Total Population Levels Research Articles

Effects of Movement and Mating Patterns on Gene Flow among Overwintering Hibernacula of the Timber Rattlesnake (Crotalus horridus)

Radiotelemetry and genetic markers have enabled herpetologists to test the hypothesis that gene flow is restricted among snake dens (a.k.a. “hibernacula”). In the present study, observations of movement and mating were compared to indirect inferences of gene flow based on genetic data (microsatellite DNA loci) for six neighboring hibernacula of the Timber Rattlesnake (Crotalus horridus) in western St. Louis County, Missouri. Behavioral results were consistent with previous findings for this species, with most individuals exhibiting high fidelity to hibernacula, and males exhibiting larger activity areas than females. Behavioral results also supported several long-standing assumptions: males tended to mate at longer distances from hibernacula than females and random pairing between males and females from different hibernacula could not be rejected. Some gravid females moved considerable distances between locations, but most returned to an area near their own hibernaculum to give birth, and birth distances tended to be shorter than the nearest-neighbor distance between hibernacula. Genetic results indicated that the observed number of heterozygotes did not deviate from Hardy-Weinberg expectations at the level of total sample population, but that a significant heterozygote excess was found within hibernacula. A small but significant proportion of the genetic variance in the total population was due to differences among hibernacula; however, Bayesian clustering algorithms could not sort individuals (or groups of hibernacula) into discrete demes. Results suggest that patterns of genetic differentiation observed among hibernacula of the Timber Rattlesnake are better explained by behavioral and demographic factors resulting in natal philopatry, sex-biased dispersal, and/or a limited number of breeding adults, than by the balance of gene flow and drift, per se.

Exploring the relationship between urbanization and energy consumption in China using ARDL (autoregressive distributed lag) and FDM (factor decomposition model)

The paper develops a function of energy consumption, population growth, economic growth and urbanization process, and provides fresh empirical evidences for urbanization and energy consumption for China over the period 1978–2008 through the use of ARDL testing approach and factor decomposition model. The results of the bounds test show that there is a stable long run relationship amongst total energy consumption, population, GDP (Gross domestic product) and urbanization level when total energy consumption is the dependent variable in China. The results of the causality test with ECM (error correction model) specification, the short run and long run dynamics of the interested variables are tested, indicating that there exists only a unidirectional Granger causality running from urbanization to total energy consumption both in the long run and in the short run. At present, the contribution share which urbanization drags the energy consumption is smaller than that in the past, and the intensity holds a downward trend. Therefore, together with enhancing energy efficiency, accelerating the urbanization process that can cut reliance on resource and energy dependent industries is a fundamental strategy to solve the sustainable development dilemma between energy consumption and urbanization.

Use of 16S rRNA gene sequencing analysis to characterize culturable intestinal bacteria in Atlantic salmon (Salmo salar) fed diets with cellulose or non-starch polysaccharides from soy

Duplicate groups of Atlantic salmon (Salmo salar L.), kept in seawater, were fed fish meal-based cold-pelleted diets. Diets with non-starch polysaccharides (NSP), either cellulose, purified soybean NSP or extruded purified soybean NSP at a dietary level of 100 g kg−1, were compared with a diet without supplemental NSP and a diet with soybean meal in a 28-day feeding trial. Isolation and characterizations were limited to culturable bacteria and population levels of aerobic and facultative aerobic heterotrophic autochthonous (adherent) and allochthonous (transient) bacteria present in the mid and distal intestines of Atlantic salmon fed the five different diets estimated using traditional bacteriological techniques. The presence of an autochthonous microbiota was demonstrated using transmission electron microscopy. No significant effects of diet composition were observed on total population levels of culturable bacteria present in the digestive tract, but the study showed that the composition of the gut microbiota (autochthonous or allochthonous) was sensitive to dietary changes. A total of 752 culturable isolates from the intestines were characterized by biochemical and physiological properties. Of these, 188 isolates were further characterized by partial sequencing the 16S rRNA genes. Among these, 146 isolates belonged to 31 phylotypes that were >94% identical to previously described species. However, 42 isolates showed similarity <94% to species available at the National Center of Biotechnology Information. Several of the phylotypes identified in the present study have not been reported previously in the gastrointestinal (GI) tract of fish, including the Gram-negative bacteria Gelidibacter salicanalis, Pseudoalteromonas elyakovii, Psychrobacter aquimaris, Psychrobacter cibarius, Psychrobacter fozii, Psychrobacter maritimus, Psychrobacter okhotskensis and Psychrobacter psychrophilus. Among the Gram-positive bacteria identified were Arthrobacter bergeri, Arthrobacter psychrolactophilus, Arthrobacter rhombi, Bacillus pumilus, Bacillus subtilis, Exiguobacterium spp., Microbacterium oxydans, Planococcus maritimus, Sporosarcina ginsengisoli and several bacteria that have been described as unculturable previously. In addition, we identified Carnobacterium inhibens, a lactic acid bacterium that is not frequently isolated from the GI tract of fish. Psychrobacter cibarius was the dominant bacterial species and was isolated from the digestive tract of all fish investigated.

Where Strategy and Ethics Converge: Pharmaceutical Industry Pricing Policy for Medicare Part D Beneficiaries

On January 1, 2006, Medicare Part D prescription drug coverage was initiated. Concern was immediately voiced by the American Association of Retired Persons (AARP) and Families USA that, in response to this program, the pharmaceutical industry may raise prices for drugs most often used by the elderly. This article examines the ethical implications of a revenue-maximizing pricing strategy in an industry in which third party financing mitigates an end product’s true cost to the user. The perspectives of three stakeholder groups are examined: the elderly, as consumers of prescription drugs, the pharmaceutical industry, as product manufacturer and beneficiary of derived profits, and the total U.S. population, as the ultimate payer for the program via tax revenues. Key questions explored include the relationships among price strategy and access to drugs at both the micro (Medicare cohort) and macro (total population) levels, and on drug development or enhancement. The role of profit in a capitalism-based health care system is also examined. Hospital industry impact on these same stakeholder groups in response to the original 1965 Medicare law is used to compare and contrast possible outcomes of the new drug program. It is predicted that pharmaceutical firms will mimic the hospital industry, adopting a price maximizing strategy for drugs covered by the program. In the process, a utilitarian effect occurs: the benefits of increased access and diffusion of drugs counterbalance inequities in financing Medicare Part D.

Management of Soilborne Diseases in Strawberry Using Vegetable Rotations

The influence of crop rotation on soilborne diseases and yield of strawberry (Fragaria × ananassa) was determined at a site infested with Verticillium dahliae microsclerotia and at another with no known history of V. dahliae infestation during 1997 to 2000. The rotations studied at the V. dahliae-infested site were (i) broccoli-broccoli-strawberry, (ii) Brussels sprouts-strawberry, and (iii) lettuce-lettuce-strawberry; the treatments at the site with no history of V. dahliae were (i) broccoli-broccoli-strawberry, (ii) cauliflower-cauliflower-strawberry, and (iii) lettuce-lettuce-strawberry. The effects of rotation on V. dahliae and Pythium populations, strawberry vigor, Verticillium wilt severity, and strawberry fruit yield were compared with a standard methyl bromide + chloropicrin fumigated control treatment at both sites. Rotations did not alter total population levels of Pythium spp. at either study site. However, V. dahliae microsclerotia were significantly reduced with br occoli and Brussels sprouts rotations compared with lettuce rotations at the V. dahliae-infested site. Reduced propagules led to lower Verticillium wilt severity on strawberry plants in the broccoli and Brussels sprouts rotations than in lettuce-rotated plots. Strawberry vigor and fruit yield were significantly lower in lettuce-rotated plots than in broccoli- and Brussels sprouts-rotated plots. Despite no detectable microsclerotia at the other site, strawberry vigor and fruit yield were greatest in plots rotated with broccoli, intermediate with cauliflower, and lowest with lettuce. None of the rotation treatments were better than the fumigated control for all variables measured. In the absence of fumigation, rotation with broccoli and Brussels sprouts is an effective cultural practice for managing Verticillium wilt in strawberry production; whereas, in fields with no detectable V. dahliae, broccoli is also a feasible rotational crop that enhances strawberry growth and yield. According to a cost-benefit analysis, the broccoli-strawberry rotation system could be an economically viable option provided growers are able to alternate years for strawberry cultivation.

Territory occupancy rate of goshawk and gyrfalcon: no evidence of delayed numerical response to grouse numbers

Two recent studies on territory occupancy rates of goshawk Accipiter gentilis and gyrfalcon Falco rusticolus report a 2-3-year-delayed numerical response to grouse numbers, which is a requirement for a hypothesis of predator-generated grouse cycles. The time lags were assumed to reflect the average age of sexual maturity in the raptor species. In southern Norway, however, subadult (two-year-old) goshawk hens occupied only 18-25% of territories where occupancy was not recorded in the preceding year, and there was no significant relationship between the proportion of subadults among recruits and grouse indices two years earlier. We argue that territory occupancy rates are not appropriate indices of total raptor population levels, but rather reflect the proportion of territorial pairs that attempt to nest. Because this depends on the body condition of the hens, fluctuations in other important winter resident prey species (most important for the goshawk) and winter weather (most important for the gyrfalcon) should also be addressed. During 1988-2006, the annual proportion of goshawk territories with recorded nesting attempts in southern Norway was most closely related to the preceding autumn's population indices of black grouse Tetrao tetrix and mountain hare Lepus timidus, whereas the annual proportion of gyrfalcon territories with observations of falcons or with confirmed breeding attempts in central Norway were best explained by population indices of willow grouse Lagopus lagopus and ptarmigan L. mutus from the previous autumn, and by December temperatures. Hence, our studies do not support the predation hypothesis for grouse cycles.

Influence of narrow‐band UVB phototherapy on cutaneous microbiota of children with atopic dermatitis

In the present work, the effect of narrow-band ultraviolet B (UVB) phototherapy on a cutaneous microbial population was evaluated in patients with atopic dermatitis (AD) and compared with control patients (vitiligo). Count, isolation and identification of cutaneous microbiota from anticubital fossa were performed in 10 controls and 10 AD patients, both submitted to similar levels (P > 0.05) of UVB phototherapy (4.3 +/- 0.9 and 4.3 +/- 0.8 accumulated joules, respectively). Additionally, Staphylococcus aureus isolates were screened for the production of exotoxins. The total and staphylococcal cutaneous microbial population levels were higher (P < 0.05) in AD patients than in the controls. All these population levels decreased (P < 0.05) for both AD and control patients after UVB phototherapy, which also decreased the SCORAD for AD patients. All patients with AD and 50% of controls were carriers of S. aureus, and harboured the bacteria simultaneously on skin and anterior nares. All of the S. aureus strains recovered from AD patient skin produced toxin and the B type was the most frequently detected (70%), followed by C (20%) and A (10%) toxins. Only 40% of the S. aureus isolates from control patients produced toxin. After UVB treatment, microbial population levels of AD patients were similar (P > 0.05) to the ones found in control patients before phototherapy, and toxin production ability of S. aureus isolates decreased drastically. The results of the present study show the beneficial effect of UVB phototherapy on AD and suggest that this may be attributable not only to reduction of skin surface bacteria but also to the suppression of superantigen production from S. aureus.

A model of osteoporosis impact in Switzerland 2000–2020

The aim of our study was to develop a modeling framework suitable to quantify the incidence, absolute number and economic impact of osteoporosis-attributable hip, vertebral and distal forearm fractures, with a particular focus on change over time, and with application to the situation in Switzerland from 2000 to 2020. A Markov process model was developed and analyzed by Monte Carlo simulation. A demographic scenario provided by the Swiss Federal Statistical Office and various Swiss and international data sources were used as model inputs. Demographic and epidemiologic input parameters were reproduced correctly, confirming the internal validity of the model. The proportion of the Swiss population aged 50 years or over will rise from 33.3% in 2000 to 41.3% in 2020. At the total population level, osteoporosis-attributable incidence will rise from 1.16 to 1.54 per 1,000 person-years in the case of hip fracture, from 3.28 to 4.18 per 1,000 person-years in the case of radiographic vertebral fracture, and from 0.59 to 0.70 per 1,000 person-years in the case of distal forearm fracture. Osteoporosis-attributable hip fracture numbers will rise from 8,375 to 11,353, vertebral fracture numbers will rise from 23,584 to 30,883, and distal forearm fracture numbers will rise from 4,209 to 5,186. Population-level osteoporosis-related direct medical inpatient costs per year will rise from 713.4 million Swiss francs (CHF) to CHF946.2 million. These figures correspond to 1.6% and 2.2% of Swiss health care expenditures in 2000. The modeling framework described can be applied to a wide variety of settings. It can be used to assess the impact of new prevention, diagnostic and treatment strategies. In Switzerland incidences of osteoporotic hip, vertebral and distal forearm fracture will rise by 33%, 27%, and 19%, respectively, between 2000 and 2020, if current prevention and treatment patterns are maintained. Corresponding absolute fracture numbers will rise by 36%, 31%, and 23%. Related direct medical inpatient costs are predicted to increase by 33%; however, this estimate is subject to uncertainty due to limited availability of input data.

The annual frequency of root fillings, tooth extractions and pulp-related procedures in Danish adults during 1977-2003.

To investigate a hypothesized long-time decrease of endodontic treatment in a population with low caries prevalence. A Danish nationwide database including almost all dental diagnostic, prophylactic and therapeutic procedures performed in Danish adults was available. Data on the annual frequencies of root fillings, extractions, pulpotomies, direct pulp cappings and stepwise excavations between 1977 and 2003 were analysed. Data on pulpal and periapical diagnoses were not available and on patients age and gender only from 1996. Between 1977 and 2003 the annual number of root filled canals increased from 268,223 to 364,867 (36%). The annual number of root filled teeth increased from 160,119 to 191,803 (20%). During the period, the annually registered patients increased by 16%. Calculated per 1000 patients, the number of root fillings showed a statistically significant increase of 17%. In root filled teeth the canal/tooth ratio increased from 1.67 to 1.96. Root fillings were frequently recorded in all age groups with the bulk of treatments performed on patients between 40 and 60 years of age. At a total population level, the rate of root fillings decreased among younger individuals and increased among older. The annual number of tooth extractions was more than halved from 656,624 in 1977 to 346,490 in 2003. Pulpotomies decreased markedly over the period and less than 10 treatments per 1000 patients were noted for pulp capping as well as stepwise excavation procedures. The present study failed to show a long-time decrease of endodontic treatment in a population with low caries prevalence. On the contrary, an increase of root filled canals was observed between 1977 and 2003, which was probably due to a reduction of the tooth extraction rate and an increased treatment of multi-rooted teeth.

Influence of clinical case definitions with differing levels of sensitivity and specificity on estimates of the relative and absolute health benefits of influenza vaccination among healthy working adults and implications for economic analyses

Clinical illness case definitions for influenza and methods used to define influenza seasons can vary substantially from study to study. These differences often result in differing levels of sensitivity, specificity and positive predictive value for the case definitions used. We explored the implications of different case definitions and outcome periods on estimates of influenza vaccine effectiveness and cost benefit by conducting additional analyses of data collected from a randomized, double blind, placebo controlled trial of the trivalent, intranasal, live attenuated influenza virus vaccine in healthy working adults. Febrile upper respiratory tract illnesses occurring during the peak influenza period was identified as the most specific clinical case definition expected to have the highest positive predictive value for true influenza whereas events occurring on a day with any symptom occurring during the entire outcome period was identified as the most sensitive clinical case definition with the lowest positive predictive value for influenza. As expected, the former provided the highest estimates of vaccine effectiveness (28.4% reduction in work loss days, 24.6% reduction in days with impaired productivity and 40.9% reduction in days with health care provider visits) but the lowest estimates of absolute reductions in events (42.4 work loss days prevented per 1000, 79.0 impaired productivity days per 1000, and 16.5 days with health care provider visits per 1000). On the other hand, events on days with any symptom during the entire outcome period provided the lowest estimates of vaccine effectiveness (18% reduction in work loss days, 18% reduction in days with impaired productivity, and 13% reduction in days with health care provider visits) but the highest estimates of absolute reductions in events (186.4 work loss days per 1000, 271.5 impaired productivity days per 1000, and 44.8 days with health care provider visits per 1000). When applied to a cost benefit analysis, the more specific case definition provided a break even cost for vaccination of US$ 6.58 whereas the more sensitive case definition provided a break even cost for vaccination of US$ 43.07. Clearly the latter combination is most appropriate when trying to assess the total population level impact of a vaccine preventable disease and the potential cost effectiveness of vaccination whereas the former may be most appropriate for assessing whether the vaccine actually works. The definitions of clinical influenza illness and outcome periods should be selected to match the study question.

Lack of detection of ampicillin resistance gene transfer from Bt176 transgenic corn to culturable bacteria under field conditions

Population levels of total and ampicillin-resistant culturable bacteria and the putative horizontal bla gene acquirement from Bt-corn were studied in commercial fields of transgenic corn in Spain during the years 2000–2003. Commercial fields consisting of conventional corn (Dracma) and Bt176 transgenic corn (Compa CB) were located in three climatic regions. The effect of corn type, plant material, field location, stage of sampling and year of study were studied on total and ampicillin resistant bacterial population levels, on median effective dose and on the slope of the dose–response curve to ampicillin. None of the parameters measured were significantly different ( P<0.01) between transgenic and non-transgenic cornfields under the diverse conditions studied. However, in population levels of ampicillin resistant bacteria, the minimum difference between sample means to be significant with a likelihood of 80% was 8.9%. Specific detection of putative bacteria harbouring bla TEM-1 ampicillin resistance genes acquired from Bt176 corn was performed with a method based on the extraction of DNA from the culturable bacterial fraction and with PCR. Primers for PCR were targeted to the bla gene and the corresponding flanking regions present in the pUC18 cloning vector or the Bt176 construct. The culturable bacterial fraction of 144 field samples (up to 864 analysis, including ampicillin enrichments) was analysed by PCR. The estimated total number of bacteria analysed was 10 8. The level of detection of a transfer event according to the sensitivity of the methods used was 10 −6. Four samples of transgenic and five of non-transgenic corn gave positive signals. However, the amplification products did not correspond to the ones expected from Bt176 or pUC18. The limitations of the sampling design and of the methods used are discussed.

A discrete hierarchical model of intra-specific competition

A discrete hierarchical model with either age, size, or stage structure is derived. The resulting scalar equation for total population level is then used to study contest and scramble intra-specific competition. It is shown how equilibrium levels and resilience are related for the two different competition situations. In particular, scramble competition yields a higher population level while contest competition is more resilient if the uptake rate as a function of resource density is concave down. The conclusions are reversed if the uptake rate is concave up.

Inversion and allozyme polymorphism show contrasting patterns of microgeographical population structure in a natural population of Drosophila buzzatii from Argentina

Abstract Second chromosome inversions and genotypic frequencies at seven allozyme loci were determined in a natural population of the cactophilic species Drosophila buzzatii that uses as breeding sites the necrotic cladodes of the prickly pear Opuntia quimilo and the rotting stems of cardón, Trichocereus terschekii. Different processes govern the evolutionary fate of inversion and allozyme polymorphisms. A pattern of heterotic balance for inversions seems to be acting uniformly in each breeding site and could depend on different regimes of density-dependent selection within cactus hosts. Patterns of variation of allozymes revealed significant heterogeneity in allele frequencies for Esterase-1 (Est-1) among O. quimilo rots and Aldehyde oxidase (Aldox) and Xanthine dehydrogenase (Xdh) among T. terschekii substrates and showed gene-cactus effects only for Esterase-2 (Est-2). Consistent and significant excesses of homozygotes were detected at both the within-rot and in the total population levels that could be accounted for by diversifying selection among individual breeding sites.

Yeast population dynamics in five spontaneous fermentations of Malvasia must

The dynamics of the wine yeast strains presented in five spontaneous Malvasia wine fermentations have been studied. Samples were analysed for their microbiological characteristics and chemical substances. All 937 isolates were characterized using electrophoretic karyotyping and tested for their killer activity. The non- Saccharomyces population was identified using a combination of PCR-RFLP analysis of the rDNA spacer region and physiological testing. The total yeast population level in the must after sedimentation was 105cfu ml−1and included the following genera:Candida, Metschnikowia, Hanseniaspora, Rhodotorula, Issatchenkia and Debaryomyces. However, Saccharomyces sp. was not detected in fresh must samples plated on YEPD medium. Based on the chromosome length polymorphism among 649 isolates from the subsequent phases of fermentation, 46 different electrophoretic patterns of Saccharomyces cerevisiae were distinguished. The most abundant karyotypes were L1, L4, L12, P6. A sequential substitution of S. cerevisiae strains occurred during the different phases of fermentation. At the slow fermentation rate, karyotype L4was most abundant in almost all fermenters. At the beginning of the tumultuous fermentation phase, the most frequent karyotype became L1followed by karyotype L4. Finally, during the fermentation process, pattern L4was clearly replaced by karyotype L1followed by pattern L12. Despite the same fermentation source (grape must), differences among five spontaneous fermentations were observed. The population dynamics of S. cerevisiae yeasts, especially the dynamics of the major S. cerevisiae strains (L1, L4, and L12) were quite similar in all five fermenters in opposite to the minor strains of S. cerevisiae.

Lactic acid bacteria associated with the digestive tract of Atlantic salmon (Salmo salar L.)

The present study reports the effect of excessive handling stress and starvation on the lactic acid bacteria associated with the digestive tract of Atlantic salmon (Salmo salar L.). A relatively low population level (approximately 2 x 103 bacteria per gram wet tissue) of viable adherent heterotrophic bacteria was associated with the digestive tract (foregut, midgut and hindgut). Of the 752 bacterial isolates isolated from diet, water and the digestive tract, 201 isolates belonged to the carnobacteria. Of these isolates, one from the diet, one from the rearing water and 80 from the gastrointestinal tract, were further identified on the basis of 16S rDNA sequence analysis. All these isolates were identified as being Carnobacterium piscicola-like. Daily repeated stress and starvation of the fish over 11 d had no influence on the total culturable bacterial numbers or population level of C. piscicola associated with the digestive tract. C. piscicola-like isolates colonizing the various intestinal regions (foregut, midgut and hindgut) were also screened for their ability to produce growth inhibitory compounds active against the fish pathogen Aeromonas salmonicida. Of the 199 C. piscicola isolates tested, 139 inhibited growth of the pathogen.

Factors affecting changes in waterfowl populations in eutrophic wetlands in the Finnish lake district

From the 1970s to the 1990s, changes in breeding waterfowl populations were monitored at 26 well‐vegetated lakes in southern Finland. Extreme total population levels were found to differ by 40%, but between successive years fluctuations did not exceed 20%, the most unstable populations being garganey Anas querquedula, tufted duck Aythya fuligula, coot Fulica atra and pochard Aythya ferina. Multiple regression analysis was used to determine the effects of weather factors during wintering, spring and brood seasons on the variation in breeding waterfowl populations. The following weather factors were statistically significant in explaining fluctuations observed in four species; in garganey: spring temperature; in pintail Anas acuta: brood season temperature, winter severity in France and spring temperature; in goldeneye Bucephala clangula: winter severity in the Baltic and spring temperature; and in mallard Anas platyrhynchos: brood season temperature of the previous year. Mallard, teal Anas crecca, wigeon Anas penelope and goldeneye were shot in larger numbers than would be expected considering their respective proportions of the breeding waterfowl community. Hunting pressure on mallard, tufted duck and goldeneye was clearly higher in our study area than in other parts of Finland. Our results indicate that the level of hunting pressure in our study area may affect population densities of mallard.

Gene flow and allozymic population structure in the clam Venus antiqua (King of Broderip), (Bivalvia, Veneriidae) from Southern Chile

Using horizontal electrophoresis, 13 allozyme loci were screened in 144 adult clams ( Venus antiqua) (King of Broderip) from 5 geographic samples in southern Chile. Polymorphism was detected at 11 loci across the sampling localities. Gene frequency differences rather than the alternative fixation of alleles characterize these collecting sites. Direct-count heterozygosity fluctuated between 6.8% and 10.3%, with a generalized and significant heterozygote deficiency detected in every locality. Similar levels of genetic diversity were detected in both exploited banks and one presumed unmanaged population. Substantial estimates of demic structuration were found at the total population ( F ST=0.107) and regional levels ( F ST=0.143), with coinciding high inbreeding estimates ( F IS=0.57). Although no statistically significant evidence of genetic substructuring was found at the within-region comparison ( F ST=0.007), a generalized heterozygote deficiency ( F IS=0.57) also characterized that hierarchical level. Spatial correlation of gene frequencies indicated a nearly random distribution of genotypes along the latitudinal distribution of samples. The high rates of global, and the within-region rates of gene flow suggest substantial larval interchange via long-distance dispersal that prevent differentiation by drift alone. Accordingly, no discrete genetic units can be recognized for the species at any spatial scale. Apparently, high recruitment rates help in replenishing genetic variants lost by continuous overfishing, thus explaining why human extraction has not resulted in major losses of genetic variation for individual populations. The slow-growing rate and delayed sexual maturation of this clam species are apparently stronger limiting factors than human-induced genetic erosion for the conservation of natural beds and viable captive management of V. antiqua.

Do surface plant and soil seed bank populations differ genetically? a multipopulation study of the desert mustard Lesquerella fendleri (Brassicaceae)

Seed banks are an important component of many plant populations, but few empirical studies have investigated the genetic relationship between soil seeds and surface plants. We compared the genetic structure of soil seeds and surface plants of the desert mustard Lesquerella fendleri within and among five ecologically diverse populations at the Sevilleta National Wildlife Refuge in Central New Mexico. At each site, 40 Lesquerella surface plants and 40 samples of soil seeds were mapped and genetically analyzed using starch gel electrophoresis. Overall allele frequencies of soil seeds and surface plants showed significant differences across the five populations and within three of the five individual populations. Surface plants had significantly greater amounts of single and multilocus heterozygosity, and mean surface plant heterozygosity was also greater at the total population level and in four of the five individual populations. Overall soil seed (bot not surface plant) homozygosity was significantly greater than predicted by Hardy-Weinberg expectations at the total and individual population levels. Although F-alpha estimates revealed similarly small but significant genetic divergence within each life-history stage, estimates of coancestry showed that fine-scale (0.5-2 m) genetic correlations among the surface plant genotypes were roughly twice those of soil seed genotypes. An unweighted pair group method with arithrnetic mean cluster analysis indicated that in the two geographically closest sites, the surface plants were slightly more genetically similar to each other than to their own respective seed banks. We also found weak and/or negative demographic associations between Lesquerella soil seed and surface plant densities within each of the five sites. We discuss the difficulties involved with sampling and genetically comparing these two life-history stages.

Predator-prey models in heterogeneous environment: Emergence of functional response

In this work, we are interested in prey-predator models. More precisely, we study the spatial heterogeneity effects on the amount of prey eaten per predator per unit time, when different time scales occur. This amount and its relation with the amount of predators produced via the predation are interesting from an ecological point of view. Indeed, the knowledge of these quantities permits us to quantify the transfer of the biomass in the food chain. Our aim is to show how the spatial heterogeneity acts on these amounts. We consider prey-predator systems in a multi-patch environment. We show that density dependent migrations make emerge new models on the total population level and we exhibit some examples. Furthermore, we show that the aggregation method is a good tool for describing the mechanisms hidden behind complex models.

A hierarchical analysis of genetic structure and variability in patchily distributed coexisting Chiastocheta species (Diptera: Anthomyiidae)

The pattern of genetic variation in four coexisting fly species of the genus Chiastocheta was studied by allozyme electrophoresis. The fly species are confined to patches of one plant, Trollius europaeus, and thus experience very similar habitat fluctuations. Collection sites were chosen in a hierarchical fashion and F-statistics were estimated at three levels: intraregion, inter-region and total population. Population characteristic genetic parameters were compared within and among species and were related to the hierarchical level. The species were used as replicate experiments for inference of habitat history, and the hierarchical levels were used as inference for specific gene flow patterns. Genetic variability was related to relative species abundance but not to local population size. The species divided into two heterogeneity classes, C. dentifera/C. trollii, and C. inermella/C. abruptiventris, where the former pair had more genetic variation than the latter. However, among all species no differences in the average number of alleles per locus were found. The amount of variability was not related to interspecific phylogeny, and the species could thus be analysed independently for genetic structure. Species-specific genetic patterns were found, but for all species the amount of genetic differentiation was related to regional geography. For three species, differentiation within regions was often higher than at the total population level whereas the differentiation among regions was negligible. Differentiation of the fourth species, C. inermella, increased with geographical scale indicating an isolation-by-distance genetic structure. We suggest that within species the amount of genetic differentiation need not be related to intraspecific ancestry, as high differentiation was not necessarily associated with low expected geographical structure.