bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple predictions of instream habitat model outputs for fish habitat guilds in large streams
Authors: LAMOUROUX NICOLAS , SOUCHON YVES
Published: March 2003

1. In the context of a generalised modification of hydraulic conditions in medium to large streams, modelling the impacts of stream regulation on fish communities in multiple streams is an important challenge for basic and applied freshwater ecology. Conventional instream habitat models such as PHABSIM link a hydraulic model with preference curves for various species to estimate habitat value changes with discharge in stream reaches. Despite world‐wide applications, they have been scarcely used in multiple sites with multiple species.

2. We assigned 21 size classes of European fish species to four habitat guilds (cluster analysis grouping size classes with comparable microhabitat preference curves). Then, we ran a conventional instream habitat model on 28 French stream reaches belonging to the `barbel zone', to estimate habitat values versus discharge curves for the 21 size classes. We summarised the outputs as mean habitat values for guilds, and tested if they were predictable from average characteristics of reaches (discharge, depth, width, particle size).

3. As was obtained elsewhere for populations, habitat values for guilds were strongly related to average, dimensionless characteristics of reaches. The Reynolds number of reaches, equivalent to a discharge per width unit, reflected most of the discharge‐dependent changes in habitat values (within reaches). In particular, habitat values of species preferring bank (respectively midstream) microhabitats decreased (respectively increased) with increasing Reynolds number. The Froude number at median discharge was the major predictor of reach‐dependent but discharge‐independent variations in habitat values. Habitat values of species preferring riffle versus pool or bank microhabitats were higher in reaches with high Froude numbers. These relationships were consistent with existing knowledge on the different species.

4. Such results suggest that the input variables required to estimate habitat values for fish communities can be greatly simplified, as illustrated by a general estimation of the sensitivity of species preferring midstream habitats to discharge changes in any reach. Cost‐efficient alternatives to conventional instream habitat models should facilitate their validation in multiple sites, a point that remains critical in instream habitat modelling of fish communities.
Effects of longitudinal variations in stream habitat structure on fish abundance: an analysis based on subunit‐scale habitat classification
Authors: Inoue Mikio , Nunokawa Masanori
Published: March 2003

SUMMARY 1. Stream reaches contain assortments of various habitat types that can be defined at different spatial scales, such as channel unit (e.g. pools, riffles) and subunit (patches within channel units). We described longitudinal (upstream–downstream) patterns of stream habitat structure by considering subunits as structural elements, and examined their effects on the abundance of masu salmon (Oncorhynchus masou) and rosyface dace (Leuciscus ezoe) in a third‐order tributary of the Teshio River in northern Hokkaido, Japan.

2. Nine subunit types were determined on the basis of water depth, current velocity and substrate, using 0.5 × 0.5 m grids. Although both masu salmon and rosyface dace used pools as a major habitat, the former preferred a subunit type occurring at pool heads (PH subunit) while the latter preferred a slow‐current edge type (SE‐2 subunit).

3. Along the course of the stream, slow‐edge subunits (SE‐1, 2 and 3) increased in frequency downstream while fast‐edge subunits (FE‐1 and 2) decreased, suggesting a downstream development of slow‐current edges. Regression analyses indicated that longitudinal variation in masu salmon abundance was explained by the area of PH, rather than pools. Masu salmon density increased with the area of PH. Rosyface dace abundance was explained by a combination of water depth and the area of SE‐2, both effects being positive.

4. Longitudinal variations in the abundance of both species were related to the abundance of their preferred habitat at the subunit scale, rather than channel‐unit scale. The results emphasise the importance of fine‐scale patchiness when examining stream fish habitats.
Effects of augmentation of coarse particulate organic matter on metabolism and nutrient retention in hyporheic sediments
Authors: Crenshaw C. L. , Valett H. M. , Webster J. R.
Published: March 2003

SUMMARY 1. Metabolic and biogeochemical processes in hyporheic zones may depend on inputs of coarse particulate organic matter. Our research focused on how differing quantity and quality of organic matter affects metabolism and nutrient retention in the hyporheic zone of a first‐order Appalachian stream.

2. Sixteen plots were established on a tributary of Hugh White Creek, NC, U.S.A. Sediment was extracted and treated with leaves, wood, plastic strips or remained unamended. Following treatment, sediment was returned to the stream and, approximately 3 months later, samples were removed from each plot.

3. Aerobic and anaerobic metabolism were measured as the change in O2 and CO2 in recirculating microcosms. At the same time, we monitored other possible terminal electron accepting processes and changes in nutrient concentrations. Aerobic metabolism was low in all treatments and respiratory quotients calculated for all treatments indicated that metabolism was dominated by anaerobic processes.

4. Rates of anaerobic respiration and total (combined aerobic and anaerobic) respiration were significantly greater (P < 0.05) in plots treated with leaf organic matter compared to controls.

5. Addition of leaves, which had a low C:N ratio, stimulated respiration in hyporheic sediments. Anaerobic processes dominated metabolism in both control and amended sediments. Enhanced metabolic rates increased retention of many solutes, indicating that energy flow and nutrient dynamics in the subsurface of streams may depend upon the quantity and quality of imported carbon.
Effects of experimentally induced cyanobacterial blooms on crustacean zooplankton communities
Authors: Ghadouani Anas , Pinel‐Alloul Bernadette , Prepas Ellie E.
Published: March 2003

SUMMARY 1. Large in situ enclosures were used to study the effects of experimentally induced cyanobacterial blooms on zooplankton communities. A combination of N and P was added to shallow (2 m) and deep enclosures (5 m) with the goal of reducing the TN : TP ratio to a low level (∼5 : 1) to promote cyanobacterial growth. After nutrient additions, high biomass of cyanobacteria developed rapidly in shallow enclosures reaching levels only observed during bloom events in eutrophic lakes.

2. In the shallow enclosures, particulate phosphorus (PP) was on average 35% higher in comparison with deep enclosures, suggesting that depth plays a key role in P uptake by algae. Phytoplankton communities in both deep and shallow enclosures were dominated by three cyanobacteria species –Aphanizomenon flos‐aquae, Anabaena flos‐aquae and Microcystis aeruginosa– which accounted for up to 70% of total phytoplankton biomass. However, the absolute biomass of the three species was much higher in shallow enclosures, especially Aphanizomenon flos‐aquae. The three cyanobacteria species responded in contrasting ways to nutrient manipulation because of their different physiology.

3. Standardised concentrations of the hepatotoxic microcystin‐LR increased as a result of nutrient manipulations by a factor of four in the treated enclosures. Increased biomass of inedible and toxin producing cyanobacteria was associated with a decline in Daphnia pulicaria biomass caused by a reduction in the number of individuals with a body length of >1 mm. Zooplankton biomass did not decline at moderate cyanobacteria biomass, but when cyanobacteria reached high biomass large cladocerans were reduced.

4. Our results demonstrate that zooplankton communities can be negatively affected by cyanobacterial blooms and therefore the potential to use herbivory to reduce algal blooms in such eutrophic lakes appears limited.
Exotic crayfish in a brown water stream: effects on juvenile trout, invertebrates and algae
Authors: Stenroth Patrik , Nyström Per
Published: March 2003

SUMMARY1. The impact of the introduced omnivorous signal crayfish (Pacifastacus leniusculus) on trout fry, macroinvertebrates and algae was evaluated in a brown water stream in southern Sweden usingin situenclosures. We also examined the gut content of all surviving crayfish in the enclosures. Two crayfish densities in addition to a control without crayfish were used in replicate enclosures (1.26 m2) in a 1‐month experiment. Additionally, 20 trout fry (Salmo trutta) were stocked in each enclosure to assess the effects of crayfish on trout survival and growth.

2. Detritus was the most common food item in crayfish guts. Animal fragments were also frequent while algae and macrophytes were scarcer. Crayfish exuviae were found in crayfish guts, but the frequency of cannibalism was low.

3. Trout survival in enclosures was positively related to water velocity but was unaffected by crayfish.

4. Total invertebrate biomass and taxon richness were lower in crayfish treatments. The biomass of all predatory invertebrate taxa was reduced but only three of six non‐predatory taxa were reduced in the crayfish treatments.

5. Epiphytic algal biomass (measured as chlorophylla, on plastic strips) was not related to crayfish density, whereas the biomass of epilithic algae (measured as chlorophylla) was enhanced by high water velocity and high crayfish density. The latter was possibly mediated via improved light and nutrient conditions, as active crayfish re‐suspend and/or remove detritus and senescent algal cells during periods of low water velocity.

6. We conclude that the introduced signal crayfish may affect stream communities directly and indirectly. Invaded communities will have reduced macroinvertebrate taxon richness and the signal crayfish will replace vulnerable invertebrate predators such as leeches. In streams that transport large amounts of sediment or organic matter, a high density of crayfish is likely to enhance benthic algal production through physical activity rather than via trophic effects.
Stem CO2 fluxes in two Sahelian shrub species (Guiera senegalensis and Combretum micranthum)
Authors: Levy P. E. , Jarvis P. G.
Published: March 2003

1. Measurements are presented of CO2 flux from woody stems of two shrub species in the Sahelian zone of West Africa (Guiera senegalensis and Combretum micranthum). Measurements were made on excised stems and in situ.

2. An experiment suggested that the respiration rate was closely related to the stem surface area but showed little relationship with stem volume, and was therefore associated with the cambium and phloem rather than the sapwood. This contrasts with several studies in which sapwood volume appeared to be the dominant component and the difference is attributed to the comparatively small diameter of stems in the shrubs studied here.

3. Measurements were made of the response of stem CO2 flux to photosynthetic photon flux density (Q) and gave evidence of corticular photosynthesis in the stems.

4. The response of stem respiration to temperature was determined in situ. The data were analysed using a variant on the standard exponential relationship with temperature, R = (Rom + Rog) exp(k T), where R is respiration rate, Rom is maintenance respiration rate at 0 °C, Rog is growth respiration rate at 0 °C, k is a temperature coefficient and T is temperature. Data from the dry season were assumed to represent maintenance respiration and used to define Rom and k. The Rog term thus quantifies the increase in respiration during the wet season beyond this baseline level, presumably attributable to growth. Values of Rom were 0·054 and 0·074μmol m–2 s–1 in G.senegalensis and C. micranthum, respectively, whilst Rog ranged between 0·061 and 0·96μmol m–2 s–1 during the wet season.

5. At ecosystem scale on an annual basis, stem respiration represented 17% of leaf photosynthesis, whilst corticular photosynthesis was at most 11·1% of stem respiration.
Regulation of integumentary colour and plasma carotenoids in American Kestrels consistent with sexual selection theory
Authors: Negro J. J. , Bortolotti G. R. , Tella J. L. , Fernie K. J. , Bird D. M.
Published: March 2003

1. Sexually selected traits are expected to vary seasonally, with the maximal expression of the character being evident during mate choice; however, the mechanisms controlling or regulating such traits are generally poorly known.

2. Carotenoid pigments responsible for bright red or yellow coloration in the feathers, skin or other integumentary structures of birds are generally believed to vary seasonally because of diet.

3. Variation in carotenoid‐dependent skin colour between winter and spring (mating season) was investigated, as was variation in plasma carotenoids across the breeding season in captive American Kestrels, Falco sparverius, fed a uniform diet.

4. Kestrels were more brightly coloured in the mating period than in winter, and plasma carotenoid concentrations declined from the time of mating to the rearing of young.

5. Although carotenoid levels were highly sexually dimorphic during mating and laying, males and both breeding and non‐breeding females all had similar levels by the incubation period, and the pattern of variation over time suggests rheostatic regulation.

6. These results suggest kestrels may have the ability to regulate (rather than merely control) their colour physiologically, the variation in colour and carotenoids is consistent with that expected of a sexually selected trait, and the loss of colour after breeding may suggest a trade‐off between the show and health functions of carotenoids.
A satiation model for the temporal organization of grazing in limpets
Authors: Chelazzi G. , Parpagnoli D. , Santini G.
Published: March 2003

1.A compartmental model of the limpet alimentary system was designed to simulate the effects of functional constraints and substrate characteristics on the temporal patterning of grazing in these gastropods. Limitations are imposed by gut capacity and processing time. A maximum operating frequency is set for the radula activity, and a negative feedback on the grazing frequency is related to gut replenishment.

2.When holding constant the ‘morphofunctional’ parameters of the model, variations in the ‘richness’ of the substrate (i.e. in the amount of matter extracted per single rasp) generated different patterns of grazing activity, from constant grazing at different frequencies, to the appearance of distinct grazing–non‐grazing subphases with a periodicity corresponding to the processing time. Moreover, when varying the digestibility of the matter (i.e. its processing time), temporary saturations were produced.

3.Automatic recording of radula activity in specimens ofPatella caeruleaL. collected from a Mediterranean boulder beach and transferred to tidal tanks showed that each activity phase (performed during the high‐tide period) may be differently structured: from almost continuous grazing, with more or less pronounced and sometimes periodic oscillations, to alternation of grazing and non‐grazing subphases. Continuous and non‐continuous grazing patterns are shown also by the same specimen during subsequent activity phases.

4.The results of the model are consistent with empirical observations and suggest that satiation events related to the characteristics of the substrate encountered by the limpets when foraging, can produce highly variable grazing patterns with implications for the energetics of foraging in this group of grazers.
Close association of RGR, leaf and root morphology, seed mass and shade tolerance in seedlings of nine boreal tree species grown in high and low light
Authors: Reich P. B. , Tjoelker M. G. , Walters M. B. , Vanderklein D. W. , Buschena C.
Published: March 2003

1. To test hypotheses concerning adaptation and acclimation of tree species to shaded habitats we determined the growth, biomass partitioning and morphology of seedlings of nine near‐boreal tree species in high‐ and low‐light greenhouse environment (25 and 5% of full sunlight, respectively), comparable to sunlit gap and shaded microsites in boreal forests. The species differ widely in shade tolerance, seed size and leaf life span.

2. In low light, all species allocated proportionally more biomass to stems and less to roots, but the same to foliage, compared with the high‐light environment. At a common size, all species had finer leaf morphology (higher specific leaf area, SLA) but coarser root morphology (lower specific root length, SRL) in low than high light. From a whole plant perspective, all species enhanced leaf area per unit plant mass (leaf area ratio, LAR) in low light and root length per unit plant mass (root length ratio, RLR) in high light.

3. Shade‐intolerant deciduous species had higher RGR, SLA and SRL than larger seeded evergreens: ranking from Populus, Betula and Larix spp., then to five evergreen Pinus, Picea and Thuja spp., which were generally comparable in these traits. There were no changes in growth rankings of species between high‐ and low‐light environments, nor consistent differences among species in biomass partitioning. Hence, species differences in leaf and root morphology (SLA, SRL) drove whole plant patterns, such as Populus, Betula and Larix had greater total leaf area and root length per unit plant mass (LAR and RLR, respectively) than the evergreens. Interspecific variation in RGR in both high and low light was positively correlated (r≈ 0·9) with SLA, SRL, LAR and RLR, and negatively correlated (r≈–0·9) to seed mass and leaf life span.

4. These data suggest that SLA, SRL, NAR and RGR are closely associated with variation in life‐history traits and that variation in leaf and root structure more strongly influences patterns of RGR among species and light environments than does biomass partitioning.
Effects of defoliation and girdling on fruit production inIlex aquifolium
Authors: Obeso J. R.
Published: March 2003

1.The effects of defoliation and girdling on fruit production in European hollyIlex aquifoliumwere studied in a northern Spanish population. Three defoliation treatments (control, 50% and 100% leaf removal) were applied at branch level in 10 trees. Six branches were used per treatment in each tree and half of these branches were girdled (a ring of bark and cambium was removed from the branch base).

2.Leaf removal from ungirdled branches had little effect on fruit set, fruit production and reproductive allocation at branch level. However, these variables decreased as the extent of defoliation increased on girdled branches.

3.Fruit production in undefoliated branches did not differ between girdled and ungirdled branches, showing that girdled branches were autonomous for fruit production when undamaged. Mean fruit mass of girdled‐100% defoliated branches averaged 8% of fruit mass produced by control branches.

4.Fruit production of ungirdled‐100% defoliated branches did not differ from control branches, showing the importance of resource importation from other branches. Hence the branches may be regarded as only partially autonomous for fruit production.

5.Fruit production of girdled‐50% defoliated branches was 42% of fruit production of control branches, while ungirdled‐50% defoliated branches amounted to 70% of controls. These results also demonstrated resource importation but did not support the existence of photosynthetic compensatory mechanisms.

6.The ability of resource importation developed by fruiting branches might be a mechanism to reduce the effect of reproductive costs in this species.
Colour‐associated mating success in a polymorphic Ladybird Beetle, Harmonia axyridis
Authors: Ueno H. , Sato Y. , Tsuchida K.
Published: March 2003

1. Body size is often an important character in mating success, but has been only infrequently mentioned in regard to colour polymorphism. In this study, mating success was investigated in a colour polymorphic Ladybird Beetle, Harmonia axyridis, with reference both to colour morph and to body size.

2. In the non‐melanic males the mating individuals were significantly larger than solitary individuals, while in melanic males there was no significant difference.

3. The mating pattern was close to random mating with respect to colour morph and there was no significant deviation.

4. The results suggest both body size and colour morph affect the male mating success and males of different body size obtain mating advantage according to the colour morph. Colour polymorphism in this species is controlled by alleles on a single locus. Thus, the alleles on that locus significantly influence the effect of selection on the quantitative character.
Ecological correlates of seed size in the British flora
Authors: Hodkinson D.J. , Askew A.P. , Thompson K. , Hodgson J.G. , Bakker J.P. , Bekker R.M.
Published: March 2003

1. The association between seed size and habitat shade within the British flora was investigated using a data set of seed masses, life histories and quantitative measures of habitat shade for 504 species; the association between seed size and seed longevity was investigated using a data set of seed masses, life histories and seed longevities for 301 species.

2. The data were analysed using the method of phylogenetically independent contrasts (PICs) calculated using the software package CAIC (Comparative Analysis by Independent Contrasts).

3. Seed mass was found to be positively correlated with habitat shade and negatively correlated with seed longevity, after variation owing to life history had been accounted for.
Partitioning of dry mass and leaf area within plants of three species grown at elevated CO2
Authors: Gunn S. , Bailey S. J. , Farrar J. F.
Published: March 2003

1. We tested the hypothesis that the net partitioning of dry mass and dry mass:area relationships is unaltered when plants are grown at elevated atmospheric CO2 concentrations.

2. The total dry mass of Dactylis glomerata, Bellis perennis and Trifolium repens was higher for plants in 700 compared to 350 μmol CO2 mol–1 when grown hydroponically in controlled‐environment cabinets.

3. Shoot:root ratios were higher and leaf area ratios and specific leaf areas lower in all species grown at elevated CO2. Leaf mass ratio was higher in plants of B. perennis and D. glomerata grown at elevated CO2.

4. Whilst these data suggest that CO2 alters the net partitioning of dry mass and dry mass:leaf area relationships, allometric comparisons of the components of dry mass and leaf area suggest at most a small effect of CO2. CO2 changed only two of a total of 12 allometric coefficients we calculated for the three species: ν relating shoot to root dry mass was higher in D. glomerata, whilst ν relating leaf area to total dry mass was lower in T. repens.

5. CO2 alone has very little effect on partitioning when the size of the plant is taken into account.
Predicting responses to climate change: the effect of altitude and latitude on the phenology of the Spittlebug Neophilaenus lineatus
Authors: Fielding C. A. , Whittaker J. B. , Butterfield J. E. L. , Coulson J. C.
Published: March 2003

1. The phenology of Neophilaenus lineatus (Homoptera: Cercopidae) was studied along altitudinal and latitudinal transects in the UK. The response of the life cycle to these existing temperature gradients has been used to predict the likely effects of future climatic warming.

2. The date of spring egg hatch varied by a maximum of 4 weeks across the altitudinal gradient (440 m) and by 2 weeks in different years of the study. Autumn and winter temperatures do not determine hatching date because the eggs are in diapause during this period. It is only when the eggs terminate diapause in early spring that temperature differences between years and altitudes (or as a result of climatic warming) start to affect the date of egg hatch.

3. The delayed egg hatching with increasing altitude meant that the start of nymphal development was later at higher altitudes. The development rate of nymphs at higher altitudes was not significantly different from that at lower altitudes because the altitudinal lag in temperature was partially compensated for by the more advanced state of the season. Annual differences in spring and summer temperatures resulted in variations in nymphal development rate between years, with a 1 °C temperature rise shortening nymphal development by 3·5 days.

4. The appearance of adults was delayed by 5·6 days for every 100 m increase in altitude, largely as a consequence of the later egg hatch at higher altitudes. The later appearance of the adults at higher altitudes and in colder years, reduces the length of the potential oviposition period as females are killed by autumn frosts. Climatic warming would expand the length of the oviposition period and thus increase the upper altitude limits of N. lineatus.

5. A 4·5 ° latitude difference within the UK appeared to have little effect on the timing of development in N. lineatus, possibly as a result of a geographical cline in temperature or photoperiod response.

6. Annual insects, such as N. lineatus, are likely to show a relatively small geographical displacement as a consequence of climatic warming. This is because of the temperature mitigating responses of diapause and the relative stability of the length of the development period over wide altitudinal and latitudinal ranges.
Does immune challenge affect torpor duration?
Authors: BURTON R. S. , REICHMAN O. J.
Published: March 2003

1. Hibernation may alter the relationship between pathogens and their hosts; low host temperatures can prevent pathogen replication. Therefore, manipulating the timing and duration of torpor bouts could allow animals to gain an advantage over pathogens.

2. Thirty‐two Turkish Hamsters (Mesocricetus brandti) were placed in short‐day, cold conditions. After 10 weeks, 20 animals were challenged with an antigen to simulate a pathogen infection. Ten of these animals were returned to the cold (‘cold‐challenged’). The other 10 animals were placed in warm conditions (‘warm‐challenged’). Twelve animals received saline injections and were returned to the cold (‘cold‐control’). Cold‐challenged animals spent significantly more time in torpor than did cold‐control animals.

3. After 6·5 weeks, all animals were housed in warm conditions and ceased torpor. Both cold‐challenged and warm‐challenged animals received a second injection of antigen. There was no correlation between time spent euthermic and level of secondary humoral response of cold‐challenged animals. The secondary humoral response of the cold‐challenged animals was significantly lower than that of warm‐challenged animals.

4. In this study immune status influenced torpor duration, and torpor caused immunosuppression. Hibernators may manipulate body temperature in order to combat pathogens while their own immune systems are suppressed.
A test of two hypotheses explaining the seasonality of reproduction in temperate mammals
Authors: Fournier F. , Thomas D. W. , Garland T.
Published: March 2003

1. Two proposed hypotheses about energy allocation were tested to explain the patterns of seasonal reproduction found in temperate mammals. The two hypotheses predict either that total demand for energy is greater during reproduction than during winter (when thermoregulatory costs are high) (Increased Demand Hypothesis) or that total costs during winter are greater than or equal to total costs during reproduction (Reallocation Hypothesis).

2. Data were compiled from the literature on summer (non‐reproducing) and winter metabolic rates of temperate mammals, and were used on litter sizes and a published equation to predict metabolic rates during lactation.

3. All three measures of metabolic rate scaled to body mass with slopes significantly less than one. Metabolic rates during winter averaged ≈ 2 times greater than those of non‐reproducing mammals during summer. On average, predicted metabolic rates during lactation were not significantly greater than during winter, but for some individual species they clearly were.

4. It is suggested that neither the Reallocation nor the Increased Demand Hypothesis can fully explain seasonal reproductive patterns in temperate mammals.
Blood parasites, leucocytes and plumage brightness in the Cirl Bunting,Emberiza cirlus
Authors: Figuerola J. , Muñoz E. , Gutiérrez R. , Ferrer D.
Published: March 2003

1.Although a female preference for pairing with brightly plumaged males has been reported in many species, the reasons for this choice are not fully understood.

2.Parasites have been proposed as playing an important role in shaping these preferences because, by pairing with brightly coloured individuals, females can obtain parasite‐free and/or more healthy mates.

3.In this paper one of the predictions of this hypothesis is tested, namely a higher health level in brightly coloured individuals, by analysing the relationships among blood parasites, leucocyte levels and plumage brightness in the Cirl Bunting,Emberiza cirlus.

4.Two species of blood parasites were detected. Whereas a lower body condition was detected in individuals infected byLeucocytozoon cambournaci,no such differences were associated withPlasmodium relictuminfections. Infected individuals showed higher total leucocyte counts than non‐infected individuals.

5.Colour intensity of carotenoid derived colorations was negatively correlated to the relative proportion of lymphocytes and positively correlated to the relative presence of heterophils. Furthermore, the size of yellow feathered areas was positively correlated with the absolute number of leucocytes and the relative presence of heterophils. Only some of these relationships were found for non‐carotenoid derived traits.

6.These results suggest that male plumage yellow coloration in the Cirl Bunting is a reliable indicator of health status and supports the hypothesis that females obtain more parasite‐free mates if they pair with brightly coloured individuals.
The defensive strike of the Eastern Brownsnake, Pseudonaja textilis (Elapidae)
Authors: Whitaker P. B. , Ellis K. , Shine R.
Published: March 2003

1. The Eastern Brownsnake, Pseudonaja textilis, is a large (to 2 m), slender‐bodied, highly venomous elapid that causes most snakebite human fatalities in Australia. The response of recently captured snakes to human harassment was quantified. Using high‐speed film, the type of neck display, time taken to strike, strike accuracy, strike speed and effectiveness of bite were recorded.

2. The snakes were surprisingly tolerant of harassment, especially at body temperatures similar to those that they exhibit in the field during the activity season. Smaller snakes spent more time trying to escape than did larger snakes. Most snakes gave warning prior to the strike, 58% by full (high) display and 19% by partial (low) display. Some 25% of strikes were bluff.

3. Body temperature (over the range 18–36 °C) had little effect on most of the variables measured, including: the frequency of display and bluff, the duration of the strike (mean 0·28 s), the strike distance (mean 0·34 m), the mean overall strike speed (1·1 m s−1, range 0·25–1·80), the mean fastest strike speed (during 1/25 s, = 1·7 m s−1, range 0·3–3·4), or the accuracy of the strike.

4. Instead, the type of prestrike display was related to strike speed and accuracy: strikes preceded by a full neck display were slower but more accurate (and more likely to involve venom transfer) than those preceded by minimal display.

5. Contrary to popular opinion, Eastern Brownsnakes are reluctant to deliver firm bites in response to human harassment even when continuously provoked. It is estimated that only 15% of the strikes recorded had the potential to cause significant envenomation.
Influence of temperature on hydrodynamic costs of morphological defences in zooplankton: experiments on models of Eubosmina (Cladocera)
Authors: Lagergren R. , Lord H. , Stenson J. A. E.
Published: March 2003

1. If swimming speed is correlated to fitness (e.g. by affecting food intake or the chance to evade predators) or considerable energy is expended in swimming, zooplankton wearing protruding structures (as predator defence) that significantly increase drag resistance must pay a cost for the better protection against predators that these traits imply.

2. In an experiment with plastic models, the drag and energy consumption of swimming in two species of Eubosmina were examined. Eubosmina longispina has a typical Bosmina morphology with a low carapace and short antennule, whereas E. coregoni gibbera has a very high carapax and long antennule.

3. At 5 °C, E. c. gibbera had 32–45% higher drag than E. longispina. At 20 °C, the difference is 20–45%.

4. A mathematical model of swimming predicts that these differences in drag should result in 18–20 (at 5 °C) or 14–16 (at 20 °C) percentage lower speed for E. c. gibbera than for E. longispina if they use the same amount of energy in swimming.

5. The relative difference in drag or swimming speed between the two species was highest at low Reynolds number (i.e. low speed or low temperature). These results show that hydrodynamic costs of extreme morphology may increase with decreasing temperature.

6. The increased cost of morphological antipredator defence at low temperatures may be enlightening with regard to the role of temperature in the induction of cyclomorphic traits in zooplankton. This may be one explanation for why extreme forms of E. c. gibbera and some Daphnia are only found in the summer when water temperature is high.
The evolution of sexual dimorphism in relation to mating patterns, cavity nesting, insularity and sympatry in the Anseriformes
Authors: Figuerola J. , Green A. J.
Published: March 2003

In addition to genetic drift, both natural and sexual selection may be responsible for interspecific differences in male and female size and coloration. Comparative methods were used to analyse the patterns of dimorphism in the Anseriformes (wildfowl) in relation to mating patterns, nest placement, insularity and number of closely related, sympatric species.

The following predictions were tested about the evolution of dimorphism: (a) that evolutionary changes are more common in male than in female coloration; (b) that the intensity of sexual selection is correlated with the evolution of bright coloration and sexual dimorphism; (c) that the nature of nest sites influences the evolution of bright coloration in females via its effect on predation risk, and the extent of size dimorphism via the limits to the size of females using cavities; (d) that insular species show more size dimorphism and less colour dimorphism than mainland species; and (e) that sexual dichromatism is more common in species living in sympatry with a larger number of similar species.

Evolutionary changes in plumage brightness were found to be more frequent in males than in females. Changes in mating patterns were significantly correlated with changes in plumage brightness in both males and females and in plumage dichromatism, but not with changes in size dimorphism. Evolutionary transitions from open to hole nesting did not affect plumage dichromatism or size dimorphism. A significant association was detected between insularity and the probability of changes in male brightness, but there was no relationship between insularity and size dimorphism. Sexual dichromatism and bright male (but not female) plumage tend to occur in wildfowl sympatric with a high number of species from the same tribe.

In conclusion, mating patterns, insularity and sympatry appear to have evolved in correlation with changes in sexual dichromatism and plumage brightness in the Anseriformes, but not with changes in sexual size dimorphism.
Effects of display size and position on individual floral longevity in racemes of Narthecium asiaticum (Liliaceae)
Authors: Ishii H. S. , Sakai S.
Published: March 2003

We analysed the longevity of individual flowers and the effect on pollination success with respect to floral display size of racemes (number of flowers open at one time) for the sequentially blooming plant Narthecium asiaticum (Liliaceae). The longevity of lower‐ and middle‐positioned flowers (about 7 days in 1998 and 6 days in 1999) was much greater than the length of time required for the completion of male (about 3 days) and female (within 3 days) functions.

 We suggest that such prolonged longevity benefits the plant in terms of pollinator attraction, because prolonged longevity in lower and middle flowers leads to large display sizes of racemes. Increased display size would not have resulted in an increase of geitonogamy in this species, because most pollinators left racemes after probing only one flower. Rather, large displays attracted more pollinators and increased pollen dispersal from individual flowers.

 The longevity of upper‐positioned flowers (about 4 days in 1998 and 3 days in 1999) was less than that of lower‐ and middle‐positioned flowers – almost the same as the length of time required for the completion of male and female functions. This difference is possibly because upper flowers open later within racemes: if there were no subsequent flowers, prolonged floral longevity would not benefit the plants and would only consume resources used to maintain the flower.

 Floral longevity within inflorescence should be understood in relation to the effects of floral display size and floral positions, in addition to the accrual rates of male and female functions and the maintenance cost of individual flowers.
Moa ghosts exorcised? New Zealand’s divaricate shrubs avoid photoinhibition
Authors: Howell C. J. , Kelly D. , Turnbull M. H.
Published: March 2003

An intriguing feature of the New Zealand flora is the high frequency of ‘divaricate’ shrubs and tree juveniles. These plants have numerous interlacing wide‐angled branches with small leaves and no or few leaves in the outer canopy. They comprise 10% of native woody species, and have evolved in 18 different plant families.

 We tested the hypothesis that the leaves of divaricate plants are sensitive to cold‐induced photoinhibition, and that self‐shading by outer branches reduces light intensities enough to prevent photodamage. In a field experiment, leaves of three divaricate species (Aristotelia fruticosa A. Cunn., Corokia cotoneaster Raoul and Coprosma propinqua Hook. f.) inside the north (sunny) side of the shrubs were exposed to one of three experimental treatments over winter: (i) control leaves which were not manipulated; (ii) exposed leaves which had their outer screen of branches pruned away leaving them open to full sun; or (iii) shaded leaves which were exposed by pruning, then sheltered from direct sunlight with shade cloth.

Experimental removal of the shielding branches in winter led to rapid (< 20 days), large (23–31%) and persistent (> 3 months) reductions in the maximum photosynthetic capacity (Amax) and photochemical efficiency (dark adapted Fv/Fm) in exposed leaves, but not in shaded leaves. Full recovery of photosynthetic capacity and photochemical efficiency was displayed by Coprosma propinqua, but very little capacity for recovery was displayed by Aristotelia fruticosa or Corokia cotoneaster.

When the effects of self‐shading and photoinhibition were combined, control leaves photosynthesized faster than exposed leaves at all ambient irradiances in A. fruticosa, and in bright light (> 500 µmol m−2 s−1) in C. cotoneaster.

Our data show that by shielding their leaves within an outer screen of branches, the three divaricate species studied reduce photoinhibition of photosynthesis. We contend that this architectural self‐shading in divaricate plants maximizes potential carbon fixation by minimizing photoinhibition.
Forward attack modes of aquatic feeding garter snakes
Authors: Alfaro. M. E
Published: March 2003

Previous studies have suggested that piscivorous snakes generally use sideways head sweeping to capture prey in order to minimize drag on the skull and/or to avoid pushing prey items away from the mouth. However, some aquatic species of garter snakes (genus Thamnophis) have been reported to use fast forward strikes to capture fish and amphibians. To characterize fast forward striking as a mode of piscivory in snakes and compare its use among specialist and generalist species, the aquatic specialists Thamnophis couchii and T. rufipunctatus, and a terrestrial generalist, T. sirtalis, were filmed at 250 fps (frames per second) while preying on minnows.

 Both T. couchii and T. rufipunctatus oriented visually toward prey items and struck forward rapidly with peak head velocities that approached speeds attained by fast striking booid, colubrid and viperid species on land. In contrast, T. sirtalis did not orient visually toward specific prey items and displayed strikes that were four to six times slower than those of specialist species.

 Aquatic specialists used moderate amounts of cranial rotation during jaw opening and achieved maximum gape within 20 ms of jaw opening. In the generalist T. sirtalis, jaw opening took 40–60 ms and was due almost entirely to mandibular rotation.

 Significant differences in the prey capture kinematics of the two aquatic specialists are consistent with the hypothesis that T. couchii is an open water hunter, whereas T. rufipunctatus is an ambush predator. Thamnophiine snakes display a diversity of aquatic prey capture styles that reflect different behavioral and mechanical solutions to the problem of feeding in water.
Nest scrape design and clutch heat loss in Pectoral Sandpipers (Calidris melanotos)
Authors: Reid J. M. , Cresswell W. , Holt S. , Mellanby R. J. , Whitfield D. P. , Ruxton G. D.
Published: March 2003

1. The reasons why birds construct nest scrapes, and the extent to which scrape designs reflect functional optima, are poorly understood. Working on Pectoral Sandpipers (Calidris melanotos, Vieillot), we investigated whether scrapes function to insulate clutches and are efficiently designed to reduce heat loss rates.

2. Excavating a scrape and using lining material reduced the rate at which an object positioned within a scrape lost heat by 9% and 25%, respectively, suggesting that lined scrapes insulate clutches.

3. The rate of heat loss from an object within a scrape increased with scrape depth and decreased non‐linearly with lining depth. The extent to which wind increased forced convective heat loss decreased with scrape depth.

4. On average, Pectoral Sandpipers used the minimum lining depth that approximately minimized heat loss through the lining. Mean scrape depth approximately minimized convective cooling in windy conditions while minimizing heat loss to the ground. Pectoral Sandpiper scrapes therefore efficiently reduced heat loss given conflicting environmental thermal pressures.

5. Available lining materials differed in insulative quality when both damp and dry. Pectoral Sandpipers used lining materials that insulated relatively well when damp more than expected given random collection of locally available materials. Linings therefore insulated efficiently given the damp nesting environment.
Food pulses increase longevity and induce cyclical egg production in Mediterranean fruit flies
Authors: Carey J. R. , Liedo P. , Harshman L. , Liu X. , Müller H.‐G. , Partridge L. , Wang J.‐L.
Published: March 2003

1. Inasmuch as virtually all studies on mortality and reproduction in insects are conducted under conditions in which food availability is constant, little is known about the demographic response of insects to variable food environments. For example, it is not known if and to what extent the life expectancy of insects subjected to shortages of high‐quality food will increase and/or whether this increase is associated with major decreases in lifetime reproduction.

2. Therefore cohorts of 100 individual female medflies were subjected to different sets of conditions of protein availability (interspersed with sugar‐only diets) including ad libitum sugar‐only (no protein), ad libitum protein and full (protein) diet either every 2nd, 4th, 6th, 11th or 21st day, as well as two lag‐treatments (1 day full diet followed by 30 days sugar‐only, followed by one of two cyclical treatments).

3. Both life expectancy and lifetime reproduction were strongly affected by specific treatments. Specifically (i) mortality was inversely related to frequency of protein availability whereas lifetime reproduction was directly related; (ii) distinct cycles in reproduction began to appear when food pulse cycles were as short as every 4 days. However, egg‐laying peaks and troughs were particularly pronounced in the 10‐ and 20‐day food pulse cycles; (iii) the peak and trough levels were inversely related to cycle length; and (iv) the within‐cycle height was independent of cycle length, occurring 4 days after protein food was made available to the cohort whether the cycle length was 5, 10 or 20 days.

4. The results shed new light on the within‐ and between‐cycle and lifetime dynamics of reproduction when insects are subjected to variable food environments and indicate that medfly females track food level very closely.
Hydraulic differentiation of Ponderosa pine populations along a climate gradient is not associated with ecotypic divergence
Authors: Maherali H. , Williams B. L. , Paige K. N. , Delucia E. H.
Published: March 2003

1. 
Pinus ponderosa occurs in a range of contrasting environments in the western USA. Xeric populations typically have lower leaf : sapwood area ratio (AL/AS) and higher whole‐tree leaf specific hydraulic conductance (KL) than mesic populations. These climate‐driven shifts in hydraulic architecture are considered adaptive because they maintain minimum leaf water potential above levels that cause xylem cavitation.

2. Using a common garden study, we examined whether differences in biomass allocation and hydraulic architecture between P. ponderosa populations originating from isolated outcrops in the Great Basin desert and Sierran montane environments were caused by ecotypic differentiation or phenotypic plasticity. To determine if populations were genetically differentiated and if phenotypic and genetic differentiation coincided, we also characterized the genetic structure of these populations using DNA microsatellites.

3. Phenotypic differentiation in growth, biomass allocation and hydraulic architecture was variable among populations in the common garden. There were no systematic differences between desert and montane climate groups that were consistent with adaptive expectations. Drought had no effect on the root : shoot and needle : stem ratio, but reduced seedling biomass accumulation, leaf area ratio, AL/AS and KL. Stem hydraulic conductance (KH) was strongly size‐dependent, and was lower in droughted plants, primarily because of lower growth.

4. Although microsatellites were able to detect significant non‐zero (P < 0·001) levels of differentiation between populations, these differences were small and were not correlated with geographic separation or climate group. Estimates of genetic differentiation among populations were low (<5%), and almost all the genetic variation (>95%) resided within populations, suggesting that gene flow was the dominant factor shaping genetic structure.

5. These results indicate that biomass allocation and hydraulic differences between desert and montane populations are not the result of ecotypic differentiation. Significant drought effects on leaf : sapwood allocation and KL suggest that phenotypic differentiation between desert and montane climates could be the result of phenotypic plasticity.