bluuebunny/crossref_metadata_2025_split huggingface dataset:
Causes of vertical stratification in the density of Cameraria hamadryadella
Authors: BROWN JESSI , VARGO STEVE , CONNOR EDWARD , NUCKOLS MICHAEL 
Published: November 2003

1. The density of Cameraria hamadryadella, a leaf‐mining moth, is vertically stratified within the crown of oak trees. It occurs at higher densities on foliage in the lower crown.2. Oviposition preference tests indicate that females display no preference to oviposit on foliage from the lower tree crown over foliage from the upper tree crown.3. Experiments in which potted trees were placed at various heights indicate that foliage nearest ground level receives more oviposition, and that the higher rates of oviposition on foliage near the ground is not caused by differences in quality between foliage from low or high in the tree crown.4. Host‐plant‐ and natural‐enemy‐mediated juvenile mortality and the abundance of parasitoids did not differ between the upper and lower crown.5. Vertical differences in the timing of leaf production within the tree crown are unlikely to account for the observed gradient in the abundance of C. hamadryadella. Furthermore, the mean date of leaf fall does not differ among heights within the tree crown.6. It is argued that microclimatic gradients and interspecific competition are also unlikely to account for the observed gradients in the density of C. hamadryadella within the tree crown.7. Because of the absence of effects of other potentially causal factors, the most likely explanation for the gradient in density of C. hamadryadella is a lack of movement by females into the upper tree crown from overwintering, emergence, or resting sites located in the lower tree crown, combined with egg depletion by females as they move from the lower to the upper tree crown.8. It is suggested that the lack of movement and egg depletion hypothesis should serve as the null hypothesis in studies of vertical stratification of tree‐feeding insects. In the absence of evidence of an effect of foliage quality, natural enemies, plant phenology, interspecific competition, or microclimate, the movement and egg depletion hypothesis is the most reasonable.
Detecting chaotic dynamics of insect populations from long‐term survey data
Authors: ZHOU X. , PERRY J. N. , WOIWOD I. P. , HARRINGTON R. , BALE J. S. , CLARK S. J. 
Published: November 2003

1. Estimates of the Lyapunov exponent, a statistic that measures the sensitive dependence of the dynamic behaviour of a system on its initial conditions, are used to characterize several sets of insect time series.2. A new method is described to overcome the difficulty of defining the dynamics of an observed, noisy, short ecological time series. This method provides two test statistics for the estimated Lyapunov exponent.3. This method is applied to forty‐six time series comprising six aphid species from five sites and four moth species from six sites. There are few positive Lyapunov exponents and none is sufficiently large to characterize its time series as chaotic.4. Two methods to estimate the Lyapunov exponent are compared; that based on logarithmically transformed counts yields less variable estimates for highly variable insect data than that based on untransformed counts.
Drought reduces breeding success of the butterfly Aglais urticae
Authors: POLLARD E. , GREATOREX‐DAVIES J.N. , THOMAS† J.A. 
Published: November 2003

1. Published laboratory work suggests that Aglais urticae may be affected adversely by drought, as the larvae thrive on actively growing plants with high leaf water and nitrogen.2. The weekly counts from the Butterfly Monitoring Scheme were used to test the hypothesis of an association between changes in abundance and drought in field data.3. The analysis supported the hypothesis; breeding success of the summer generation from 1976 to 1995 was greater when the early summer weather was cool and wet than when it was warm and dry.
Abiotic and biotic factors influencing nest‐site selection by Halictus rubicundus, a ground‐nesting halictine bee
Authors: POTTS SIMON , WILLMER PAT 
Published: November 2003

1. The nest‐site selection behaviour of the bee Halictus rubicundus (Christ) was examined both within and across sites in the U.K. Females utilized a range of edaphic and microclimatic conditions when choosing a site to excavate a nest. Factors with broad tolerances included slope and hardness; those with much narrower limits included aspect, soil humidity and soil particle composition.2. There was a preference for softer soils that were easier to dig within a site with a low overall density, but in much denser aggregations problems of maintaining the structural integrity of a nest led to the utilization of harder soils.3. The thermal advantages of having a warm nest meant that the most suitable areas were those with a southern aspect and a slope that maximized the absorption of solar radiation.4. Limited areas of substrate with the most desirable characteristics resulted in gregarious nesting (‘limited substrate hypothesis’).5. Natal nest‐site fidelity complemented the ‘limited substrate’ hypothesis in producing an aggregation of nests.
The influence of ants and water availability on oviposition behaviour and survivorship of a facultatively ant‐tended herbivore
Authors: WAGNER DIANE , KURINA LIANNE 
Published: November 2003

1. The lycaenid butterfly Hemiargus isola associates facultatively with the ant species Formica perpilosa in arid areas of south‐western North America. Ants solicit liquid food rewards from butterfly larvae as larvae feed on the host plant, Acacia constricta. Previous studies have shown that tending by F. perpilosa enhances larval growth and pupal survivorship.2. The effects of ants and plant water content on oviposition behaviour and survivorship to the last larval instar were tested by excluding ants and supplementing water to host plants in a two‐way factorial experiment.3. Butterflies, which lay eggs singly on host plant inflorescences, laid significantly higher egg numbers and densities (eggs/inflorescence) on plants with ants than on plants without ants. This is the first report of a facultative, generalized ant‐associate using ants as oviposition cues. Water supplements increased the number, but not the density, of eggs laid on plants. Therefore, it appears that egg‐laying butterflies responded to number of inflorescences, rather than plant tissue water per se.4. Plants with ants had significantly greater numbers of inflorescences during the experiment than plants without ants. Water supplements increased number of inflorescences slightly, but not significantly.5. Ants increased larval survivorship. Twice as many fourth‐instar larvae survived per egg laid on plants with ants than on plants without ants. Ants did not reduce the number of predators present on acacias, but may have reduced predator effectiveness. Ants also did not reduce the numbers of potential H. isola competitors present.6. Water supplementation affected neither the survivorship of H. isola larvae, nor the intensity of ant tending. Water supplementation did not affect the abundance of predators on plants, but did increase the abundance of several herbivorous insect taxa.
Defensive larval secretions of leaf beetles attract a specialist predator Parasyrphus nigritarsis
Authors: KÖPF ALFRED , RANK NATHAN , ROININEN HEIKKI , TAHVANAINEN JORMA 
Published: November 2003

1. Noxious larval secretions of leaf beetles, which repel generalist predators, do not deter specialist syrphid fly predators (genus Parasyrphus). These flies cause considerable mortality to the beetles, but little is known about their foraging behaviour.2. Larvae of Parasyrphus nigritarsis were attracted to the volatile larval secretions produced by two prey species Phratora vitellinae and Linaeidea aenea. Parasyrphus nigritarsis feeds on both beetles in nature. Phratora vitellinae feeds on willows and utilizes host plant compounds for secretion production, while the alder‐feeding L. aenea produces an autogenous secretion.3. Fly larvae were strongly attracted to pieces of filter paper treated with larval secretion of the beetles. They attempted to feed on them for up to 7 min, and were equally attracted to the secretions of Ph. vitellinae and L. aenea. Fly larvae were also attracted to pure salicyl aldehyde, the main component of the secretion of Ph. vitellinae.4. Fly larvae searched extensively for prey on leaves that had been damaged by beetle larvae. They also followed trails made with solutions containing faecal matter of prey larvae. They showed no differential preference for Ph. vitellinae or L. aenea, but always rejected larvae of the non‐prey leaf beetle Agelastica alni.5. Beetle secretions thus play an important, but unexpected, role in the feeding behaviour of P. nigritarsis. This predator uses the beetle secretion to locate its prey. The implications of these results for three trophic level interactions are discussed.
Oceanographic variability and changes in Antarctic krill (Euphausia superba) abundance at South Georgia
Authors: Trathan P. N. , Brierley A. S. , Brandon M. A. , Bone D. G. , Goss C. , Grant S. A. , Murphy E. J. , Watkins J. L. 
Published: November 2003

AbstractOceanographic data collected to the north of South Georgia were examined for three consecutive summers (1996/97, 1997/98, 1998/99). The results show the existence of a shelf break front during each period. The most reliable means of defining the front was the potential density anomaly at the near‐surface potential temperature minimum. In each year, off‐shelf waters were separated from on‐shelf waters by water with a potential density anomaly between 27.22 and 27.29 kg m−3. During 1997/98, the near‐surface potential temperature minimum was much colder and much shallower than in other years and was consistent with waters originating from much further south than South Georgia; these differences were further evident at a single deep off‐shelf station. The oceanographic changes during 1997/98 were consistent with a mesoscale or large‐scale movement of the southern Antarctic Circumpolar Current front.Acoustically determined densities of Antarctic krill, Euphausia superba, at South Georgia showed consistent patterns between years. Densities were substantially higher over the shelf compared with off‐shelf, with the highest densities at the shelf edge; densities were also higher to the east of the island. During 1997/98, acoustic densities of krill were substantially higher than in other years. The coincidence of the elevated acoustic density and the cooler oceanographic conditions was explored. When data from all years were combined and analysed by Generalized Additive Model, an inverse relationship between acoustic density and temperature was apparent. Historical data were also examined and it was noted that the only other occurrence of such a high estimate of krill density at South Georgia, was when oceanographic conditions were also colder.
Atmospheric deposition of sulphur and nitrogen species in the U.K.
Authors: CAMPBELL GlENN , LEE DAVID 
Published: November 2003

1. The foundations of our understanding of acid deposition were laid in the last century, but the scale and scope of damage to sensitive receptors has only been subject to intensive investigation over the last 30 years or so. Negotiations are now well underway to reduce emissions, and for some pollutants policy is in place, so that these receptors may be protected adequately. Crucial to this has been the ‘critical loads’ approach adopted in the U.K. and elsewhere in Europe over the last 6 years.2. This paper describes the source of acidic emissions, how these emissions are transformed in the atmosphere and subsequently deposited. Measurements of wet deposition are made at a number of sites in the U.K. and some of the results from the networks are presented. These results allow wet and dry deposition to be mapped and the methodologies and underlying assumptions to these procedures are described, and S deposition has been estimated for the U.K. Acid Waters Monitoring Network sites.
The energetic importance of terrestrial arthropod inputs to three warm‐water streams
Authors: CLOE III WILLIAM , GARMAN GREG 
Published: November 2003

1. Inputs of terrestrial arthropods (number and mass m–2 d–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater (P < 0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m–2 d–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish (Lepomis auritus) and bluegill (L. macrochirus) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.4. Estimates of the potential annual energetic contribution (kJ m–2 d–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream ecosystems.
Reconstructing the past density of planktivorous fish and trophic structure from sedimentary zooplankton fossils: a surface sediment calibration data set from shallow lakes
Authors: JEPPESEN ERIK , MADSEN ESBEN AGERBO , JENSEN JENS PEDER , ANDERSON N. 
Published: November 2003

1. As quantitative information on historical changes in fish community structure is difficult to obtain directly from fish remains in lake sediments, transfer function for planktivorous fish abundance has been developed based on zooplankton remains in surface sediment (upper 1 cm). The transfer function was derived using weighted average regression and calibration against contemporary data on planktivorous fish catch per unit effort (PF‐CPUE) in multiple mesh size gill nets. Zooplankton remains were chosen because zooplankton community structure in lakes is highly sensitive to changes in fish predation pressure. The calibration data set consisted of thirty lakes differing in PF‐CPUE (range 18–369 fish net–1), epilimnion total phosphorus (range 0.025–1.28 mg P l–1) and submerged macrophyte coverage (0–57%).2. Correlation of log‐transformed PF‐CPUE, total phosphorus and submerged macrophyte coverage v the percentage abundance in the sediment of the dominant cladocerans and rotifers revealed that the typical pelagic species correlated most highly to PF‐CPUE, while the littoral species correlated most highly to submerged macrophyte coverage. Consequently, only pelagic species were taken into consideration when establishing the fish transfer function.3. Canonical correspondence analysis (CCA) revealed that the pelagic zooplankton assemblage was highly significantly related to PF‐CPUE (axis 1), whereas the influence of total phosphorus and submerged macrophyte coverage was insignificant. Predicted PF‐CPUE based on weighted average regression without (WA) and with (WA(tol)) downweighting of zooplankton species tolerance correlated significantly with the observed values (r2 = 0.64 and 0.60 and RMSE = 0.54 and 0.56, respectively). A marginally better relationship (r2 = 0.67) was obtained using WA maximum likelihood estimated optima and tolerance.4. It is now possible, quantitatively, to reconstruct the historical development in planktivorous fish abundance based on zooplankton fossil records. As good relationships exist between contemporary PF‐CPUE data and indicators such as the zooplankton/phytoplankton biomass ratio, Secchi depth and the maximum depth distribution of submerged macrophytes, it is now also possible to derive information on past changes in lake water quality and trophic structure. It will probably prove possible further to improve the transfer function by including other invertebrate remains, e.g. chironomids, Chaoborus, snails, etc., and its scope could be widened by including deeper lakes, more oligotrophic lakes, more acidic lakes and lakes with extensive submerged macrophyte coverage (in the latter case to enable use of the information in the fossil record on plant‐associated cladocerans).
Inferring the minimum pH of streams from macroinvertebrates using weighted averaging regression and calibration
Authors: HÄMÄLÄINEN HEIKKI , HUTTUNEN PERTTI 
Published: November 2003

1. Data on macroinvertebrates and stream chemistry were collected from sixty‐four streams in Finland. Weighted averaging (WA) regression and calibration models were constructed to infer the minimum pH of streams from their invertebrate assemblages. The purpose was to develop an instrument for biological assessment and monitoring of stream acidification. The WA method was compared with simpler approaches, based on qualitative invertebrate data and pH tolerance limits, that are widely used.2. Performance of the two approaches was assessed in terms of correlation between the inferred and observed minimum pH within the ‘training set’, and in terms of root mean squared differences (predicted – observed) (RMSEP) estimated by cross‐validation or bootstrap resampling techniques. The models were further tested using independent data from the literature representative of a wide geographical range.3. The predictive power of the WA models was reasonable (RMSEP 0.40–0.44 pH units) in the training set and consistently better than that of the tolerance limit method. In contrast to the latter, the WA models were able to infer a minimum pH above 5.5, suggesting they could detect the early stages of acidification.4. The WA models performed better than the tolerance limit method in inferring pH from the independent literature, further demonstrating the superiority and generality of the WA approach.5. The weighted averaging technique could be an effective and widely applicable tool for contemporary biological monitoring and assessment using aquatic invertebrates.
Do simultaneous hermaphrodites choose their mates? Effects of body size in a planarian flatworm
Authors: PETERS ANNE , MICHIELS NICOLAAS 
Published: November 2003

1. We tested whether or not the simultaneous hermaphrodite Dugesia polychroa mates randomly with respect to partner size, a strong indicator of female fecundity.2. The number and duration of copulations were recorded in forty‐eight pairs over 5 days. To minimize effects of individual differences in copulatory activity, all animals were each tested twice: once with an equally large partner (n = 24 equal‐sized pairs) and once with a partner of different size (smaller or larger, respectively, ratio 1 : 1.5, n = 24 unequal‐sized pairs).3. The animals copulated frequently. No significant differences were observed between treatments in the number of pairs that copulated. Mating behaviour of equal‐sized and unequal‐sized pairs was compared in a pair‐wise analysis. Latency to the first copulation and the average number of copulations did not differ when mating with an equal‐ or unequal‐sized partner. Average copulation duration increased with increasing size in equal‐sized pairs, but not in unequal‐sized pairs.4. In an additional experiment, where three large and three small animals were combined (three replicates) and observed for 1–3 days, the mating pattern did not differ from random mating by size.5. Our data indicate that in D. polychroa the decision to mate is essentially random with respect to size. We argue that this is not caused by, for example, high costs of mate searching, but that simultaneous hermaphrodites with reciprocal insemination mate indiscriminately when (i) matings are easy to obtain and (ii) the cost of mating is low or compensated for by sperm digestion.
Modelling of underwater light in freshwater lakes using survival and failure time analysis
Authors: RØRSLETT BJØRN 
Published: November 2003

1. This study presents a new approach to modelling subsurface irradiance using concepts from survival and failure time analysis. The model applies a modified Weibull distribution function to predict downwelling irradiance. Data sets from forty‐seven Norwegian sites show extremely high coefficients of determination, up to 99.99%, when analysed by the Weibull model.2. The uncritical use of a single kd value to model underwater light conditions is likely to result in poor estimates of received irradiance. This error may amount to several hundred per cent. The practice of force‐fitting linear least‐squares regressions to log‐transformed irradiance data inevitably leads to highly biased estimates of the true fraction of incident irradiance entering the water.3. Wave effects causing fluctuations of subsurface irradiance are modelled with synthetic data and compared with field observations. Fluctuations of surface elevation by waves produce skewed frequency distributions of the underwater light field. The result of these effects, which are to reduce the accuracy of estimated model parameters, can be largely eliminated by carefully designing field procedures used for the acquisition of subsurface light data.
Environmental variation and behaviour: resource availability during ontogeny and feeding performance in salamander larvae (Ambystoma texanum)
Authors: MAURER ERIC 
Published: November 2003

1. The effects of resource availability during ontogeny on subsequent feeding performance were investigated in larvae of the small‐mouthed salamander (Ambystoma texanum).2. Salamander larvae were reared individually in either high or low prey density treatments for 7 weeks prior to intermediate prey density foraging trials. Larvae from the low prey density treatment were on average 35% smaller in body size than individuals from the high prey density treatment.3. Resource availability during development influenced larval feeding rates and altered the relationship between body size and three feeding performance measures (attack rates, capture success and feeding rates). Feeding rates in predation trials were also positively correlated with growth rate early in the larval period (until the end of week 5).4. These results suggest that the environment to which developing organisms are exposed can have significant effects on subsequent behaviour, and that small‐mouthed salamander larvae may show state‐dependent changes in feeding behaviour in response to differences in long‐term feeding history. Additionally, differences in feeding performance may influence the probability of survival to the adult stage for organisms that utilize ephemeral habitats.