The response of lions and spotted hyaenas to sound playbacks as a technique for estimating population size

Overall, 217 lions (>1 year) Panthera leo (Linnaeus) and 2069 spotted hyaenas (>8 mo) Crocuta crocuta (Erxleben) responded to broadcast vocalizations, call‐ins, during six surveys in the Masai Mara National Reserve, Kenya.
Carnivore response varied seasonally and was significantly higher and more uniform when migratory prey were absent. Variation in wildebeest abundance, by affecting food availability, was the only significant predictor of response. Variability in response with overall prey abundance was higher for lions than hyaenas. Lion response occurred within a radius of 2·5 km, was independent of age and sex but dropped virtually to zero whenever lions possessed a carcass at the time of broadcasting.
An independent total census recorded 547 lions (all ages) in the Reserve, 9·96% of which were nomads. This proportion increased by 7·94% following the influx of migrants and raised lion (>1 year) density from 0·292 to 0·320 lions/km². The call‐in estimate of 0·294±0·009 (95% c.l.) lions/km² practically equalled the total count. The high precision and low bias (−0·224%) of this estimate imply that call‐in surveys are reliable and may be employed to effectively monitor carnivore populations in the long term. Under simple random sampling, covering about 20% of an area would seem adequate to produce reliable density estimates.     

Lion density and population structure in the Selous Game Reserve: evaluation of hunting quotas and offtake

In 1992, tourist hunting in the Selous Game Reserve generated 1.28 million dollars for the Tanzanian government, of which 0·96 million dollars were returned to wildlife conservation. Lions ( Panthera leo ) are one of three critical species for tourist hunting, consistently generating 12%–13% of hunting revenue from 1988 to 1992. Because of their ecological and economic importance (and intrinsic value), it is important that lion quotas be set so that offtake is sustainable. The population density of lions in Selous ranges from 0·08 to 0·13 adults km⁻², comparable to unhunted ecosystems. The adult sex ratio (36–41% male) and the ratio of cubs to adults (29% cubs) are similar to those of unhunted populations. The ratio of lions to hyaenas is lower in heavily hunted areas (0·17 lions/hyena) than in unhunted areas (0·43 lions/hyena). Hunting levels between 1989 and 1994 took 2·7–4·3% of adult males annually, which is sustainable. The current quota is 10–16% of the adult male population, which exceeds natural mortality rates for male lions. To remain stable if the quota was filled, the population would have to compensate via increased fecundity, increased juvenile survival, or an altered sex‐ratio. Compensation occurs in Selous by producing (or raising) more male than female cubs (66–81% of juveniles are male). Only 28% of the Selous quota was filled in 1992. The percentage of quota filled (both in Selous and nationwide) has dropped since 1988 as quotas have increased. The current intensity of lion hunting in Selous is sustainable, but the quota cannot be filled sustainably.     

Phenotypic identification of non-clinical isolates of Acinetobacter species

Five different phenotypic identification systems were used in attempts to place 164 Acinetobacter strains obtained from a biological nutrient removal plant and 16 reference cultures into the genospecies of Bouvet and Grimont, and Tjernberg and Ursing. Of these strains only four, including two of the reference strains, were identified at a Willcox probability level of >0·95 and a modal likelihood fraction of > 0·0001 by all five systems. These different identification schemes were compared for their usefulness with such non-clinical isolates.     

Habituation to acid in Escherichia coli: conditions for habituation and its effects on plasmid transfer

Induction of acid resistance (habituation) in Escherichia coli at pH 5·0 took ca 5 min in broth at 37°C and 30–60 min in minimal medium. Induction occurred at a range of pH values from 4·0 to 6·0; it was dependent on continuing protein and RNA synthesis but substantial acid resistance appeared in the presence of nalidixic acid. Acid resistance was long-lasting; organisms grown at pH 5·0 retained most of their resistance after 2 h growth at pH 7·0. Organisms grown at pH 5·0 showed increased synthesis of a number of cytoplasmic proteins compared with the level in cells grown at pH 7·0. DNA repair-deficient strains carrying recA, uvrA or polAl mutations were more acid-sensitive than the repair-proficient parents but were able to habituate at pH 5·0. Organisms grown at pH 5·0 transferred the ColV plasmid much more effectively at acid pH than did those grown at pH 7·0 and habituated recipients appeared better able to repair incoming acid-damaged plasmid DNA than did those that were non-habituated. Induction of acid resistance at pH 5·0 may be significant for the survival of organisms exposed to periodic discharges of acid effluent in the aquatic environment and habituation may also allow plasmid transfer and repair of acid-damaged plasmid DNA during or after such exposure.     

Neutralization efficacy of Dey-Engley medium in testing of contact lens disinfecting solutions

A quantitative assay for the demonstration of neutralizer efficacy was developed to monitor contact lens disinfecting solutions. Adequate neutralization of disinfecting agents is essential to the accurate determination of disinfecting activity with time. This method employed the recovery of small numbers of micro-organisms from neutralizing medium containing a disinfectant. A statistical estimation of significance between treatments demonstrated that Dey-Engley medium (DE; Difco) was generally effective when tested as an agar growth medium with several bacterial test organisms. DE medium from another vendor was less effective, underscoring the need for laboratory quality control and monitoring. DE agar (Difco) adequately neutralized all solutions tested at a 1:20 dilution. The solutions included those containing Dymed^TM (polyaminopropyl biguanide, 0·00005%), chlorhexidine (0·005%), Polyquad® (0·001%), chlorhexidine (0·005%) and thimerosal (BP, 0·001%), thimerosal (BP, 0·002%) and Tris(2-hydroxyethyl) tallow ammonium chloride (0·013%), and a solution preserved with 115 ppm benzalkonium chloride (BAK). A modification of this medium was developed which retained virtually all of the neutralizing efficacy for the solutions tested while allowing the use of automated testing procedures.     

A preliminary investigation of allozyme genetic variation and population geographical structure in Aphanius fasciatus from Italian brackish-water habitats

A total of 150 individuals from Aphanius fasciatus from coastal brackish-water habitats was analysed by allozyme electrophoresis to collect data on its genetic variation. From 22 enzymes, 43 putative enzyme-coding loci were resolved, 12 of which were polymorphic at P_0·99 level. Only one of the 31 probability tests showed a significant departure from the Hardy-Weinberg equilibrium. Aphanius fasciatus showed low levels of genetic polymorphism, with expected heterozygosity values ranging from 0·027 (S.E.=0·013) to 0·064 ( s.e. =0·023). Nei's genetic distances between populations ranged from 0·002 to 0·042. Weir & Cockerham F -statistics showed high levels of genetic heterogeneity among populations (jackknifed θ=0·302, s.e. =0·045) and estimates of N _m were < 1, indicating restricted gene flow. Significant positive correlation between genetic distance and geographical distance matrices, detected by Mantel's test ( g =1·941; P 0·001), is consistent with the prediction that the species is genetically structured by isolation-by-distance.     

Temporal stability of sea louse Lepeophtheirus salmonis Krøyer populations on Atlantic salmon Salmo salar L. of wild, farm and hybrid parentage

Atlantic salmon salmo salar smolts of wild, hybrid and farmed parentage were individually tagged then reared in a sea cage for 8 months. The fish were sampled three times during this period. On all occasions, farmed Atlantic salmon displayed the highest abundance and density of sea lice Lepeophtheirus salmonis , whilst no significant differences were observed between hybrid and wild Atlantic salmon. Percentage variation between the lowest and highest infected groups was as high as 175 and 144% for L. salmonis abundance and density respectively (sample 2). The temporal stability of interindividual sea lice infection levels was investigated pair‐wise between samples using correlation (sample 1 v . 2, 1 v . 3 and 2 v . 3). When calculated using sea louse abundance, correlations ranged from r ² = 0·11, P  < 0·01 to r ² = 0·39, P  < 0·001, but, when the effects of fish size were controlled for by converting abundance to density, all correlations were <  r ² = 0·1. Therefore, these data indicate that a fish's relative infection level in one sample was a weak predictor of its relative infection level in another sample. This suggests that identification of individual Atlantic salmon that display reduced susceptibility to sea lice, may be problematic.     

A relatively small change in sodium chloride concentration has a strong effect on adhesion of ocular bacteria to contact lenses

Adhesion of bacteria to hydrogel lenses is thought to be an initial step of ocular colonization allowing evasion of normal host defences. The salt concentration of media is an important parameter controlling microbial adhesion. Salinity varies from 0·97% NaCl equivalents in the open eye to 0·89% in the closed eye state. In this study, the effect of sodium chloride in the concentration range of 0·8–1·0% (w/v) NaCl on adhesion of ocular bacteria to soft contact lenses was investigated using a static adhesion assay. Pseudomonas aeruginosa was found to adhere to lenses in significantly greater amounts than Serratia marcescens, Flavobacterium meningosepticum, Stenotrophomonas maltophilia and Staphylococcus intermedius . Increasing NaCl from 0·8% to 1·0% (w/v) increased adhesion of all bacteria tested. This adhesion was strong since the organisms could not be removed by washing in low ionic buffer. Adhesion of these organisms did not correlate with their cell surface properties as determined by bacterial adhesion to hydrocarbons (BATH) and retention on sepharose columns.     

Glucose-induced acid tolerance appearing at neutral pH in log-phase Escherichia coli and its reversal by cyclic AMP

Escherichia coli shifted from broth at external pH (pH₀) 7·0 to pH₀ 7·0 broth plus glucose rapidly induced marked acid tolerance which also appeared, albeit to a lesser extent, plus maltose, sucrose or lactose. Tolerance appeared without the medium pH becoming acidic. Tolerance was most substantial when glucose was added at pH₀ 7·0 but was also appreciable at pH₀ 7·5, 8·0 and 8·5. Induction of tolerance by glucose was markedly reduced by cyclic AMP and essentially abolished plus NaCl or sucrose ; the induction process was also reduced but not fully inhibited by chloramphenicol, tetracycline and nalidixic acid. Glucose-induced organisms showed less acid damage to DNA and β-galactosidase and it is likely that this is because glucose induces a new pH homeostatic mechanism which keeps internal pH close to neutrality at acidic pH₀. In conclusion, it is clear that glucose induces a novel acid tolerance response in log-phase E. coli at pH₀ 7·0 ; it is now known that induction of this response involves the functioning of extracellular induction components including an extracellular induction protein.     

Factors affecting early mortality in the South American fur seal (Arctocephalus australis) in Peru: density-related effects and predation

Early mortality in the South American fur seal ( Arctocephatus australis ) in Peru is considerably higher than that seen in any other population of fur seal; 31–49% in the first month as opposed to a maximum of 20% in other populations. In 1987 and 1988, pup mortality was found to be enhanced by density-related effects and predation on pups by the southern sea-lion ( Olaria byronia ). At a high density beach, where 60% of the fur seals bred, mortality correlated with the number of females ashore as did aggression. Female aggression was driven to high levels by a combination of high density and movement within the colony to thermoregulate. However, even at a low density, beach mortality remained high due to a high level of predation by male southern sea-lions (low density beach 5·0–8·3% of all pups; high density beach 0·2%). Predation rates were lower at the high density beach because male fur seals expelled most attacking sea-lions during the breeding season (low density beach 10·0% of attacking sea-lions expelled; high density beach 58·8%).     

Bacteriological Examination of Seawater: Observations on Factors Affecting the Performance of Media

The performance of MacConkey broth and minerals modified glutamate lactose medium was examined in a series of experiments. It was found that the addition of seawater with or without antibacterial activity and the addition of 3·2% NaCl solution to double strength media all had similar harmful effects on their performance. Also a concentration of 3·2% NaCl in ordinary lactose broth caused a great decrease ( P =0·02) in the number of tubes containing coliform organisms. It is concluded that the high salt content of seawater interferes with lactose fermentation by coliforms. This interference was found to be so great that the number of tubes in which coliform organisms and Escherichia coli were detected, dropped from 2·5 to 3·5 times when an equal volume of seawater was added to double strength MacConkey and glutamate media. The results of the last experiment suggest that for best performance of the media, the volume ratio of seawater to medium should be equal or less than 1/10. Also glutamate medium was superior to MacConkey broth ( P <0·001), especially in the detection of E. coli .     

Factors affecting the survival of Salmonella and Escherichia coli in anaerobically fermented pig waste

The survival of Salmonella typhimurium was investigated in acidogenic, anaerobically fermented pig wastes and in synthetic media, each containing volatile fatty acids (VFA). Salm. typhimurium survived at pH 6·8, but not at pH 4·0, when incubated at 37°C for 24 h in either fermented or synthetic medium containing VFA. The minimum inhibiting concentration of VFA for Salm. typhimurium after 48 h incubation at 30°C at pH 4·0 was 0·03 mol/l and for Escherichia coli it was 0·09 mol/l. Fermented pig wastes in a digester, maintained at pH 5·9, were inoculated with Salm. typhimurium and then incubated at 37°C for 24 h. The pH was adjusted to either 4·0 or 5·0 and after a further 48 h at 30°C, Salm. typhimurium survived at pH 5·0 but not at pH 4·0. It was concluded that pH is critical in determining the survival of this organism in acidogenic anaerobically fermented pig waste.     

METHODS FOR THE ISOLATION OF FAECAL STREPTOCOCCI (LANCEFIELD GROUP D) FROM BACON FACTORIES

SUMMARY: Two methods have been developed for isolating and enumerating group D faecal streptococci from localities such as bacon factories where they are heavily outnumbered by other organisms. The first depends on presumptive counts in a Lab-Lemco-peptone-glucose broth (pH 6·0) containing 0·1% of thallous acetate with confirmation by streaking on tetrazolium agar. The other method involves direct plating on tetrazolium-glucose agar (pH 6·0) containing 0·1% of thallous acetate. On the tetrazolium medium differentiation can be made between Streptococcus faecalis and its variants zymogenes and liquefaciens and the other group D organisms, Strep. faecium, Strep. durans and Strep. bovis .     

Development and application of a simple filter paper imprinting technique for the detection and enumeration of colonies of ureolytic micro-organisms

A rapid, simple and inexpensive method has been devised to determine the proportion of colonies of ureolytic organisms in cultures of complex microbial populations. Spiral plated cultures displaying well separated colonies are tested for ureolytic micro-organisms by imprinting the colonies onto filter papers impregnated with a solution of 1 mol/l urea and phenol red (0·1% w/v) in 0·1 mol/l phosphate buffer (pH 6·8). A rapid colour change indicates ureolytic activity. The proportion of ureolytic colony-forming units in cultures of saliva specimens from 90 school children ranged from less than 1% to 40% (mean 9·9%± 7·7). Saliva and dental plaque specimens from 16 adult subjects were also tested and the occurrence of urease-positive organisms was substantially less in plaque (3·6%± 3·7, range 0·1–12) than saliva (18·7%± 13·8, range 1·3–51). The predominant ureolytic oral species was Streptococcus salivarius , 75 (54·7%) of 137 tested isolates being urease-positive.     

Grand Canonical Monte Carlo Simulation for Solubility Calculation in Supercritical Extraction

Abstract

The Grand Canonical Ensemble Monte Carlo (GCEMC) technique is used to simulate highly nonideal dilute mixtures in the near vapor-liquid critical region. These systems are commonly found in supercritical fluid extraction processes. Mixtures composed of model CO₂/naphthalene/water molecules are studied. Very large and highly correlated concentration fluctuations were observed. It was found that when the total number of molecules in the system exceeded about 150, system size dependence was not significant. The GCEMC method breaks down when the system density exceeds about 1.5 times the solvent critical density due primarily to the low probability of successful addition and removal of the large naphthalene molecules. In some systems, the presence of a small amount of water caused a dramatic increase in the system density and in naphthalene solubility. By examining the radial distribution functions in these mixtures, the origin of this effect can be attributed to the preferential aggragation of the solute naphthalene molecules around the highly polar water molecules.     

The volitional travel speed varies with reproductive state in mature female brown trout Salmo trutta

This study tested the effect of reproduction on the volitional travel speed of mature female brown trout Salmo trutta L. The downstream travel speed in the pre-spawning state was 0·25 m s⁻¹ (95% CI : 0·19, 0·34) while it increased significantly to 0·65 m s⁻¹ (95% CI: 0·49, 0·87) in the post-spawning state. The results suggest state-dependent travel speed in S. trutta .     

Factors affecting the survival of dace, Leuciscus leuciscus (L.), in the early post-hatching period

Young dace fry were stocked into nylon mesh cages at densities ranging from 0·044 to 7·230 1^-1, and the cages anchored in a backwater area where the fry gathered naturally. The fry began feeding on small organisms drifting into the cages 2-4 days after hatching. The growth rate of the fry was inversely proportional, and the death rate directly proportional, to initial density. Soon after the exhaustion of endogenous food reserves (as determined from unfed fry), there was a period of massive mortality at the highest initial densities, probably due to starvation. After 20 weeks, the cages stocked at the two highest initial densities contained the lowest biomass of fry. Transfer of fry to cages with a larger mesh size produced increased growth and 46% survival over 20 weeks at the lowest initial density. These fry reached an overwintering length of 35·5 mm compared with 48·0 mm for naturally occurring fry.     

Basking shark occurrence off south-west England in relation to zooplankton abundance

Basking sharks Cetorhinus maximus >3 m total length arrived off Plymouth, U.K. directly after the increase in zooplankton density in May, while young-of-the-year basking sharks (<3 m) occurred when zooplankton density was lower (0·8-1·1 g m⁻³). No basking sharks were seen after July when the zooplankton density was least.     

Adaptive and evolutionary significance of a reproductive thermal threshold in Barbus barbus

From 1989 to 1996, barbel in the River Ourthe started spawning under variable environmental conditions, except for water temperature. Each year, spawning was initiated when water daily minimum temperature reached or exceeded 13·5° C. Any decrease of temperature below this value later in the spawning period caused spawning to be suspended. Analyses of offspring growth provided evidence that 13·5° C was the value below which 0+ barbel stop growing. It was hypothesized that barbel trade off the lower initial probability of survival against a larger size at the onset of winter. To test empirically for this hypothesis, the adequacy of alternative—theoretical—strategies associated with other thermal thresholds (12, 15·0, 17·1 and 20·2° C) was modelled with respect to: (1) the feasibility of spawning (inhibition of sexual maturation by a decreasing photoperiod); (2) the impact of the temperature on embryonic development; (3) the effect of water level variations on the integrity of spawning grounds until the emergence of larvae; (4) the size of the offspring at the onset of winter. On an 8-year (1989–1996) average, the present spawning strategy would have produced a higher recruitment than alternative strategies (relative adequacy of 33·23, 85·64, 93·17 and 17·62%, respectively). However, alternative strategies would have produced better annual scores on five of eight occasions in the River Ourthe environment, and a better overall score in environments 1·5 or 3·5° C warmer than now. The consistency of the thermal threshold over years, despite a low selection pressure by the environment, was interpreted as the expression of a phenotypic mechanism (thermal homing) promoting the selection of the lowest efficient thermal threshold, and enabling breeders to relay to the next generation some form of thermal stability in a variable environment.     

Factors affecting production and activity of phospholipase C by Yersinia enterocotttica

The production of phospholipase C by Yersinia enterocolitica strain SG was optimum at 37†C at pH 6·5. No enzyme activity could be detected when the organism was grown at extreme pH values (pH > 8·5 or <5·0). The enzyme production was maximum when the organism was grown under static conditions in TSB medium. All solvents and salts inhibited the enzyme activity, whereas loss of activity was 95% in presence of methanol (20%) and 99% in presence of sodium azide (0·2 mol/l). The enzyme activity was increased twofold in the presence of cyste-ine and decreased by 98% in the presence of sodium perchlorate (0·2 mol/1).