Distinct Patterns Of Variation Research Articles

Species composition and standing crop variation in an unfertilized meadow and its relationship to climatic variability during six years

Year-to-year variability of species composition and hay yield were investigated during a six-year period (1988–1993) in a traditionally mown meadow of great species richness at Negrentino in southern Switzerland Climatic parameters (temperature duration of sunshine, global radiation, precipitation, evaporation, relative moisture) measured at a nearby weather station were calculated for ten-day units and compared to quantitative vegetation data. Yields of the first and second harvest were positively correlated with the mean relative moisture during the first and second growth period. Distinct variation patterns were recognized among the 48 species and interpreted as direct or indirect responses of interacting species to climatic conditions during three periods of the year. The first variation pattern including abundant graminoids reflects a strong direct effect by weather conditions in the first growth period. Species of the other variation patterns responsed differently to extreme summer droughts with apparent time-lags. Some species reflect warm and humid conditions in early spring followed by dry conditions in a particular year; others combine features of different variation patterns. *** DIRECT SUPPORT *** A02DO006 00002

Prediction of forest-floor moisture content under diverse jack pine canopy conditions

Moisture contents of organic forest-floor materials were studied by strata in a semimature jack pine (Pinusbanksiana Lamb.) stand in relation to their within-stand locations and changes in both duff moisture code and fine fuel moisture code, the two weather-based components of the Canadian Forest Fire Weather Index System. The resulting best-fitting curvilinear regressions (Y = aebX) of the duff moisture code showed distinctive patterns of variation so that both the surface and subsurface forest-floor strata were consistently more moist in stand openings than under stand canopy. An initial moisture inversion between the surface and subsurface forest-floor materials manifested itself near the start of the regressions wherever live Schreber's moss (Pleuroziumschreberi (Brit.) Mitt.) and litter were the combined surface materials; otherwise, pure surface litter was consistently drier than the subsurface materials. Combinations of all these materials down to mineral soil showed intermediate moisture contents both in stand openings and under stand canopy. In contrast, the best-fitting regressions of the fine fuel moisture code just for surface forest-floor strata were of the straight line (Y = a + bX) category and had generally lower r2 values than those for the corresponding curvilinear regressions (Y = aebX) of the duff moisture code.

Prediction of forest-floor moisture content on jack pine cutovers

Moisture contents of organic forest-floor materials were studied by strata on a clear-cut jack pine (Pinusbanksiana Lamb.) site in relation to slash distribution and changes in both duff moisture code and fine fuel moisture code, the two weather-based components of the Canadian Forest Fire Weather Index System. The best-fitting curvilinear regression (Y = a + b/X) of the duff moisture code showed distinctive patterns of variation, so that both the surface and subsurface forest-floor strata were consistently moister under slash cover than in slash openings, and for each of these two slash conditions, the subsurface forest-floor strata were consistently moister than the surface strata. Combinations of these materials down to mineral soil showed intermediate moisture contents both in slash openings and under slash cover. The straight line regression (Y = a + bX) of the fine fuel moisture code was the best-fitting moisture content relationship for the surface forest-floor materials, but only in slash openings; under slash cover, the curvilinear regression (Y = a + b/X) of the duff moisture code was more suitable. The coefficients of correlation, r, as derived from these varied regressions, were all very highly significant at P < 0.001.

Geographical Variation inFundulus heteroclitus: Tests for Concordance Between Egg and Adult Morphologies

Recent studies have shown distinct patterns of variation in the egg morphology (oil droplet number, diameter and density of chorionic filaments) of Fundulus heteroclitus along the east coast (including Chesapeake and Delaware bays). We tested the hypothesis that variation in adult morphology and in electromorphs is concordant with that of egg morphology over the same range by subjecting data for these character sets to the Mantel test. This analysis was based on data for three egg characters, nineteen adult morphological (meristic and morphometric) characters and five protein characters from locations along the Atlantic coast. If the geographical differences observed among locations reflect genetic differences between two forms that have established secondary contact after isolation, we would expect general concordance between the different character sets. We would expect little concordance between the sets if they are each affected by different selectional and/or developmental responses to environmental regimes. Our analyses indicate that patterns of variation among localities for meristic, egg, and genetic character sets are all concordant, and thus the observed differences among locations are likely the result of secondary intergradation between two previously isolated forms. These conclusions are supported by similar patterns of geographical variation in spawning site preference and body coloration. Thus, these results support our earlier suggestion that these morphs should be treated as separate taxa, with F. h. heteroclitus occurring along the east coast from New Jersey south to Florida including lower Chesapeake and Delaware bays and F. h. macrolepidotus distributed from Connecticut north to Newfoundland with disjunct populations in upper Chesapeake and Delaware bays. Intergrade zones occur where the two morphs come together along the east coast in northern New Jersey and on Long Island, as well as in Chesapeake and Delaware bays

Line-narrowed fluorescence spectra and site-dependent transition probabilities ofNd3+in oxide and fluoride glasses

The fluorescence spectra, branching ratios, and decay of the $^{4}F_{\frac{3}{2}}$ state of ${\mathrm{Nd}}^{3+}$ in glass were measured under excitation by tunable pulsed laser radiation. The following glass types were studied: silicate, phosphate, borate, fluoroberyllate, and fluorophosphate. Measurements were made at liquid-helium temperatures by exciting into the $^{2}P_{\frac{1}{2}}$ state, and line-narrowed fluorescence spectra were obtained as a function of excitation wavelength. Large variations in Stark splitting of the $^{4}I_{\frac{9}{2}}$ and $^{4}I_{\frac{11}{2}}$ states have been observed and attributed to site-to-site differences in the local crystal field. The probabilities for radiative decay and for nonradiative decay by multiphonon emission also exhibit variations with excitation wavelength. Although similarities exist, each different glass type shows its own distinctive patterns of variation in crystal-field splitting and relative quantum efficiency. In the fluorophosphate glass, which contains large numbers of both fluorine and oxygen anions, comparison of the laser-excited fluorescence spectra and lifetime of ${\mathrm{Nd}}^{3+}$ with the corresponding results from pure oxide and fluoride glasses demonstrates the presence of ${\mathrm{Nd}}^{3+}$ sites having both fluorine and oxygen nearest-neighbor coordination.

Diurnal variation of phytoplankton in Loch Lomond

A study of diurnal variation over a 48 hour period was undertaken in July 1973 to ascertain the extent and timing of some major chemical, physical and biological variables in Loch Lomond. The phytoplankton population was dominated by the diatom Tabellaria fenestrata, with a maximum abundance between 04.00 and 06.00 h in surface waters on both days. A distinct diurnal variation in cell numbers was also recorded. Chlorophyll a values also showed a regular pattern of variation with a single peak between 10.00 and 14.00 h each day. Some chemical changes appeared to be a direct consequence of phytoplankton multiplication. Nitrate-nitrogen showed a decrease in concentration coinciding with the period of cell multiplication, whereas dissolved silica concentrations only fell on the completion of this process. Other common diatoms displayed less distinct patterns of variation although Fragilaria crotonensis attained its maximum abundance in surface waters. Considerable variation was recorded in the number of organisms and chlorophyll a levels at 25 cm intervals in the upper metre of the water column, with large variations in standing-crop and chemical parameters in the space of one hour. Diurnal oscillations in the position of the thermocline were recorded, with the thermal discontinuity being at its greatest depth in the early hours of the morning. The hypolimnion and thermocline regions clearly acted as a source of nutrient supply to the epilimnion. From this investigation it is apparent that for the proper understanding of diurnal variation a 24 hour study alone is insufficient and may give rise to misleading results.

A family with syndactyly type II (synpolydactyly)

Syndactyly Type II is reported in eight members of a family in four generations. Affected individuals show two distinctive patterns of variation in the expression of the gene. Distortion of dermatoglyphic patterns is associated with the severe but not the mild manifestation of the malformation. The diagnostic significance of minimal features of the condition is discussed. Linkage data suggest that loci for Syndactyly II and for blood-group antigens ABO, MNSs, P, Rh and Kell are not closely linked.

Patterns of regional variation in the vertebral column of terrestrial salamanders.

Regional variation in the vertebral column of several species of salamanders (families Ambystomatidae, Salamandridae and Plethodontidae) is analyzed. Measurements of three dimensions, centrum length, prezygapophyseal width, and transverse process length, provide the data. Ontogenetic, interspecific, intergeneric and interfamilial patterns of positional variation are diagrammed and discussed. Distinctive patterns of variation characterize the families, genera, and to a lesser extent, the species. The patterns of ambystomatid salamanders are the most generalized, and probably reflect derivation from a primitive ancestral stock. The most specialized conditions occur in the fully terrestrial plethodontids, a group generally considered to be highly derived. Data such as those presented here will aid in the identification of fossils. The patterns described have functional significance. For example, species which have an aquatic larval stage and which return to aquatic breeding sites have vertebrae which taper in length and width behind the pelvis. This is a feature associated with production of a traveling wave in the tail which is necessary for propulsion in water. Fully terrestrial species do not have a tapering column. In them, standing waves, such as occur in the trunk region of all species, typically occur in the tail. The caudal vertebrae of terrestrial species are rather uniform in dimensions for some distance, and the tail is cylindrical in form. Other functionally important features include the narrowing and shortening of some anterior vertebrae, associated with the development of a neck in some species with tongue feeding mechanisms. In contrast, species which use their heads as wedges during locomotion have broadened anterior vertebrae which serve as sites of origin for hypertrophied neck muscles.