bluuebunny/crossref_metadata_2025 huggingface dataset:
Predation and potential transfer of pollen in a population of Saxifraga hirculus
Authors: Olesen Jens Mogens , Warncke Esbern
Published: July 2006

Body surface pollen load and gut pollen (pollen diet load) of flower visitors in a Danish population of Saxifraga hirculus were analyzed. The four most frequent visitors, Eurimyia lineata (Syrphidae), Neoascia tenur (Syrphidae), Asindulum nigrum (Mycetophilidae), and Zygaena trifolii (Zygaenidae) had total surface loads (and S. hirculus loads) of 1031 (771), 137 (106), 108 (78), and 318 (27) pollen grains, respectively. Other syrphid visitors had on average a load of 407 (192) pollen grains. Males of E. lineata, N. tenur, and A. nigrum carried more surface pollen than the females; females of E. lineata had a lot of pollen from Ranunculus acris and S. hirculus and males had a lot from S. hirculus. Females of N. tenur carried pollen mostly from S. hirculus, Lotus uliginosus and Galium uliginosum; males carried pollen mostly from S. hirculus. The surface pollen load of A. nigrum was dominated by S. hirculus pollen, whereas that of Z. trifolii was dominated by Cirsium palustre and Lychnis flos‐cuculi pollen. The amount and kind of pollen varied enormously both intraspecifically and interspecifically. Eurimyia lineata, N. tenur and other syrphids had total pollen diet loads (and S. hirculus pollen diet loads) of approximately 14900 (657), 3739 (2327) and 17784 (13040). The average syrphid contained pollen from five plant species, only one to two, however, were quantitatively important. The average diet load in females was nine times that in males in both E. lineata and N. tenur. Eurimyia lineata ate a lot of R. acris; N. tenur ate a lot of S. hirculus and G. uliginosum. Generally, no correlation was observed between size or season and the composition of surface load and diet load. Eurimyia lineata made most of the pollen visits. Thus, the seed set from this Danish population of S. hirculus was dependent on a single syrphid species.
The role of habitat barriers in woodlot recolonization by small mammals
Authors: Kozakiewicz Michal , Jurasińska Elżbieta
Published: July 2006

The immigration and colonization of small mammals into a small depopulated wooded area surrounded by meadows was monitored by live‐trapping and then compared with the same processes in an open forest following removal trapping. Rate of recolonization was lower in the depopulated woods than in the continuous forest. Bank voles, Clethrionomys glareolus, predominated the small mammal communities before removal; however, after removal the percentage of bank voles decreased and species diversity increased. When comparing the bank voles from the wooded area with the continuous forest, we found a higher percentage of sexually active animals, the lack of reproducing females and slightly lower body weights. Based on these characteristics the bank voles that recolonized the small woods were regarded as dispersers. The meadow belt surrounding the depopulated wood acted as a “filter” which stopped some bank voles and allowed others to pass through, and also “selected” different species crossing it according to their mobility. Some effects of such habitat barriers on the functioning of metapopulations are discussed.
Year class splitting in the woodlouse Philoscia muscorum explained through studies of growth and survivorship
Authors: Grundy A. J. , Sutton S. L.
Published: July 2006

Year class splitting has been observed in a population of the terrestrial isopod Philoscia muscorum (Scopoli) in a fixed dune grassland. In this population, individuals born in one season differentiate into two forms, one of which grows to maturity in one year, the other in two.

Laboratory investigations of growth, fecundity and survivorship of individuals showed fundamental positive relationships between rate of growth and the ambient temperature/day light regime and between parental size and the number of offspring produced. Size also affected survivorship, with adults surviving better than juveniles. A link between survivorship and the temperature/day light regime was only obvious in small juveniles.

No direct physiological cause for the year class split could be derived from the laboratory studies, but a trade‐off between the need for delayed or early breeding could result in the patterns of growth and reproduction observed in the field population. Delayed breeding allows continued growth of adults and hence larger numbers of offspring. Early breeding allows more growth of juveniles which greatly improves their chances of winter survival.
Comparative analysis of temporal and spatial variability in above‐ground production in a deciduous forest and prairie
Authors: Briggs J. M. , Seastedt T. R. , Gibson D. J.
Published: July 2006

Production patterns of tallgrass prairie and adjacent eastern deciduous forest were summarized for a five to seven year period. Each system responded differentially to annual or growing season rainfall and solar energy (measured by pan water evaporation). Overall, forest productivity was negatively correlated with annual precipitation; the prairie exhibited no relationship with precipitation. These differences probably reflect the lack of water limitation of the forest and the “downstream” position of the forest.

Wood and seed production in the forest were the most variable components measured in our study. Neither variable was related to forest foliage production. Seed production in the prairie was also variable within and between years but was related to prairie foliage production. Prairie seed production was not correlated with seed production of the forest.

The two ecosystems respond differentially and independently of each other within the range of climatic variation observed here. Such differences have potential significance to consumers who use both systems for habitat or resources.
Thermal ecology and spatio‐temporal distribution of the Mediterranean lizard Psammodromus algirus
Authors: Carrascal Luis M. , Díaz José A.
Published: July 2006

We studied summer activity patterns and thermoregulation in the Mediterranean lizard Psammodromus algirus in a holm oak wood in Central Spain. The circadian rhythm curve was bimodal, with a pronounced peak after sunrise, a minimum at noon and a second lower peak in the afternoon. Increased activity in the morning could be explained by insolation levels, whereas the midday low was caused by the rise in temperature.

There was a strong positive correlation between body temperature and both air and ground temperatures. Nevertheless, there was no significant correlation between body and air temperatures when the effect of radiation was removed, which was done by considering only individuals in the shade at high temperatures.

Activity showed a bell‐shaped relationship with body and air temperatures, with maximum activity at 24.5°C (air temperature) and 31.4°C (body temperature). The spatial distribution pattern of P. algirus (selection of sunny areas and distance to the vegetation edge) reflects the environmental temperatures that are optimal for activity; the lizards show a strong preference for sunny patches when air temperature is lower than the optimum. We conclude that heliothermy is the only viable thermoregulation pattern in Mediterranean forest environments, with heat conduction playing a negligible rote.
Life cycle variation and habitat longevity in waterlily leaf beetles
Authors: Otto Christian , Wallace J. Bruce
Published: July 2006

Waterlily leaf beetles inhabiting Nuphur luteum leaves in S. Sweden and Georgia, USA. differed markedly with respect to several life history traits. Developmental time (from oviposition to adult) was about 47 days in Sweden, while it was only 19 days in Georgia. In S. Sweden two generations were reached per year, while the corresponding number in Georgia could be eight. Instantaneous growth rate was three times as high in Georgia as in S. Sweden. Swedish eggs, larvae and imagines were larger than in the Georgian ones. However, clutch size was larger in Georgia, and total estimated fecundity was higher in Georgian females. Mortality rate of immature stages was higher in Georgia. Altogether, the results suggest two different species.

Swedish N. luteum leaves were unpalatable to Georgian larvae, and the larvae died from starvation. Longevity of unprotected, grazed Swedish N. luteum leaves was about 28 days, while those protected from grazing lasted for 72 days. In Georgia the corresponding time periods were 13 and >42 days. Thus, it was impossible for beetles to cover all their immature stages on the same leaf, and drowning was presumed to be the main mortality factor. Swedish larvae and imagines were unpalatable to wagtails, and accumulated unpalatable plant chemicals may serve as chemical defences.
The influence of different age classes on the seasonal activity and reproduction of four medium‐sized carabid species inhabiting cereal fields
Authors: Wallin Henrik
Published: July 2006

Reproduction and survival of four carabid species commonly occurring in cereal fields in central Sweden were investigated. The adult‐overwintering Pterostichus cupreus L. bred in early summer (June), and the largest proportion of sexually active beetles were found to be in their first breeding year; only a minority were 2 (or more) years old. In contrast, the larval‐overwintering P. melanarius Illiger, P. niger Schaller and Harpalus rufipes De Geer had a biennal life cycle, and mainly old beetles (2 years or older) contributed to the population's reproductive effort each year. The long prereproductive adult phase in the larval‐overwintering species and the relatively short summer in central Sweden prevented many new‐generation adults from breeding in their first year. Several overlapping breeding cohorts are therefore present each year, and overwintered beetles bred throughout summer and during part of the autumn. Mandible wear (combined with other characters) was used to determine the age of beetles. However, the rate of mandible wear also was found to vary, depending upon the extent to which each species burrowed in the ground. The ecological significance of (a) a long adult life and (b) the existence of several overlapping breeding cohorts for reproduction and survival of populations in cereal fields is discussed.
Breeding dynamics of Triturus carnifex at a pond in northwestern Italy (Amphibia, Urodela, Salamandridae)
Authors: Andreone Franco , Giacoma Cristina
Published: July 2006

A population of the Italian crested newt (Triturus carnifex) was studied in 1984 at a pond near Druento (Turin, Piedmont, northwestern Italy). Animals entering and leaving the pond fell into paired pit‐fall traps during both spring and autumn migrations. A positive correlation found between rainfall and migration, a shortening of migration periods and summer inactivity suggest that, in the Mediterranean region, air moisture may be a limiting factor for newt activity. During their aquatic period adults showed strong individual differences in weight changes that cannot be explained on the basis of initial body weight or length. High variability in crested newt life history traits may be the result of repeated bottlenecks caused by environmental stress and high population isolation.
Spatial interrelationships between terrain, snow distribution and vegetation patterns at an arctic foothills site in Alaska
Authors: Evans Barry M. , Walker Donald A. , Benson Carl S. , Nordstrand Earl A. , Petersen Gary W.
Published: July 2006

A multidisciplinary approach combining field surveys, aerial photographic techniques, digital terrain modelling, and GIS technology was used to analyze spatial interrelationships at a study site in the northern foothills of the Brooks Range, The sensitivity of snow drifting to topography at the site is pronounced. The drift patterns indicate winter winds are predominantly from the south with a major secondary component from the southwest. These southwest winds are likely in conjunction with storm events. The deepest snow beds are found on the steeper, north‐facing slopes. Snow also has an effect on vegetation that is evident at the scale of mapping (1:6000). Communities dominated by Cassiope tetragona are associated with deeper snow regimes, and may be useful indicators of deeper snow regimes even at much smaller scales because of their unique spectral signatures. The analyses conducted to date demonstrate the power of the GIS for analyzing terrain‐geobotanical interrelationships, which will increase as we add new layers for other variables, and are able to correlate these with satellite data.
Seasonal geochemistry of an arctic tundra drainage basin
Authors: Everett K. R. , Marion G. M. , Kane D. L.
Published: July 2006

The snow melt food at Imnavait Creek takes place sometime between 12 May and 2 June and constitutes the single most important hydrological and geochemical event. Three years of study indicate this event spans 7 to 10 days and that peak discharge can be expected to be between 0.6 and 0.9 cu. mes. Ion concentrations peak during the first 15% of the event while pH is at a minimum. In all cases, ion concentrations in the spring runoff are 4 to 9 times those of the snow pack, Precipitaion, including dryfall, contributes significant amounts of Ca, Mg, K, Na, Cl and SO4. Postassium is present in surface waters only during melt‐off and for a short time after. Calcium. Mg. suspended solids and electrical conductivity all reach broad, poorly defined peaks in mid‐summer. Only pH shows a significant relationship to discharge. On a seasonal basis a substantial charge imbalance favoring cations occurs. It seems probable that the, as yet, unmeasured negative charge is associated with organic anions. No seasonal trends were recorded for Mg, K or Mn in subsurface flow in the surrounding slopes. Calcium. Fe and Al showed a late season peak, and the concentration of Na and Si decreased as the melt season progressed.
Some physical and chemical characteristics of an arctic beaded stream
Authors: Oswood Mark W. , Everett K. R. , Schell Donald M.
Published: July 2006

Imnavait Creek is a tundra stream in the Arctic Foothills of Alaska. The stream is beaded, i.e. consists of pools (up to ∼ 2 m deep) connected by narrow channels. Peat dominates pool and channel substrate materials with occasional rock and moss substrates. The watershed is underlain by ice‐bonded till and is hydrologically watertight. Because of low rates of weathering, bedrock and till do not contribute significantly to ionic composition of the stream water. Breakup occurs in late May to early June with surface flow until September. During periods of low rainfall, channel flow is reduced and pools become hydrologically isolated and thermally stratified (with very high surface water temperatures). Streamwater is acidic (pH values 5.3–6.1) with very low alkalinity (≤3 mg l−1). The major transport of ions occurs in early flow derived from snow melt. Organic carbon concentrations are high with very high ratios of dissolved to particulate organic carbon. Dissolved inorganic nitrogen concentrations appear to be very low. High concentrations of dissolved organic material may indicate a central role for DOM in trophic dynamics.
Soil‐plant element relationships in a tundra ecosystem
Authors: Marion G. M. , Hastings S. J. , Oberbauer S. F. , Oechel W. C.
Published: July 2006

The objectives of this study were to (1) provide a baseline estimate of soil and plant element concentrations for an intensive research site at Imnavait Creek in northern Alaska, and (2) examine the relationships between soil and plant elements in an arctic ecosystem. Soil and plant element concentrations were highly variable along biotic, spatial, and temporal axes. Deciduous shrubs had higher leaf concentration of N, P. K and Mg, whereas an evergreen shrub had higher leaf concentrations of Ca, Mn, Al and Si. Based on high required solution phase turnover rates, the most likely elemental deficiencies are N > P > K > Ca = Mg. Based on low required solution phase turnover rates and high soil concentrations. Fe, Mn, Zn and Cu deficiencies are unlikely. Manganese could be present in toxic concentrations. The nutrient bottleneck in tundra ecosystems appears to be the rate of nutrient movement to the solution phase.
Standing biomass and production in water drainages of the foothills of the Philip Smith Mountains, Alaska
Authors: Hastings Steven J. , Luchessa Scott A. , Oechel Walter C. , Tenhunen John D.
Published: July 2006

In the foothills of the Philip Smith Mountains, Brooks Range, Alaska, tussock tundra is the most widely distributed vegetation, and it occurs on rolling hills and in valleys that were shaped by a sequence of Pleistocene glaciations. In this study, aboveground standing biomass and production were compared in “intertrack tundra” areas that were relatively homogenous with respect to downslope drainage and adjacent “water tracks” that acted to channel water flow to the valley bottom stream. Comparisons of biomass, leaf area index, and specific leaf weight were also made between upper and lower slope positions. Similarities and differences of vegetation structure are examined with respect to graminoid, deciduous shrub, evergreen shrub, herbaceous, and bryophyte components.

Water tracks were found to have 1.5–1.7 times the biomass of intertrack tundra, and production (excluding secondary growth) in water tracks was 40% greater than in intertrack tundra. The aboveground biomass for all areas studied and the annual production values were similar to those found in other studies of tussock tundra. While only slight differences in depth of thaw occurred in water tracks and intertrack tundra during June and early July, water tracks thawed more deeply with the onset of summer rains. Warmer temperatures at 40 cm depth in July and August may have increased nutrient availability, whereas greater rooting depth and movement of water may have increased nutrient capture in water tracks as compared with the intertrack areas. Greater biomass and a deeper thaw depth occurred at upper slope locations.
Maximum CO2‐assimilation rates of vascular plants on an Alaskan arctic tundra slope
Authors: Oberbauer Steven F. , Oechel Walter C.
Published: July 2006

Light‐saturated CO2‐assimilation rates of 19 vascular plant species were measured on a tundra slope in the foothills of the Brooks Range, Alaska. Maximum assimilation capacities on a leaf area basis ranged from 20.3 μmol m−2 s−1 for the forb, Bistorta plumosa, to 6.0 μmol m−2 s−1 for the evergreen, Empetrum hermaphroditicum. Graminoids, deciduous shrubs, and forbs fell within a similar range of maximum photosynthetic rates on a leaf area basis. Evergreens had the lowest rates. On a leaf weight basis, maximum assimilation rates were greatest for forbs, followed by deciduous shrubs, graminoids, and evergreens. Rates of evergreens were less than half those of all other growth forms. Cassiope tetragona had the lowest rates per unit leaf weight of any species tested; mean maximum rates of C. tetragona were only 14% of those of B. plumosa, the species with the highest rates. When the data were subjected to canonical analysis, only a partial correspondence was found between species growth form and photosynthetic characteristics.
The effect of nutrient and water additions on elemental mobility through small tundra watersheds
Authors: Marion G. M. , Everett K. R.
Published: July 2006

The objective was to quantify elemental movement through small tundra watersheds as affected by nutrient and water additions. Nutrient (slow‐release NPK fertilizer) and water additions were applied to small tundra watersheds along Imnavait Creek Northern Alaska. Suction lysimeters and weired watersheds were used to monitor elemental mobility. Elemental concentrations in undisturbed watersheds were similar to Hubbard Brook watersheds except for NO3‐N which was much higher and PO4‐P which was lower in the Hubbard Brook watersheds. The water addition treatment led to a significant increase in Ca, Mg, Na, Fe, Mn and SO4 concentrations which was attributed to contamination originating from within the water distribution system. Increased elemental concentrations in the irrigated watersheds were found up to 85 m below the point of application. Ammonium and NO3 originating from the fertilizer were detected 6 m below the application point within two weeks of application. The NH4 and NO3 concentrations remained above background levels for two field seasons following fertilization. Both the irrigation and fertilization studies show that disturbances in tundra ecosystems may spread far beyond the initially impacted area both with respect to time and space.
Comparative effects of downslope water and nutrient movement on plant nutrition, photosynthesis, and growth in Alaskan tundra
Authors: Oberbauer S. F. , Hastings S. J. , Beyers J. L. , Oechel W. C.
Published: July 2006

Changes in water and nutrient movement are common disturbances resulting from human activities in arctic regions. To assess the influence of water and nutrient movement on different plant growth forms, we added water and NPK fertilizer along 10 to 20 m linear transects across small natural drainages on an Alaskan tundra slope. Water was added by continuous‐flow emitters from a drip irrigation system at a rate of 450 L m−1 d−1 during the 1986 growing season and 110 L m−1 d−1 in the 1987 growing season. NPK in the form of Osmocote, a slow release fertilizer, was applied at 0.5 kg per linear meter in early and mid‐season of the 1985 growing season. Tissue N and P contents, light‐saturated photosynthetic rates, and aboveground biomass production were measured at peak season for key species 2 m above and 2 and 6 m below the water and nutrient applications in 1986 and 1987.

Mean leaf N and P of the species tested increased slightly 2 m below the water addition sites and dramatically below the fertilizer addition sites. Increases in tissue N and P were also found 6 m below the fertilizer addition points. Leaf photosynthesis tended to increase 2 m below the water and nutrient additions for the species tested. Six meters below the treatment application points, photosynthesis was minimally affected in 1986 but increased in 1987. Increases in leaf area on the irrigation treatments were found only for the evergreen species, Ledum palustre and Vaccinium vitis‐idaea, 2 m below the site of addition. In contrast, fertilizer addition caused large increases in leaf area production for all species tested at 2 m below the treatment, and for some species at 6 m below treatment. The overall effects of the two treatments were similar, but were greater for the fertilizer addition.
Germination characteristics of some plant species from calcareous fens in southern Germany and their implications for the seed bank
Authors: Maas D.
Published: July 2006

Seeds of 25 plant species from calcareous fen hay meadows were exposed to different experimental conditions and their germination was characterised. Constant temperature inhibited germination especially in Cyperaceae. Both gibberellic acid and potassium nitrate failed to terminate dormancy. Increased germination rates were found in dicot species after treatment with gibberellic acid. Temperature fluctuations increased germination of Cyperaceae as well as dicotyledons. Treatment with gibberellic acid removed the chilling requirement in some of the species. Dormancy of small seeds with thin seed coats was broken by the application of gibberellic acid or fluctuating temperature; large thick‐coated seeds were unaffected by gibberellic acid. No obligatory darkness requirement was found in any species; three species germinated irrespective of light treatments. All other species achieved higher percentage germination in daylight or in red (670 nm) light. Permanent darkness and far‐red light (730 nm) reduced germination drastically. The results indicate that germination characteristics of the species investigated can be related to their seed bank types.
Landscape and habitat dependence in cyclic and semi‐cyclic small rodents
Authors: Hansson Lennart
Published: July 2006

Habitat dependence and foraging for bark of semi‐cyclic and cyclic voles were examined on clearcuts in central and northern Sweden. Both populations showed inconsistent and weak relationships to habitat variables. Population dynamics of the northern cyclic population was more clearly related to landscape composition. Snow depth explained a large proportion of the total variation between clearcuts when the populations were pooled. Snow and landscape effects agree with recent hypotheses that 3–4 yr cyclic densities are related to predator impact. The negligible effects of other habitat variables may be due to generalized habitat selection by northern rodents and the historical growth of populations in different macrohabitats since population crashes. The relations between density and bark consumption differed between the two regions, indicating a threshold density for more intense bark use. From an applied point of view, areas with seedling damage can be predicted at regional rather than at local scales.
Population structure and dynamics of wood mouse Apodemus sylvaticus in Iceland
Authors: Bengtson Sven‐Axel , Nilsson Anders , Rundgren Sten
Published: July 2006

Five‐year‐studies of two wood mouse populations (Apodemus sylvaticus L.) were carried out outside the village Vík. S. Iceland, and in a birch forest close to the lake Mývatn, N. Iceland. The population at Vík was studied on a 1.10 ha grid on a slope covered with Angelica archangelica L., the seeds of which constituted a major food resource for the mice. Altogether 948 individuals were caught, marked and followed during 1973–1978. No other free‐living small mammals occur in Iceland, and predator pressure is low and considered non‐existent on the Angelica slope. The population density was extremely high; highest autumn density recorded was 150 ind ha−1. Like other Apodemus populations, the one at Vík showed a typical seasonal pattern in numbers: a winter decrease, relatively stable numbers in late summer, and an autumn peak. Breeding started in late April or early May and ended in late September; no winter breeding was observed. Three or four litters were produced, and the last litter(s) of the season greatly contributed to the autumn increase. The output of young per reproductive female throughout the year was negatively correlated with spring density, and autumn peak density with the number of females in August. Also overwinter success and weight changes appeared to be associated with population density (and weather). Survival rates did not vary much between years and seasons and were consistently rather high. Autumn survival of juveniles was positively correlated with mean minimum temperatures. Juvenile survival was, at least at times, negatively affected by the presence of adult males. Trapping outside the main grid did not indicate any marked dispersal, though some immigration to the grid must have occurred, especially in spring and early summer. Among the factors governing the population density and dynamics of wood mouse at Vík we emphasize the absence of interspecific competition and predation, the rich and dependable food resources (mainly Angelica seeds), the mild (though moist and windy) climate, the shelter of dense Angelica stands, the abundance of crevices (e.g. nest‐sites), and the social interactions.

The birch forest in northern Iceland was low productive and the wood mouse population differed from the Vík population by exhibiting low density, short breeding season, and high vagility; characteristics we consider to be representative for most Apodemus populations in Iceland.
Why don't Svalbard reindeer migrate?
Authors: Tyler N. J. C. , Øritsland N. A.
Published: July 2006

Reindeer and caribou are best known as migratory, seasonally nomadic animals; many continental populations, for example, travel between distinct summer and winter ranges which may lie hundreds of km apart. Much less is known about the movements of animals belonging to island populations. This paper describes seasonal and annual movements of wild reindeer Rangifer tarandus platyrhynchus on the high arctic archipelago of Svalbard, based on observations of nine animals captured and individually marked in Adventdalen, Spitsbergen, between 1977 and 1982. Four ear‐tagged reindeer (one male and three females) were followed extensively for between four and seven years. Five radio‐collared females were followed intensively for seven months in 1982. Svalbard reindeer seem neither to undertake long migrations nor to be nomadic within seasons like mountain reindeer or barren‐ground caribou. They appear instead to use small, traditional, seasonal home ranges more, for example, like red deer or wild sheep. This atypical behaviour is discussed in relation to the dispersion of reindeers' resources in Svalbard.
A theoretical basis for understanding and managing biological populations with particular reference to the spruce bark beetle
Authors: Berryman Alan A. , Stenseth Nils Chr.
Published: July 2006

The applicability of qualitative analysis and modelling is discussed with reference to the population dynamics of the spruce bark beetle Ips typographus. On the basis of a set of assumptions and postulates, the structure of the population dynamical interactions is discussed. Dynamic analysis suggest that the Scandinavian spruce bark beetle population is a stable system which may be triggered into “boom and bust” dynamics. We suggest that qualitative analysis should proceed, explicitly, through four steps: (1) An explicit statement of the biological assumptions and postulates. (2) A structural analysis, wherein the critical interaction network of the system is defined. (3) An equilibrium analysis, wherein the potential equilibrium points of the key organism (e.g., the pest species) are deduced. (4) A dynamic analysis, wherein the multispecies equilibrium points are found and their sensitivity to pertuberation analyzed. This formal approach should expose many and varied population systems to the interpretive and explanatory powers of qualitative analysis.
A simple population model for bark beetles providing general guidelines for the application of aggregation and anti‐aggregation pheromones
Authors: Stenseth Nils Chr.
Published: July 2006

Pest control programs are usually evaluated without considering the population dynamics effects of the particular manipulation being recommended. A simple mathematical model is analysed which demonstrates that neglecting population dynamics may be disastrous. Emphasis is placed on the kinds of questions that must be asked before a pest control strategy can be fully evaluated. The discussion must necessarily be speculative since we lack the essential empirical basis for evaluating the effects of suggested pest control treatments. In itself, it is indeed alarming that this discussion must be speculative.
A model for the conquest of a tree by bark beetles
Authors: Stenseth Nils Chr.
Published: July 2006

A model for the interaction between attacking bark beetles and a tree is developed and discussed. It is shown that in addition to the more intuitive outcomes where the tree wins or the beetles win, it is also deduced that under certain conditions there may exist a stable coexistence (at least for some period of time) between the beetles and a living tree. Finally, it is demonstrated that the outcome of the tree‐beetle interaction often depends on initial conditions such as the number of colonizing beetles.

These results are discussed with reference to empirical findings, as well as to the development of proper population dynamics models for bark beetles in a forest stand, and models developed for assisting forest managers in avoiding bark beetle outbreaks and for minimizing the damage caused by a bark beetle outbreak.
A model for the timing of swarming of Tomicus piniperda (Coleoptera: Scolytidae)
Authors: Saarenmaa Hannu
Published: July 2006

Tomicus piniperda is the first bark beetle to swarm in the spring in Fennoscandia. The intensity of swarming is directly related to air temperature above a certain threshold and reaches 100% asymptotically. While temperature sums above the threshold accumulate, swarming rate slows down. A non‐linear model was built on these considerations. The model was calibrated to window trap material from northern Finland, and it was validated against published material mainly from Norway. The threshold temperatures in these materials were 10.8°C and 11.6°C, respectively. The predictions of the model were satisfactory, and the model will be tried as a part of an entire population dynamics model. The possibilities to predict not only timing, but also the frequency of attack are discussed.
An overview of the TAMBEETLE model of Dendroctonus frontalis population dynamics
Authors: Coulson Robert N. , Feldman R. M. , Sharpe P. J. H. , Pulley P. E. , Wagner T. L. , Payne T. L.
Published: July 2006

Population dynamics of the southern pine beetle Dendroctonus frontalis has been the subject of intensive research in the USA for more than a decade. TAMBEETLE, an acronym for the mechanistic model of population dynamics of D. frontalis, was developed to abstract contemporary knowledge on the insect. This model was developed as a joint venture between the Biosystems Research Group of Industrial Engineering and the Department of Entomology at Texas A&M University. The approach used to develop the model and the structure of component submodels is described. Research leading to the development of the model involved a series of field and laboratory studies aimed at various aspects of the population system of the insect. This research is reviewed. Important areas needing further research are identified. Studies dealing with factors involved in initiation of infestions, biome‐level epidemiology, host susceptibility, stand modeling, and dynamics of within‐tree mortality were emphasized as important topics for further research.
Host tree resistance influencing pheromone production in Ips typographus (Coleoptera: Scolytidae)
Authors: Birgersson Göran
Published: July 2006

Analyses of volatiles in hindguts of Ips typgraphus males from different spruce trees and attack phases are reviewed. The composition of monoterpenes, and the chirality of α‐pinene, have been determined in phloem samples. Relationships between compounds emanating from spruce trees and bark beetles, respectively, have been studied. Male beetles depend on their host tree for the production of pinene alcohols. The ratio between the pinene alcohols is almost constant in males boring in the same tree but can vary widely between males from different spruce trees. Very good correlations were found between some host tree monoterpene hydrocarbons and bark beetle produced pinene alcohols. The production of the essential pheromone component 2‐methyl‐3‐buten‐2‐ol, was not correlated with the monoterpene content in the host trees, while the production of the other essential pheromone component, cis‐verbenol, depends on the amount of the precursor, (−)‐α‐pinene in the phloem. Male beetles boring in a resistant spruce tree will continue to produce the pinene alcohols, including cis‐verbenol, as long as the tree defends itself with resin.
Individual variation in bark beetle and moth pheromones ‐ a comparison and an evolutionary background
Authors: Schlyter Fredrik , Birgersson Göran
Published: July 2006

The presently published data of variation in pheromone content in bark beetles (Coleoptera: Scolytidae) and moths (Lepidoptera) are reviewed. In both taxa high coefficients of variation, often up to around 100% for amount of pheromone, seem to be the rule. The contribution to the variation from errors in the chemical methods was small in most studies compared with the intrinsic biological variation. Examples arc given of variation in both absolute amounts, proportions of geometric isomers and in enantiomeric composition. Ratios of isomers often had lower coefficients of variation (25% or less). A lower average variation among sex pheromone in moths could relate to a mating system involving singly calling females, compared with the aggregation pheromone of bark beetles, which often call in large groups. The origin of a resource‐based aggregation pheromone system by evolution working via individual selection is outlined.
Within‐harem competition among Ips females, an overlooked component of density‐dependent larval mortality
Authors: Kirkendall Lawrence R.
Published: July 2006

Intraspecific larval competition is commonly believed to be the major component of egg‐to‐adult mortality in bark beetles. Larval mortality is usually shown to be density dependent. In this study I looked specifically at competition among females in the same gallery system, in a sparse but highly female‐biased population of Ips acuminatus breeding in cut pine branches near Kongsberg, southeastern Norway. Supplementary data from a slightly female‐biased population in western Norway and a population with intermediate female bias in W. Germany are also provided.

Survivorship from egg to adult or pupa was measured in laboratory experiments, for the area in which larvae from different arms potentially competed relative to survivorship in areas away from competition. Survivorship was significantly correlated with both average interarm distance (r2= 0.76) and food per larva (cm2 per larva: r2= 0.73). There was no evidence that females could detect the presence of other, nearby egg arms: neither egg spacing (on the arm sides nearest each other) nor interarm distance increased when two arms were near each other. Nor did females distribute themselves optimally within harems, though the distribution of egg arms within harems was significantly different from that expected from random settling. analysis of interarm distances and harem sizes in 1984 branches revealed that a minimum of 34% of arm sides could be expected to suffer considerably reduced larval survivorship due to within‐harem competition.

Harem size in Ips typographus is reviewed, and data on the distribution of females within harems is presented for Norwegian populations of I. Typographus, Orthotomicus erosus and O. laricis. Evidence from the literature is presented to show that uneven distribution of females between harem sides is not uncommon. I suggest that the findings for Ips acuminatus are applicable to a wide range of harem polygynous scolytids, including I. typographus: the factors influencing density cannot be fully understood without taking into account the distribution of females among males and the distribution of females within harems.
Causes and effects of individual quality in bark beetles
Authors: Anderbrant Olle , Schlyter Fredrik
Published: July 2006

A summary of the present knowledge of variation in individual quality within a bark beetle population is given, with emphasis on the spruce bark beetle Ips typogrophus, A major causal factor is density, mediated by competition during larval development. Density negatively influences individual quality measured as weight, fat content and pheromone production. Together with decreasing mean values at higher densities, the skewness of the frequency distributions goes from negative to positive, while variance changes little. High densities, which often occur in the field, thus result in a large fraction of “low quality beetles”. They have lower reproductive capacity and presumably lesser dispersal ability, lower survival, and earlier response to pheromone. This might concentrate the population in the next generation with increased competition as a result. It is suggested that a decrease in beetle “quality” due to increasingly intense intraspecific competition can contribute to the decline of an epidemic population.
Semiochemicals and bark beetle populations: Exploitation of natural phenomena by pest management strategists
Authors: Borden John H.
Published: July 2006

An analysis of semiochemical communication between host trees, bark beetles and commensal or entomophagous insects discloses five principal means by which semiochemicals can influence the population dynamics of bark beetles. These are: mediation of aggregation and mass attack on new hosts, cessation of aggregation and shifting of attack to uninhabited hosts, induction of aggregation by competing species, inhibition of aggregation by competing species, and mediation of host finding by commensal and entomophagous insects. Further analysis suggests major points of natural vulnerability which lead to six fundamental strategies for potential pest management: prevention of production of aggregation pheromones, sabotage of olfactory perception, exploitation of semiochemical‐based secondary attraction, exploitation of antiaggregation pheromones, exploitation of repellent allomones, and exploitation of the kairomonal response by entomophagous insects. Investigations of the many possible tactics arising from these strategies have led to three types of operational pest management programs: prevention of pheromone production by excluding bark beetles from their hosts; suppression of bark beetle populations through the utilization of semiochemical‐baited traps, trees or logs; and the use of antiaggregation pheromones to protect vulnerable hosts from attack.
Trapping a local population of spruce bark beetles Ips typographus (L.): Population size and origin of trapped beetles
Authors: Weslien Jan , Lindelöw Åke
Published: July 2006

A method of trapping local populations of Ips typographus was investigated in the field. The size of a population emerging from a hibernation site in the forest litter was estimated using tent traps. This estimate was compared with another estimate where beetles from the population were marked and recaptured in pheromone traps. The estimate of population size with mark‐recapture was much higher than the estimate with tent traps, indicating a high degree of immigration. According to calculations only a minor part (less than 20%) of the beetles caught in the pipe traps originated in the local population. Re‐emerging parent‐adults were marked and released during the second flight period. The recapture rate was 29.8%, almost the same as during the first flight. Immigration during the first and second flight periods was estimated to be of similar magnitude. The results show that it is difficult to suppress local populations of highly mobile bark beetles by trapping.
The recent Ips typographus outbreak in Norway ‐ experiences from a control program
Authors: Bakke Alf
Published: July 2006

During the period 1971‐81 there were severe outbreaks of the bark beetle Ips typographus in southern Norway that damaged trees equivalent to 5 million cubic metres of timber. The outbreaks were caused partly by an extensive windblow and partly by drought. Trap trees were used until 1979, when pheromone‐baited traps were introducted as part of an extensive control program. The various aspects of this program are outlined and problems of scientific, technological, economical‐administrative and informative character are discussed. Possible explanation for the decline of the epidemic after 1980 is presented and the main conditions which must be fulfilled for achieving successful mass trapping of insect pests are listed.
Variable floral phenology: temporal resource heterogeneity and its implication for flower visitors
Authors: Rotenberry John T.
Published: July 2006

I investigated within‐ and between‐year patterns of flowering phenology of entomophilous plants in an isolated old field in northern Michigan, USA. The number of open flowers was censused at 5‐d intervals from June‐September of 1984–1986, and the data analyzed by detrended correspondence analysis. DCA axis 1 reflected within‐year phenology, was highly correlated with date of censusing, and implied substantial constancy in flowering sequences. However, DCA axis 2 revealed significant between‐year variation in abundances of flowers; years differed significantly in their scores on axis 2, and these differences were driven by variable plant species abundances during late summer. Within‐year patterns showed that the floral community consisted of three more‐or‐less distinct temporal “guilds” of plants, and that the rate of turnover in community composition throughout the season was not uniform. The appearance of these guilds was not synchronous across years.

Insects foraging on these species throughout the floral season can expect constancy in the relative timing of blooming, but are exposed to considerable temporal heterogeneity in flower resource abundance both between‐ and within‐years. Opportunities for coevolutionary specialization are therefore likely to be constrained.
Soil factors influencing the distribution of macrofungi in oak forests of southern Sweden
Authors: Rühling Åke , Tyler Germund
Published: July 2006

The macrofungal flora (species producing fruitbodies) of oak forest in Scania and N.E. Småland, south Sweden, is compared on the basis of soil chemical and stand structural properties and general differences in the deposition of acid and acidifying pollutants between these two regions. Deposition in Scania is, on average, twice as high and the mean base saturation of the oak forest humus only half of that in Småland. Species characteristic of soils with high base saturation/pH values (e.g. Cortinarius nemorensis, Entoloma nidorosum, Camarophyllus spp., Marasmius epiphyllus) were usually more common in Småland, whereas the opposite was true for most species characteristic of highly acidic soils (e.g. Entoloma cetratum, Lactarius camphoratus, L. theiogalus, Mycena sanguinolenta). Known changes of soil acidity and base saturation in south Sweden during recent decades and information from this and related studies suggest that the species composition of the macrofungal flora in deciduous forest of south Sweden is gradually changing as a result of changing soil chemistry.
Ammonium uptake by field‐grown Eriophorum vaginatum roots under laboratory and simulated field conditions
Authors: Marion G. M. , Kummerow J.
Published: July 2006

Nitrogen (N) deficiencies in tundra ecosystems could be caused, in part, by the kinetics of root N uptake. The objectives of this study were to quantify NH4uptake by field‐grown excised roots ofEriophorum vaginatumI. under controlled NH4concentrations (0‐250 μmol I‐1) and temperatures (5‐20°C) and to evaluate this laboratory derived model as a means of estimating field NH4uptake. There was no consistent temperature effect on root NH4uptake which suggests a relative in‐sensitivity ofE. vaginatumroots to short‐term temperature fluctuations. The Michaelis‐Menten equation parameters for NH4uptake were Vmax= 22.1 μmol h‐1g‐1and Km= 191 μmol I‐1. Using field NH4concentrations, fieldE. vaginatumroot biomass data, and the Michaelis‐Menten equation, an estimate was made of NH4uptake over a 42 day period; this estimate of NH4uptake accounted for 28% of the net incorporation of N into leaves and roots which is a reasonable estimate forE. vaginatumwhich relies primarily on N retranslocation for supplying new leaves and roots. Major uncertainties in field N uptake rates, model parameterization, and site characterization preclude an accurate model validation and indicate research areas most in need of future study.