bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms underlying the stable co‐existence of two genetically distinct populations of Chironomus plumosus (Diptera: Chironomidae) in Lake Tystrup‐Bavelse, Denmark
Authors: Pedersen Bo Vest
Published: July 2006

During April–December in 1980 and 1981 larvae and pupae of Chironomus plumosus from Lake Tystrup‐Bavelse, Denmark, were sampled with short intervals On the basis of morphometric data of the larvae, counts of larvae and pupae, and measurements of the oxygen conditions in the lake it was concluded that adults emerge at different times depending on e.g. depth‐conditions. Adults originating from the deep Lake Tystrup appear over two periods yearly (April‐June) and (September‐October). In the intervening period which is characterized by stagnation and shortage of oxygen there is no emergence of adults. Adults from the shallow Lake Bavelse appear mainly during June‐August. This shallow lake‐part has no, or at the most very short, periods with stagnation and lack of oxygen. The observed temporal difference in the emergence of adults in the two lake‐parts is proposed to be the main reason for the maintenance of two different Mendelian populations of Chironomus plumosus in Lake Tystrup‐Bavelse.
Field test of resource regulation by the bud‐galling sawfly, Euura mucronata, on Salix cinerea
Authors: Roininen Heikki , Price Peter W. , Tahvanainen Jorma
Published: July 2006

The attack by the bud‐galling sawfly, Euura mucronata, on its willow host was simulated by removing every other living bud from previous year's shoots in a natural stand of Salix cinerea. The impact of simulated attack on the growth of the willow and the subsequent attack by E. mucronata was estimated after one growing season. Experimental bud‐killing resulted in a growth reaction in S. cinerea characterized by significant increase in the length of new shoots produced by the remaining buds Also the number of buds and E. mucronata galls per shoot were significantly higher on bud‐removal branches as compared with control branches. The overall survival of E. mucronata larvae was better on long shoots than on short shoots. The result shows that sawfly attack increases the amount of high quality resources for the subsequent generation of the same sawfly as predicted by “resource regulation hypothesis”. We conclude that these highly specialized insect herbivores have adapted to utilize and to maintain the willow's juvenile traits. Rapid regrowth of willows after damage may have originally arisen as an adaptation in response to other, less specific pressures such as mammal browsing or snow and ice damage.
Intestinal helminth communities in long‐billed curlews: the importance of congeneric host‐specialists
Authors: Goater Cameron P. , Bush Albert O.
Published: July 2006

This paper examines patterns of structure in the helminth communities of long‐billed curlews collected on their breeding grounds in Alberta, Canada. The communities are neither large nor species rich but they do show evidence of having structure which is mediated by interactive mechanisms between some helminths. In particular, we focus on the role played by congeneric host‐specialists in contributing to community patterns and suggest that even in low diversity systems, some species may set the stage around which other species must assort.
Seasonal occurrence of Ixodes ricinus (Acari) in vegetation and on small mammals in southern Sweden
Authors: Nilsson Anders
Published: July 2006

Seasonal activity of Ixodes ricinus L. was studied with two different sampling methods at three localities in southern Sweden: blanket dragging in vegetation and collection from small mammal hosts (mainly larvae in the latter case). The blanket method yielded all development stages. The seasonal pattern ‐ bimodal, with one peak in spring and another in autumn – was clearer for larvae collected on small mammals. The nymphs had a similar seasonal activity pattern as the larvae, but nymphal activity usually started somewhat earlier in spring. Adults had three activity peaks – spring, summer and autumn – in the vegetation.

The autumn peak seems similar to that found in other European countries, but the timing of the spring peak differs. Weather, influencing development rates, seems to be the main agent behind these differences, since ambient weather (above a certain threshold) cannot explain the patterns. Abundance and activity of hosts (different hosts for different developmental stages) probably also plays a certain role.
Bird communities of the Iberian shrubsteppes
Authors: Tellería J. L. , Suárez F. , Santos T.
Published: July 2006

Bird communities of high, cold shrubsteppes (páramos) and low, warm shrubsteppes (semideserts) of the Iberian Peninsula were studied using the line‐transect method. The seven censused areas are distributed from north to south approximately forming a climatic gradient along which temperature increases and precipitation decreases. Alauda arvensis and Oenanthe oenanthe are typical of páramos and O. hispanica and the genus Galerida of semideserts, while Calandrella cinerea is the most widely distributed passerine. Páramos tend to have high spring densities whereas semideserts have high densities and greater diversity during winter. Changes of density between spring and winter are less pronounced in semideserts, showing a relation with the temperature decrease from north to south. These tendencies agree with those found in other habitats (scrublands and forests) along a north‐south transect throughout the Iberia Peninsula, indicating that distribution and abundance of the winter avifauna respond positively to increase of temperature.
Thermal preference in the pool frog Rana lessonae: impact on the reproductive behaviour of a northern fringe population
Authors: Sjögren Per , Elmberg Johan , Berglind Sven‐Åke
Published: July 2006

A documented warmth preference in the pool frog Rana lessonae is also expressed in the reproductive behaviour of a northern fringe population (60°N). During the breeding period of 31 days, individually marked frogs were observed during chorus. Male choruses were formed in the warmest parts of the pond, but moved between three areas. At night, these areas maintained the highest water temperatures in the pond, especially at low temperatures prevailing in the beginning of the breeding period. Oviposition occurred in the current chorus areas, and 86% took place during the first two weeks of the breeding period. That the choruses and oviposition changed locations within the favourable breeding areas can be explained by a pronounced thermal preference in the frogs, and winds moving the warm surface water in different directions.

The water temperature required to initiate oviposition was 16°C, which is similar to those reported from related more southern populations. The thermal preference expressed in the breeding behaviour of both sexes and the tendency for early oviposition may be behavioural responses to environmental constraints on reproduction in the short season at 6O°N.
Development of empirical feeding models for a benthic predator
Authors: Linton L. R. , Davies Ronald W.
Published: July 2006

Feeding on Chironomus riparius, Glyptotendipes paripes (Chironomidae). and Daphnia magna by the predatory freshwater leech, Nephelopsis obscura, was investigated in the laboratory and predictive models developed to estimate prey capture rate in the field. Experimental arena (container) size significantly affected predation rates when arena diameter was less than twice the total body length of the predator. Both chironomid and Daphnia magna capture rates were influenced by predator size, temperature and prey density.
Daylight responses to overhead cover in stream channels for fry of four salmonid species
Authors: Heggenes Jan , Traaen Tor
Published: July 2006

Brown trout (Salmo trutta), Atlantic salmon (Salmo salar), brook trout (Salvelinus fontinalis) and lake trout (Salvelinus namaycush) fry entering the free‐feeding stage, were tested for overhead cover preferences in stream channels at different temperatures and water velocities. Atlantic salmon showed strong preferences for overhead cover, brown trout moderate preferences, whereas lake trout had preferences only at high temperatures, i.e. 12.4–19.2°C. Brook trout showed no cover preferences. Temperature influenced cover preferences of Atlantic salmon and brown trout considerably. The fry tended to seek more cover at low temperatures, i.e. 6.0–8.3°C
Xestia communities (Lepidoptera, Noctuidae) in eastern Finnish Forest Lapland as indicated by light trap sampling
Authors: Pulliainen Erkki , Itämies Juhani
Published: July 2006

Xestia moths (Lepidoptera, Noctuidae, subgenera Anomogyna and Pachnobia) were collected with eleven light traps installed in various virgin habitats in the Värriötunturi fell area, E Finnish Forest Lapland (67° 44′N, 29° 37′E). Seven Xestia species were caught during the years 1978–84. The most abundant species, X. tecta and X. alpicola inhabited the widest range of habitats, from spruce‐covered ravines up to the treeless summit. The other species were almost entirely caught in the sprucecovered ravine. The largest catches were obtained in odd years, although some moths were also caught in the even years. There was a striking male dominance. The trap catches were separated into three groups, corresponding to the original classification of the trap habitats. Of the habitats, the open pine forest was nearest to the summit and the spruce forest farthest away. X. alpicola and X. tecta appear to be ecologically related species, while X. gelida and X. laetabilis are located at the other end of this ecological scale.
Variation in growth rate in shoot populations of the clonal dwarf shrub Linnaea borealis
Authors: Eriksson Ove
Published: July 2006

This study was based on two years of field observations of aLinnaea borealispopulation in a coniferous forest in Sweden. Detailed information on performance and survivorship of shoots were gathered from consecutively made drawings of 90 individually marked shoot systems ofLinnaeadistributed among 15 plots in the forest. Branching of the shoot systems was correlated to growth of the main shoot. Increasing light flux negatively affected growth ofLinnaea. A tendency for a competitive effect onLinnaeaofVacciniumspp. was also found. In contrast, the surrounding mosses, and intraspecific density ofLinnaeahad no significant effect on the shoot systems. The growth rate of the shoot population was analysed by matrix models. Population growth rate was most dependent on survivorship and growth of main shoots inLinnaea, while the survivorship of lateral shoots was of less importance. In spite of an average decrease in the population size as revealed by the matrix model simulation, the incorporation of the observed spatial variation in shoot growth increment, branching and shoot survivorship, yielded varying population growth rates. Parts of the population increased in size. The importance of choice of spatial scale in population analyses of forest understory plants is emphasized.
Male body size and mating success in swarms of the mayfly Epeorus longimanus
Authors: Flecker Alexander S. , Allan J. David , McClintock Nancy L.
Published: July 2006

Epeorus longimanus is a widely distributed mayfly in the western United States that forms relatively large mating swarms. The operational sex ratio of swarms is highly male biased and males are potentially polygynous, suggesting that male‐male competition over mates may be intense. We investigated whether body size influenced male mating success in E. longimanus, as evidence of sexual selection. Males collected as mating pairs had significantly greater body lengths compared with males collected randomly from the swarm on each of six sampling dates examined, and had significantly greater head widths than males from random collections on two dates. There was no indication that large males occupied preferred positions within the swarm, and we suspect that the large male advantage may be due to greater success in pursuing females. We found no evidence of size‐assortative mating in E. longimanus indicating that males attempt to male with every female encountered, consistent with the brief copulatory period in mayflies and overall low parental investment of males.
Do intrinsic or extrinsic factors limit reproduction in cyclic populations of Clethrionomys glareolus and C. rufocanus?
Authors: Löfgren Ola
Published: July 2006

Changes in reproduction and functional age structure of females in cyclic populations of Clethrionomys glareolus and C. rufocanus were studied by live‐trapping individually marked voles during 1980 to 1984 in northern Sweden. A complete population cycle was observed in both species, with a synchronous ‘summer‐decline’ in 1982. In both species, the length of the breeding season became successively shorter towards the peak, and it was extremely short at the decline. When the populations expanding, the density of breeding females increased in a sigmoid way, and thereafter it remained fairly constant throughout the summer. At the decline, the density of breeding females decreased successively from spring to autumn. Year‐born females matured and bred in all years except at the decline. Intrinsic factors, such as spacing behaviour of breeding females, are thought to limit the density of breeders in general, but only when the populations are expanding. Other factors such as deteriorating food conditions are more likely to operate at the decline.
Population size and survivorship of the common garter snake, Thamnophis sirtalis, near the northern limit of its distribution
Authors: Larsen Karl W. , Gregory Patrick T.
Published: July 2006

The common garter snake, Thamnophis sirtalis. has frequently been studied, but never in the far north where climatic influences on distribution and abundance might be expected to be severe. We examined the structure and dynamics of a communal den population at the northern limit of the species' range. Snakes were sampled at the hibernaculum from spring 1983 to spring 1987. Males were more easily caught than females, and few inferences could be made about the latter. Population estimates, though possessing wide standard errors, seemed to indicate that the denning population of 500–600 snakes, mostly adults, was stable. Annual survivorship of large males (≥400 mm SVL) was high (0.68–0.98) and was not correlated with body size. Thirty‐four snakes that were first marked in 1983 were recaptured in the spring of 1987, indicating that they had survived at least six years, assuming they were a minimum of two years old when first marked. Recruitment to the denning population consisted of an influx of ‘new’ individuals (450–550 mm SVL) each autumn. It is not known where these snakes spend the first few years of their existence. The relative Stability of numbers and high overwinter survivorship observed over the course of this study contrast sharply with the only previous study of T. sirtalis in cold climates.
Changes in stream benthic organic matter following watershed disturbance
Authors: Golladay S. W. , Webster J. R. , Benfield E. F.
Published: July 2006

Benthic organic matter was collected quarterly from streams draining a 9‐yr‐old clearcut, an 18‐yr‐old “old‐field”, a 25‐yr‐old successional forest, and two reference watersheds at Coweeta Hydrologic Laboratory in the Appalachian Mountains of North Carolina. USA. Samples were separated into large benthic organic matter (LBOM >1 mm) and fine benthic organic matter (FBOM <1 mm). An additional survey of large (>5 em diam.) and small (1–5 cm diam.) wood was conducted. Standing stocks of LBOM ranged from 124 to 235 g AFDM m−2 (ash tree dry mass) and were significantly higher in streams draining reference watersheds and the successional forest than in either the recent clearcut or old‐field. Reference sites exhibited LBOM peaks in late autumn and spring. No seasonal patterns were observed in disturbed streams. Standing stocks of FBOM averaged 113 to 387 g AFDM m−2, and the stream draining the successional forest had significantly higher FBOM levels than the other sites. In reference streams, FBOM abundance peaked in spring. In disturbed streams, FBOM standing stocks were highest in summer or late autumn. Standing stocks of large wood ranged from 0 to 3956 g AFDM m−2 and were significantly higher in the reference streams than in streams draining the old‐field or successional forest. Small wood averaged 11 to 342 g AFDM m−2 and was significantly lower in the stream draining the old‐field than at the other sites. Comparisons of organic matter inputs with standing stocks indicated that disturbed streams at Coweeta receive less material and process it faster than reference streams. Disturbed streams also appear to be less retentive than reference streams and exhibit a gradual decline in FBOM during the winter when large, long‐duration storms combined with low particle generation rates deplete accumulated FBOM.
Temporal and spatial patterns in the production of pollen, ovules and seeds in pseudogamous blackberries (Rubus subgenus Rubus)
Authors: Nybom Hilde
Published: July 2006

Significant variation in the number of stamens and ovules per flower, the stamen/ovule ratio, and the number of seeds per berry was found among seven blackberry species, each represented by one clone, and to a much lesser extent among inflorescences within species. Inflorescence size and architecture were found to have no major influence on these reproductive parameters.

The position of a flower within the inflorescence strongly influences its onset of anthesis, which in turn is closely correlated with these reproductive parameters. Ovule number decreases with time, although in some species it increases again at the end of the flowering season. Number of seeds decreases more or less linearly with time, although there is an unexpectedly high number of the earliest berries of the triploid species, which is probably the result of interspecific pollination. Pollen production estimated in one species decreases with time, per theca, per flower and per ovule, whereas the percentage of good pollen grains remains unaltered.
The life history of Ranunculus glacialis, an arctic‐alpine perennial herb, in Finnish Lapland
Authors: Järvinen Antero
Published: July 2006

Dynamics and performance of established individuals of Ranunculus glacialis at the time of peak flowering were monitored in a mountain area in Finnish Lapland for five years (1982–1986). The plants reproduced only sexually, and their spatial distribution in 40 1‐m2 quadrats was clumped. During the study period the mean density rose from 8.5 to 10.3 individuals m−2. The mean annual growth rate and birth rate of the population was 4% and 8.5%, respectively. The mean annual death rate of established individuals was 3.7%. The estimated mean life expectancy of an established individual was 27 yr. Death rate per quadrat was positively related to R. glacialis density, but birth rate per quadrat was negatively related to the percentage cover of stones per quadrat. High R. glacialis density per quadrat had negative effects, but high nitrogen availability had positive effects on the number of leaves per individual. An important factor reducing flowering was small rodent herbivory. In the same genets, the correlation between the number of leaves per individual in year t and the number of flowers per individual in year t+4 was significant. The below‐ground biomass of R. glacialis comprised about 70% of the total biomass, and there was a close correlation between the above‐ and the below‐ground biomass of an individual. The individuals flowered abundantly each year and produced a great number of small‐sized achenes.
Ecology of the invading moss species Orthodontium lineare in Sweden: Spatial distribution and population structure
Authors: Hedenäs Lars , Herben Tomáš , Rydin Håkan , Söderström Lars
Published: July 2006

The moss species Orthodontium lineare, originally from the southern hemisphere, has been spreading in Europe during this century. We have monitored the distribution patterns of the species in Sweden.

The age distribution differed between localities due to variation in the proportion of colonies in old age classes. We attributed this to differences in colony mortality. Although O. lineare had a high spore output in most localities, the colonies showed a clumped pattern, indicating strong neighbourhood effects in the colonization of new spots within the locality.

The regional distribution was uneven and markedly southwestern. The distribution was related to regional and local availability of suitable habitats (decaying wood in not‐too‐dense forests), and to a lesser extent to climatic variables.

Spore transport and establishment are suggested to be the limiting factors for colonization of suitable habitats of O. lineare.
Egg development, nymphal growth and life cycle strategies in Plecoptera
Authors: Lillehamnur Albert , Brittain John E. , Saltveit Svein Jakob , Nielsen Per S.
Published: July 2006

Interspecific and intraspecific differences in egg development, nymphal growth and the life cycles of Fennoscandian stoneflies are examined in relation to zoogeographical aspects and evolutionary trends. Data on other European and North American species are also considered.

Egg development shows considerable diversity, the main categories being ovovivipary, egg development with diapause and non‐diapause development. Egg development in species in the non‐diapause category can be classified as eurythermal, cold stenothermal or warm stenothermal. Temperature has a marked effect on nymphal growth of some species but not others. The distribution of several species can be explained by their temperature relationships, either in the egg or nymphal stage. Several species modify their life cycle to fit local climatic conditions. In some species, such as Leuctra hippopus, environmental selection has been so strong that they have probably recently evolved into subspecies and/or species in northern Europe.

Morphological and ecological variations in the Plecoptera have facilitated their colonization of the variety of freshwater biotopes that occur in Fennoscandia.
Bioenergetics of cross‐ice movements by Microtus pennsylvanicus, Peromyscus leucopus and Blarina brevicauda
Authors: Lomolino Mark V.
Published: July 2006

Laboratory and field experiments were conducted to investigate bioenergetics of winter dispersal and to compare winter (cross‐ice) dispersal abilities of three small mammals: Microtus pennsylvanicus, Peromyscus leucopus and Blarina brevicauda. Total metabolic rates increased with running activity and decreased as ambient temperatures increased for all species. Thermal conductance was significantly higher for running than for resting Microtus and Peromyscus, but decreased significantly with activity for Blarina.

Winter dispersal abilities, calculated from treadmill experiments, increased with ambient temperature and with body size of the species. The superior dispersal ability of Microtus in comparison with Peromyscus results from the former's ability to utilize more energy reserves during running. The comparatively low winter dispersal ability of Blarina, which was less than a third of the two rodent species, resulted from its high weight specific cost of transport at winter temperatures and its relatively low energy stores and/or energy utilization during running.
Nutrient and water flux in a small arctic watershed: an overview
Authors: Oechel Walter C.
Published: July 2006

The “Response, Resistance, Resilience to, and Recovery from Disturbance in Arctic Ecosystems” (R4D) program initially concentrated on impacts of altered water and nutrient inputs on tussock tundra vegetation. The intensive site is at Imnavait Creek (68°C 37′ N, 149° 17′ E), near Toolik Lake. Alaska in the foothills of the Brooks Range, approximately 200 km south of Prudhoe Bay. Tussock tundra was selected for initial study because it has an extensive distribution in the Alaskan Arctic (80% of the arctic region), the majority of the pipeline corridor north of the Brooks Range passes through tussock tundra, and disturbances of arctic tundra are expected to occur in the future. Also important is that 18% of the circumpolar arctic primary productivity and 47% of the circumpolar arctic stored carbon are in tussock tundra.

Water and nutrient additions were performed because they frequently accompany disturbance and development in the Arctic. Emphasis was placed on determining responses of physical, physiological, and ecosystem processes to environmental change in such a way that extrapolations to other areas would be facilitated. The hills near Imnavait Creek are covered by glacial till of the Sagavanirktok River glaciation. with a deep organic layer on the less exposed hill slopes and valleys. The vegetation is dominated by Eriophorum vaginatum L., Betula nana L., Vaccirtium uliginosum L, Vaccinium viiis‐idaea L., Ledum palustre L., Salix pulcbra L., and Sphagnum spp. Winds were rarely calm but seldom exceed 17 m s−1, generally from the east‐southeast to the south‐southwest (66%). Precipitation in 1986 was 344 mm, about half of which was snowfall. Mean temperature in 1986 was −8.1°C, with an absolute minimum of −43°C. Mean July temperature was between 9.8 and 13.7°C. Nutrients are more mobile than previously thought, moving an estimated 10 m downslope in the first growing season. It underscores the importance of the winter environment to biological and hydrological processes. Greater water flow results in increased plant growth rates, leaf area, and biomass.

Effects of changes in nutrient and water supply on photosynthesis were minimal. Where increases in productivity took place, they occurred more likely as a result of changes in allocation patterns, including an initial redirection of carbohydrate stores to new leaf development, than from increases in photosynthetic rates.

The work reported here indicates that the downslope transmission of nutrient and water flow effects caused by altered drainage and nutrient supply may result in a larger area of impact than previously thought.
Terrain, vegetation and landscape evolution of the R4D research site, Brooks Range Foothills, Alaska
Authors: Walker D. A. , Binnian E. , Evans B. M. , Lederer N. D. , Nordstrand E. , Webber P. J.
Published: July 2006

Maps of the vegetation and terrain of a 22 km2 area centered on the Department of Energy (DOE) R4D (Response, Resistance. Resilience to and Recovery from Disturbance in Arctic Ecosystems) study site in the Southern Foothills Physiographic Province of Alaska were made using integrated geobotanical mapping procedures and a geographic‐information system. Typical landforms and surface forms include hillslope water tracks, Sagavanirktok‐age till deposits, nonsorted stone stripes, and colluvial‐basin deposits. Thirty‐two plant communities are described; the dominant vegetation (51% of the mapped area) is moist tussock‐sedge, dwarf‐shrub tundra dominated by Eriophorum vaginatum or Carex bigelowii. Much of the spatial variation in the mapped geobotanical characters reflects different‐aged glaciated surfaces. Shannon‐Wiener indices indicate that the more mature landscapes, represented by retransported hillslope deposits and basin colluvium, are less heterogeneous than newer landscapes such as surficial till deposits and floodplains. A typical toposequence on a mid‐Pleistocene‐age surface is discussed with respect to evolution of the landscape. Thick Sphagnum moss layers occur on lower hillslopes, and the patterns of moss‐layer development, heat flux, active layer thickness, and ground‐ice are seen as keys to developing thermokarst‐susceptibility maps.
Hydrology of Imnavait Creek, an arctic watershed
Authors: Kane D. L. , Hinzman L. D. , Benson C. S. , Everett K. R.
Published: July 2006

An ecological study is presently being carried out at the headwaters of Imnavait Creek to develop a better understanding of the dynamics of an arctic ecosystem. While all ecosystems are driven by both energy and muss inputs, in an arctic setting this is much more evident. Therefore it is critical that we have a detailed understanding of the hydrology of the basin. In the United States, no hydrological studies of an arctic watershed have been made where measurements are continued throughout the winter season. While most biological processes are dormant throughout the winter, this is not true of physical processes such as active layer freezing and thawing and snow accumulation and redistribution by wind. This paper summarizes what we have learned hydrologically from three years of study al an arctic watershed, Imnavait Creek.
Modelling bark beetle flight: a review
Authors: Helland Inge S. , Anderbrant Olle , Hoff Jann Morten
Published: July 2006

In studying the attraction of spruce bark beetles Ips typographus to a pheromone trap, we have proposed a simple diffusion model with drift as a description of the flight of the bark beetles. The model predictions were compared with the results of a release‐recapture experiment, and here we recapitulate the main results from the fitting of models to the data. Several modifications of the basic model were necessary in order to describe the data adequately.
Flight initiation and survival in the bark beetle Ips typographus (Coleoptera: Scolytidae) during the spring dispersal
Authors: Byers John A. , Löfqvist Jan
Published: July 2006

Temperatures in the forest litter of Norway spruce Picea abies were recorded throughout the day to obtain environmental parameters that could be used to design realistic flight‐activity experiments in the laboratory. Flight activity and survival were monitored electronically in plastic chambers where the conditions were controlled by an environmental chamber. Flight attempts of the bark beetle Ips typographus were initially lower in chambers with forest duff but were prolonged compared with those of beetles in chambers with a metal screen substrate. Small bark slabs and spruce twigs in the duff were utilized as food and extended the period of flight and survival. A thermal gradient in duff from 25° at the surface down to 13.8°C at a depth of 4 cm also slightly increased the survival of beetles compared with a constant 25°. A daily ambient temperature cycle as well as the duff thermal gradient increased the survival from about 3 d to more than 8 d. The latter length in the laboratory agreed with survival rates of caged beetles in a clearcut forest area, while beetles caged in the forest survival for more than 14 d. Temperatures were monitored at the duff surface of the caged beetles and compared with the catches of beetles that were attracted to a pheromone trap and collected with an electronic fraction collector. Information on flight and survival during the dispersal period is necessary to the design of ecologically sound management programs for control of bark beetles.
Behavioral mechanisms involved in reducing competition in bark beetles
Authors: Byers John A.
Published: July 2006

Bark beetles feed and reproduce in the phloem/cambium tissue of trees where severe competition between individuals of the same and different species significantly reduces their reproductive success. In this coevolutionary setting, individuals that can avoid competition whenever possible by means of genetically controlled behavioral mechanisms are naturally selected. Avoidance of intraspecific and interspecific competition is accomplished in part even before landing by olfactory perception of specific pheromones and allomones. These olfactory systems may function at least as well after landing. In several species the uniform distribution of attacks on host trees indicates that individuals avoid competition by only attacking if they are at least a minimum distance from other established attacks. Once beetles are under the bark their tunneling patterns indicate that a behavioral mechanism exists to avoid intersecting nearby galleries of competing individuals. Finally, beetles may choose to re‐emerge if the expected chances of successful reproduction by continuing their stay become less than the probabilities of finding another host and successfully reproducing.
Reemergence and second brood in the bark beetle Ips typographus
Authors: Anderbrant Olle
Published: July 2006

The knowledge about reemergence of parent spruce bark beetles Ips typographus. their dispersal, and production of a second brood is reviewed. A majority of the beetles reemerge after their first brood. The process is mainly determined by temperature but high breeding density decreases the average time spent in the tree. The difference between males and females in reemergence seems to be small. In the field, a positive relationship between residence time and fat content at reemergence seems to exist, whereas the opposite tendency is found under laboratory conditions. In the laboratory, the survival of beetles reemerging late is on the average lower than that for early reemerging beetles. The time of reemergence and size of the first brood do not, however, seem to influence the production of a second brood. A large proportion of the reemerging beetles are able to establish a new brood in the laboratory, but calculations based on the number of attacked trees and estimated reemergence in forests in South Norway suggest that only about one third of the beetles actually produce a second brood. In northern Europe, successful colonization of new trees by the reemerging beetles seems to require a period of several warm days during the main reemergence period.
The European struggle to control Ips typographus ‐ past, present and future
Authors: Vité J. P.
Published: July 2006

The achievement of the Scandinavian campaign is seen in the swift development and unorthodox transfer of an innovative trapping technique into the management of pest populations of the spruce engraver Ips typographus without the use of pesticides. The pheromone traps proved to be far more efficient in the prevention of engraver reproduction and the reduction of beetle numbers than the cumbersome trap trees they replaced. The wholesale application of pheromone traps as an integrated part of engraver pest management is justified alone by the empirically proven benefits that result from a “surveillance with the intent to control”, although appraisal of the actual impact of trapping on the population density remains scientifically ambiguous for the lack of reliable methodology. Furthermore, the campaign opens a new era in bark beetle management by stipulating for the commercial availability of pheromones and traps as well as for research on basic and applied aspects. As the years to come may show, behaviour chemistry is likely to bear more promises to engraver management than just trapping techniques.
Environmental factors affecting basic nitrogen metabolism and seasonal levels of various nitrogen fractions in tissues of bilberry, Vaccinium myrtillus
Authors: Lähdesmäki P. , Pakonen T. , Saari E. , Laine K. , Havas P.
Published: July 2006

Bilberry tissues accumulated nitrogen for the winter in the form of reduced low‐molecular weight amino compounds. The storage organ was principally the underground stem and the oldest parts of the aerial shoot. Most of the nitrogen was stored in arginine and ammonium compounds, and less in glutamine and other amino acids. Proteins did not accumulate during the winter. The soluble nitrogenous compounds were discharged from storage in May, when nitrogen was translocated from the lower parts of the stem to the growing leaves and buds. Amino acid compositions and concentrations in winter were almost identical under the snow and in snowless areas, only the concentration of glutamine being lower and that of glutathione higher in the snowless area. The level of total protein, particularly in the leaves and buds was much higher in a nitrogen‐polluted industrial area than in unpolluted urban forests. The same difference was observed in total amino compounds, but among individual substances it only appeared in ammonium compounds. Certain species differences in the amino acid pool were recorded between V. myrtillus and V. vitis‐idaea.
Patterns of coexistence: ectoparasites on small mammals in northern Fennoscandia
Authors: Lundqvist Lars , Brinck‐Lindroth Gunvor
Published: July 2006

The total aestival ectoparasitic burden of six small mammal species (Sorex araneus, Clethrionomys glareolus, C. rutilus, C. rufocanus, Microtus agrestis, and M. oeconomus) was investigated in terms of frequency distribution, frequency of occurrence, species diversity and joint occurrences. The mammals were collected in northern Fennoscandia during peak density years. The frequency distribution of the ectoparasites was best described as negative binomial on C. glareolus, M. agrestis, and M. oeconomus but not so on S. araneus, C. rutilus and C. rufocanus. The distribution did not fit the Poisson distribution in any species. The percentage of S. araneus that had ectoparasites was 49%, and of the microtidae species, 73‐96% had ectoparasites. The median number of ectoparasites on the vole species was between 2 and 9 specimens of 1 or 2 species. There was a significant, positive correlation between the number of ectoparasitic species and the total number of individuals on all host species. Pairs of ectoparasitic species occurring together more or less often than expected by chance were found on all host species. However, the pairs rarely repeated themselves on the same host species under different environmental conditions, or on other host species under similar circumstances. Differences in total infestation between reproductive categories and sexes were observed in M. agrestis but not in S. araneus and C. glareolus.
Food habits and the survival and growth of nestlings in two sympatric kites (Milvus milvus and Milvus migrans)
Authors: Veiga J. P. , Hiraldo F.
Published: July 2006

A comparative study of the Red Kite and Black Kite was conducted in the Don̄ana National Park in southwestern Spain. Although the diets of both kites were similar, the Red Kite captured significantly more prey items from scrub habitats close to nesting areas than from marsh habitats, which were further away. Habitat differences in prey abundance and distance from breeding areas suggest that the Red Kite depended on a less abundant but more stable food supply. Nestling mortality from starvation was highest for the last hatched nestlings in both species. The growth rate of Black Kite nestlings was markedly higher than that of Red Kite nestlings. Moreover, growth rates increased with clutch size in the Red Kite, whereas they were constant in the Black Kite. Differences between species in reproductive traits are discussed mainly with regard to their feeding ecology. The slower growth and greater effect of sibling asymmetry on mortality of the Red Kite are consistent with our interpretation that the Red Kite's food supply is less abundant than the Black Kite's.
Density and distribution of the ringed seal in the Bothnian Bay
Authors: Härkönen Tero , Heide‐Jørgensen Mads‐Peter
Published: July 2006

A modified strip census of basking ringed seals in the Bothnian Bay was carried out during the last week of April and the first week of May 1988. Of the total ice covered area, 23174 km2, 3236 km2 (14%) was covered by the transects. The mean density in the area was 0.101 ringed seals km‐2, with substantial regional and local variation. Highest densities were found in the compact drift ice area. The estimated total population of ringed seals on the ice was 2093 in the Bothnian Bay proper and 248 in the North Quark. The 95% confidence limits of the estimates are ±24%.
Trend in the pup production of grey seals Halichoerus grypus at Froan, Norway, from 1974 to 1987
Authors: Wiig Øystein , Ekker Morten , Ekker Tørris , Røv Nils
Published: July 2006

Pup counts of grey seals at Froan, Norway, during the period 1974 to 1987 are given. The counts indicate an increase in pup production from 1974 to 1983. The counts from 1985 to 1987 indicate a stagnation and possibly a decrease in production. This is probably due to culls at the breeding ground, particularly during the 1984 breeding season.
An experimental test of frequency‐dependent food selection: winter browsing by moose
Authors: Lundberg Per , Åström Mårten , Danell Kjell
Published: July 2006

Penned moose Alces alces (L.) offered birch and rowan trees in various proportions in experimental tests showed a clear preference for birch both in terms of selection and use of trees. Both tree selection and tree use was frequency‐independent, i.e. the preference for birches did not vary with either the number of birches, or total birch biomass available. The preference for birch was not absolute, i.e. rowans were also present in the diet. Birch were more profitable than rowans in terms of biomass intake rate, whereas rowans were more “nutritious” than birches. The results are consistent with both the optimal diet theory and the “nutrient mixture” hypothesis, although neither of the hypotheses are unambiguous regarding frequency‐dependent food selection. It is argued, however, that tree selection and use by moose rather should be considered as a patch use problem and that trees should not be regarded as particulate food items as in most foraging models.
Fine scale patterning of species distributions in a saxicolous lichen community at Jonas Rockslide, Canadian Rocky Mountains
Authors: John Elizabeth A.
Published: July 2006

Distinct patterns of species distribution upon individual rockfaces are found n a saxicolous lichen community growing on a rockslide in the Canadian Rockies. A grid system was used for sampling individual rockfaces and the likelihood of finding a species on particular parts of the rockface was analysed. Use of chemicals in the field and collection of apothecia allowed specific identification of individual lichen thalli. Lichens were divisible into three groups: those which are distributed apparently at random over the rockfaces, those which are more likely to occur on upper, outer and southerly portions of the rockfaces and those which are found more often on lower, inner and northerly portions of the rockfaces. The upper rockface surfaces are often snow‐free in winter while the lower rockface group experiences deeper and more persistent snow cover. Simple microclimatic measurements suggest that temperature also differs across the surface of a rockface.

It is hypothesised that lichen distributions are at least in part explained by ecophysiological adaptations to their particular microhabitat, while it is recognised that competition may also play a role in community organisation.
Early plant succession in two abandoned cut‐over peatland areas
Authors: Salonen Veikko
Published: July 2006

Initial stages of plant succession (from 0 to 8 or 9 yr) were studied on abandoned peat harvest sites of two adjacent areas in Finland. At the Mustasuo area only 13 field layer species, all perennials, and 3 ground layer species became established during that period and species composition stayed relatively constant. All species occurred sparsely with low biomass. The Riitasuo area was colonized by 43 field layer and 19 ground layer species during the first 8 yr of succession. In that area the originally plantless sites were totally covered by plants within a few years. Many of the first species to arrive were annuals, most of which were soon replaced by perennial species. The great differences between the two areas in the rate and pattern of early succession are suggested to arise from differences in the seed sources and in the physical and chemical characteristics of the soil. The areas were found to differ especially by the thickness of the remaining peat layer, by the particle size distribution of the peat soil and by the contents of nitrate and ammonium nitrogen of the soil.
The capture of voles and shrews by male and female ermine Mustela erminea in captivity
Authors: Vaudry Réal , Raymond Michel , Robitaille Jean‐François
Published: July 2006

The capture of meadow vole Microtus pennsylvanicus and short‐tailed shrew Blarina brevicauda by male and female ermine Mustela erminea was observed in an indoor enclosure which simulated field conditions. We made 114 trials using 15 different male and 17 different female ermine. Each trial involved one ermine deprived of food for either 0, 10 or 20 h, and only one individual of either prey species. In most trials, the hunting efficiency (indicated by search and handling durations, and number of captures) of male ermine was greater than that of females. Females hardly ever captured shrews, whereas males hunted them successfully independently of the level of food deprivation. However, when deprived of food for 20 h, females spent less time than males in searching for voles. These results suggest that smaller females may be specialized and more effective at hunting meadow voles than larger males under severe food deprivation. This advantage may allow them to channel a greater proportion of energy into reproduction.
Choice of feeding sites by moose during summer, the influence of forest structure and plant phenology
Authors: Hjeljord Olav , Hövik Nils , Pedersen Helge B.
Published: July 2006

We observed forage and habitat selection in radio‐collared moose at feeding sites in southeast Norway. Use of older forest increased from spring to autumn. Birch Betula spp. and bilberry Vaccinium myrtillus accounted for c. 75% of the diet. Occurrence of important forage plants, height of browse, and difference in phenology between plant species all appeared to play a role in moose selection of feeding sites. Shading influences moose forage by delaying plant phenology and possibly through its effect on leaf content of water and secondary compounds. On single birch trees, feeding was concentrated to the top branches at midsummer; during spring and autumn more leaves from side branches were eaten. Greater discrimination as vegetation matured was also evident from the wider variety of forage species used at midsummer. Selection of feeding sites was not related to density of important browse species. We propose that variations in light/shade conditions may play a role in moose choice of feeding sites and that moose on summer range will benefit from a heterogeneous mixture of plantations and older forest stands.
Effects of shredding amphipod density on watercress Nasturtium officinale breakdown
Authors: Newman Raymond M.
Published: July 2006

Shredding stream invertebrates should have a positive influence on the breakdown rates of leaf litter via direct consumption and particle fragmentation. To determine the effects of shredder density on litter breakdown, breakdown of the emergent stream macrophyte, Nasturtium officinale, was investigated using three litter bag mesh sizes [fine (0.2 mm), medium (1 mm) and coarse (3 mm) mesh] and four stocking densities of the shredder, Gammarus pseudolimnaeus, (0, 4, 8 and 16 per bag). Watercress decayed very rapidly, with breakdown rates (k values) ranging from 0.075 d‐1 for fine mesh with no shredders to 0.24 d‐1 for coarse mesh. Stocked Gammarus increased breakdown rates significantly in fine mesh bags (p < 0.001), but only marginally in medium mesh bags (p < 0.1). Breakdown rates also increased significantly with mesh size. A regression model showed a significant relation of breakdown rate to Gammarus density and mesh size. These results clearly show that shredders can significantly influence breakdown rates and can account for up to 30% of breakdown, but that mesh size effects such as particle size reduction and loss are also very important.