THE EFFECT OF VARYING RELATIVE DENSITY AND VARYING FOOD SUPPLY ON INTERSPECIFIC COMPETITION BETWEEN HELISOMA DURYI AND BULINUS TRUNCATUS (GASTROPODA, PLANORBIDAE)

Interspecific competition between Helisoma duryi and the intermediatehost of schistosomes, Bulinus truncatus results in reduced growthand reproduction of B. truncatus and the effects are more pronouncedas the density of H. duryi is increased. The drastic reductionin reproduction of B. trunauus is the result of a predationby H. duryi on egg masses. It appears that increasing the foodsupply cannot completely eliminate the effects of competition.Although the growth and reproduction of B. truncatus in competitionwith H. duryi increases significantly with the increased foodsupply, both growth and reproduction are still reduced comparedto control snails given the same amount of food. The effectsof food supply and competition on the allometric size-weightrelationships of the two species are slight. (Received 23 February 1987; accepted 4 May 1988)     

Applying Landscape-Scale Habitat-Potential Models to Understand Deer Spatial Structure and Movement Patterns

Abstract: Ecologically based management must incorporate components that consider how individuals associate temporally and spatially to environments that provide specific habitat requirements. Recent research has assessed how environments could be classified based on potential to provide deer (Odocoileus virginianus) habitat components. If habitat potential (HP; i.e., capability of habitat types to provide annual life requisites) classifications can be correlated to deer spatial structure and seasonal movement patterns, managers could better understand how spatial distribution of habitat components influences deer distribution. We analyzed home-range distribution and seasonal movement patterns from 45 adult (≥2 yr old) female deer radiocollared between 1999-2002, and deer habitat characteristics in northeastern Lower Peninsula, Michigan, USA, to investigate whether we can predict deer seasonal movement patterns based on the distribution of HP. We constructed logistic regression models that calculated the probability of deer migration given specific HP within seasonal home ranges of migratory and nonmigratory deer. Our results suggested that the probability of seasonal deer migrations relates to the juxtaposition (arrangement) of different habitat types that collectively provide all annual life requisites. We demonstrated that use of habitat-type classifications and HP models can track and predict deer movement patterns, which can facilitate establishment of management units and ecologically based deer management practices.     

Isolation of corn stunt spiroplasma in Jamaica, and probable dual infection with maize mosaic virus

Females of Cydia ptychora oviposited on cowpea, Vigna unguiculata ssp. unguiculata in the field between 18.00 and 19.00 h commencing about 30 days after planting with a few eggs laid on the leafbuds and the undersides of leaves. Oviposition increased as the host plant developed the preferred sites, floral sepals and their remains on pods, and peaked at about 58 days after planting regardless of planting date. First instar larvae were found wandering on the plant between 06.45 and 11.15 h but other larval instars were rarely encountered outside the pod except when changing pods or leaving pods to pupate in the soil. Contrary to previously reported observations, larval development occurred in leafbuds and inside flowers both in the field and in laboratory rearing. Development was optimal on pods, and mortality was high in leafbuds.     

Observations on Askenasia volvox (Claparède & Lachmann, 1859)

Specimens of Askenasia volvox from southwestern Indiana have a variable body shape and a size range of 29 × 22 μ m to 42 × 27 μ m. The pectinelles, membranelles, and cirri each number 47–48, and respectively have a length of 8–10, 20, and 30 μ m. The pectinelles arise from ciliary rows consisting of ～10 kinetosomes, and every membranelle originates from 2 adjacent rows of ～14–17 kinetosomes. Different algae as well as Bodo and certain other protozoa are ingested. The macronucleus, micronucleus, the cytoplasm and its inclusions, trichites, the function of the contractile vacuole, and movements and behavior are described.     

Interference with Deposition of Minerals in a Coccolithophorid Protozoon

Laboratory studies with axenic culture of the coccolithophorid,Hymenomonas MP 156, in chemically defined media have establishedthat this primitive protist deposits its minerals in essentiallythe same manner as multicellular organisms. An appreciable numberof inhibitors and natural compounds prevent deposition of mineralsin laboratory experiments. Among these cations other than Ca⁺²,certain amino acids, select intermediates of carbohydrate metabolism,and inhibitors of enzymes occupy a prominent place. Interferencewith deposition of minerals does not necessarily abolish proliferationof the coccolithophorid. However, electron-microscopic, autoradiographic,histological, and analytical studies of the various modes ofinterference reveal a profound alteration of organelles andphysiological activities. The ability of the protist to useits own extracellular, mineralized, calcareous structures asa source of Ca⁺² for growth under conditions of reduced cationsin the environment suggests a possible role for these microorganismsin cation equilibria of natural waters.     

The land–atmosphere water flux in the tropics

Tropical vegetation is a major source of global land surface evapotranspiration, and can thus play a major role in global hydrological cycles and global atmospheric circulation. Accurate prediction of tropical evapotranspiration is critical to our understanding of these processes under changing climate. We examined the controls on evapotranspiration in tropical vegetation at 21 pan-tropical eddy covariance sites, conducted a comprehensive and systematic evaluation of 13 evapotranspiration models at these sites, and assessed the ability to scale up model estimates of evapotranspiration for the test region of Amazonia. Net radiation was the strongest determinant of evapotranspiration (mean evaporative fraction was 0.72) and explained 87% of the variance in monthly evapotranspiration across the sites. Vapor pressure deficit was the strongest residual predictor (14%), followed by normalized difference vegetation index (9%), precipitation (6%) and wind speed (4%). The radiation-based evapotranspiration models performed best overall for three reasons: (1) the vegetation was largely decoupled from atmospheric turbulent transfer (calculated from Ω decoupling factor), especially at the wetter sites; (2) the resistance-based models were hindered by difficulty in consistently characterizing canopy (and stomatal) resistance in the highly diverse vegetation; (3) the temperature-based models inadequately captured the variability in tropical evapotranspiration. We evaluated the potential to predict regional evapotranspiration for one test region: Amazonia. We estimated an Amazonia-wide evapotranspiration of 1370 mm yr⁻¹, but this value is dependent on assumptions about energy balance closure for the tropical eddy covariance sites; a lower value (1096 mm yr⁻¹) is considered in discussion on the use of flux data to validate and interpolate models.     

Regulation of growth response to water stress in the soybean primary root. I. Proteomic analysis reveals region‐specific regulation of phenylpropanoid metabolism and control of free iron in the elongation zone

In water‐stressed soybean primary roots, elongation was maintained at well‐watered rates in the apical 4 mm (region 1), but was progressively inhibited in the 4–8 mm region (region 2), which exhibits maximum elongation in well‐watered roots. These responses are similar to previous results for the maize primary root. To understand these responses in soybean, spatial profiles of soluble protein composition were analysed. Among the changes, the results indicate that region‐specific regulation of phenylpropanoid metabolism may contribute to the distinct growth responses in the different regions. Several enzymes related to isoflavonoid biosynthesis increased in abundance in region 1, correlating with a substantial increase of isoflavonoid content in this region which could contribute to growth maintenance via various potential mechanisms. In contrast, caffeoyl‐CoA O‐methyltransferase, which is involved in lignin synthesis, was highly up‐regulated in region 2. This response was associated with enhanced accumulation of lignin, which may be related to the inhibition of growth in this region. Several proteins that increased in abundance in both regions of water‐stressed roots were related to protection from oxidative damage. In particular, an increase in the abundance of ferritin proteins effectively sequestered more iron and prevented excess free iron in the elongation zone under water stress.