Effect of competition and leaf age on visible and infrared reflectance in pine foliage

Abstract. The effect of plant competition on spectral reflectance in the 400–2500 nm wavelength region was determined for 3-month-old and 15-month-old leaves of loblolly pine ( Pinus taeda L.). Strong competition decreased water potentials and Mg concentrations, and increased K in young and old leaves. Also, competition decreased Ca and total chlorophyll in young leaves. As measured with a scanning radiometer, reflectance in young leaves at 551 nm decreased from 20 to 14% as water potentials increased from -2.2 to -0.9 MPa (r²= 0.82). For young and old leaves reflectance at 551 nm decreased from 20 to 10% with increasing total chlorophyll (r²= 0.64). Reflectance decreased slightly with increasing K in young leaves (401 nm, r²= 0.55), and with increasing Mg in old leaves (470 nm, r²= 0.57). Increased visible reflectance under strong competition may have resulted primarily from decreased water potentials. Reflectances were much greater in young versus old leaves in the 750–1300 nm range, and were greater in old rather than young leaves from 1400–2500 nm. Infrared reflectances were not, however, significantly affected by competition.     

The relationship between foraging behaviour and energy expenditure in Antarctic fur seals

By using time-depth recorders to measure diving activity and the doubly-labelled water method to determine energy expenditure, the relationship between foraging behaviour and energy expenditure was investigated in nine Antarctic fur seal females rearing pups. At-sea metabolic rate (MR) (mean of 6.34 ± 0.4 W. kg^-1; 4.6 times predicted BMR) was positively correlated to foraging trip duration (mean of 4.21 ± 0.54 days; r²= 0.5, P < 0.04). There were no relationships between MR and the total number of dives, the total time spent diving or the total vertical distance travelled during the foraging trip. There was, however, a close negative sigmoidal relationship (r²= 0.93) between at-sea MR and the proportion of time at sea spent diving. This measure of diving behaviour may provide a useful, inexpensive means of estimating foraging energy expenditure in this species and possibly in other otariids. The rate of diving (m.h^-1) was also negatively related to at-sea MR (r²= 0.69, P < 0.005). Body mass gain during a foraging trip had a positive relationship to the time spent at sea (r²= 0.58, P < 0.02) and the total amount of energy expended while at sea (r²= 0.72, P < 0.004) such that, while females undertaking long trips have higher metabolic rates, the energetic efficiency with which females gain mass is independent of the time spent at sea. Therefore, within the range of conditions observed, there is no apparent energetic advantage for females in undertaking foraging trips of any particular duration.     

Temporal patterns of milk production in Antarctic fur seals (Arctocephalus gazella)

The timing of milk production in Antarctic fur seals was studied at Bird Island, South Georgia. Like all lactating otariid seals (Pinnipedia: Otariidae), Antarctic fur seal females alternate between short nursing periods ashore and regular foraging trips to sea. Females do not necessarily return to the colony with full mammae, which indicates that mammary volume capacity is unlikely to limit foraging trip duration. Upon arrival at the colony, milk fat (r²= 0.33, P < 0.04) and protein (r²= 0.60, P < 0.002) content were positively correlated to the time spent at sea. A similar trend was observed in the milk produced on land. The rate of milk energy production was much lower at sea (5.02 ± 0.05 MJ day^-1) than on land (23.66 ± 4.4 MJ^-1 day^-1). The rate of milk energy production during the foraging trip was negatively correlated to the time spent at sea (r²= 0.29, P < 0.05), whereas the rate of milk energy production on land was positively correlated (r²= 0.61, P < 0.001) to the duration of the preceding foraging trip. The total amount of milk energy delivered to the pup during each twoday nursing period was positively correlated (r²= 0.60, P < 0.002) to the duration of the previous foraging trip. The overall rate of milk energy delivery, however, was independent of foraging trip duration. This accords with previous observations that the growth rates of Antarctic fur seal pups are unaffected by maternal foraging trip duration patterns.     

Chlorophyll fluorescence measured using the Fraunhofer line-depth principle and relationship to photosynthetic rate in the field

Abstract. A field study was conducted to determine the relationship of solar-excited chlorophyll a fluorescence to net CO₂ assimilation rate in attached leaves. The Fraunhofer line-depth principle was used to measure fluorescence at 656.3 nm wavelength while leaves remained exposed to full sunlight and normal atmospheric pressures of CO₂ and O₂. Fluorescence induction kinetics were observed when leaves were exposed to sunlight after 10 min in darkness. Subsequently, fluorescence varied inversely with assimilation rate. In the C₄ Zea mays , fluorescence decreased from 2.5 to 0.8 mW m^-2 nm^-1 as CO₂ assimilation rate increased from 1 to 8 μmol m^-2 s^-1 (r²= 0.520). In the C₃ Liquidambar styraciflua and Pinus taeda , fluorescence decreased from 6 to 2 mW m^-2 nm^-1 as assimilation rate increased from 2 to 5 or 0 to 2 μmol m^-2 s^-1 (r²= 0.44 and 0.45. respectively). The Fraunhofer line-depth principle enables the simultaneous measurement of solar-excited fluorescence and CO₂ assimilation rate in individual leaves, but also at larger scales. Thus, it may contribute significantly to field studies of the relationship of fluorescence to photosynthesis.     

Effect of temperature on swimming performance of sea bass juveniles

At four temperatures ( T= 15, 20, 25 and 28° C) swimming performance of Dicentrarchus labrax was significantly correlated with total length (23–43 mm L _T); r²=0.623–0.829). The relative critical swimming speed ( RU _crit= U _crit L _T⁻¹), where U _crit is the critical swimming speed, was constant throughout the L _T range studied. The significant effect of temperature on the relative critical swimming speed was described binomially: RU _crit=−0.0323T²+ 1.578 T −10.588 (r²=1). The estimated maximum RU _crit (8.69 L _T s⁻¹) was achieved at 24.4° C, and the 90% performance level was estimated between 19.3 and 29.6° C.     

Environmental determinants of recruitment and their influence on the population dynamics of stream-living brown trout Salmo trutta

The relative importance of endogenous feedback mechanism vs environmental factors in the dynamics of animal populations is a long-standing, but not fully resolved yet, issue in ecology. We have addressed this subject by examining the dynamics of a stream-resident population of Salmo trutta in a northwestern Spain stream. Recruitment was the major determinant of population size and the abundance of recruits resulted from a combination of regional and local environmental factors. Stream discharge in March determined the amount of stream area suitable for newly emerged trout (r²=0.59–0.79%), that in turn determined the abundance of recruits at each site (r²=0.51–0.77%). Stream discharge determines the overall strength of annual recruitment. Discharge, however, combines with stream morphology at the site scale to result in a site-specific area suitable for juveniles and, hence, site-specific recruitment. Thus, our study exemplifies how an environmentally driven animal population may persist on time with little or no operation of endogenous regulatory mechanisms.     

Elevated pyruvate,orthophosphate dikinase (PPDK) activity alters carbon metabolism in C3 transgenic potatoes with a C4 maize PPDK gene

Changes in carbon metabolism and δ¹³C value of transgenic potato plants with a maize pyruvate,orthophosphate dikinase (PPDK; EC 2.7.9.1) gene are reported. PPDK catalyzes the formation of phospho enol pyruvate (PEP), the initial acceptor of CO₂ in the C₄ photosynthetic pathway. PPDK activities in the leases of transgenic potatoes were up to 5.4‐fold higher than those of control potato plants (wild‐type and treated control plants). In the transgenic potato plants, PPDK activity in leaves was negatively correlated with pyruvate content (r²= 0.81), and was positively correlated with malate content (r²= 0.88). A significant increase in the δ¹³C value was observed in the transgenic potato plants, suggesting a certain contribution of PEP carboxylase as the initial acceptor of atmospheric CO₂. These data suggest that elevated PPDK activity may alter carbon metabolism and lead to a partial operation of C₄‐type carbon metabolism. However, since parameters associated with CO₂ gas exchange were not affected, the altered carbon metabolism had only a small effect on the total photosynthetic characteristics of the transgenic plants.     

Evaluation of flow cytometry as a method for quantification of circulating blood cell populations in salmonid fish

Flow cytometry was used to estimate the proportions of different blood cell types in brown and rainbow trout. On the basis of forward light scatter and 90° side scatter three populations were differentiated. The relative abundance of these cells correlated with that of erythrocytc (r²= 0.994), lymphocyte plus thrombocyte(r²= 0.676) and neutrophil populations (r²= 0.571) enumerated by direct microscopy. By density gradient separation of cells, cell sorting and acridine orange staining it was confirmed that these cell types could be assigned to the populations detected. Changes in blood cell populations were monitored by flow cytometry in a group of experimental fish placed under confinement stress. Flow cytometry proved to be a rapid and reliable method for monitoring cell population dynamics in fish blood.     

Nutrient and energy content of freshwater fishes

The analyses of fresh total body homogenates of 2385 freshwater fishes from 17 species originating in natural waters and aquaculture facilities resulted in average values of 19.1–37.8% dry matter, 13.6–18.3% crude protein, 0.8–18.3% crude fat, 0.16–2.17% nitrogen-free extracts (NFE), 2.2–2.9% nitrogen and 0.39–1.02% phosphorus. The gross energy content ranged from 3.83 to 11.49 MJ/kg. With increasing fat content in the fishes, water content decreased and dry matter content increased. Through this interdependence, a significant correlation was found between dry matter and crude fat and energy content (r²=0.92–0.97). The values of crude protein, crude ash, NFE, nitrogen and phosphorus did not show any significant influence on dry matter content (r²=0.0005–0.46). Based on the significant correlation between dry matter and gross energy (gross energy [MJ/kg]=0.0253 dry matter [%]^1.6783), the energy content of freshwater fishes can easily be estimated by the dry matter content in the total body.     

Genetic diversity within vertebrate species is greater at lower latitudes

The latitudinal gradient of species diversity is one of the oldest recognized patterns in biology. While the cause of the pattern remains debated, the global signal of greater diversity toward the tropics is widely established. Whether the pattern holds for genetic diversity within species, however, has received much less attention. We examine latitudinal variation of intraspecific genetic diversity by contrasting nucleotide distance within low- and high-latitude animal groups. Using mitochondrial DNA markers across 72 vertebrate species that together span six continents, two oceans, and 129 degrees of latitude, we found significantly greater genetic diversity at low latitudes within mammalian species, and trends consistent with this pattern in reptiles, amphibians, fish, and birds. The signal held even after removing species whose current geographic ranges include areas recently covered by glaciers during the late Pleistocene and which presumably have experienced colonization bottlenecks in high latitudes. Higher genetic diversity within species was found at low latitudes also for genera that do not possess higher species richness toward the tropics. Moreover, examination of a subset of species with sufficient sampling across a broad geographic range revealed that genetic variation demonstrates a typical gradient, with mid-latitude populations intermediate in genetic diversity between high and low latitude ones. These results broaden the pattern of the global latitudinal diversity gradient, to now include variation within species. These results are also concordant with other studies indicating that low latitude populations and species are on different evolutionary trajectories than high latitude ones, and we speculate that higher rates of evolution toward the equator are driving the pattern for genetic diversity within species.     

Determining patterns of use by black bream Acanthopagrus butcheri (Munro, 1949) of re-established habitat in a south-eastern Australian estuary

Acoustic telemetry was used to assess patterns of utilization by black bream Acanthopagrus butcheri of regions with and without re-introduced large woody debris (LWD) in two estuaries of south-eastern Australia, the Mitchell and Tambo Rivers. The fish ( n = 46) were implanted with acoustic transmitters in December 2004 and March 2005 and monitored for c. 12 months. The two principal metrics from the telemetry data, number of visits per day ( N day⁻¹) and residency (amount of time, s) were highly correlated ( r > 0·948), and subsequent analyses were based on N day⁻¹. Rates of N day⁻¹ varied inconsistently among estuarine regions across diel periods and times of year for each river. In the Tambo River during autumn, winter and spring, the N day⁻¹ was greatest in the middle and upper estuarine regions during the day, and often greater in the lower region at dawn and dusk, but varied little among regions in summer. The provision of LWD had little effect on N day⁻¹ in the Tambo River. In the Mitchell River, N day⁻¹ varied little among estuarine regions without LWD, regardless of the time of day, and these patterns were consistent across seasons, but N day⁻¹ was significantly greater to the LWD during the day in winter and spring. Freshwater flows had little effect on monthly patterns of N day⁻¹ among regions in either estuary. The perceived 'benefits' to A. butcheri of re-establishing LWD within estuarine systems of south-eastern Australia depended strongly on the time of year, time of day and river system, but acoustic telemetry was a useful method of evaluating the use by fish of these artificial structures.     

Correlations between net primary productivity and foliar carbon isotope ratio across a Tibetan ecosystem transect

Warming climate could affect leaf-level carbon isotope composition (δ¹³C) through variations in photosynthetic gas exchange. However, it is still unclear to what extent variations in foliar δ¹³C can be used to detect changes in net primary productivity (NPP) because leaf physiology is only one of many determinants of stand productivity. We aim to examine how well site-mean foliar δ¹³C and stand NPP co-vary across large resource gradients using data obtained from the Tibetan Alpine Vegetation Transects (1900–4900 m, TAVT). The TAVT data indicated a robust negative correlation between foliar δ¹³C and NPP across ecosystems (NPP=−2.7224δ¹³C-67.738, r²=0.60, p<0.001). The mean foliar δ¹³C decreased with increasing annual precipitation and its covariation with mean temperature and soil organic carbon and nitrogen contents. The results were further confirmed by global literature data. Pooled δ¹³C data from global literature and this study explained 60% of variations in annual NPP both from TAVT-measures and MODIS-estimates across 67 sites. Our results appear to support a conceptual model relating foliar δ¹³C and nitrogen concentration (N_mass) to NPP, suggesting that: 1) there is a general (negative) relationship between δ¹³C and NPP across different water availability conditions; 2) in water-limited conditions, water availability has greater effects on NPP than N_mass; 3) when water is not limiting, NPP increases with increasing N_mass.     

Radio-transmitted electromyogram signals as indicators of physical activity in Atlantic salmon

Surgical methods developed to implant EMG (electromyogram) transmitters in Atlantic salmon Salmo salar were tested to calibrate electromyograms from axial red musculature to swimming speed in a swim speed chamber, and to compare electromyograms of fish from two stocks (Lone and Imsa). Ten Lone and eight Imsa salmon were equipped with internal EMG transmitters. Surgical procedures were acceptable, with 100% survival of all implanted fish during the study. It was possible to calibrate EMG pulse intervals to swimming speed in 14 of the 18 salmon run in the swim speed chamber ( r²= 0·35-0·76 for individuals, 0·63 for pooled data). Individuals differed in their EMG resting levels (EMGs recorded at 0·5 ms⁻¹), and so higher correlations were obtained between swimming speed and an activity index (EMG pulse intervals at different speeds/EMG resting levels) (pooled data, r² =0·75). The linear relationship between swimming speed and EMG pulse intervals differed significantly between the two stocks ( P <0·05). This successful calibration of EMGs to swimming speed opens the possibility of calibrating EMGs to oxygen consumption and the measurement of the metabolic costs of activity in field experiments.     

Accumulation of PSP toxins in Atlantic mackerel: seasonal and ontogenetic variations

Atlantic mackerel Scomber scombrus are known to be lethal vectors of paralytic shellfish poisoning (PSP) toxins to predators. To elucidate dynamics of PSP toxin accumulation in this species, mackerel were sampled in the Gulf of St Lawrence from May to October 1993. Mackerel appear to retain toxins (saxitoxin, gonyautoxins 2 and 3) year-round. The toxin content of the liver, as determined by high performance liquid chromatography, increased significantly with fish age ( r² =0.40) and length ( r² =0.52), suggesting that mackerel progressively accumulate PSP toxins throughout their life. The toxin content of the liver also increased significantly during the summer feeding sojourn in the Gulf of St Lawrence. Comparison of profiles of saxitoxin derivatives indicated that zooplankton were the likely source of PSP toxins found in mackerel. The mean ± S.D toxin content was 17.4 ± 10.6 nmol liver⁻¹ and the mean ± S.D. PSP toxicity was 112.4 ± 67.0 μg saxitoxin equivalents 100 g⁻¹ liver wet weight ( n =247).     

The energetic importance of terrestrial arthropod inputs to three warm-water streams

1. Inputs of terrestrial arthropods (number and mass m^–2 d^–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater ( P < 0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.
2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m^–2 d^–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.
3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish ( Lepomis auritus ) and bluegill ( L. macrochirus ) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.
4. Estimates of the potential annual energetic contribution (kJ m^–2 d^–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.
5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream ecosystems.     

Egg development of the stoneflies Siphonoperla burmeisteri(Chloroperlidae) and Dinocras cepùnalotes(Perlidae)

SUMMARY. 1. The duration of egg incubation ( Y ) in Dinocras cephalotes and Siphonoperla burmeisteri was related to constant temperatures from 4 to 24°C, by the regression equations Y=2382 T ^{− 1, 402}(r²=0.992, P<0.001) and y= 2683 T ^−1.667 ( r ²=0.994, P <0.001), respectively. No diapause was observed in either species.
2. Egg incubation in D. cephaloles was slow and took 784.9±92.7 (mean ± SD) degree days between 12 and 20°C. significantly more than in S. burmeisteri (445±76.17 degree days: t = 7.44. d.f.=13, P <0.001).
3. For D. cephalotes hatching occurred at temperatures between 12 and 24°C, and for S . burmeisteri between 8 and 20°C. The mean volume of the eggs of D. cephalotes was about 5 times greater than that of S. burmeisteri and the mean body lengths of the newly-hatched nymphs were 1.13 mm and 0.95 mm respectively.
4. This study shows that the freshwater fauna of northern Fennoscan- dia also contains species with warm stenotherm eggs. D. cephalotes. which is of a Mediterranean origin (Zwick, 1981a), may exist at the limit of its distribution in northern Fennoscandia.     

The energetic importance of terrestrial arthropod inputs to three warm-water streams

1. Inputs of terrestrial arthropods (number and mass m^–2 d^–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater ( P < 0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.
2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m^–2 d^–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.
3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish ( Lepomis auritus ) and bluegill ( L. macrochirus ) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.
4. Estimates of the potential annual energetic contribution (kJ m^–2 d^–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.
5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream ecosystems.     

Maturation of walleye by age, size and surplus energy

The probability of annual sexual maturation by male and female walleye Stizostedion vitreum was related to age, size and an index of condition, I _VF=[arcsine(visceral fat)^0·5(body mass)^−0·5]. Most males first matured at ages 2 and 3 years; size explained first maturation, but condition explained later maturation. In contrast, most females first matured at ages 4 and 5 years; maturity of females was more dependent upon condition. Maturity of females at ages 4 and 5 years was significantly correlated with average I _VF of the population ( PI _VF). The size reached by age 2 years (early growth) was correlated with the PI _VF. Growing degree-days, Secchi depth, latitude and lake morphology were not correlated with the PI _VF. Annual variations in female spawning stock size were related to the condition of the females, presumably reflecting the net acquisition of energy in the preceding growing season. Annual variations within lakes in the net acquisition of energy may exceed the variations in energy availability between lakes, dictated by lake morphology and geography. Thus, assessment of condition could be used to predict annual potential spawning stock size and egg production.     

The morphological development of the locomotor and cardiac muscles of the migratory barnacle goose (Branta Leucopsis)

The masses of the locomotor and acardiac muscles of wild barncale goose gollings, from migratory population, were examined systematically during development and their values compared to those of pre-migratory geese. Pre-flight development was typified by approximately linear increases of body, leg, and heart ventricular mass with respect to age. Flight muscle showed an exponential increase in mass. Pectoralis muscle mass was 14.2 ± 0.3% of body mass (1297 ± 73g, n=7) in early flying goslings compared to 16.6 ± 0.3% of body mass (2318 ± 109g, n=8) in pre-migratory geese. Post-flight development was typified by stasis of leg muscle mass but hypertrophy of Ventricular and pectoralis muscle mass in proportion to body mass. Ventricular mass relative to body mass showed the lowest values at 5 weeks of age (0.62 ± 0.01%) with peak values at 1 week of age (10.4 ± 0.04%). The latter may be associated with both requirements of thermoregualation in these precocial, arctic breeding geese and the need to forage approximately 24 hours post-hatch. Peak values for leg muscle mass, relative to body mass, were found at 3 weeks of age (12.7 ± 0.36%), with lowest values in the pre-migratory geese (6.7 ± 0.21%), while peak values for pectoralis muscle mass were expressed in the premigratory geese with lowest values at 1 week of age (0.94 ± 0.07%). Ventricular mass was proportional to leg muscle mass up to 5 weeks of age (M_v= 0.38M_t^0.68, r²=0.95), but subsequent increase in ventricular mass was proportional to pectoralis muscle mass (M_v= 0.25M_p^0.73, r²= 0.81).     

Geographical variation in AdhF and alcoholic resource utilization in Indian populations of Drosophila melanogaster

Indian geographical populations of Drosophila melanogaster, collected at latitude 10–32.3 ^oN, longitude 76.1–80.1 ^oE and altitude 16–2050 m, were analysed for changes in Adh ¹ frequency and utilization potential of diverse alcoholic resources. Until now, there have been limited data on climatic association of correlated changes on these aspects in continental populations of D. melanogaster. Indian populations demonstrate an increase in Adh ^F frequency by 0.04 per degree latitude and significantly higher utilization of ethanol (9.0–15.2%), acetic acid (8.1–12.5%), n-propanol (2.55-4.25%), 2-propanol (1.5-3.5%), n-butanol (2.15 3.5%) and 2-butanol (0.68-1.2%). Data also revealed significant correlation with latitude as well as altitude. Regression analysis of climatic data from collection sites confirmed the observed clinal variation of Adh ^F as well as alcoholic utilization in D. melanogaster. On the Indian subcontinent, variation in Adh ^F frequency and alcoholic resource utilization along increasing latitude as well as altitude are due to climatic selection factors such as temperature and rainfall.