Patterns of abundance of fire ants and native ants in a native ecosystem

Abstract 1. This correlational study examines the relationship between the red imported fire ant (Solenopsis invicta) and native ants in a longleaf pine savanna. Fire ants are frequently associated with a decline in native ants throughout the invaded range, but fire ant invasion is often coupled with habitat disturbance. Invasion of fire ants into the longleaf pine savanna provides an opportunity to examine the structure of the ant community in the absence of habitat disturbance. 2. Pitfall trapping was conducted within the longleaf pine savanna as well as across a naturally occurring soil moisture gradient, in plots that had been artificially watered. 3. Species richness did not vary as a function of fire ant density. There was an inverse relationship between native ant density and fire ant density, but this abundance pattern does not necessarily imply a causal link between fire ant invasion and native ant decline. For individual species, fire ant densities were negatively correlated with the densities of only two native ant species, including Solenopsis carolinensis, a native species that potentially limits the invasion of fire ants. Additionally, fire ants and native ants respond differently to soil moisture, with native ants favouring drier conditions than fire ants. 4. The possible exclusion of fire ants by some native ants, as well as differences in habitat preferences, provide alternative explanations for the frequently observed negative correlation between fire ants and native ants.     

Antibiotic Resistance among Escherichia coli O-serotypes from the Gut and Carcasses of Commercially Slaughtered Broiler Chickens: a Potential Public Health Hazard

Presumptive coliform counts and the distribution of Escherichia coli O-serotypes were investigated in chicken rectal contents (175) abdominal cavities (152) and on the carcasses of 44 which had been commercially raised, slaughtered and prepared for sale. Large numbers of E. coli resistant to at least one antibacterial agent were found at each site; comparison of the O-serotypes suggested heavy contamination of the carcass with strains from the gut. The range of O-serotypes was similar to that found in man and some public health implications of cross-infection particularly by handling uncooked birds in the kitchen, are discussed.     

COMPARATIVE ASPECTS OF THE ONTOGENY OF TASTE

Pigs are proposed as a useful laboratory model for the investigationof taste preferences and other controls of ingestive behaviorin the newborn. Suckling pigs can be easily trained to feedthemselves from an artificial feeding apparatus so that intakecan be measured directly. In this manner preferences for glucose,sucrose, fructose and lactose were found in pigs 3 wk of age.The preference threshold for glucose is considerably higherthan that reported for more mature pigs. Taste aversion wasdemonstrated in suckling pigs 2 wk of age. After the taste ofglucose had been paired with LiCl injection, poisoned pigs didnot show the strong glucose preference shown by control pigs.In addition to oropharyngeal controls of intake, gastrointestinalcontrols of intake in the newborn pig were investigated.Loadsof milk or 5% glucose, but not 0.9% NaCl, given by gavage depressedsubsequent intake in piglets 1 wk of age. Caloric or glucostaticmechanisms, but not volume alone, appear to be involved in satietyin the newborn pig. ^*Supported by USPHS Special Fellowship 5F03 AM55321-02 to K.A.H.Request for reprints should be sent to Dr. K. A. Houpt, Dept.of Physiology, N.Y.S. College of Veterinary Medicine, Ithaca,New York 14853, U.S.A.     

Population increase of Ditylenchus dipsaci (Kühn) in the narcissus and the spread of the nematode through the soil

A bioassay technique, using forty onion seedlings per pot, was used to determine the soil population of the narcissus race of Ditylenchus dipsaci .
In experiments with narcissus, a progressive increase of D. dipsaci populations was shown, reaching a peak at the end of the growing season. This rise in population in May/June was associated with a rise in temperature. Increase in inoculum gave a significantly larger population in the foliage but not in the bulbs. Nematodes moved actively and were transported passively both up and down within the host plant. The presence of spikkels was associated with nematodes in the active intercalary meristem.
Migration from the plant into the soil and back into the plant, mostly via the base of the bulb, was continuous throughout the growing season and related to the population increase within the plant. Migration of nematodes from wetted dried leaf tissue continued over 60 days. Spread of the nematode through the soil was slow in the absence of external agencies, such as water run-off and methods of cultivation.     

Carbohydrate Utilization by the Soil Amoeba Hartmannella castellanii

SYNOPSIS. Carbohydrate utilization by 9 strains of Hartmannella castellanii has been studied by growing the amoebae in a chemically defined medium which did not support growth without an added energy source. Strains differed in the utilization of sucrose, raffinose, melibiose and mannitol. The strains which did not use sucrose for growth were shown to metabolize this sugar: ¹⁴CO₂ was produced and ¹⁴C incorporated into TCA isoluble compounds when the amoebae were grown in the presence of radioactive sucrose.     

Ear Structure and Function in Modern Mammals

The acoustic portions of the mammalian ear display greater morphologicaldiversity in peripheral than in central portions. In many mammalsthe pinna is of negligible auditory significance. The tympano-ossicularsystem of all mammals sensitive to air-borne sounds must transformair vibrations to fluid vibrations in the inner ear by matchingthe acoustical impedances. Within the cochlea the energy ofthe fluid vibrations is transduced into nerve impulses. In highly specialized mammals the morphology of these transformerand transducer mechanisms is adapted for the reception of extremefrequencies. Echolocating bats and whales possess different,but effective, specializations for the reception of ultrasonicfrequencies. Moles and kangaroo rats, on the other hand, havespecialized ear structures for the reception of low frequencies.     

The significance of biological races of Ditylenchus dipsaci and their hybrids

Pure cultures of six races of Ditylenchus dipsaci derived from a single female, namely, lucerne race (LR), red clover race (RCR), white clover race (WCR), narcissus race (NR), tulip race (TR) and oat race (OR) were inoculated into eight plant species growing in pots. Onion was host to all six races, and tulip to all except RCR, whereas lucerne was susceptible only to LR and slightly to WCR. Hyacinth was not very susceptible to any race. The TR and OR were the most polyphagous. Severe symptoms were not necessarily associated with large nematode populations. Parthenogenesis did not occur. Ten fertile hybrids between races were produced and the host range of five of these was tested. On average the hybrids multiplied less than their parent races and their host ranges showed no relationship to those of their parent races. RCR and TR inoculated together into tulip produced significantly fewer nematodes than did TR alone and more than RCR alone. Mixed populations of races occur in nature which are probably a mixture of parental races, their hybrids and back-crosses. Repeated back-crossing of the hybrids with parental types and the slower multiplication of the hybrids is an explanation for the variation in host range of known races and the failure to record new races.     

THE INFLUENCE OF THE pH OF THE NUTRIENT SOLUTION AND THE FORM OF IRON SUPPLY ON THE COUNTERACTION OF IRON DEFICIENCY IN PEAS, SOYBEAN AND FLAX BY HIGH CONCENTRATIONS OF MOLYBDENUM

The prevention of chlorosis in flax by high concentrations of molybdenum in a nutrient solution was associated with a delay in the precipitation of iron from ferric citrate, a slower drift of pH towards alkalinity and an increase in the iron content of the root. These effects were greater with ammonium than with sodium molybdate and occurred with solutions started at pH 4.6 but not at pH 6.6.
When FeEDTA was the source of iron, a similar delay in pH drift in the solution and accumulation of iron in the root occurred, but there was no chlorosis or precipitation of iron in the control treatment, so the effect of high molybdenum could not be fully determined.
When ferric chloride was used, high molybdenum did not prevent chlorosis nor delay iron precipitation or cause accumulation of iron in the root, though the rate of pH drift resembled that of solutions containing the organic forms of iron.
Similar results were obtained with peas and soybeans receiving high molybdenum treatment, but suppression of chlorosis was only temporary.
It is suggested that the capacity of molybdenum to offset chlorosis is due to the formation, in acid solution, of a complex with phosphorus which renders iron more available by delaying the formation of ferric phosphate. This seems to occur only when iron is supplied in the organic form.     

Microbial activity associated with seston in headwater streams: effects of nitrogen, phosphorus and temperature

SUMMARY 1. The influences of temperature and dissolved nitrates and phosphates on microbial activity associated with suspended fine particulate organic matter (seston) were evaluated in four headwater streams in the southern Appalachian Mountains.
2. Temperature manipulations of ± 5°C always induced significant changes in [¹⁴C] glucose mineralization (ANOVA; P <0.05) and [³H]thymidine incorporation (ANOVA; P <0.05).
3. Nutrient amendments of 1.0 mg NO₃ I⁻¹ and 0.05 mg PO₄I⁻¹ induced no significant alterations in bacterial mineralization of [¹⁴C]glucose (ANOVA; P >0.05) or incorporation of [³H]thymidine (ANOVA; P >0.05) in short-term (i.e. 3 h) experiments.
4. Microorganisms attached to refractory particulate organic matter do not appear to be limited by nitrogen or phosphorus even in streams with ambient nutrient concentrations as low as 0.06 mg NO₃ I⁻¹ and <0.03 mg PO₄ I⁻¹.
5. Our results indicate that variations in water temperature resulting from diurnal and seasonal temperature fluctuations, forest clear-cutting, and catchment elevation and aspect can have marked effects upon microbial activity and production, while short-term alterations in nutrient regime appear to have no significant effect on microbial activity associated with seston.