bluuebunny/crossref_metadata_2025 huggingface dataset:
Windows of opportunity and the temporal structuring of foraging activity in a desert solitary bee
Authors: Stone Graham N. , Gilbert Francis , Willmer Pat. , Potts Simon , Semida Fayez , Zalat Samy.
Published: May 2003

1. Females of the desert solitary bee Anthophora pauperata collect nectar and pollen almost exclusively from Alkanna orientalis (Boraginaceae). The bee and plant are found together in the early spring, living in the bottom of steep‐sided wadis (dry river valleys) at an altitude of 1500 m in Egyptian Sinai.

2. Female A. pauperata showed clear morning and afternoon peaks in foraging activity, separated by a 2–3 h midday period spent in their underground nests. This study analyses the following in order to identify the factors structuring this daily pattern: thermal aspects of the bee and its environment, temporal patterns of resource provision by the plant, and female nectar and pollen foraging behaviour.

3. Although A. pauperata can generate substantial heat endothermically, morning and evening ambient temperatures well below 10 °C defined a thermal window within which foraging occurred. Maximum air temperatures were moderate (25–30 °C), and examination of the physiology and behaviour of A. pauperata suggests that the midday reduction in flight activity was not due to thermal constraints.

4. Alkanna orientalis produces protandrous hermaphroditic flowers. Female A. pauperata collected pollen from male‐phase flowers and harvested nectar preferentially from female‐phase flowers. Although the nectar standing crop was relatively constant throughout the day, pollen availability peaked strongly in the early afternoon.

5. Female A. pauperata visited young male‐phase flowers as soon as they opened, generating an early afternoon peak in pollen foraging activity and depleting the pollen standing crop rapidly. A morning peak in pollen foraging occurred when females gleaned remnant pollen from flowers that had opened the previous day. Pollen availability in the morning was far lower than in the early afternoon, and the time taken to collect a full pollen load in the morning was significantly longer. Collection of pollen in the morning despite very low resource availability suggests that pollen may be a limiting resource for A. pauperata.

6. In contrast to many existing examples of bimodal activity patterns in highly endothermic bees, the bimodal activity patterns of female A. pauperata appear to be driven not by thermal considerations but by daily patterns of pollen release from its principal food source.
The effects of parasitoid fecundity and host taxon on the biological control of insect pests: the relationship between theory and data
Authors: Lane S. D. , Mills N. J. , Getz W. M.
Published: May 2003

1. A simple, intuitive argument and the tenets of the biological control literature both suggest that, in general, parasitoids with a greater fecundity will provide better control of their hosts, and will thus be better biological control agents.

2. A model of host‐parasitoid dynamics, based on the standard Thompson–Nicholson–Bailey approach and incorporating the effects of parasitoid fecundity‐limitation and host density‐dependence, also indicates that as parasitoid fecundity decreases so does local stability and the degree of host suppression.

3. A taxonomically diverse data set obtained from the biological control record failed to support this theoretical prediction, but at the same time indicated a strong effect of host taxon on the outcome of biological control.

4. The hypothesis that the fecundity of parasitoids is correlated positively with their ability to suppress host populations is supported by data exclusively from the host order Lepidoptera.

5. Possible explanations for the divergence between the fecundity‐limitation hypothesis and the complete data set include: the ability of parasitoids to provide long‐term control of pests without the presence of a stable host–parasitoid equilibrium; differences between the concepts of successful control in theory and practice; evolutionary trade‐offs between fecundity and other parasitoid life‐history features, such as search efficiency, leading to better pest control by parasitoids with low fecundity; and differing windows of vulnerability to parasitoid attack between host taxa.
Experimental evidence for predation risk sensitive oviposition by a mosquito, Culiseta longiareolata
Authors: Stav Gil. , Blaustein Leon. , Margalith Joel.
Published: May 2003

1. Females should choose to oviposit in habitats where risk of predation and competition are low. The ovipositional responses of a mosquito, Culiseta longiareolata, to a predator and to species sharing the same trophic level as this mosquito (controphic species) were assessed experimentally in outdoor artificial pools.

2. The predator, larval Anax imperator, which strongly reduced larval C. longiareolata survival, resulted in a 52% reduction of C. longiareolata egg rafts. The controphic species (primarily Daphnia magna), which had a small but statistically significant negative effect on the survival of C. longiareolata larvae, did not have a statistically significant influence on the number of egg rafts.

3. Laboratory trials indicated that only a small fraction of the reduced number of egg rafts seen in predator pools may be due to consumption of the egg rafts by A. imperator.

4. The experimental evidence indicates that the reduced number of C. longiareolata egg rafts found in the presence of A. imperator is due largely to oviposition habitat selection, i.e. C. longiareolata females choose pools with low risk of predation for their offspring.
Sociometry and sociogenesis of colonies of the harvester ant, Pogonomyrmex badius: distribution of workers, brood and seeds within the nest in relation to colony size and season
Authors: Tschinkel Walter R.
Published: May 2003

1. The vertical distribution in the nest of chambers, workers, callow workers, brood and seeds was studied in the harvester ant, Pogonomyrmex badius, in northern Florida. On each of four sample dates (May, July, October, January), six to seven colonies, chosen to represent the full range of sizes, were excavated. All chamber contents were collected and counted. Chambers were mapped and measured. In a preliminary study, two nests were excavated after preventing vertical migration by driving barriers into the wall of a pit next to the nest, severing the vertical tunnels. The vertical distribution of these barrier‐nests differed little from unrestrained nests, indicating that unrestrained excavation produced a reasonable picture of vertical distributions.

2. Nest depth, chamber number and total area increased with colony size. Chamber area declined sharply with depth, as did chamber number, such that more than half of the total area was found in the upper quarter of the nest.

3. The proportion of dark‐coloured (older) workers also declined strongly with depth, but this decline was weaker in the spring, and depended to a modest degree on colony size. Conversely, in the distribution of callow (young) workers, the proportion increased towards the bottom of the nest. Mean worker age was inversely related to the depth at which workers were found. The proportion of the brood also increased towards the bottom of the nest, with worker brood, sexual brood, pupae and larvae all being distributed similarly.

4. By contrast, seeds were stored at a preferred absolute depth between 40 and 100 cm. Colonies shallower than 100 cm stored seeds in their deepest chambers. Larger colonies stored most seeds in the upper third of the nest, but patterns were somewhat erratic because chambers were either filled completely with seeds or were empty.

5. Because chamber area decreased sharply with depth, the densities (individuals cm–2) of all colony members, including dark workers, were lowest near the surface and highest in the deepest parts of the nest. Here, worker densities ranged from 2 to 8 cm–2, and brood from 2 to 25 cm–2.

6. The regularity of the patterns of distribution suggests that harvester ant colonies have considerable spatial and temporal structure, which serves or is the outcome of important colony processes. A simple mechanism that could generate several of these patterns is discussed. New workers produced deep in the nest move upwards as they age. As they leave the brood zone they change from brood care to general nest

duties, including increased nest excavation, leading to the top‐heavy pattern of nest area. As they appear at the surface, they change to guarding and foraging. Thus, age polyethism may be partly the result of this upward migration of workers.
Mixture models of soybean growth and herbivore performance in response to nitrogen–sulphur–phosphorous nutrient interactions
Authors: Busch Johannes W. , Phelan P. Larry
Published: May 2003

1. It is widely established that plant‐mineral nutrition is an important determinant of herbivore developmental performance and behavioural preference. Unfortunately, the specific effects of minerals on herbivory have been variable and few unifying principles have emerged. Advances in this area may be impeded in part by an experimental approach that emphasises single nutrients without regard to nutrient ratios.

2. In this study, mixture‐design experiments were adapted to the study of mineral nutrition and herbivore performance. The interactive effects of nitrogen, sulphur, and phosphorous on the development of soybean looper(Pseudoplusia includens)and two‐spotted spider mite(Tetranychus urticae)feeding on soybeans (Glycine max) were quantified by polynomial regression.

3. Although significant effects of individual minerals were measured, the actual responses to these nutrients depended on the proportions of the other components in the nutrient solution. For example, over a range of decreasing nitrogen concentration, resulting soybean looper pupal mass first declined then increased when replaced by a high sulphur : phosphorous blend, but just the opposite response was measured when replaced with high phosphorous : sulphur ratio.

4. Moreover, responses to mineral proportions were generally nonlinear and the effects of mineral proportion were not only species‐specific, but varied for different responses within a species.

5. These studies demonstrate that understanding the role of mineral nutrients in host‐plant quality requires that mineral proportions be considered in addition to concentration. Mixture modelling, which is largely unknown to ecologists, is a powerful new tool that could significantly advance the study of the interactive effects of mixture components, such as in plant‐nutrient blends.
Invertebrate communities in a tropical rain forest canopy in Puerto Rico following Hurricane Hugo
Authors: Schowalter T. D. , Ganio L. M.
Published: May 2003

1. Canopy invertebrate responses to Hurricane Hugo, tree species, and recovery time were examined at the Luquillo Experimental Forest in Puerto Rico during 1991–92 and 1994–95. Six tree species representing early and late successional stages were examined in paired plots representing severe hurricane disturbance (most trees toppled) and light hurricane disturbance (all trees standing and most branches intact).

2. Hurricane disturbance affected invertebrate abundances significantly. Sap‐suckers and molluscs were more abundant, and defoliators, detritivores, and emergent aquatic insects were less abundant in recovering tree‐fall gaps than in intact forest during this 5‐year period. These changes in functional organisation are consistent with comparable studies of arthropod responses to canopy removal during harvest in temperate forests.

3. Tree species also affected invertebrate abundances significantly, but invertebrate communities did not differ significantly between the three early successional and three later successional tree species.

4. Most taxa showed significant annual variation in abundances, but only two Homoptera species showed a significant linear decline in abundance through time, perhaps reflecting long‐term trends during recovery.

5. Leaf area missing, an indicator of herbivore effect on canopy processes, showed significant seasonal and annual trends, as well as differences among tree species and hurricane treatments. Generally, leaf area missing peaked during the wet season each year, but reached its highest levels during an extended drought in 1994. Leaf area missing also tended to be higher on the more abundant tree species in each disturbance treatment.

6. Herbivore abundances and leaf area missing were not related to concentrations of nitrogen, phosphorous, potassium, or calcium in the foliage.

7. This study demonstrated that invertebrate community structure and herbivory are dynamic processes that reflect the influences of host species and variable environmental conditions.
Modification of coevolved insect–plant interactions by an exotic plant pathogen
Authors: Storer Andrew J. , Wood David L. , Gordon Thomas R.
Published: May 2003

New perspectives

New Perspectives is intended to allow the communication of comments, viewpoints, and speculative interpretation of issues in ecology pertinent to entomology. Comments, viewpoints, or suggestions arising from published papers intended to fuel discussion and debate are also welcome. Contributions should be as concise as possible, normally not exceeding two thousand words. Formal research reports will not be acceptable, but summarised novel data, suitably supported by statistics, may be allowed.
The role of body size in mating success of Sphenarium purpurascens in Central Mexico
Authors: Del Castillo Raúl. Cueva , Núñez‐Farfán Juan. , Cano‐Santana Zenón
Published: May 2003

1. The effect of body size on the assortative mating and reproductive behaviour of the univoltine grasshopper Sphenarium purpurascens (Charpentier) was studied in Central Mexico.

2. Assortative mating by size was observed in the field. Evidence of positive assortative mating in relation to body size was found in laboratory experiments. Female fecundity and male success in contests were also correlated with body size.

3. Larger females had a higher number of eggs per pod. Larger males usually won fights and were able to take over females from other males, and to resist takeovers by other males while guarding.

4. Individuals of both sexes were observed copulating with more than one sexual partner in the field, suggesting polygamy. Male–male contests determined access to females, and males exhibited a postcopulatory prolonged mate‐guarding behaviour lasting up to 18 days.

5. In a 2‐year study, sex ratio was male‐biased at the beginning of the reproductive season and decreased to 1:1 by the end of the season, suggesting that the population is protandrous.

6. The results of this study indicate that assortative mating results from male–male competition and female availability, and suggests that body size is a potential target of natural and sexual selection.
Behavioural responses of the leaf‐chewing guild to the presence of Eriocrania mines on silver birch (Betulapendula)
Authors: Fisher A. E. I. , Hartley S. E. , Young M.
Published: May 2003

1. Interactions between early season leaf‐miners from the genus Eriocrania Zeller (Eriocraniidae: Lepidoptera), and the leaf‐chewing guild of silver birch (Betula pendula Roth) were investigated.

2. Field observations indicated that a negative association between damage caused by Eriocrania, and leaf‐chewers could be observed under certain conditions, namely at higher damage densities in the final week of mine development on trees with relatively high densities of mines.

3. Experimental manipulation of Operophtera brumata L. (Geometridae: Lepidoptera) densities in the field confirmed the negative association between established mines of Eriocrania, and this species of free‐living folivore.

4. The behaviour of O. brumata was modified further in the presence of mines. On branches where mined leaves were present, O. brumata larvae consumed a larger proportion of leaf tissue, by continuing to feed on the same leaf longer rather than shifting to a new leaf. Increased consumption may indicate some modification of leaf quality beyond the leaves occupied by Eriocrania. Alternatively, it may indicate an association between Eriocrania, and higher quality leaf material.
Movement of the Apollo butterflyParnassius apollorelated to host plant and nectar plant patches
Authors: Brommer Jon. E. , Fred Marianne S.
Published: May 2003

1. The movement of adults of the endangered Apollo butterfly,Parnassius apollo, was studied using mark–recapture data, within a population consisting of discrete patches of the species’ host plant (n = 43), which were segregated spatially from patches of the species’ main nectar plants (n = 14).

2. The Apollo routinely moved large distances (median 260 m, maximum 1840 m), and moved frequently between the two types of patches. Only 27% (28/105) of the recaptures were made on the same host plant patch as the release.

3. The population acts as a patchy population where the adults mix over the whole area, but successful reproduction can only take place in the discrete host plant patches.

4. Occurrence on a host plant patch was restricted by the area size of the host plant patch and the spatial configuration of nectar plant patches. Thus, although the Apollo is a good flyer, its movement over the patches is still constrained by the segregation of adult and larval resources.
Dung pad residence time covaries with male morphology in the dung beetle Onthophagus taurus
Authors: Hunt John. , Kotiaho Janne S. , Tomkins Joseph L.
Published: May 2003

1. The immigration and emigration behaviours of Onthophagus taurus were investigated in a combination of field and laboratory experiments to examine patterns of dispersal in this species.

2. On average, the mean proportion of major males immigrating to baited pitfall traps decreased significantly with time. In contrast, the mean proportion of minor males and females did not change with time.

3. The time taken to emigrate from a dung pad differed significantly among major males, minor males, and females. This difference arose because major males spent a significantly shorter period of time residing within the dung pad. On average, more than 50% of major males had emigrated from the dung pads after 30 h, some 4 h earlier than minor males and females.

4. When the effects of body size were controlled, major males with longer horns were shown to have longer wings. Because major males spend more time in flight, longer wings may be an adaptation to more frequent dispersal. Alternatively, longer wings in major males may compensate for the production of aerodynamically costly horns.
Influenza– and Respiratory Syncytial Virus–Associated Morbidity and Mortality in the Nursing Home Population
Authors: Ellis Shelley E. , Coffey Christopher S. , Mitchel Edward F. , Dittus Robert S. , Griffin Marie R.
Published: May 2003

Objectives: To estimate winter viral‐related morbidity and mortality in Tennessee nursing home residents during 4 consecutive years.

Design: A retrospective cohort study.

Setting: Three hundred eighty‐one Tennessee nursing homes.

Participants: Nursing home residents.

Measurements: Viral surveillance data were used to define three seasons: influenza (influenza and respiratory syncytial virus (RSV) cocirculating), RSV (RSV alone circulating), and non winter‐viral (neither virus circulating). Adjusted seasonal differences in rates of cardiopulmonary hospitalizations, antibiotic prescriptions, and deaths during these three seasons were calculated to estimate annual hospitalizations, courses of antibiotics, and deaths attributable to influenza and RSV from 1995 to 1999.

Results: Nursing home residents had 81,885 person‐years of follow‐up. In the 63% of residents with comorbid conditions that increase influenza morbidity, influenza infection contributed to an estimated average of 28 hospitalizations, 147 courses of antibiotics, and 15 deaths per 1,000 persons annually. Similarly, RSV accounted for an annual average of 15 hospitalizations, 76 courses of antibiotics, and 17 deaths per 1,000 persons. Influenza and RSV accounted for 7% of cardiopulmonary hospitalizations and 9% of total deaths in high‐risk residents during the 4 study years. Absolute morbidity and mortality were lower in residents without identified comorbid conditions but accounted for 15% of hospitalizations and 14% of deaths. These estimates depend on the assumption that morbidity and mortality from other respiratory viruses were distributed evenly between the three defined seasons.

Conclusion: Influenza and RSV substantially increased hospitalization rates, antibiotic use, and deaths in elderly nursing home residents each winter. These data should encourage persistent efforts toward disease prevention, and thoughtful study of vaccine development and delivery, diagnostic tools, and methods of prophylaxis and therapy.
Horizontal movements of bigeye tuna (Thunnus obesus) near Hawaii determined by Kalman filter analysis of archival tagging data
Authors: Sibert John R. , Musyl Michael K. , Brill Richard W.
Published: May 2003

Geolocation data were recovered from archival tags applied to bigeye tuna near Hawaii. A state‐space Kalman filter statistical model was used to estimate geolocation errors, movement parameters, and most probable tracks from the recovered data. Standard deviation estimates ranged from 0.5° to 4.4° latitude and from 0.2° to 1.6° longitude. Bias estimates ranged from −1.9° to 4.1° latitude and from −0.5° to 3.0° longitude. Estimates of directed movement were close to zero for most fish reaching a maximum magnitude of 5.3 nm day−1 for the one fish that moved away from its release site. Diffusivity estimates were also low, ranging from near zero to 1000 nm2 day−1. Low values of the estimated movement parameters are consistent with the restricted scale of the observed movement and the apparent fidelity of bigeye to geographical points of attraction. Inclusion of a time‐dependent model of the variance in geolocation estimates reduced the variability of latitude estimates. The state‐space Kalman filter model appears to provide realistic estimates of in situ geolocation errors and movement parameters, provides a means to avoid indeterminate latitude estimates during equinoxes, and is a potential bridge between analyses of individual and population movements.
Vertical movements of bigeye tuna (Thunnus obesus) associated with islands, buoys, and seamounts near the main Hawaiian Islands from archival tagging data
Authors: Musyl Michael K. , Brill Richard W. , Boggs Christofer H. , Curran Daniel S. , Kazama Thomas K. , Seki Michael P.
Published: May 2003

To learn more about the movement patterns of bigeye tuna (Thunnus obesus), we deployed archival tags on 87 fish ranging in fork length from 50 to 154 cm. Thirteen fish were recaptured, from which 11 archival tags were returned, representing in aggregate 943 days‐at‐liberty. We successfully retrieved data from 10 tags, representing 474 days in aggregate. The largest fish recaptured was 44.5 kg [131 cm fork length (FL)] and the smallest 2.8 kg (52 cm). The deepest descent recorded was 817 m, the coldest temperature visited 4.7°C, and minimum oxygen level reached ∼1 mL L−1. Fish spent little time at depths where water temperatures were below 7°C and oxygen levels less than ∼2 mL L−1. Five fish were recaptured near the offshore weather buoy where they were tagged. Based on vertical movement patterns, it appeared that all stayed immediately associated with the buoy for up to 34 days. During this time they remained primarily in the uniform temperature surface layer (i.e. above 100 m). In contrast, fish not associated with a floating object showed the W‐shaped vertical movement patterns during the day characteristic of bigeye tuna (i.e. descending to ∼300–500 m and then returning regularly to the surface layer). Four fish were tagged and subsequently recaptured near Cross Seamount up to 76 days later. These fish exhibited vertical movement patterns similar to, but less regular than, those of fish not associated with any structure. Bigeye tuna appear to follow the diel vertical movements of the deep sound scattering layer (SSL) organisms and thus to exploit them effectively as a prey resource. Average night‐time depth was correlated with lunar illumination, a behaviour which mimics movements of the SSL.
Latitudinal differences in the duration of development of Neocalanus plumchrus copepodites
Authors: Batten Sonia D. , Welch David W. , Jonas Tanya
Published: May 2003

Quasi‐synoptic sampling along a transect from Alaska to California carried out in spring and summer 2000 using Continuous Plankton Recorders reveals that the abundant calanoid copepod Neocalanus plumchrus (Marukawa) reaches the surface at approximately the same time across the region. However, monthly sampling also reveals that the timing of peak biomass (when 50% of the population consists of copepodites at stage CV) occurs about 5 weeks earlier at the southernmost part of its range than at the northernmost part, with intermediate areas having intermediate timings. Surface water temperature differed by about 4°C between the warmer south and the cooler north, and we suggest that such a difference would reduce development duration by about 3 weeks. If food supply in the north is more conducive to lipid accumulation, as seems possible from phytoplankton biomass data, then the use of the differences in timing of peak N. plumchrus biomass in each area as a measure of the differences in development time may not be accurate. We find that the estimate of the time of peak biomass varying by about 5 weeks between north and south may be an exaggeration of the actual difference in the development duration. Temperature is probably the most important factor governing the shorter development duration of N. plumchrus in southern latitudes.
The effect of vertical and horizontal distribution on retention of sardine (Sardinops sagax) larvae in the Northern Benguela – observations and modelling
Authors: Stenevik Erling Kåre , Skogen Morten , Sundby Svein , Boyer David
Published: May 2003

In the present study, a modelling experiment is conducted to simulate the transport of sardine (Sardinops sagax) eggs and larvae in the Northern Benguela. Based on historical and newly obtained data, different scenarios of vertical and horizontal distribution are applied and the effects on retention are discussed. The simulations showed that vertical and horizontal distribution were important for retention of sardine larvae in the Northern Benguela. By using age‐dependent data on vertical distribution, it was shown that retention of particles in the simulation was substantially enhanced compared with a scenario where particles were distributed in the offshore moving Ekman layer. Retention was lowest during October–December (when upwelling intensity is high) and highest during February–April (when upwelling intensity is somewhat lower). When different spawning areas were considered, highest retention was observed in an area near Walvis Bay. It is concluded that the behaviour of sardine larvae is adapted to the circulation system in the Northern Benguela in a way that promotes retention of the larvae in inshore nursery areas.
Modelling the effect of buoyancy on the transport of anchovy (Engraulis capensis) eggs from spawning to nursery grounds in the southern Benguela: an IBM approach
Authors: Parada C. , Van Der Lingen C.D. , Mullon C. , Penven P.
Published: May 2003

An individual‐based model (IBM) was used to investigate the effects of physical and biological variables on the transport via a jet current of anchovy (Engraulis capensis) eggs from spawning to the nursery grounds in the southern Benguela ecosystem. As transport of eggs and early larvae is considered to be one of the major factors impacting on anchovy recruitment success, this approach may be useful to understand further the recruitment variability in this economically and ecologically important species. By coupling the IBM to a 3D hydrodynamic model of the region called Plume, and by varying parameters such as the spatial and temporal location of spawning, particle buoyancy, and the depth range over which particles were released, we could assess the influences of these parameters on transport success. A sensitivity analysis using a General Linear Model identified the primary determinants of transport success in the various experimental simulations, and model outputs were examined and compared with patterns observed in field studies. Model outputs compared well with observed patterns of vertical and horizontal egg distribution. Particle buoyancy and area of particle release were the major single determinants of transport success, with an egg density of 1.025 g cm−3 maximizing average particle transport success and the western Agulhas Bank being the most successful spawning area. This IBM may be useful as a generic prototype for other upwelling ecosystems.
Competition between Asian pink salmon (Oncorhynchus gorbuscha) and Alaskan sockeye salmon (O. nerka) in the North Pacific Ocean
Authors: Ruggerone G. T. , Zimmermann M. , Myers K. W. , Nielsen J. L. , Rogers D. E.
Published: May 2003

The importance of interspecific competition as a mechanism regulating population abundance in offshore marine communities is largely unknown. We evaluated offshore competition between Asian pink salmon and Bristol Bay (Alaska) sockeye salmon, which intermingle in the North Pacific Ocean and Bering Sea, using the unique biennial abundance cycle of Asian pink salmon from 1955 to 2000. Sockeye salmon growth during the second and third growing seasons at sea, as determined by scale measurements, declined significantly in odd‐numbered years, corresponding to years when Asian pink salmon are most abundant. Bristol Bay sockeye salmon do not interact with Asian pink salmon during their first summer and fall seasons and no difference in first year scale growth was detected. The interaction with odd‐year pink salmon led to significantly smaller size at age of adult sockeye salmon, especially among younger female salmon. Examination of sockeye salmon smolt to adult survival rates during 1977–97 indicated that smolts entering the ocean during even‐numbered years and interacting with abundant odd‐year pink salmon during the following year experienced 26% (age‐2 smolt) to 45% (age‐1 smolt) lower survival compared with smolts migrating during odd‐numbered years. Adult sockeye salmon returning to Bristol Bay from even‐year smolt migrations were 22% less abundant (reduced by 5.9 million fish per year) compared with returns from odd‐year migrations. The greatest reduction in adult returns occurred among adults spending 2 compared with 3 years at sea. Our new evidence for interspecific competition highlights the need for multispecies, international management of salmon production, including salmon released from hatcheries into the ocean.
Competition between tree seedlings and herbaceous vegetation: support for a theory of resource supply and demand
Authors: Davis Mark A. , Wrage Keith J. , Reich Peter B.
Published: May 2003

1 We measured competition intensity (CI) between herbaceous vegetation and tree seedlings (Quercus macrocarpa and Q. ellipsoidalis) along an experimental moisture–light gradient. Contrasting theories were tested by comparing variation in competition intensity to changes in neighbour biomass and resource supply and demand.

2 CI based on survival was inversely correlated with net soil water supply (gross supply minus demand by herbaceous vegetation). CI was not positively correlated with either gross resource supply or neighbour biomass, contrary to predictions of Grime's triangular model for plant strategies.

3 Many of the inconsistencies and conflicting results that have characterized the recent literature on plant competition could be eliminated if changes in competition intensity along a resource gradient are compared with changes in net resource supply rather than changes in productivity or neighbour biomass.

4 Tree seedling success in savannas and grasslands may be strongly influenced by the intensity of competition from herbaceous vegetation. Factors that reduce soil water content are likely to increase competition intensity (and reduce seedling success) in these environments, while factors that increase soil water content will favour seedling success through decreased competition for water with herbaceous vegetation.
Advantages of early germination for growth and survival of seedlings of Acer mono under different overstorey phenologies in deciduous broad‐leaved forests
Authors: Seiwa Kenji
Published: May 2003

1  Acer mono is one of the earliest germinating species in hardwood forests of northern Japan. To evaluate the advantage of early germination for the seedling establishment, differences in the temporal pattern of leaf development between the seedlings and overstorey trees were investigated, together with the timing of dry mass gain and allocation, survival and mortality agents of seedlings. These traits were contrasted at four sites with different types of foliage phenology in the overstorey trees (FU‐1 and FU‐2, forest understorey in which overstorey trees unfolded and shed the leaves as a flush and succeedingly, respectively; SG, small gaps; and FE, forest edge).

2  Seasonal growth patterns of the seedlings were greatly affected by the differences in the coupling of leaf development between the seedlings and the overstorey trees. For early germinating cohorts of Acer mono, 79, 61, 50 and 53% of annual dry mass gain occurred within 2 months of germination, in FU‐1, FU‐2, SG and FE, respectively. After this point (canopy closure) mass increment decreased abruptly in both FU sites, but continued to increase in both SG and FE. Seedling mass, however, increased after September again in FU‐2 but not in FU‐1, mainly due to earlier leaf shedding of the canopy trees in FU‐2.

3  After canopy closure, leaf mass ratio was greatest in FU‐1 where light was most limited, but lowest in FE. In contrast, root mass ratio was greatest in FE but lowest in FU‐1 where soil moisture was most abundant. These traits might lead to the optimization of growth by making all resources equally limiting even after canopy closure in forest understorey.

4  Higher seedling survival resulting from early germination was observed in all four sites, since predators and pathogens selectively attacked late germinating individuals. The advantage of early germination was greater in both FU‐1 and FU‐2 than in FE, mainly due to large differences in available light for early vs. late germinating individuals in both FU sites compared with the FE site.

5  These observations suggest that phenological traits of A. mono such as rapid germination in early spring and earlier deployment of leaves compared with overstorey trees has been selected to maximize annual mass gain and survival in understorey habitats of deciduous broad‐leaved forests.
Effects of population size on performance in the rare plant Gentianella germanica
Authors: Fischer Markus , Matthies Diethart
Published: May 2003

1  We studied the relationships between population size, reproduction and population growth rate in 23 populations of the rare, short‐lived plant Gentianella germanica. We also investigated a possible correlation of population size effects with environmental variation in climate, topography, soil, vegetation, and management. To ascertain whether the differences between populations have a genetic basis, we grew 20 seed families from each of the populations in a common garden experiment.

2  In 1993, population sizes ranged from 40 to 5000 flowering plants in the field populations (geometric mean 386). Plants in small populations had fewer seeds per fruit and fewer seeds per plant than plants in larger populations, whereas seed mass was independent of population size. From 1993 to 1995 population size decreased in most populations (mean annual population growth rate 0.876), and this decrease was larger in small populations than in large populations.

3  In the common garden the positive correlation between the number of surviving plants per planted seed and original population size increased steadily over time. After 17 months there were significantly more flowering plants and more flowers per planted seed for seeds from large populations than for those from small populations.

4  Although environmental variables accounted for significant variation in population growth rate and plant performance both in the field and in the common garden, effects of population size detected in stepwise multiple regressions were not confounded with environmental effects.

5  We conclude that the reduced performance observed in plants from smaller populations was explained by genetic effects rather than by habitat quality, although pollinator limitation may have contributed to fitness reductions in the field. The observed patterns suggest further reductions of population sizes in Gentianella germanica in the future, especially in already small populations. Our study lends support to the view that genetic problems are a major concern in plant conservation.
Effects of raised CO2 on potential CH4 production and oxidation in, and CH4 emission from, a boreal mire
Authors: Saarnio Sanna , Alm Jukka , Martikainen Pertti J. , Silvola Jouko
Published: May 2003

1  In a glasshouse experiment we studied the effect of raised CO2 concentration (720 p.p.m.) on CH4 emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH4 production and oxidation was measured at the end of the emission experiment.

2  The vascular cores (‘Sedge’) consisted of a moss layer with sedges, and the moss cores (‘Sphagnum’) of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures.

3  In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the potential CH4 oxidation. A raised concentration of CO2 increased CH4 efflux weakly and only at the highest peat temperatures (17–20 °C).

4  The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO2 concentrations, and would thus retard any consequent increase in CH4 emission.
Forage variation in brood‐rearing areas used by pacific black brant geese on the Yukon‐Kuskokwim delta, Alaska
Authors: Person Brian T. , Babcock Christopher A. , Ruess Roger W.
Published: May 2003

1  We investigated the effects of grazing by black brant geese on Carex subspathacea lawns on the Yukon‐Kuskokwim delta, Alaska.

2  We compared variation in growth and forage quality in both grazed and temporarily exclosed sites to determine responses of C. subspathacea to grazing at landscape scales within two nesting colonies that had experienced different population dynamics over recent decades.

3  Landscapes differed in forage quality, grazing patterns, and in the effect grazing had on C. subspathacea forage characteristics. We found no effect of grazing on net above‐ground primary productivity (NAPP) over a wide range of natural grazing intensities at the landscape scale.

4  No differences in forage quality, NAPP, or response of C. subspathacea growth rates to grazing pressures could be detected between colonies. This suggests that goose grazing does not have deleterious effects on C. subspathacea in this ecosystem.

5  It has been suggested that gosling growth rates are sensitive to seasonal declines in forage availability and quality. Spatial variation in forage quality and availability per sampled area exceeded seasonal variation in these characteristics and is likely to have dramatic effects on gosling growth and recruitment rates.
A new species index for forest vascular plants: development of functional indices based on mineralization rates of various forms of soil nitrogen
Authors: Diekmann Martin , Falkengren‐Grerup Ursula
Published: May 2003

1  Soil nitrogen mineralization rates for ammonium, nitrate and total‐N were determined by incubation experiments for 661 sample plots of deciduous forest from different regions in southern Sweden.

2  Species N indices for nitrate and ammonium were calculated as the weighted averages of mineralized N in those plots where the species were present.

3  Optimized linear models were used to combine mineralization rates for NH+4 + NOminus;3 to produce a functional N index for plots (FNIP) and to combine the species indices for NH+4 + NOminus;3 to produce a functional N index for species (FNIS).

4  The sample scores along the first axis of a detrended correspondence analysis (DCA) were highly correlated with soil acidity and mineralized ammonium, whereas total‐mineralized N accounted for most of the variation along the second DCA axis. The species scores along the first axis were highly correlated with the ammonium index.

5  FNIP was somewhat better correlated with the sample scores along axis 1 than mineralized ammonium, but only slightly better correlated than total‐mineralized N relative to axis 2. Similar results were obtained for FNIS.

6  Ammonium index and FNIS explained more of the floristic variation along the ordination axes than Ellenberg's N indicator values. Weighted averages of these indices also showed higher correlations with the sample scores along the axes than corresponding averages of Ellenberg's N values. However, when ammonium index and FNIS for the most frequent species were transformed into classes, they were generally similar to the Ellenberg scale.

7  The ammonium indices differed considerably between regions, caused by differences in N deposition, total‐N mineralization and nitrification rate. In one of the regions with comparatively low nitrification, the ammonium index was found to be uncorrelated with the species scores along the first DCA axis. FNIS differed much less between regions and thus was more robust; it appears to be a good and generally applicable expression of the species’ responses to N availability in deciduous forest soils.
The carbon balance of grazed and non‐grazed Spartina anglica saltmarshes at Skallingen, Denmark
Authors: Morris James T. , Jensen Arne
Published: May 2003

1  Canopy‐level CO2 exchange and biomass were measured monthly for 9 consecutive months during 1990 on grazed and non‐grazed portions of a Danish salt marsh dominated by Spartina anglica. The empirical measurements were used to calibrate a model of canopy photosynthesis and soil respiration that was subsequently integrated to provide estimates of annual net ecosystem production (NEP).

2  Standing total and green biomass on the non‐grazed site reached maxima during September of 1.9 ± 0.2 and 1.1 ± 0.2 kg m–2 ( ± 1 SD, n = 3), respectively. Corresponding maxima (0.8 ± 0.1 and 0.5 ± 0.05 kg m–2), were achieved during July at the grazed site.

3  Sediment organic matter as a percentage of dry weight was 31.6% and 5% at the non‐grazed and grazed sites, respectively. Accounting for the higher sediment bulk density at the grazed site meant that concentrations of organic carbon were 0.027 and 0.021 g cm–3 at non‐grazed and grazed sites, respectively. Thus, the fraction of NEP removed by grazing animals significantly reduced the accumulation of sediment organic matter.

4  Estimate of NEP varied between 17 and 38 mol m–2 year–1 of carbon at the grazed site and between 5 and 38 mol m–2 year–1 at the non‐grazed site, depending on assumptions about canopy geometry. Soil respiration, 36 mol m–2 year–1, did not differ between sites. Canopy respiration was less (21 mol m–2 year–1) at the grazed site than at the non‐grazed site (28 mol m–2 year–1), and accounted for 22–29% and 28–41% of gross photosynthesis at grazed and non‐grazed sites, respectively. The decrease in canopy respiration compensated the grazed canopy for losses to herbivores.

5  A canopy photosynthesis model was used to calculate a theoretical envelope of canopy biomass, termed the production window, inside of which NEP is positive and outside of which NEP is negative. The production window is bisected by the optimum canopy biomass, which is the theoretical biomass at which NEP is maximized. The seasonality of NEP is determined by the trajectory of actual canopy biomass through the production window. It was shown that canopy biomass on the grazed site was close to the theoretical optimum biomass late in the season, while the non‐grazed canopy biomass was supraoptimal.
Attributes of the seed bank after a century of primary succession on islands in Lake Hjälmaren, Sweden
Authors: Grandin Ulf , Rydin Håkan
Published: May 2003

1  A large number of islands was created when the water table of Lake Hjälmaren, south central Sweden, was lowered between 1882 and 1886. We have complete lists of vascular plant species for 40 of these islands from 1886, 1892, 1903–04, 1927–28 and 1984–85.

2  We have investigated the seed bank on nine of these islands and compared species composition at different soil depths with the species lists from the islands in 1886–1985, and with the present vegetation in the area of seed bank sampling. We have also investigated the distribution in the soil of seeds from species with different ecological attributes, including seed longevity, successional status, seed weight, seed form and species longevity.

3  Seeds in soil samples were allowed to germinate over the course of two summers with an intermediate cold storage. We found 1944 seeds representing 65 taxa. The mean seed density was 84 seeds dm–2.

4  The similarity between the surface soil (0–3 cm) seed bank and the vegetation at the different vegetation analyses increased from 1886 to 1993. The similarity between the present vegetation and the seed bank decreased with increasing soil depth, and the soil at 12–15 cm had no species in common with the present vegetation. Several species now absent from the vegetation were found in the seed bank.

5  Deeply buried seeds came from early successional, annual species with long‐term persistent and low‐weight seeds, as expected from seed bank theories, but were slightly elongated, which was in contrast to theories. Spherical seeds were associated with the surface soil, as were short‐lived and high‐weight seeds from late successional, perennial species.
Nutrients, competition and plant zonation in a New England salt marsh
Authors: Levine Jonathan M. , Brewer J. Stephen , Bertness Mark D.
Published: May 2003

1  We examined the effects of nutrient availability on the competitive interactions of the New England salt marsh perennials that occupy discrete vegetational zones parallel to the shoreline.

2  Fertilized and unfertilized plots of pair‐wise mixtures and monocultures of Spartina alterniflora, S. patens and Juncus gerardi were compared in order to assess the effects of nutrient addition on the competitive dynamics of these species in the field. In addition, we examined competition between some of these species and Distichlis spicata, a species common to disturbed marsh habitats.

3  After two growing seasons, changes in above‐ground biomass of the species indicated that in fertilized plots, S. alterniflora outcompeted S. patens, S. patens outcompeted J. gerardi, and D. spicata outcompeted both J. gerardi and S. patens. This was the reverse of the interactions seen under ambient marsh conditions, and suggested that, under conditions of nutrient limitation, competitive dominance may result from efficient competition for nutrients.

4  Using a conceptual model of salt marsh zonation as a function of competition, physical stress and nutrient limitation, we hypothesize that a nutrient‐induced reversal in the competitive dynamics among salt marsh perennials may result in modification of the pattern of plant zonation in this and similar marshes.