bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and diversity of stream invertebrate assemblages: the influence of temperature with altitude and latitude
Authors: JACOBSEN DEAN , SCHULTZ RIKKE , ENCALADA ANDREA
Published: November 2003

1. Structure and diversity of the macroinvertebrate fauna were studied in relation to altitude and latitude among three groups of streams from Ecuador (lowland: 100–600 m, Central Valley: 2600–3100 m, páramo: 3500–4000 m), and one group from the temperate lowland region of Denmark. The streams in the four regions were comparable with regard to physical characteristics such as size, current and substratum.

2. In terms of faunal composition the Ecuadorian highland streams bore more resemblance to the Danish lowland streams than the Ecuadorian lowland streams. The greater similarity between the Ecuadorian highland and the Danish streams, however, was due to the large number of insect families in the Ecuadorian lowlands, many of which were not found in the other regions. Of ten physico‐chemical parameters measured, maximum stream temperature explained by far the most variability in faunal composition.

3. The number of insect orders and families increased linearly with maximum stream temperature and therefore decreased with altitude and latitude. A compilation of literature data on insect richness and maximum water temperature from streams around the world confirmed this pattern, yielding a common linear relation for both temperate and tropical streams. This pattern may arise due to a direct temperature effect on speciation but is probably also related to geological history and the influence of climatic changes on stream ecosystems. We estimate that small, tropical, lowland streams have, on average, a two‐ to fourfold higher species richness than temperate lowland streams.
Structural characteristics of phytoplankton assemblages in tidal and non‐tidal freshwater systems: a case study from the Schelde basin, Belgium
Authors: MUYLAERT KOENRAAD , VAN KERCKVOORDE ANDY , VYVERMAN WIM , SABBE KOEN
Published: November 2003

1. The Schelde estuary, its side basins and their tributaries were sampled in August 1995 and April 1996 for phytoplankton abundance, biomass, diversity and species composition. In order to clarify the underlying causes of differences in phytoplankton communities, the results were related to some important abiotic variables.

2. Although species richness and diversity did not differ significantly between the riverine and the freshwater tidal stations, multivariate ordination techniques based on species abundances differentiate between these two ecosystems. While in the rivers phytoplankton standing stocks were as high in summer as in spring, standing stocks in the freshwater tidal estuary were significantly higher in the August samples.

3. It is postulated that due to the resuspension of suspended solids by estuarine currents, light is limiting phytoplankton development in the freshwater tidal reaches in spring. At that stage, phytoplankton populations have already developed in the rivers. In summer, zooplankton prevent any further increase of riverine phytoplankton populations. In the freshwater tidal estuary, however, increased light levels, a higher residence time compared to rivers and the absence of zooplankton due to low oxygen concentrations permit phytoplankton populations to bloom.
Reproduction and adult longevity of five species of planktonic cyclopoid copepods reared on different diets: a comparative study
Authors: HOPP ULRICH , MAIER GERHARD , BLEHER RAINER
Published: November 2003

1. The nutritional value of a pure algal food, the phytoflagellate Chlamydomonas reinhardtii, and a mixed diet was tested for five planktonic cyclopoid copepods (Acanthocyclops robustus, Cyclops vicinus, Cyclops abyssorum, Mesocyclops leuckarti and Thermocyclops crassus). The algae were offered at high density (4.5 × 105 cells ml–1; 22.5 mg C l–1) in a flow‐through system. The mixed diet consisted of concentrated natural plankton (rotifers, copepod nauplii, small copepodites and large phytoplankton forms) in the size range 50–150 μm and with a dry mass > 20 mg l–1. Reproductive parameters (clutch size, interclutch periods, number of clutches produced) and adult longevity were monitored as indicators of nutritive value.

2. All species had a significantly lower reproductive output and a shorter or unchanged adult lifespan on the algal compared with the mixed diet.

3. The species differed considerably in their ability to use algae. Mesocyclops leuckarti produced no clutches with algae, and females died earlier than with the mixed food. Acanthocyclops robustus and C. vicinus produced smaller and fewer clutches, displayed a longer interclutch period and shorter (A. robustus) or similar (C. vicinus) lifespan on the algal food than on the mixed food. Thermocyclops crassus and C. abyssorum produced smaller clutches with the algal food, but interclutch period was shorter with the algal than with the mixed diet (T. crassus) or of the same length with both diets (C. abyssorum). Adult lifespan was the same under both food regimes. Unfed females produced no eggs.

4. The ability to utilize algae, the reproductive output and the reproductive allocation were not related to body size. Acanthocyclops robustus, a species of intermediate size, produced by far the largest clutches and the most eggs per lifetime under both food regimes and invested more in reproduction than the other species.

5. Reproduction was costly. Unfed and non‐reproducing females of C. vicinus and C. abyssorum reached the same age or lived longer than fed and reproducing ones.

6. The adult cyclopoids tested are primarily omnivorous, but utilize algae which are frequently sufficient for egg production.
Relationships between benthic biota and hydrological indices in New Zealand streams
Authors: CLAUSEN BENTE , BIGGS BARRY
Published: November 2003

1. The objective of this study was to identify the most ecologically relevant hydrological indices for characterizing hydrological regimes in New Zealand streams. To do this we related measures of periphyton chlorophyll a, ash‐free dry mass (AFDM), species richness, and diversity and invertebrate density, species richness and diversity, to thirty‐four hydrological variables derived from daily flow records at eighty‐three sites. The hydrological variables included some describing average flow conditions, flow variability, floods, and low‐flow characteristics.

2. A principal components analysis showed that the interrelationship between many of the hydrological variables was high, and most variables correlated significantly with Principal Component 1 (PC1). The flood frequency variables formed a distinct component of the flow regime and were the main contributor to PC2.

3. We found that both the average flow conditions and some measure of variability were significantly related to most of the biological variables, and these individual hydrological variables were more strongly correlated to the biological measures than the composite principal components. Only four of the thirty‐four flow variables were significantly correlated (P < 0.05) with measures of periphyton biomass (chlorophyll a and AFDM), whereas twenty‐four variables were correlated with periphyton diversity. Conversely, thirty‐one of the thirty‐four flow variables were correlated with total invertebrate density, whereas only four variables correlated with diversity.

4. We selected the flood frequency (FRE3), where a flood is defined as flows higher than three times the median flow, as the most ecological useful overall flow variable in New Zealand streams because it explained a significant amount of the variance in four out of the six main benthic community measures, and it had a clear mechanism of control of the biota which was commensurate with current stream ecosystem theory. Periphyton biomass decreased with increasing FRE3, whereas invertebrate density had an increasing/curvilinear relationship with FRE3. Periphyton species richness and diversity decreased with increasing FRE3.
Interactive effects of diet and thermal regime on growth of the midge Pseudochironomus richardsoni Malloch
Authors: GRESENS SUSAN
Published: November 2003

1. Larvae of Pseudochironomus richardsoni were reared to pupation in individual enclosures, in one of three thermal habitats in a northern California stream. The average temperature range in cold seeps was 15–21 °C, while the main channel ranged from 20 to 27 °C, and side pools ranged from 18 to 33 °C. Diet consisted of either diatoms or algal detritus.

2. Specific growth rate ranged from 0.057 to 0.267 day–1. Specific growth and developmental rates were highest on a diatom diet, and increased with temperature. Regressions of growth rate on mean microsite temperature were also significantly altered by diet. Differences in specific growth rate due to diet are magnified at higher temperatures.

3. Pupae reared on diatoms were larger than those reared on detritus. The mass of pupae reared on detritus decreased with increasing temperature. However, there was no significant relationship between pupal mass and temperature for larvae reared on diatoms.

4. The combined effects of food quality and thermal environment on growth of the midge P. richardsoni are significantly different from the independent effects of diet and temperature. Interactive effects of food quality and temperature may influence the contribution of certain aquatic habitats (algal mats) to invertebrate secondary production.
Spatial and temporal response of stream bacteria to sources of dissolved organic carbon in a blackwater stream system
Authors: KOETSIER III PETER , McARTHUR VAUN , LEFF LAURA
Published: November 2003

1. We hypothesized that changes in bacterial colony growth would be correlated to shifts in riparian vegetation (via leachate quality) along a river continuum of a south‐eastern, blackwater stream (U.S.A.). Spatially, we expected bacterial assemblages from downstream reaches to utilize more sources of leachate and at higher concentrations than bacteria collected from headwater reaches. Temporally, we predicted higher colony growth on leachate from autumn‐shed (senescent) leaves compared with leachate from fresh, green leaves.

2. We examined spatial differences in assemblage growth by culturing bacteria sampled along the stream continuum on gradient plates using leachates from four common riparian species (Taxodium distichum, Carya spp., Acer rubrum and Decumaria barbara). Bacteria from the lowest site were able to use all sources provided and at all concentrations, whereas bacteria from upper reaches could not. Colony density was correlated to relative leachate concentration at all sites along the continuum.

3. Leachates from fresh and senescent A. rubrum leaves were used to determine temporal differences. Winter assemblages of bacteria could not grow on fresh leaf leachate at any concentration but grew well on autumn leaf leachate at higher concentrations. Differential response of bacterial assemblages indicated local adaptation to potential sources of dissolved organic matter.

4. Growth response of stream bacterial colonies appeared to be dependent on the timing and source of leachate as well as on sources of dissolved organic carbon from further upstream. Growth of bacterial assemblages exhibited ‘generalist’ characteristics in headwater reaches and ‘specialist’ characteristics at the mouth of our study stream drainage. Thus, our findings lend support to the argument that variable resource habitats favour a small, generalist assemblage, while environments with stable resource supplies allow for highly diverse assemblages dominated by specialists.
Size‐dependent flight initiation by a lotic mayfly in response to a predatory fish
Authors: SCRIMGEOUR GARRY , CASH KEVIN , CULP JOSEPH
Published: November 2003

1. Laboratory experiments were performed to determine whether flight initiation by lotic mayfly larvae of Baetistricaudatus exposed to the longnose dace (Rhinichthyscataractae) is affected by an individual’s size and its physiological state.

2. We used a three factorial ANOVA design to test whether flight initiation distances (FIDs) were affected by Baetis size (small, large), starvation level (low, high), and the length of a predator‐free foraging period (short, long).

3. FIDs were significantly affected by the interaction between Baetis size and starvation level, and the main level effects of starvation and Baetis size. FIDs of small larvae were unaffected by starvation level and the length of the predator‐free feeding period, whereas starvation reduced FIDs of large larvae 2‐fold.

4. Subsequent experiments showed that size‐dependent differences in FIDs could not be attributed to size‐specific differences in the economics of rates of food intake or gut evacuation. For both small and large larvae, food intake rates declined with increasing time spent foraging and both small and large larvae consumed the majority (70–75%) of food within the first 3 h of the 12‐h feeding period. Similarly, gut evacuation declined with increasing starvation time and rates of evacuation did not differ between small and large larvae. These data suggest that size‐dependent differences in flight initiation by Baetis larvae do not involve the energetics of food intake or processing.
Landscape influences on water chemistry in Midwestern stream ecosystems
Authors: JOHNSON LUCINDA , RICHARDS CARL , HOST GEORGE , ARTHUR JOHN
Published: November 2003

1. Landscape characteristics of sixty‐two subcatchments within the Saginaw Bay Catchment of central Michigan were examined to identify relationships with stream water chemistry. Land use, land cover and elevation were quantified for both entire catchments and the upland–river ecotone (100 m stream buffer strip). Catchment and ecotone data were then empirically compared with stream water chemistry using multivariate and regression analyses. Redundancy analysis was used to partition variance among land use, geology, and the shared influence of land use and geology.

2. Major catchments dominated by rowcrop agriculture had the highest alkalinity, total dissolved solids and nitrate + nitrite concentrations.

3. Strong seasonal differences were observed in total nitrogen and nitrite + nitrate, but not in total phosphorus or suspended solids. Land use and landscape structure factors such as slope and patch density (number of land use patches per km2) accounted for most of the observed variance in summer.

4. In both autumn and summer, landscape factors accounted for much of the observed variation in total dissolved solids and alkalinity. During autumn, geological factors and the shared influence of geology/landscape structure plus land use exerted more influence than did land use alone.

5. Total phosphorus and total suspended solids were much better explained by land use within the stream ecotone in summer than in other seasons. However, total nitrogen, nitrate, orthophosphate and alkalinity were equally well explained by land use within the ecotone and throughout the whole catchment. Only total dissolved solids in summer and ammonium in autumn were explained better by the whole catchment than the ecotone.

6. Our results show that relatively coarse spatial databases can provide useful descriptors of regional water quality.
The effects of temperature on the web‐building behaviour of the common house spider, Achaearanea tepidariorum
Authors: BARGHUSEN L. E. , CLAUSSEN D. L. , ANDERSON M. S. , BAILER A. J.
Published: November 2003

1. Because spiders are ectothermic animals, the temperature regime of the microhabitat in which an individual finds itself may affect important performance traits of that individual. The present study examined the effects of temperature on attributes of webs spun by Achaearanea tepidariorum (C. L. Koch), as well as testing temperature preference in this species. The effects of temperature on the amount of silk per web produced by Achaearanea tepidariorum and the prey‐capture efficiency of webs produced at different temperatures were determined by using webs constructed at 5, 10, 15, 20, 25 and 30°C. The temperature preferences of A. tepidariorum within a thermal gradient were also determined.

2. Web mass was related to temperature, exhibiting a quadratic relation with a maximum web mass occurring at approximately 20°C.

3. Number of strands per cm3 of webs varied directly with web mass; webs with greater strand densities were more efficient at capturing flies.

4. The number of spiders observed in each temperature range in the thermal gradient indicated a non‐uniform distribution, with the spiders avoiding temperatures in the highest range (27·3±2·0°C).

5. These data suggest an optimal temperature for web construction at which webs produced are more efficient at capturing prey. The data also suggest that this species may avoid sites that do not provide an adequate thermal environment.
Mass regulation in juvenile Starlings: response to change in food availability depends on initial body mass
Authors: WITTER M. S. , SWADDLE J. P.
Published: November 2003

1. The adaptive mass‐regulation hypothesis suggests that birds should respond to worsening or unpredictable foraging conditions by increasing body mass and energetic reserves. However, previous work on adult European Starlings, Sturnus vulgaris L., has revealed that the response to worsening foraging conditions varies according to the seasonal status of the birds. Photosensitive birds respond to decreased time available to feed by increasing mass, whereas photorefractory birds regulate mass at a fixed level. Juvenile Starlings are in a state of photorefractoriness until puberty. In this paper, we examine whether photorefractory juvenile Starlings respond to worsening foraging conditions by regulating mass at a fixed level, like adults, or whether they increase in mass, in accordance with the adaptive regulation hypothesis.

2. Birds were divided into two treatment groups: control and food deprived. Control birds remained on food ad libitum throughout the experiment. Food‐deprived birds had their food removed for 5h every other day over a 6‐week period. The effects of these manipulations on the resulting changes in body mass and fat reserves were examined.

3. Food‐deprived birds increased fat reserves and body mass in comparison with controls. However, the response to food availability depended on the initial body mass of the birds. Birds with the lowest initial mass exhibited the largest response to the manipulation. This may be because birds with low energetic reserves are more severely affected by changes in the availability of food.

4. Juvenile photorefractory Starlings show a response to changes in food availability that is unlike the response of photorefractory adults. We suggest that the mechanism of responding to environmental change, in addition to being modulated seasonally, may be age structured. We speculate that the function of this age effect may be related to the low competitive status of juvenile Starlings. This subdominant age‐class may be displaced to less favourable feeding or roosting sites; as a result, they may have to respond flexibly to a rapidly changing and unpredictable energetic environment.
Ecophysiological responses to simulated canopy gaps of two tree species of contrasting shade tolerance in elevated CO2
Authors: E KUBISKE M. , PREGITZER K. S.
Published: November 2003

1. One‐year‐old seedlings of shade tolerant Acer rubrum and intolerant Betula papyrifera were grown in ambient and twice ambient (elevated) CO2, and in full sun and 80% shade for 90 days. The shaded seedlings received 30‐min sun patches twice during the course of the day. Gas exchange and tissue–water relations were measured at midday in the sun plants and following 20 min of exposure to full sun in the shade plants to determine the effect of elevated CO2 on constraints to sun‐patch utilization in these species.

2. Elevated CO2 had the largest stimulation of photosynthesis in B. papyrifera sun plants and A. rubrum shade plants.

3. Higher photosynthesis per unit leaf area in sun plants than in shade plants of B. papyrifera was largely owing to differences in leaf morphology. Acer rubrum exhibited sun/shade differences in photosynthesis per unit leaf mass consistent with biochemical acclimation to shade.

4.
Betula papyrifera exhibited CO2 responses that would facilitate tolerance to leaf water deficits in large sun patches, including osmotic adjustment and higher transpiration and stomatal conductance at a given leaf‐water potential, whereas A. rubrum exhibited large increases in photosynthetic nitrogen‐use efficiency.

5. Results suggest that species of contrasting successional ranks respond differently to elevated CO2, in ways that are consistent with the habitats in which they typically occur.
Body size, granivory and seasonal dietary shifts in desert gerbilline rodents
Authors: DEGEN A. A. , KHOKHLOVA I. S. , KAM M. , NAGY K. A.
Published: November 2003

1. Desert gerbilline rodents consume mainly plant material, in particular seeds. However, seeds are less available following winter rains than in summer and many rodents shift their diets from predominantly seeds to ones containing more vegetation. This shift results in a proportionately greater preformed water intake and, as these rodents do not drink, an increase in the water influx to field metabolic rate ratio (WI : FMR; ml kJ–1). Thus, this ratio is indicative of the food consumed, being low when gerbils are consuming seeds and high when consuming green vegetation.

2. Smaller animals are more dependent on a highly digestible, high energy diet such as seeds and are more vulnerable to extreme air temperatures than are larger animals. It was predicted that: (1) gerbils consume less seeds in winter than in summer but the difference between seasons in seed intake is less pronounced in smaller than in larger rodents; and (2) smaller gerbils are more sensitive to extreme air temperatures than are larger gerbils. To examine these hypotheses, two coexisting desert gerbils, Gerbillus henleyi (8–12 g) and Meriones crassus (50–110 g), were studied.

3. It was predicted that: (1) the WI : FMR ratio would be greater in winter than in summer in both species, but the proportionate increase would be smaller in G. henleyi than in M. crassus; and (2) energy expenditure would be greater in winter than in summer in both species, but the proportionate increase would be greater in G. henleyi than in M. crassus. To test these predictions, winter and summer water influx and field metabolic rates in these species were measured under free‐living conditions using doubly labelled water.

4. The WI : FMR ratio in summer was 0·048 in G. henleyi and 0·069 in M. crassus, indicating that G. henleyi was consuming proportionately more seeds than M. crassus. In winter, the ratio was 0·052 in G. henleyi, indicating that there was little change in dietary composition and that this species was still consuming mainly seeds. In contrast, the ratio in M. crassus rose to 0·127, indicating a shift to a diet containing more green vegetation. The relatively higher seed intake by G. henleyi than M. crassus in both seasons and the small, if any, seasonal change in seed intake in G. henleyi agrees with the hypothesis of body size and seed intake in gerbils. Winter FMR increased over summer FMR in both species, as predicted; however, the expected greater increase in G. henleyi relative to M. crassus did not occur. The winter FMR was 1·52 times the summer FMR in G. henleyi and 1·53 times the summer FMR in M. crassuss.
Natural thermal stress and heat‐shock protein expression in Drosophila larvae and pupae
Authors: FEDER M. E. , BLAIR N. , FIGUERAS H.
Published: November 2003

1. Whether Drosophila larvae and pupae naturally experience temperatures that can cause heat damage or death is poorly understood, but bears directly on numerous investigations of the thermal biology and heat‐shock response in Drosophila. Accordingly, the temperatures of necrotic fruit, which Drosophila larvae and pupae inhabit, the temperatures of larvae and pupae outside the laboratory, and the levels of the heat‐shock protein hsp 70 expressed by larvae in nature were examined.

2. When necrotic fruit was sunlit, internal temperatures rose to levels that can harm indwelling insects. Fruit size and evaporative water loss affected these temperatures. Temperatures of larvae and pupae in the field commonly exceeded 35 °C, with living larvae recorded at >44°C and pupae at >41°C. Natural mortality was evident, presumably because of heat.

3. In the laboratory, these temperatures kill larvae rapidly, with LT50s (time taken for half the sample to be killed) of 30 min at 39 °C, 15 min at 40 °C and 8·5 min at 41 °C. Gradual transfer from 25°C to these temperatures resulted in no lesser mortality than did direct transfer.

4. Hsp 70 levels in lysates of whole larvae were measured by ELISA (enzyme‐link immunosorbent assay) with an hsp 70‐specific antibody. For larvae within necrotic apples experimentally transferred from shade to sun and within necrotic fruit in situ, hsp 70 levels equalled or exceeded levels detected in parallel laboratory studies of whole larvae or cells in culture.

5. These data provide an ecological context for studies of thermal stress and the heat‐shock response in Drosophila that has heretofore been lacking.
The impact of grazing on plant fractal architecture and fitness of a Mediterranean shrub Anthyllis cytisoides L.
Authors: ESCÓS J. , ALADOS C. L. , EMLEN J. M.
Published: November 2003

1. We examined natural grazing by livestock (sheep and goats) on Albaida Anthyllis cytisoides L. with the aim of determining whether variation in the allometric relationships between plant parts provides a sensitive indicator of the impact of grazing.

2. The intra‐individual variation in translatory symmetry with scale and increased complexity of fractal structures reflect environmental disturbance under heavy grazing pressure and lack of grazing.

3. Fitness consequences of grazing were also investigated. Grazing promotes growth and adult survival, and a drop in seed production as a consequence of consumption. In spite of that, total inclusive fitness (population rate of change) tends to increase with grazing.

4. Moderate grazing, while promoting growth, also enhances stability of vegetative structures. The favourable effect of moderate levels of herbivory on A. cytisoides is reflected in the homeostatic maintenance of its translatory symmetry and in the increased complexity of its fractal structures.
Energy allocation in polymorphic Brown Trout
Authors: JONSSON N. , JONSSON B.
Published: November 2003

1. To evaluate differences in energy allocation to gonadal development of resident and anadromous Brown Trout, Salmo trutta, we analysed tissue composition and energy contents of adults of the two morphs from three small streams in southernmost Norway. Somatic energy per unit mass of anadromous spawners (5·0 ± 0·6 kJ g–1 wet weight) was 1·1 times that of the residents. This difference was chiefly due to a 1·4 ‐times higher lipid content in anadromous (4·9 ± 1·5%) than resident trout. The somatic protein and carbohydrate contents per unit mass were higher in resident than anadromous fish.

2. Somatic energy content per unit mass increased linearly with body length in resident but not anadromous fish. This increase was due to a significant increase in lipid content with fish size in resident contrary to anadromous trout.

3. The mass‐specific energy content of the ovaries was higher for residents (8·4 ± 0·4 kJ g–1 wet weight) than anadromous (7·81 ± 0·5 kJ g–1 wet weight) trout. This was due to higher lipid and protein contents per unit mass in resident than anadromous females. In males, no similar differences between morphs were found (5·9 ± 0·8 kJ g–1 wet weight). The mass‐specific energy content of the ovaries was c. 1·4 higher than that of the testes, mainly caused by a 2·3–2·6 higher lipid content per unit mass of eggs.

4. The mean gonadosomatic index (kJ %) was higher in anadromous (34·0 ± 9·4) than resident (28·6 ± 5·5) females, but not in males (≈ 3%). In females, but not in males, gonadal energy increased linearly with increasing somatic energy of the fish.

5. Female gonadal energy at corresponding somatic energies was higher than that of males. On average, the energetic investment in gonads relative to soma of first‐time spawners in the year of maturation was estimated at 11% in males and 67% in females.
Trade‐off between height growth and stem diameter growth for an evergreen Oak, Quercus glauca, in a mixed hardwood forest
Authors: SUMIDA A. , ITO H. , ISAGI Y.
Published: November 2003

1. Patterns of stem growth of a mid‐successional evergreen Oak species (Quercus glauca) in a mixed hardwood forest were examined to explore the trade‐off relationship between stem‐diameter growth and height growth.

2. The mean cross‐sectional area (and the corresponding mean diameter) of a stem at a point in time was defined as the stem volume divided by tree height. Based on this definition, a simple equation representing the trade‐off relationship between the height growth and mean diameter growth was formulated.

3. In the long term, allocation to height growth was encouraged at the seedling stage and it gradually declined with time, with the decline in the suppressed seedlings being more pronounced than in the dominant trees.

4. However, both the suppressed and the dominant trees showed acceleration of height growth at various ages. Such a fluctuation in the allocation of biomass to height growth is likely to have been caused by chronological changes in light conditions, and meandered the trajectory of allometry between the height and mean diameter.

5. The observed stem growth patterns of the individual trees could explain the chronological changes in the diameter–height relationship of the population.
Geographical pattern in photosynthetic light response of Pinus sylvestris in Europe
Authors: LUOMA S.
Published: November 2003

1. The geographical aspects in photosynthetic light response and stomatal conductance in the shoots of Pinus sylvestris were studied together with structural properties of shoots and needles. Seven stands within the natural distribution area of P. sylvestris in Europe were chosen. CO2 exchange, irradiance and stomatal conductance (gs) for water vapour were measured and the maximum photosynthetic rate (Pm) was determined from the CO2 exchange measurements.

2. There was a clear pattern in the average values of Pm along the latitudinal gradient. Highest values of Pm were found in the middle parts of the distribution area and they decreased towards both ends of the transect. The highest value was almost twice as high as the lowest one.

3. The between‐site variation explained 70% of the total variation in the maximum photosynthetic rate. Pm was not clearly correlated with any single climatic variable or nitrogen concentration in the needles.

4.
Pm was closely coupled with stomatal conductance (r2=0·74). The differences in Pm and gs between the sites is likely to reflect adaptation and acclimation to different climates.
Reproductive investment and parasite susceptibility in the Great Tit
Authors: ALLANDER K.
Published: November 2003

1. Reproduction and parasite defence are assumed to be costly activities for hosts, and therefore trade‐offs might exist between reproduction and parasite defence.

2. Brood sizes were manipulated in a population of Great Tits (Parus major L.) to assess trade‐offs between reproduction and parasite defence. Blood samples were taken from males and females during the late nestling phase, and parasite prevalence was compared among parents raising enlarged, reduced and control broods.

3. A higher prevalence of protozoan blood parasites dominated by Haemoproteus majoris was found among parents with enlarged broods, as compared with parents with control and reduced broods, respectively. Brood size manipulation did not affect parasite prevalence between the sexes or between age classes differently.

4. Mean parasite intensity (number of parasites per microscope field) among adult birds only infected with H. majoris was higher for parents with experimentally enlarged broods than controls and reduced broods, respectively.

5. These results support the hypothesis of a trade‐off between parasite defence and reproduction.
The adrenocortical responses to stress in breeding Willow Warblers Phylloscopus trochilus in Sweden: effects of latitude and gender
Authors: SILVERIN B. , ARVIDSSON B. , WINGFIELD J.
Published: November 2003

1. In the present study we tested the hypothesis that birds suppress their adrenocortical response to stress when breeding in a severe environment.

2. We measured increases in circulating levels of corticosterone following capture and handling in populations of Willow Warblers, Phylloscopus trochilus, breeding in a rich deciduous forest in southern Sweden and in Willow Warblers breeding in a subarctic environment in Swedish Lapland. Data from an 8‐year study on survival rates and nest predation in southern and northern Sweden are also included.

3. By comparing the changes in corticosterone levels immediately following capture, handling and restraint, and then up to 1‐h post‐capture across gender and latitude, we were able to assess possible ecological influences.

4. Willow Warblers had about the same survival rates in northern and southern Sweden (0·27 and 0·30, respectively). Depredated clutches were normally replaced in southern Sweden (72%), but not in northern Sweden (1%).

5. A reduced adrenocortical response to stress was found in Willow Warblers of both sexes breeding in northern Sweden where conditions were more severe and the nesting season shorter than in southern Sweden. At the southern site, males had a significantly more robust adrenocortical response to stress than females, whereas at the northern site changes in corticosterone following capture were identical in males and females. Maximum corticosterone levels generated by the capture stress protocol were significantly higher in males at the southern site than in all other groups.

6. There were marked individual variations in the patterns of corticosterone changes following capture in all groups, but there were no significant relationships of dynamics of corticosterone changes to body mass or fat score in males. However, in females at the southern site, the maximum corticosterone level and the rate of corticosterone increase during the capture stress protocol were positively correlated with body mass. In contrast, at the northern site females showed negative correlations of body mass with maximum corticosterone and rate of corticosterone increase. These differences may reflect different ecological bases for modulation of the adrenocortical response to stress with latitude, and with gender.
The costs of becoming nocturnal: feeding efficiency in relation to light intensity in juvenile Atlantic Salmon
Authors: FRASER N. H. C. , METCALFE N. B.
Published: November 2003

1. Most animals are active by day or by night, but not both; juvenile salmonids are unusual in that they switch from being predominantly diurnal for most of the year to being nocturnal in winter. They are visual foragers, and adaptations for high visual acuity at daytime light intensities are generally incompatible with sensitive night vision. Here we test whether juvenile Atlantic Salmon Salmo salar are able to maintain their efficiency of prey capture when switching between diurnal and nocturnal foraging.

2. By testing the ability of the fish to acquire drifting food items under a range of manipulated light intensities, we show that the foraging efficiency of juvenile salmon is high at light intensities down to those equivalent to dawn or dusk, but drops markedly at lower levels of illumination: even under the best night condition (full moon and clear sky), the feeding efficiency is only 35% of their diurnal efficiency, and fish will usually be feeding at less than 10% (whenever the moon is not full, skies are overcast or when in the shade of bankside trees). Fish were unable to feed on drifting prey when in complete darkness.

3. The ability of juvenile salmon to detect prey under different light intensities is similar to that of other planktivorous or drift‐feeding species of fish; they thus appear to have no special adaptations for nocturnal foraging.

4. While winter drift abundance is slightly higher by night than by day, the difference is not enough to compensate for the loss in foraging efficiency. We suggest that juvenile salmon can nonetheless switch to nocturnal foraging in winter because their food requirements are low, many individuals adopting a strategy in which intake is suppressed to the minimum that ensures survival.
Energetic costs of activity by lizards in the field
Authors: CHRISTIAN K. A. , BAUDINETTE R. V. , PAMULA Y.
Published: November 2003

1. The available data related to the activity energetics of lizards in the field were collated with respect to three indices of activity energetics: the ecological cost of transport (ECT) expressed as a percentage of the total energy, the proportion of total energy used in all forms of activity (%AR), and the sustained metabolic scope (SusMS), defined as the ratio of the total energy expenditure to the total resting metabolism.

2. The ECT values of lizards ranged from 3 to 36% with five of 11 species having values >20%. The percentage AR ranged from 23 to 80% for lizards during active seasons, with most species having values > 50%. The SusMS ranged from 1·1 to 5·1.

3. Values of ECT are higher for lizards than for mammals, in part because the costs of maintenance metabolism are higher in mammals.

4. The percentage AR and SusMS values of mammals are higher than those of lizards.

5. It follows from the previous two points that the proportion of the total daily energy that is expended in non‐locomotory activities is disproportionately higher in mammals compared with lizards.

6. The energy expended in locomotion is a significant portion of the energy budget of lizards. This is generally true for all seasons in which there is activity.
The use of inositol hexaphosphate as a phosphorus source by mycorrhizal and non‐mycorrhizal Scots Pine (Pinus sylvestris)
Authors: COLPAERT J. V. , VAN LAERE A. , VAN TICHELEN K. K. , VAN ASSCHE J. A.
Published: November 2003

1. The external mycelia of the ectomycorrhizal fungi Thelephora terrestris and Suillus luteus, associated with Pinus sylvestris roots, exhibited a substantial extracellular acid phosphatase activity. The activity was positively correlated with the ergosterol concentration in the growth substratum and decreased with an increasing P nutrition.

2. The pioneer species T. terrestris grew best at a high Pi nutrition level whereas S. luteus, a ‘late‐stage’ mycobiont, produced more active biomass at a low Pi nutrition level.

3. The phytase activity of the external mycelia could not be detected; at the root surface a phytase activity was observed. Mycorrhizas had significantly higher activities than uninfected roots.

4. The addition of a relatively high concentration of a soluble phytate to the growth substratum resulted in an increased relative growth rate (RGR) in both mycorrhizal and non‐mycorrhizal plants. The influence of the mycorrhizal fungi on the use of the phytate‐P was small, despite the phytase activity of the mycorrhizal feeder roots.

5. The addition of phytate fixed on a HPLC resin did not result in an increase of the RGR and P uptake neither in the non‐mycorrhizal nor in the mycorrhizal Pines. The experiment did not support the hypothesis that phytate, which has a low solubility in soils, is a useful P source for ectomycorrhizal plants.
Phytochrome signalling in plant canopies: testing its population‐level implications with photoreceptor mutants of Arabidopsis
Authors: BALLARÉ C. L. , SCOPEL A. L.
Published: November 2003

1. A number of signalling mechanisms are responsible for triggering plastic morphological and physiological responses of plants to the proximity of neighbours. Among these mechanisms, the phytochrome‐mediated control of branching and elongation in response to alterations in red:far‐red ratio (R:FR) has been investigated in considerable detail.

2. While the role of phytochrome B in R:FR perception has been well established, and the consequences of neighbour photo‐detection on competitive ability are receiving attention, several important issues remain to be addressed regarding the ecology of plant–plant signalling in canopies. In particular, the role of other photoreceptors in neighbour detection and the impact of neighbour detection on population‐level attributes, such as size structure and productivity:density relationships are poorly characterized.

3. In the experiments reported here we addressed these questions using wild‐type (WT) plants and photomorphogenic mutants of Arabidopsis thaliana that are specifically deficient in phytochrome A, phytochrome B, all phytochromes or the blue‐light photoreceptor cryptochrome. Plants were grown in monocultures of different densities (between ~300 and 2400 plants m–2) from planting to seed set. Full competition among neighbouring plants was allowed both above‐and below‐ground.

4. WT plants responded to crowding with the predictable increase in elongation growth and by producing more steeply orientated leaves. Similar responses were observed in mutants deficient in phytochrome A or cryptochrome. Mutant plants lacking phytochrome B had an ‘elongated’ phenotype even when grown at low density and, in comparison with the other genotypes, showed markedly reduced morphological responses to crowding.

5. All genotypes having functional phytochrome B had similar biomass production and fruit production, and fruit production per unit area was constant over the range of densities used. Stands of phytochrome‐B‐deficient plants were as productive as WT canopies at intermediate densities, but had significantly reduced fruit production at low and, more strikingly, also at high densities. Size inequality among neighbours, measured as the coefficient of variation of reproductive output per plant, increased with density in all genotypes, but significantly more in phytochrome‐B‐deficient stands than in WT crops.

6. Our results suggest that: (1) phytochrome B plays a unique role in neighbour photo‐detection, while other photoreceptors appear to be less important in this respect; (2) in WT stands, phytochrome‐B‐mediated neighbour detection leads to inverse rank‐dependent morphological adjustments (i.e. greater fractional response in the small plants), which tend to buffer the plant population against size structuring; (3) the strong size‐structuring in populations of R:FR ‘blind’ phytochrome‐B mutants results in reduced stand fecundity at high densities.
Male larval nutrition influences the reproductive success of both sexes of the Spruce Budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae)
Authors: DELISLE J. , HARDY M.
Published: November 2003

1. It has recently been demonstrated that the species of host plant used by males during larval development may significantly affect the reproductive success of both sexes in a polygophagous tortricid, Choristoneura rosaceana (Delisle & Bouchard 1995). In the present study, using the Spruce Budworm, C. fumiferana, the hypothesis was tested that in oligophagous species, similar effects would result from within‐species variability in foliage quality.

2. It was demonstrated that male larval diet (young and old Balsam Fir foliage (YF vs OF) or artificial diet (AD)) significantly influences the reproductive success of both sexes of C. fumiferana.

3. Male body size and spermatophore size were positively correlated, with AD > YF > OF; however, males fed on YF had better mating success than those on OF and AD, indicating that size may not always be a good estimate of male quality.

4. The propensity of females to resume calling (CA+) and remate (RM+) was significantly lower, and the length of the refractory period longer, following first mating with high (YF) rather than low (OF and AD) male quality.

5. Females that resumed calling (CA+) had a lower reproductive output than those that did not (CA–), with the effect being more pronounced following mating with males fed on low (OF and AD) rather than high (YF) quality diet. A similar trend was observed in the proportion of females that were unsuccessfully mated, as shown by their low incidence of fertility (<25%). In contrast to their reproductive output, females that resumed calling lived as long as those that did not, regardless of male larval diet. However, the resumption of calling was also observed in a large number of highly fertile (48%) females, indicating that infertility was not the only reason for the resumption of sexual receptivity.

6. Females that remated (RM+) following an initial mating with low quality males (OF and AD) had fecundities and longevities similar to those that did not (RM–). However, their incidence of fertility was significantly higher. In contrast, females that remated following an initial mating with high quality males (YF) were more fecund and lived slightly longer than those that did not (RM–). A similar pattern was observed with females initially mated with OF and AD males, if only individuals with high fertility following first mating were considered in the analyses.

7. Male larval diet had no effect on fecundity, percentage fertility and longevity in females that remained refractory following their first mating.

8. The first mating occurred earlier in the night and lasted longer than the second, with both variables being independent of the diet of the first mate. This may explain why overall the proportion of females that remated was lower than that for females that resumed calling following mating.
Associations between shell morphology and land crab predation in the land snail Cerion
Authors: QUENSEN III J. F. , S WOODRUFF D.
Published: November 2003

1. The land crab Gecarcinus lateralis is a significant predator of the abundant Bahamian land snails of the genus Cerion. The crabs typically ‘scissor’ the cylindrical shells in half or break the lip and peel back the shell to reach the animal which withdraws two or three whorls into the shell. Scars on shells of live adults at 73 sites in the Bahamas and Florida Keys show that about 8% (range: 0–44%) of the snails have survived attacks of this type.

2. An artificial crab claw was used to investigate the compressive force required to break Cerion shells of different morphotypes. Defining shell strength as the ability to withstand compressive forces, 10 morphotypes were found that exhibited mean relative strengths of between 30 and 300 newtons. Feeding trials with one adult crab showed that snails whose shells could withstand compressive forces of > 95 N were safe from this individual predator.

3. Multiple linear regression analyses showed that both shell size (length and width) and shell wall thickness were the ultimate determinants of shell strength. Ribs strengthen the shell by contributing to wall thickness and also by increasing overall shell width. The thickened adult shell lip and collabral ribs provide effective protection from attack by peeling.