants that established before 1986 and survive, the apparent number of plants present at the site has more than doubled between 1975 and1991.     

Estimation of some population parameters of Drosophila limbata V. Roser in a greenhouse

Summary Size and survival rate of a population of Drosophila limbata in a cucumber greenhouse in the vicinity of Groningen, The Netherlands, were estimated twice in the summer of 1975 by mark-release-recapture experiments, using the Fisher-Ford model. The second time, an independent check was carried out by directly estimating the number of emergences. At the end of June, estimated population size was about 13,600, with a survival rate per day of 53.4%, at the end of July population size was estimated at 49,600, with a survival rate per day of 83.4%. The number of emergences per day was at the end of July 5,300, which is reasonably in line with the expectation from the mark-release-recapture experiment. At the end of June there was an excess of females, later there was an excess of males. Reliability of estimates, differences between estimates and growth of the population are discussed. Extrapolation from these data leads to an estimate of 3 million adult flies as the total maximum population size in the local area.     

Variations of skull-body regressions of the lemming (Dicrostonyx groenlandicus) under laboratory and field conditions

Collared lemmings, Dicrostonyx groenlandicus , maintained in the laboratory under short-day photoperiods (2 h light: 22 h dark) grew faster than their cohorts kept under long-day photoperiods (22 h light: 2 h dark). Significant differences in cranial, visceral and body components were found in both sexes. Linear regressions of skull-body parameters were compared to those of wild lemmings trapped at Eskimo Point, Northwest Territories, Canada, during three consecutive summers from 1973 to 1975. The data support the conclusion that variation in body size and skull development associated with changes in population density are, in part, due to photoperiod influences. The importance of this facultative response is discussed in relation to current theories on thermal regulation and variations in subnivial breeding success observed in this species.     

Mortality in babies with achondroplasia: Revisited

BACKGROUND: Natural history studies performed 30 years ago identifying higher mortality among children born with achondroplasia, a genetic dwarfing condition, resulted in clinical recommendations aimed at improving mortality in childhood. The objective of this study was to determine if mortality rates have changed over the past few decades. METHODS: Children born with achondroplasia during 1996 to 2003 were ascertained from the Texas Birth Defects Registry and matched with death certificate data from the Bureau of Vital Statistics through 2007. Infant and overall mortality rates, both crude and standardized to the 2005 (SMR₂₀₀₅) and 1975 (SMR₁₉₇₅) U.S. populations, were calculated. RESULTS: 106 children born with achondroplasia were identified. Four deaths were reported, with all occurring in the first year of life (mortality rate: 41.4 /1000 live‐births). Infant mortality was higher when standardized to the 2005 U.S. population (SMR₂₀₀₅:6.02, 95% CI:1.64–15.42) than the 1975 population (SMR₁₉₇₅:2.58, 95% CI:0.70–6.61). CONCLUSION: The higher SMR₂₀₀₅ compared with SMR₁₉₇₅, along with the fact that SMR₁₉₇₅ was nearly half that of a previous cohort reported 25 years ago (rate ratio: 0.53, 95% CI: 0.11–2.25), reflect a discrepancy in the changes in mortality in the overall population and in our cohort. Although an overall improvement in mortality, especially after the first year of life, is observed in our cohort, children with achondroplasia are still at a much higher risk of death compared with the general population. A longer follow‐up is needed to elucidate whether evaluation/intervention changes have resulted in significant improvement in long‐term survival among these patients. Birth Defects Research (Part A) 100:247–249, 2014. © 2014 Wiley Periodicals, Inc.     

Exogamy and Change in the Biosocial Structure of a Modern Urban Population

Change is traced in the biosocial structure of the Japanese American population of Seattle-King County, Washington, from that of a deme to a state approaching panmixis with surrounding American populations. Data from 2,767 marriage license applications of Japanese Americans between 1930 and 1975 were used to calculate rates of racial exogamy. Rates rose from prewar levels of less than 1% to over 50% in 1975. The total Japanese American county population was subdivided into a nuclear group, tracing its origins back to the original founding immigrants, and a nonnuclear group which has migrated into the area since World War II. Until 1965, the nonnuclear group consistently led the nuclear group in exogamous marriages. In both groups, females consistently out-married more frequently than did the males. Further analysis of community exogamy, i.e., nuclear member marriage to a nonnuclear Japanese American, showed that this type of exogamy within the second generation preceded the high rates of racial exogamy characterizing the marriage patterns of the third generation. Familial analysis suggested that the maternal kin ties of nuclear population females continue to influence marriage choice of their offspring. The patterns of increasing racial exogamy for Japanese Americans are examined against their rise in socioeconomic status, [biosocial structure, exogamy, population]     

Cardenolide content of Danaus chrysippus butterflies from three areas of East Africa

The African butterfly Danaus chrysippus , like other members of the family Danaidae, feeds as a larva on species of milkweeds (Asclepiadaceae). It has been demonstrated in a sample from a West African population that only a minority of adult D. chrysippus accumulated detectable amounts of poisonous and presumably emetic cardenolides from their larval foodplants. It has also been shown in D. chrysippus and the related monarch butterfly ( D. plexippus ) that the cardenolide content of adults varies with that of their respective milkweed foodplants.
Three population samples of D. chrysippus from sites in East Africa are analysed for cardenolides using the spectrophotometric technique refined by Brower, Edmunds & Moffitt (1975), which allows the assay of individual butterflies. The East African samples all have a palatability spectrum with a considerably higher percentage of cardenolide-containing individuals than the West African one.
This is discussed in terms of its effect on potential bird predators and the 'automimicry' of emetic by palatable individuals. In East Africa D. chrysippus is polymorphic and appears to act as a model in a complex mimicry ring, whereas in West Africa it is monomorphic and may have 'shed' most of its mimics. This latter hypothesis is discussed in the light of our results.     

A Measure of Sliding Sand

The Royal Commission on Medical Education recommends that the ratio of doctors to population should undergo an exponential expansion after 1975. It is suggested that the Commission does not appear to have fully recognized the implications of this proposal, nor to have considered other possible modes of expansion, which would result in substantially different estimates of future needs.     

Egg distribution and survivorship in the pierid butterfly,Colias alexandra

Summary Patterns of egg distribution and survivorship were examined for six generations (1975–79 and 1981) of a univoltine population of the pierid butterfly Colias alexandra. Unlike some other of the so-called red-egged pierids, there is no evidence of egg-recognition in this Coliadine species. Two distribution patterns were observed: contagious or clumped in 1976–1979, but random in 1981. Generation to generation, survivorship to diapause of clumped individuals relative to all individuals shows no consistent pattern. Among clumped individuals, survivorship is two times greater for the first or previously-laid individual than the second or subsequently-laid individual, suggesting that if there is a genetic basis for the common contagious pattern, selection is acting against it. The importance of obtaining data which reveals inter-year variation in assessing or interpreting egg distribution is discussed.     

Hydrobiological consequences of the addition of phosphate precipitants to inlet water of lakes

Summary In three model reservoirs (LUND, 1975) a method reducing bluegreen algal blooms in lakes was studied. Iron or aluminium were added to inlet waters for chemically binding the inflowing phosphorus.The research program, started in 1975, includes intensive monitoring of many chemical and hydrobiological variables, the determination of water and mass balances and since 1977 measurements or primary production rates with¹⁴C. In this paper only the results found in 1977 are discussed. An attempt is made to describe quantitatively how growth rates and changes in biomass are interconnected and how phosphorus precipitation changes these variables.In all reservoirs a large discrepancy was observed between the actual rate of increase in the algal population and the relative production rate. The latter appeared to be higher by one order of magnitude. The relative death rate due to grazing can account for the large difference between these growth rates only when selective grazing of zooplankton on phytoplankton is assumed.It can be concluded that treatment of inlet water with AVR, an aluminium salt, is unsuccessful in reducing algal development. Treatment with ironsulphate may be successful, but a reduction of the relative growth rates was not observed. The effects of grazing of zooplankton andDreissena polymorpha need further investigation.     

Better up,worse down: bidirectional consequences of three decades of climate change on a relict population of Erebia cassioides

Orophilous species are often unable to escape the consequences of climate change because mountains are surrounded by unsuitable habitats. Among them, several endemic species belonging to the genus Erebia Dalman (Lepidoptera, Nymphalidae, Satyrinae) can be considered as key species to assess the risk of biodiversity loss of mountain habitats. The aim of this paper is to measure changes that have occurred in the altitudinal distribution of Erebia cassioides on the Pollino Massif (Southern Italy) during the last 37 years. Sixteen sites sampled in 1975 have been resampled after about three decades (2004, 2012). In 1975 56 % of the sampled population inhabited sites above and 44 % sites below the treeline, while in 2004 and 2012 99 % of the population were observed above the treeline. Furthermore, we observed an uphill shift of 180 m in the barycentre altitude of the species distribution and an unexpected increased density of the population above the treeline which led to a range reduction coupled to population increase of E. cassioides. This pattern contrasts with the usually observed one that couples habitat reduction to population decreasing. The reason for the observed pattern is unclear, but the implication for conservation strategies could be important if confirmed for other species. In fact, during coming decades local extinctions as a consequence of climate change might be fewer and more delayed than expected, and relict populations of cold adapted species could be preserved for a longer time span within optimal habitat refugia.     

The ethology of saccades: a non-cognitive model

It is proposed that there is a low-level automatic component of visual scanning in which saccades are triggered probabilistically in time by nonfoveal stimulus features. By ignoring cognitive factors and memory, a first-order Markov approach is taken, which is tractable for spatially homogeneous stimuli. The predicted distributions of saccade magnitude, fixation duration, fixation position, and how they are related to stimulus size are in good agreement with empirical observations by Bahill et al. (1975), Enoch (1959), and Harris et al. (1988). Ways in which this low-level process could be modulated by cognitive factors are discussed.