The growth, yield and nutrient uptake of winter wheat following root-pruning

The effect of root-pruning on shoot growth was investigated in winter wheat growing in lysimeters. Removal of half of the root axes at the beginning of stem elongation reduced shoot dry matter, determined 1 month after pruning, by 13% and grain yield by 8%. Removal of either the seminal or nodal root system during tillering reduced shoot dry weight, measured during the growing season, by 7% and grain yield by 25%. Root-pruning had negligible, or only transient, effects on the concentration of nitrogen, phosphorus, potassium, magnesium and manganese in the shoots. The harvest index was not affected by root-pruning.     

Variation in Photosynthesis and Enzyme Activity in Cenchrus ciliaris L.

Populations of Cenchrus ciliaris differ significantly in relativegrowth-rate (R), net assimilation rate (E), and leaf-area ratio(F). Differences in R were related to differences in E ratherthan in F. The populations also differed in the rate of apparentphotosynthesis of individual leaves as measured by infra-redgas analysis. Warburg and ^l4CO₂ techniques. Temperature andlight-response measurements revealed optimum temperature forphotosynthesis of 35 °C and the rate in most populationscontinued to increase up to the highest levels of irradianceemployed (200 W m²). The relative order of the populations wassimilar in all methods of analysis, but there was no relationshipevident between leaf photosynthesis and E derived from growthanalysis. The activity of the enzyme PEP carboxylase, expressedin terms of unit leaf area, was correlated with photosyntheticrate of the leaf. Activities of PEP carboxylase and of proteinsynthesis in vitro expressed on a basis of soluble protein contentwere correlated with E, but no such relationship was found forthe enzymes acid phosphatase and alanine--ketoglutarate aminotransferase.     

Wintering site fidelity and movement patterns of Western Sandpipers Calidris mauri in the San Francisco Bay estuary

Western Sandpipers Calidris mauri are the most numerous shorebird species in the San Francisco Bay estuary during winter. A sample of 106 Western Sandpipers was captured in mist nets and radio-marked with 1-g transmitters to examine their wintering site fidelity and movements. Differences in distances moved, home range extent and core area size were examined by age, sex, season, site, time of day and tide. All birds remained in the south San Francisco Bay region during winter and exhibited strong site fidelity, with a mean home range of 22.0 km² or only 8% of the study area. First-year birds had larger home ranges (26.6 ± 3.6 km²) than adults (17.2 ± 2.5 km²) in winter, but home range sizes of males and females were not significantly different in any period. Home range sizes were similar between seasons, but core areas were smaller in spring (6.3 ± 1.2 km²) than in early (9.6 ± 4.0 km²) or late (11.6 ± 1.6 km²) winter. Movements and home range size were similar for radio-marked birds located during day and night. The high degree of regional and local site fidelity demonstrated that the mixture of natural mud fiats and artificial salt ponds in southern San Francisco Bay provided sufficient resources for large wintering populations of Western Sandpipers.     

Life budgets for a population of Tipula sacra (Diptera; Tipulidae)

Abstract.

• 1 A population of Tipula sacra was studied intensively from 1969 to 1974 in a series of abandoned beaver ponds. Beavers recolonized the ponds from 1974 to 1976 and again in 1978.
• 2 The basic life-cycle is of 2 years duration, but cohort-splitting occurs in the autumn as a result of some larvae growing faster and completing the life-cycle in 1 year.
• 3 Some periods are more favourable for growth than others and the size of the fast-growing cohort varies from year to year. This insight allows some anomalies in the estimates of population size to be explained and life budgets have been produced for three year-classes.
• 4 The short-fall in realization of egg potential is massive, apparently due to heavy female mortality by predation and the prevention of oviposition by inclement weather.
• 5 Mortality rate is relatively low and constant from stage II larvae until pupation, but increases to adult emergence. There is a correlation between larval density and mortality rate.
• 6 Certain aspects of the life-history (e.g. high fecundity, variability in growth rate) appear to fit the species to life in a temporally unstable habitat.

     

The Conservation of Sea Turtles: Practices and Problems

The various techniques in common use for conservation and restorationof depleted sea turtle populations are reviewed, namely: banninginternational commerce; operating artificial hatcheries, bothin the natural beach environment and in styrofoam and othertypes of incubators; "head-starting" of hatchlings in captivity;protection of nesting females by means of beach patrols; andtranslocation of eggs or hatchlings to distant areas from whichturtles have been extirpated or to which it is desired to introducenew colonies. The difficulties of monitoring the results ofall of these techniques are discussed, and potential dangersor disadvantages of each approach are reviewed. It is concludedthat, until unequivocal data become available, turtle conservationistsshould continue to pursue common sense or logically sound restorationprograms, but should constantly re-evaluate their actions inthe light of the latest available knowledge and modify or desistfrom current approaches as necessary.     

Differential responses of UK upland plants to nitrogen deposition

Native upland species, Nardus stricta , Eriophorum vaginatum , Erica cinerea and Vaccinium vitis-idaea were given 3 or 60 kg N ha⁻¹ yr⁻¹, over 2 yr, applied as a mist (NH₄NO₃). The high N treatment increased above-ground biomass in all four species, but only significantly in E. cinerea , E. vaginatum and N. stricta . Biomass increases in E. vaginatum and N. stricta resulted from enhanced tiller production rather than shoot elongation. Root growth increased in N. stricta , so that root:shoot ratio in this species was unchanged by N. Root growth in E. vaginatum , E. cinerea and V. vitis-idaea did not respond to N and their root:shoot ratios decreased. Tissue N concentrations increased in both shoots and roots of all species in response to N. The accumulated foliar N did not increase the proportion of N allocated to Rubisco and the photosynthetic capacities of N. stricta , E. vaginatum and V. vitis-idaea were unchanged. Thus growth responses to N were due to altered allocation rather than increased rate of photosynthesis per unit leaf area. The high N treatment increased flower production significantly in E. cinerea but not in the other species. Although in this experiment dwarf shrubs were more responsive than graminoids to N, in the field at current N inputs the enhanced tillering of the graminoids may be more competitively advantageous, especially where gaps develop in the canopy. Thus increasing N deposition may lead to increased grassiness of upland heath, and in particular, a spread of N. stricta .     

Wingbeat frequency, temperature and body size in bees and flies

ABSTRACT. This paper describes the relationship between ambient temperature and wingbeat frequency in bees and flies of different sizes, and presents new data from insects in free fight. The slope of the relationship changes with the size of the insect, and was different for insects in hovering flight compared with individuals of the same species in forward flight.     

Size variation facilitates population divergence but does not explain it all: an example study from a widespread African monkey

Subspecific variation is widespread in vertebrates. Within Africa, several mammals have extensive geographic distributions with attendant morphological, ecological, and behavioural variations, which are often used to demarcate subspecies. In the present study, we use a primate species, the vervet monkey, Cercopithecus aethiops, as a case study for intraspecific divergence in widespread mammals, assessed through hard tissue morphology. We examine intraspecific differences in size, shape, and non‐allometric shape from a taxonomic perspective, and discuss the macroevolutionary implications of findings from microevolutionary analyses of geographic variation. A geometric morphometric approach was used, employing 86 three‐dimensional landmarks of almost 300 provenanced crania. Many of the taxonomic differences in skull morphology between vervet populations appear to be related to geographic proximity, with subspecies at opposite extremes of a west‐to‐east axis showing greatest divergence, and populations from central and south Africa being somewhat intermediate. The classification rate from discriminant analyses was lower than that observed in other African primate radiations, including guenons as a whole and red colobus. Nonetheless, taxonomic differences in shape were significant and not simply related to either geography or size. Thus, although shifts in size may be an important first step in adaptation and diversification, with size responding more quickly than shape to environmental change, the six vervet taxa currently recognized (either as species or subspecies) are not simply allometrically scaled versions of one another and are probably best viewed as subspecies. Holding allometry constant when examining inter‐population differences in shape may thus help to reveal the early stages of evolutionary divergence. The vervet case study presented here hence has relevance for future studies examining intraspecific differentiation in other large mammals, particularly through the methods used to identify small but biologically meaningful divergence, with attendant implications for conservation planning. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 823–843.