bluuebunny/crossref_metadata_2025 huggingface dataset:
Competition for tracer 15N in tussock tundra ecosystems
Authors: Marion G. M. , Miller P. C. , Black C. H.
Published: July 2006

The objectives of this study were to assess the roles of plant species, time, and site on competition for tracer 15N (without carrier) in tussock tundra ecosystems. Six experimental sites were located in northern Alaska. After one year across the experimental sites, the recovery of 15N by litter (11.3–16.3%) and mosses (5.4–16.4%) was significantly greater than for aboveground vascular plants (2.6‐5.0%). 15N recoveries by tundra vascular plants (2.6–5.0%) were low when compared to forest trees (9–25%) which suggest that competition for nitrogen is particularly severe in these cold‐dominated tundra ecosystems. There were no significant differences among sites in 15N recoveries by vascular plants, by mosses, or by litter. There was a statistically significant decline in 15N recovery with time for Vaccinium vitis‐idaea and Eriophorum vaginatum between the second and third year. The shallow rooted Vaccinium vitis‐ideae was more highly labeled than the deep rooted Eriophorum vaginatum. Nearness to the source of the applied 15N played a critical role in competition for surface applied nitrogen.
Specialized pelagic feeding by Erpobdella montezuma (Hirudinea)
Authors: Blinn Dean W. , Davies Ronald W. , Dehdashti Behrooz
Published: July 2006

The pelagic amphipod, Hyalella montezuma comprised nearly 90% of the diet of the leech, Erpobdella montezuma in the near thermally constant environment of Montezuma Well, Arizona. This restricted diet, confirmed by both gut content and serological analyses, occurred even though other potential prey were abundant throughout the year in the pelagic column, littoral vegetation and sediments. Seasonal electivity indices for this pelagic prey species were ≥0.9. It is suggested that the highly predictable environmental conditions in Montezuma Well have contributed to this very close predator–prey relationship.
The role of environmental factors in the ecology of tubificid oligochaetes ‐ an experimental study
Authors: Reynoldson Trefor B.
Published: July 2006

The effects of temperature, oxygen and substrate on growth rates of three tubificid oligochaetes were examined in the laboratory. Two species Tubifex tubifex and Limnodrilus hoffmeisteri (Tubificidae, Oligochaeta) had similar narrow temperature ranges over which growth occurred, from 10–13°C and both showed a considerable tolerance to extended periods of anoxia, of at least 16 and 10 weeks respectively. However no growth was observed under anoxic conditions. A third common species Ilyodrilus templetoni was sensitive to anoxia and could not survive more than four weeks. There was no evidence of differences in substrate quality affecting growth rates of either T. tubifex or L. hoffmeisteri. The temperature and oxygen responses of these three species may explain their distribution in some lakes of the English Lake District.
Communities of ground‐living spiders in six habitats on a mountain in Quebec, Canada
Authors: Koponen Seppo
Published: July 2006

Ground‐living spiders were studied, using pitfall traps, in six habitats between 580 and 960 m (deciduous forest, fir forest, forest‐line and three alpine mountain top sites) on Mont du Lac des Cygnes. Altogether 88 species of spiders were found during the study summer (June‐mid‐September 1985), of which 51 belonged to Linyphiidae (s. lat.), 9 to Lycosidae and 8 to Gnaphosidae. The highest species number and diversity were found in the forest‐line habitat, the highest individual number on the main summit and the lowest in deciduous forest, the lowest site. Lycosidae and Gnaphosidae species and individuals characterized the alpine habitats. Linyphiidae (especially Linyphiinae) the forested sites and Amaurobiidae and Agelenidae the deciduous forest site. Erigoninae occurred commonly at all sites; their individual numbers were very high at coniferous forest sites. The dominant species in all three alpine habitats was Pardosa concinna, on the forest‐line Hybocoptus gibbosus, in balsam fir forest Sisicottus montanus and in deciduous forest Amaurobius borealis. The material included several (sub)arctic‐alpine species.
The effects of inundation on marine littoral Collembola
Authors: Witteveen J. , Joosse E. N. G.
Published: July 2006

The impact of inundation was studied on two marine littoral collembolan species: Isotoma viridis and Hypogastrura viatica.

The unwettable integument causes the collembolans to drift on the water surface during inundation. When trapped under water they try to climb up from below the water level. Their survival on the water surface is higher than under water.

H. viatica, occurring in a habitat that is inundated relatively frequently and over a long time, had a greater ability to survive on the water surface than I. viridis.

The mortality on the water surface was caused by starvation. A strong correlation between the mortality and the metabolic rate was shown. The highest mortality was found at lower salinities, where oxygen consumption of the animals is highest. The metabolic rate and mortality was lower at salinities up to 75% S.W. At 100% S.W. there was again a rise in metabolic rate and mortality. This is probably due to energy‐demanding processes concerning internal osmotic and ionic regulation.

After flooding, transport by sea currents can play a role in the distribution of the species. Reproductive synchronization after inundation is considered to be a mechanism for restoring a disturbed population.
Microcrustacean community structure and biomass in marsh and lake habitats of the Okefenokee Swamp: seasonal dynamics and responses to resource manipulations
Authors: Schoenberg Steven A.
Published: July 2006

Microcrustacean community and biomass dynamics were studied for two years in a Nymphaea‐Eriocaulon macrophyte marsh and a nearby shallow lake which lacked macrophytes in the Okefenokee Swamp. In this blackwater, acidic wetland, microcrustacean diversity and biomass were similar to other circumneutral lakes and littoral areas, contributing to a productive fish assemblage. In the lake, the annual biomass pattern (15–1627 μg 1−1) was unimodal and was dominated by the crustaceans Diaptomus sinuatus and Eubosmina tubicen. Rotifers were occasionally important, constituting up to 55% of total biomass. Over the long term, mean annual biomass in this post‐drought study are higher than in pre‐drought years. In the marsh, biomass (11–777 μg 1−1) fluctuated biomodally with late winter depressions corresponding to low temperatures and midsummer declines indicative of increasing fish predation. Summer dominance shifted between years from Macrothricidae in 1982 to Sididae in 1983. Variation in biomass correlated most strongly with algal chlorophyll in the marsh and with bacterial density in the lake.

In field enclosure experiments in which primary production was reduced by shading, microcrustacean responses varied between lake and marsh habitats and with season. Lake zooplankton were consistently suppressed by reduced algal resources in winter, spring and summer experiments, with greatest responses to shading in the summer. Marsh microcrustacea were most affected in the winter experiment and became less sensitive to manipulated resource levels in spring and summer. Decoupling of these consumers from autotrophic resources in the marsh, but not in the lake, coincides with times of high macrophyte turnover and warming temperatures which promote the conversion of detritus into heterotrophic resources such as bacteria. The conflict between interactions implied by the experimental approach vs statistical criteria emphasizes a need to interpret resource dependence from seasonal dynamics of field populations with caution.
Chironomidae (Diptera) of peatlands in northwestern Ontario, Canada
Authors: Rosenberg David M. , Wiens Allen P. , Bilyj Bohdan
Published: July 2006

Eighty‐four species of Chironomidae were collected, using emergence traps, from three poor fens located in the Experimental Lakes Area (ELA) of northwestern Ontario. Of these, 37 were considered to be true peatland fauna. The majority (23) of the peatland species are new North American or Canadian records and, of these, 10 are previously undescribed. Numbers m−2 yr−1 emerging from the fens were similar to neighbouring lakes but biomass (mg) m−2 yr−1 emerging was much less, indicating the small average size of the fen chironomids. Emergence began in early May and was virtually completed by late July‐early August in all three years of the study. Most of the emergence occurred early in the season. Eight species accounted for ≥90% of the emergence. Five of these, Gymnometriocnemus (R.) acigus Saeth., Doithrix villosa Saeth. and Subl., Pseudorthocladius (s.s.) destitutus Saeth. and Subl., P. (s.s.) curtistylus (Goetgh.), and Paramerina nr. smithae (Subl.) had univoltine life cycles and relatively stichronous emergences. Pseudosmittia forcipata (Goetgh.) was bivoltine, and Limnophyes minimus (Meig.) and Smittia nr. nudipennis Geotgh. had protracted emergence periods that made voltinism difficult to determine. Characteristic features of the chironomid fauna of peatlands at ELA are discussed. The general applicability of these features to peatlands, and needs for further research in these neglected but extensive Canadian habitats are considered.
Bryophyte communities in mesotrophic fens in the Netherlands
Authors: van Baaren Michele , During Heinjo , Leltz Georgette
Published: July 2006

Seven bryophyte and three vascular plant community types were described from eight small fens in the Vechtplassen area (prov. of Utrecht, the Netherlands). Clear relationships between the species composition of the bryophyte and vascular plant layer were found. The bryophyte species composition shows a gradual change from quaking fens dominated by Calliergon cordifolium to fens dominated by several species of Sphagnum. Fens dominated by C. cordifolium have relatively high pH and conductivity values and are strongly quaking, whereas fens dominated by Sphagnum have relatively low pH and conductivity values and the peat layer is continuous down to the bottom sediment. A comparison of the present‐day vegetation with an earlier successional scheme for this vegetation type (Segal 1966) indicates a raise in nutrient levels and a decrease in the amount of seepage water welling up at the sites, both due to human activities. We suggest that in early successional phases bryophytes react faster to these changes, whereas in later phases vascular plants react faster.
Ecology and production of invertebrates in a Canadian coldwater spring‐springbrook system
Authors: Williams D. Dudley , Hogg Ian D.
Published: July 2006

Valley Spring is a hardwater rheocrene consisting of a single point issue and a springbrook some 60 m long. The fauna consists of > 60 taxa, with insects and mites predominating. During 1985–86, benthic densities varied both along the springbrook and at single stations over time (range 58 to 756 animals 900 cm−2). A clear longitudinal zonation of many of the major taxa occurred with the Diptera tending to be more abundant downstream, the Plecoptera and Acari more abundant upstream, and the Copepoda and Bivalvia most abundant in mid‐ and downstream sections. The Gastropoda and Trichoptera occurred throughout the system although, in the case of the latter, there were distributional differences at the species level (e.g. Diplectrona modesta downstream, Parapsyche apicalis and Lepidostoma vernale upstream). Life histories varied between major species and were grouped into: (A) those species in which there was a wide range of larval sizes for most of the year, with no easily discernible temporal succession of cohorts, e.g. L. vernale, P. apicalis, Sialis sp., Dixa sp., Metriocnemus sp., Trissopelopia sp., Micropsectra sp. and Mucronothrus nasalis (the generation time of species in this group ranged from < 1 year to > 2 years); and (B) those species in which there was a clear pattern of larval growth, with obvious temporal succession of cohorts, e.g. D. modesta, Nemoura trispinosa and Hyalella azteca (all of these species were univoltine). Differences between the “adaptive strategies” of these two life history types are discussed. Total secondary production in Valley Spring in 1985–86 was estimated to be 913.2 g wet wt yr−1. Production upstream was more than twice that downstream (11.21 and 4.01 g wet wt m−2 yr−1, respectively). The three most abundant species of caddisfly together contributed > 30% of the total production, the stonefly N. trispinosa contributed > 17%, while the chironomids accounted for >16% of production at downstream stations but only 3% upstream.
The influence of precocious sexual maturation on survival to adulthood of river stocked Baltic salmon, Salmo salar, smolts
Authors: Lundqvist H. , Clarke W. C. , Johansson H.
Published: July 2006

During three consequtive years, 1975–1977, Individually tagged Baltic salmon Salmo salar smolts of sexually immature male and female fish (n = 35027, mean size: 15.2 cm) and precocious males (n = 6518, mean size: 14.2 cm) were released into Umeälven (Ume river), northern Sweden. Rate of survival (% captured adults) based on 3714 recoveries was significantly higher (p < 0.01) for smolts from immature fish (10.2%) than those from smolts of early maturing males, i.e. precocious males (2.2%). corresponding to an average yield of 474 and 85 kg per KHX) smolts released, respectively. Gain in survival was on average 2.5% and 1.4% per cm increase in smolt size for immature smolts and smolts from precocious males, respectively. The poor survival among smolts of precocious males is suggested to he related to an interaction between sexual maturation and smolting linked to incompletely resorbed gonads leading to a non migratory behaviour. These non migratory males are then suggested to suffer heavily by predation in the river.

The two smolt categories had a similar growth pattern in sea. Smolts from precocious males did not mature early in sea indicating no relation to grisling, i.e. sexually maturing fish returning after first winter in sea. Adult weight of fish returning the fourth summer after release was related to smolt size (P < 0.05). Our Response Surface Model (RSA) predicted that large smolts (19.0 cm) had a higher specific growth rate over their life‐span compared to small smolts (<15.0 cm), 0.86% d−1 and 0.46% d−1, respectively. Large smolts (19.0 cm) attained a size of 3.0 kg during their second winter in sea about six months earlier than small smolts (13.0 cm). The paper discusses alternative release strategies that can be employed if the ultimate goal of salmon stocking is maximizing yield.
Respiratory loss and bulk export of organic matter from cattle dung pats: a field study
Authors: Holter Peter , Hendriksen Niels Bohse
Published: July 2006

Respiratory loss and bulk transport of organic matter from dung pats in a Danish pasture were measured by a chromic oxide marker technique. Measurements covered the period until a dung age of 7‐8 weeks. On average, respiration and transport contributed 46% and 54% of organic matter disappearance in three spring experiments: in three autumn experiments the corresponding values were 25% and 75%. Thus, both processes are important. The rate of transport was highest at the bottom of the pat, whereas the highest respiratory rate occurred in the top and periphery. During the first 10–14 days transport predominated, probably owing to the activity of dung insects, whereas respiration was remarkably low. During the remaining period, transport was probably affected mainly by earthworms. Respiration seemed to be mostly microbial and to proceed during dung pat decay in essentially the same way as did cellulolytic activity. Earthworms did not significantly affect the respiration of pats.
Faunal diversity and vegetation structure of some deciduous forests in South Sweden
Authors: Gerell Rune
Published: July 2006

The relationships of faunal diversity and vegetation structure were studied in twenty deciduous forest plots in South Sweden, all of them managed. Following animal groups were censused: shrews (Soricidae), bats (Chiroptera), voles (Cricetidae), fieldmice (Muridae), birds (Aves), groundliving beetles (Coleoptera), spiders (Araneida), and harvestmen (Opilionidae). The analysis of the 22 vegetation variables was made by means of repeated and rotated PCA. Rarefaction was used to ordinate the bird species richness of the different forest plots.

The multivariate vegetational analysis resulted in three distinct and readily interpretable components: horizontal and vertical spatial heterogeneity, and mean basal area. The number of small mammal species (except bats) was greatest in forests with great amount of understory while the number of bat species increased with increasing mean basal area. The number of bird species in a fixed number of territories was also highly correlated with the mean basal area. Hence, maximum bird species richness was obtained in mature forests but not in those with greatest vertical heterogeneity. The invertebrate communities showed very few distinct relationships to the vegetation structure.

Dominance decreased as vegetation complexity increased. Dominance also decreased with increasing species richness in all faunal communities studied.
Emergence phenology and ecology of aquatic and semi‐terrestrial insects on a boreal raised bog in Central Finland
Authors: Paasivirta Lauri , Lahti Tapani , Perätie Timo
Published: July 2006

Emergence of peatland insects was studied in Central Finland by sampling insects on a raised bog with tent traps from five different surfaces: muddy hollow without vegetation; hollow covered with Sphagnum; deep (0.7–0.9 m) open‐water pool; shallow (about 0.3 m) pool with bottom covered by Carex vegetation; shallow (about 0.3 m) pool with bare muddy bottom. The material was collected at two‐days intervals from 13 May until 31 August in 1981.

Biomass emerging from the sites varied considerably. In general, aquatic sites were clearly more productive than semi‐terrestrial sites. Corrected total biomass values for deep pools, shallow Carex pools, and shallow mud pools were 2.471, 1.066, and 0 514 g m−2, respectively. The corresponding values for muddy and Sphagnum hollows were 0.208 and 0.236 g m−2, respectively.

All chironomids, chaoborids and trichopterans from the aquatic sites were identified to species, and their emergence phenology and habitat preferences are discussed. 14 species were considered as eurytopic littoral species, 9 species showed strong preference for the bog pools or polyhumic lakes, and 8 species were of diverse origin. Differences in emergence patterns and habitat preferences are probably connected with species‐specific resistances to freezing and oxygen and nutrient requirements. The role of emerging insects in the peatland food webs, especially as food for breeding birds, is briefly discussed.
Seasonal quality of forages used by moose in the aspen‐dominated boreal forest, central Alberta
Authors: Renecker Lyle A. , Hudson Robert J.
Published: July 2006

Forages used by moose, Alces alces, in the aspen‐dominated boreal forest were studied to determine seasonal changes in digestibility (nylon bag technique) and chemical composition. Digestibility of all forage classes increased to 70% during spring and summer with the presence of new growth and declined to a low of 30% with plant maturation and dormancy. Mean protein contents during these periods were >20% and <7%, respectively. Nutritional quality of herbaceous forages peaked earlier and higher than that of woody plants in spring but quality declined earlier and reached slightly lower levels in late winter. Cell wall composition of grasses, sedge, and foliage varied seasonally and was correlated with forage digestibility. In multiple linear regression models, hemicellulose, cellulose, and lignin content of browse, grass, and sedge provided significant predictions of digestibility.
Influence of salinity, temperature, and nutrient availability on the respiration of saprolegniaceous fungi (Oomycetes)
Authors: Padgett D. E. , Kendrick A. S. , Hearth J. H. , Webster Wm. D.
Published: July 2006

Three isolates representing two species of the Saprolegniaceae were investigated using standard manometric techniques to determine what effect culture temperature and nutrient availability had on respiration following treatment with artificial seawater. All three isolates manifested decreased respiration following treatment in most temperatures and salinities whether or not exogenous nutrient were present, but no treatment prevented test fungi from resuming vigorous growth and infesting sterile bait after the 18.5 h treatment period. In light of previous published reports the present result suggest that saprolegniaceous fungi may become dormant in estuarine salinity regimes, but probably remain viable for prolonged periods. Ecological implications of this phenomenon are discussed.
Weather variables as predictors of Sphagnum growth on a bog
Authors: Backéus Ingvar
Published: July 2006

When surrounded by growing Sphagnum the rhizomes of Scirpus cespitosus grow vertically upwards in pace with the Sphagnum. It was found that there is a considerable variation in rhizome growth between years and it is assumed that this variation is determined by variation in Sphagnum growth. The latter variation is assumed to be dependent on the weather. Simple and multiple regression analysis of rhizome growth on various weather variables gave the following results: (1) Moisture conditions are decisive for the growth. (2) The distribution in time of the moisture is more important than mean values from a certain period. (3) Although moisture in June and August of the current year was important, the moisture conditions of August of the previous year explained ca 60% of the variation. (4) A combination of the two variables Birot's wetness index in August of the previous year and the same index in current June gave r2= 0.80.
Experiments on predation and substratum choice by larvae of the muscid fly, Limnophora riparia
Authors: Wotton Roger S. , Merritt Richard W.
Published: July 2006

Larvae of the muscid fly Limnophora riparia live in lake outlets and prey on other invertebrates living there. In experiments, we demonstrated that larvae prefer moss as a substratum, though they will bury themselves in any suitable material to avoid light. The substratum is used to anchor Limnophora larvae as they attack their prey. When given a choice of prey they preferred chironomid and black fly larvae to oligochaetes and psyehodid larvae. Larvae of the black fly Simulium noelleri were used in laboratory experiments to test the interaction of predator and prey. Limnophora larvae attacked black fly larvae of all sizes, but preferred small larvae, the body contents of which were often removed completely. Increasing prey or predator density did not affect this latter preference, though an increase in predator density, or a decrease in prey density, did cause the predator to take prey of medium size as well as small prey. Limnophora larvae showed the same size preference when attacking dead (freshly‐killed) prey and they preferred to attack larvae rather than pupae when both were available. They did not attack black fly eggs.
Chironomid wing length, dispersal ability and habitat predictability
Authors: Delettre Y. R.
Published: July 2006

Variability of Chironomid wing length was studied for males and females of four terrestrial species inhabiting heathlands in Brittany (France). The larvae of two species live permanently in the soil. The populations of the two other species are strengthened or re‐established by immigrants each year. Significant differences in average wing length were found within and between species depending on sex, year, emergence period and trapping method. The two migrant species did not have the longest wings. In contrast, within species, migrant individuals had longer wings. Relations between wingth length, wing area and wing loading are discussed with regard to life‐history tactics (larval resistance to drought, flight ability, passive dispersal). The use of wing length to predict habitat characteristics was tested but the conclusions lead to promote a restrictive use of the wing length criterion.
Migratory behavior of related moose
Authors: Sweanor Patricia Y. , Sandegren Finn
Published: July 2006

In a Swedish moose population containing both migratory and non‐migratory individuals, 15 cows, 19 first generation and 2 second generation offspring were radiocollared and monitored during 1980–87 to determine their migratory behavior. The migratory behavior of offspring was evaluated when they were > 1 year old and independent of their dams. All 11 migratory cows produced migratory offspring (10♀, 3♂). Two migratory offspring produced female calves (grandchildren to the originally sampled cows) that were also migratory. Four of the originally sampled cows were non‐migratory and they produced six non‐migratory offspring (3♀, 3♂). Distances migrated by independent offspring were related to those of their dam. No moose changed its migrant or non‐migrant nature during the study. Results indicate that the proportion of migratory moose in the population is determined by the survival and reproductive success of migratory versus non‐migratory cows. Migratory and non‐migratory moose may be regarded as two distinct phenotypes in this population.
Diurnal variations in natural light conditions at summer time in arctic and subarctic areas in relation to light detection in insects
Authors: Nordtug Trond , Mela Thor Bernt
Published: July 2006

Measurements of daily variations in the intensity, spectral composition and polarization of the direct and the indirect sunlight are presented, and the physics of light propagation through the atmosphere is discussed. Observations of daily changes in these properties of the skylight are presented from two different locations in Norway. Probable adaptations of the light detection systems of insects living at high latitudes are predicted from the observations. The adaptation processes under consideration are (1) changes in the light absorption characteristics of the visual pigments, (2) changes in the visual sensitivity to light and (3) a switch in Zeitgeber from the daily intensity changes to changes in the spectral comptisition of the light in polar regions. It is shown that in particular the intensity ratio between the ultraviolet and the green part of the diffuse light is well suited as a Zeitgeber for insects living at high latitudes.
Establishment of four Salicaceae species on river bars in interior Alaska
Authors: Krasny Marianne E. , Vogt Kristiina A. , Zasada John C.
Published: July 2006

Patterns of seed and vegetative reproduction were investigated for three floodplain species, balsam poplar Populus balsamifera L., feltleaf willow Salix alaxensis (Anderss.) Cov. and sandbar willow Salix interior Rowlee, and one upland species, trembling aspen Populus tremuloides Michx., in interior Alaska. All four species have similar patterns of seed germination in response to moisture stress and high salt concentrations when tested under laboratory conditions. In field experiments, percent germination of all four species was also very similar, ranging from 0% on dry sandy sites, to greater than 60% on mesic silty sites. Germination on salt crusts ranged from 0–40% for all species, depending on the physical characteristics of the soil surface. Colonization of mesic silty sites was almost exclusively by seed, whereas colonization of dry sandy sites was limited to those species which were able to root sucker under floodplain conditions. Root suckering was also an important means of establishment on frequently inundated sites where establishment by seed was limited by flooding. Differences between the species in their distribution on the floodplain were related to differences in patterns of vegetative reproduction, but not seed germination.
Seasonal dynamics of a mayfly (Insecta: Ephemeroptera) community in a Laurentian stream
Authors: Lauzon Michel , Harper P. P.
Published: July 2006

The purpose of our study was to compare on a seasonal basis the emergence, the drift and the benthos on a short and uniform section (18.5 m)of a stream in the Laurentian Hills of Québec. Nineteen species occurred on this stretch, but only six were abundant: Leptophlebia cupida (Say), Habrophlebia vibrans Needham, Baetis pygmaeus (Hagen), Eurylophella verisimilis (McDunnough), Stenonema modestum (Banks), and Stenonema vicarium (Walker). Emergence was monitored for 5 years; densities differed from one trap to the next, as did species dominance, but total densities were similar. These data conform to Illies' rules of constancy and harmony. Nymphal densities were high (mean of 16000 m−2). The dominant species were univoltine, except H. vibrans (semivoltine), and B. pygmaeus (polyvoltine). Larger species contributed relatively more to the production of the reach despite their low densities than did the more abundant smaller species, especially those with long life cycles. Drift was low during most of the year, except during spring and species composition varied considerably. A comparison of the three data sets (emergence, drift and benthos) shows a general agreement for the less abundant species, but for three of the dominants, H. vibrans, L. cupida and E. verisimilis, movements of individuals to and from the reach at various times in the life cycle (adult flight, nymphal drift and migration) must be taken into account in order to correlate the data. None of the methods alone gives a satisfactory picture of the community structure, each is to some extent misleading and needs to be used in conjunction with the others; the conflicting results obtained from the data sets often reveal interesting life history traits which otherwise would not have been detected.
Habitat selection and grouping of beetles (Coleoptera)
Authors: Buse Alan
Published: July 2006

Beetles were collected by pitfall trapping for a two‐year period in seven adjacent habitats in an upland site in North Wales. Positive correlations were demonstrated between number of beetle species and number and diversity of plant species. Similar correlations were shown between beetle numbers and plant species. However, only 15% of the beetle species were herbivores requiring host plants. The degree of habitat selection by individual beetle species was demonstrated, ranging from habitat specialist, being found in one habitat, lo habitat generalist, being found in most habitats. Herbivores were significantly more habitat specialist than predators or scavengers. The grouping of beetles, demonstrated by ordination analysis, was similar to, but less precise than, the grouping of plant species. The beetle groups reflect habitat selection preferences by individual species rather than a functional relationship between beetle species. They provide an example of the centrifugal structure of habitat selection theory.
The evolution and maintenance of white spruce woodlands on the Mackenzie Delta, N.W.T., Canada
Authors: Pearce C. M. , McLennan D. , Cordes L. D.
Published: July 2006

White spruce forests on the most elevated surfaces of the Mackenzie Delta are dying out and are being replaced by open spruce/lichen‐heath or spruce/bog woodlands. Soil profiles indicate that these woodlands have not received flood‐deposited sediments for many years. The active layer is only 20 to 50 cm deep by mid‐summer, and the organic soils are colder and more acidic than soils under white spruce forests flooded during spring ice breakup in 1961, 1972, and 1982. Spruce regeneration is limited to those stands that are flooded periodically, have moderately‐closed canopies, and have a ground cover of herbs rather than feathermosses and lichens. It is proposed that a decrease in flood frequency is primarily responsible for the poor regeneration of white spruce on the most elevated delta surfaces. Spruce woodlands on the delta could succeed to tundra vegetation if present fluvial regimes continue.
Variation in tissue element concentration in mire plants over a range of sites
Authors: Ohlson Mikael
Published: July 2006

Elements in surface peat and ground water were estimated on seven mire sites in central and north Sweden. The variation in tissue clement concentration was studied in eleven plants occurring on the studied sites. The elements estimated were: N, P, K. Ca, Mg, Fe, Mn, Zn, Al, Cu, Mo, Na, S, B, and Si. The species studied were; Carex diandra, Carex limosa, Carex rostrata, Epilobium palustre, Menyanthes trifoliate, Pedicularis palustris, Rumex acetosa, Saxifraga hirculus, Scirpus hudsonianus, Stellaria crassifolia and Tofteldia pusilla. In surface peat over the range of sites, the variation in total concentrations of nitrogen and phosphorus was six and tenfold, respectively. The variation in total concentration of potassium was four‐fold. Extractable concentrations of these three elements showed an even greater variation between sites. Over the range of sites, the variation in tissue element concentration was larger in roots than in above‐ground parls. In above‐ground parts, floral parts varied less in tissue element concentration than did stems and leaves. The largest variation in tissue element concentration was found in Carex rostrata and Menyanthes trifoliata. The smallest variation was found in Saxifraga hirculus. Tissues of the rich fen species Saxifraga hirculus and Stellaria crassifolia had the lowest concentrations of heavy metals. The correlation between substrate element concentration and tissue concentration differed both between tissues and species. Concentrations of N, P and K in tissues of the Carex species were highly correlated with the concentrations of these elements in the substrate, while N, P and K concentrations in tissues of the herbaceous species, especially Saxifraga hirculus. correlated less well.
Changing female spacing behaviour and demography in an enclosed breeding population of Clethrionomys glareolus
Authors: Ylönen Hannu , Kojola Taina , Viitala Jussi
Published: July 2006

The social organization of Clethrionomys glareolus Schreber was studied by live trapping in an enclosure of 0.8 ha in Central Finland between the years 1982–1986. The enclosure consisted of three habitats: abandoned field, brushwood, and moist spruce heath forest.

The population density increased from 50 voles ha−1 in 1982 and 1983 to 150 ha−1 in 1984 and 1985. In the summer of 1986 the population crashed to almost zero. In the summer of 1984 after winter breeding the number of breeding females grew to 22 compared with 6–7 in previous years. In 1984 the mature females changed from territorial to group behaviour.

During the high population density in 1984 and 1985 breeding stopped already in late July – early August, thus preventing any fence effect.

The present study supports the hypothesis stating that microtine social organization is an opportunistic strategy reacting phenotypically to changing environmental – especially food – conditions.
Intraspecific variation in nitrogen status and photosynthetic capacity within mountain birch populations
Authors: Karlsson P. S. , Nordell K. O.
Published: July 2006

The relative variation in leaf nitrogen concentration and photosynthetic capacity among individuals and sites are compared for mountain birch populations (Betula pubsecens Ehrh. ssp tortuosa (Ledeb.) Nyman).

Leaf nitrogen concentration and photosynthetic capacity showed significant differences among individuals; 35 and 26% of the total sum of squares respectively, was attributable to differences among individuals. Two measures of leaf morphology also showed differences among individuals (35–58% of total variation). The variation attributable to site differences ranged from 13% (leaf shape, P = 0.11) to 36% (leaf N concentration and photosynthetic capacity, P≤0.01). Of the variation in photosynthetic capacity, 51% was related to leaf nitrogen concentration. Possible causes for and consequences of the differences found are discussed.
Life cycle and spatial distribution of the amphipod Pallasea quadrispinosa in a lake in northern Sweden
Authors: Hill Catherine
Published: July 2006

The population structure and spatial distribution of the “glacial relict”Pallasea quadrispinosa were studied in Lake Stora “Ofsjön”. Samples were taken at three depths throughout an eleven month period. The amphipods had an annual‐biennial life cycle. The reproductive period started in October, and hatchlings were released from November until July. Four cohorts were present in November. Some one‐year‐old females appeared to reproduce more than once. Ontogenetic niche segregation occurred from June to September, when juveniles were found in shallow water and adults were found in deep water where temperatures were below 10°C. The diet included phytoplankton, zooplankton and chironomid larvae. The amphipods were infested by several parasites, including larvae of Cystidicola sp., a swimbladder nematode that infects fish.
Submersed macrophytes and grazing crayfish: an experimental study of herbivory in a California freshwater marsh
Authors: Feminella Jack W. , Resh Vincent H.
Published: July 2006

Grazing by the crayfish Procambarus clarkii (Girard) on the abundance of submersed sago pondweed, Potamogeton pectinatus (L.), was quantified during 1984 through 1986 at Coyote Hills Marsh (Alameda County, California, USA). Annual marsh surveys indicated that P. pectinatus abundance declined (from 70% to 0% of the marsh surface), whereas P. clarkii abundance increased (from 1.6 to almost 3.0 crayfish trap−1 week−1). Crayfish in a 1425 m2 trapping grid were non‐aggregated when pondweed was abundant but became aggregated in the remaining pondweed beds as pondweed abundance decreased. In situ exclusion and enclosure experiments using crayfish densities of 0 to 3 individuals m−2 were used to determine if crayfish reduced pondweed. Exclusion of crayfish from areas without pondweed, beginning in midsummer 1984, resulted in plant regrowth; addition of crayfish to these enclosed plots reduced pondweed. Exclusion of crayfish for the entire growing season in 1985 resulted in pondweed persistence in exclusion plots until August: in contrast, pondweed within adjacent, open control plots was eliminated by mid‐June. Enclosure experiments showed a strong positive relationship between crayfish density and pondweed clearance. This study demonstrates that grazing crayfish can reduce and, in some cases, eliminate macrophytes from freshwater marshes.
The marine invertebrate fauna of a British coastal salt marsh
Authors: Frid Chris , James Robert
Published: July 2006

There are few accounts in the literature of the marine fauna of European salt marshes. The marine invertebrate populations of a coastal salt marsh in eastern England were studied for two years. A total of 32 marine species were recorded. The community was composed of a subset of species from adjacent intertidal sand and mud flats, along with a brackish water component. This gave the marsh a characteristic fauna, which was dominated by infaunal and surface‐living deposit feeders. The community showed a seasonal minimum in winter, and the infauna showed an additional summer decrease. This is attributed to increased interstitial salinities. Principal component analysis revealed the importance of the tidal gradient and the structure of the habitat in determining the community. The abundance of both epibenthic and infaunal predators were negatively correlated with the abundance of some prey. Also a small number of other pairwise negative interactions were revealed, but overall there was no strong evidence of interspecific competition exerting much influence on the community. The role of habitat heterogeneity and variation in the lateral movement of adult benthos and larval recruitment as promoters of diversity are discussed.
Food habits of northern (Eptesicus nilssoni) and brown long‐eared (Plecotus auritus) bats in Sweden
Authors: Rydell Jens
Published: July 2006

Food habits of sympatric northern and brown long‐eared bats were examined by analysis of droppings collected in six maternity roosts of each species. Relatively large, nocturnal flying insects such as moths (Lepidoptera), June‐beetles (Coleoptera: Scarabaeidae), crane‐flies (Diptera: Tipulidae) and caddis‐flies (Trichoptera), were eaten by both bat species, representing 47% (by volume) of the northern and 57% of the long‐eared bat's diet. Small dipterans were important food items for the northern bat (47% of the diet) but not for the long‐eared bat, which instead consumed large amounts of diurnal or predominantly non‐flying taxa such as blow‐flies (Diptera: Calliphoridae), earwigs (Dermaptera), spiders (Araneae) and harvestmen (Opiliones) (40% of the diet). The difference in food selection by the two species is probably due to the different foraging strategies used.
Flowering and seasonal changes in flower sex ratio and frequency of flower visitors in a population of Saxifraga hirculus
Authors: Olesen J. M. , Warncke E.
Published: July 2006

The open, dish‐shaped flowers ofSaxifraga hirculusreflected ultraviolet and yellow light, contained very small amounts of nectar, and contained an average of about 75300 pollen grains per flower. Almost 11% of the pollen was inviable. Stigmatic pollen loads and seed set decreased during the course of the season. The plant appeared to be fully between‐ramet compatible and partially within‐ramet compatible. Seed set for the population was 30.3%. The protandrous flower opened during the day and had male and female phases of nine and three days, respectively. The protandrous system reduced the number of pollination days by a third.

At least 26 species of insects, 16 of which were syrphids, visited the flowers. Based on the number of flower visits, four species were the dominant visitors ofS. hirculus: Eurimyia lineataandNeoascia tenur(Diptera: Syrphidae);Asindulum nigrum(Diptera: Mycetophilidae), andZygaena trlfolii(Lepidoptera: Zygaenidae).Eurimyia lineatawas the most frequent visitor (51% of all visits). As the season advanced, the visits byE. lineatadecreased, whereas the visits byA. nigrumincreased.Z. trifollidisappeared completely towards the end of the season. Only two thirds of the pollination days were “good” foraging days for these visitor species. The four major visitor species spent an average of 11.7, 27.4, 30.7 and 22.6 s per flower, respectively. Estimates suggest that about 6.5 visits (which is equal to 2.6 min of flower‐visiting) and 2100 grains of pollen were required to produce one seed.
Ecotypic differentiation in relation to soil nitrogen in northern Scandinavian Cochlearia officinalis
Authors: Eriksen Aud B. , Nordal Inger
Published: July 2006

Ecotypic differentiation of Cochlearia officinalis L. was studied in four populations, roughly described as “beach”, “bird cliff”, “spring” and “estuary”, which occupy different habitats in the northern part of Norway. The plants were cultivated under controlled conditions on soil to which nitrogen was applied at various amounts (0, 0.2 and 1.0 g N pot−1). The above ground part of the “bird cliff” population showed the highest dry weight and nitrogen uptake at the highest nitrogen concentration. No effect of nitrogen treatment and the lowest dry weight were found in the “estuary” population. The differences in population response to added nitrogen were correlated to the nitrogen content of the soil in their natural habitat. Morphological features of the populations were also significantly different. The “estuary”, “beach” and “bird cliff” populations showed differences in all characteristics measured – ratio of length/width of the leaves, shape of the leaf base, and length of the petiole. “Beach” and “spring” differed significantly in petiole length, while “bird cliff” and “spring” differed significantly in both leaf ratio and shape of the leaf base. These morphological features were not significantly altered by the application of nitrogen to the soil. This study shows that the four populations of Cochlearia officinalis are discrete biotypes characteristic of distinct habitats, and therefore, should be considered ecotypes.
Activity patterns in moose and roe deer in a north boreal forest
Authors: Cederlund Göran
Published: July 2006

The activity patterns of a coarse browser, the moose. Alces alces, and a selective browser, the roe deer, Capreolus capreolus. in a north boreal forest, central Sweden, were compared with respect to time allocated for foraging and processing (ruminating) in different seasons. Data were quantified by measuring 24 h activity patterns which included both the duration and frequency of active and inactive periods. Activity patterns were measured from 9 female moose and 9 roe deer that were radiomarked during April 1974–May 1978 (roe deer) and February 1982–December 1984 (moose). In total, data were available from 4345 h for roe deer and 14745 h for moose. Roe deer differed from moose in having active bouts more evenly distributed over the day. Generally, both species were most active during sunrise and sunset. Total daily active time varied with season, reaching the highest value in late May – early June among roe deer (56.7% of the day) and a month later among moose (51.9%). Both species were least active in February (30–40%). Average length of active bouts did not differ significantly between the species but changed with season (roe deer 48.6–99.2 min, moose 61.6–88.7 min). Average length of inactive bouts varied significantly with season, with moose having consistently longer bouts (89.3–156.3 min) than roe deer (55.8–107.0 min). The number of activity bouts per day were also higher among roe deer. During midsummer, they changed activity nearly twice as many times as moose (26 times d−1 vs 16 times d−1).
Ecotypic differentiation and phenotypic plasticity in Saxifraga hirculus populations in central and northern Sweden
Authors: Ohlson Mikael
Published: July 2006

The perennial herbaceous mire plant Saxifraga hirculus was grown for two years in a greenhouse under two nutrient regimes. Based on metric characters, primarily those associated with the potential for lateral spread, I found ecotypic differentiation both between plants originating from three adjoining but different habitats on one mire and between plants from three widely separated habitats. The fact that seeds from the different habitats germinated in different proportions after a first and second period of stratification. suggests that there is a habitat‐specific, innate seeddormancy. Also the degree of phenotypic plasticity differed among the plants, viz. plants from the least fertile habitats exhibited the largest plasticity.
Food limitation and social regulation in a red fox population
Authors: Lindström Erik
Published: July 2006

This study evaluates a conceptual model on functional and numerical response to short‐term fluctuating vole populations of a red fox (Vulpes vulpes L.) population in south‐central Sweden. The model assumes that this particular population is located in between socially regulated stable populations to the south and direct food‐limited populations to the north. The model predicts: (1) food availability as the primary factor for limiting fox numbers, causing reduced rates of reproduction and survival during years of low vole densities, and (2) density‐dependent regulation during years of increasing and high vole densities resulting in increased group sizes within territories of fixed dimensions. During 1973–1980 data were obtained from 1216 fox scats, 874 fox carcasses, 63 tagged foxes, nine radio‐collared females and from yearly den counts in an area of 130 km2, Eight predictions of the model were tested. These concerned the occurrence of small rodents in fox diet, fluctuations in the density of foxes, variations in the number of fox litters, the effect on reproduction of providing supplemental food during January–May, the proportion of vixens bearing a litter different years, dispersal of young males relative to that of young females throughout the vole cycle, and variations in mortality rates of young males and females. All tests were in favour of the conceptual model, and contradictory to alternative models.