bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental demography of the rareGentianella germanica: seed bank formation and microsite effects on seedling establishment
Authors: Fischer Markus , Matthies Diethart
Published: July 2006

The persistence of populations of short‐lived species requires regular reproduction and seedling establishment. A persistent seed bank can buffer populations against extinction in unfavourable years. We experimentally investigated seed fate inGentianella germanica, an endangered biennial species characteristic for species‐rich nutrient‐poor calcareous grasslands in central Europe. We studied the effect of experimental gaps on seedling establishment from sown seeds and the fate of seeds buried in bags over two years. In December 1993 experiments were established at seven calcareous grassland sites in the Swiss Jura mountains. In spring 1994 seedlings emerged in all plots where seeds had been sown, including previously unoccupied patches. This suggests that limited dispersal within sites contributes to small population sizes. Significantly more seedlings emerged at sites with current populations of G.germanicathan at unoccupied sites (5.95% vs 3.40%). Because this difference was not explained by germinations from the natural seed bank it indicates differences in habitat quality. Clipping of the vegetation and disturbance of the soil reduced vegetation cover in the following spring and enhanced seedling emergence. In undisturbed plots 4.5% of seeds sown produced a seedling in spring 1994, whereas in plots with clipped vegetation 9.9% and in disturbed plots 12.7% produced seedlings (p>0.01). This suggests that management measures which create gaps in the vegetation (e.g. grazing) could positively influence population size and persistence ofG. geymanica.On average, we recovered 7.55% viable seeds after one year of burial in bags, and 4.05% after two years, indicating thatG. geymanicahas a persistent seed bank. The demographic data indicate that the number of viable seeds in the seed bank exceeds the number of established plants in a population at least by a factor of 20. Restoration of extinct populations of the species from the seed bank may thus be possible if appropriate management measures are taken within a few years.
Territorial behavior in the speckled wood butterflies Pararge xiphia and P. aegeria of Madeira: a mechanism for interspecific competition
Authors: Jones Martin J. , Lace Lesley A. , Harrison Emma C. , Stevens‐Wood Barry
Published: July 2006

Two species of speckled wood butterfly occur in Medeira. Pararge xiphia is endemic and is very similar in morphology, behaviour and general ecology to P. aegeria which was first recorded on the island in 1976. We collected behavioural data on the males of the two species at sites where the indigenous laurel forest meets non‐native forest and agriculture. It is in these areas that the two species are found together in particularly high densities. Male Pararge butterflies defend sunlit areas of vegetation and attempt to exclude other butterflies. If a territorial intruder is a conspecific or the other Pararge species, extended chases or spiraling flights may take place. Interactions between the two Pararge species are longer and more likely to be escalated than those between either species and a range of other butterfly species. Pararge aegeria is more aggressive in its territorial behaviour than P. xiphia and the latter may be suffering more from the interactions. The results demonstrate that the two species are competing for space and therefore, that territorial behaviour could be a mechanism by which interspecific competition could be taking place. Any adaptive explanation for the interspecifc territoriality remains speculative but this recent and probably natural, colonization may provide an excellent opportunity to examine the role of interspecific competition in structuring communities. The arrival of P. aegeria on Madeira has created an almost unique natural experiment, the study of which will potentially avoid many of the problems traditionally associated with the study of competition.
Bumblebees at an alpine site in northern Sweden: temporal development, population size, and plant utilization
Authors: Stenström Mikael , Bergman Peter
Published: July 2006

The bumblebee community in an alpine valley in northern Sweden was studied for two seasons. Only two species of bumblebees, Bombus alpinus and B. hyperboreus. are common at the site. Bombus hyperhoreus is an obligate nest parasite on B. alpinus: the latter species is four times more abundant than the former. The number of captures on any given day was very low. However, the number of queens foraging in the area was estimated by a mark‐reacapture method to ca 350 specimens, indicating that the queens forage over large areas. The dates for capturing queens carrying pollen in their corbiculae and the emergence of workers and males indicate that the queens only have time to produce one batch (or possibly two overlapping batches) of workers. The utilization of different plant species corresponds well with their flowering phenology at the site. The unspecialized flowers of Saxifraga oppositifolia are the main pollen and nectar source in the early part of the season. The bumblebees switch to Astragalus alpinus and Bartsia alpina as soon as they come into flower: these species show a typical bee pollination syndrome, the corbicular loads most commonly consisted of 91‐100% of pollen from a single species. The change in flower utilization and the composition of the corbicular loads give no support for the hypothesis that aretie bumblebees should be more generalistic in their foraging than temperate species. The preference for Astragalus and Bartsia will probably have an effect on outcrossing in late‐flowering specimens of Saxifraga oppositifolia, which has a very extended flowering period.
Individual variation and the effects of weather, age and flowering history on survival and flowering of the long‐lived perennial Gentiana pneumonanthe
Authors: Rose R. J. , Clarke R. T. , Chapman S. B.
Published: July 2006

Gentiana pneumonanthe, the marsh gentian, is a declining species in both Britain and Europe as a result of loss of its heathland habitat or inappropriate management of that which remains. We analysed long‐term demographic data sets (1977‐1991) from four populations of the plant to test the hypotheses that an individual plant's survival and its chances of flowering in any year are related to its age and performance in previous years, taking into account the climatic conditions that existed in those years The results show that: 1)‘new’plants (2 yr old) had a higher mortality rate (mean = 20.8%) than‘young’(3 yr old) plants (mean = 5.0%), which in turn had a higher mortality than older, ‘mature’ (four or more year old) plants (mean = 3.8%): 2)‘new’ plants had a higher mortality rate after either a growing season with below average rainfall or an above average winter rainfall; 3) mortality of‘mature’plants was independent of age, indicating no evidence of senescence; 4)‘mature’plants had a higher mortality rate after above average rainfall during the previous winter; 5) plants that have flowered within the previous two years are most likely to flower in the current year indicating high individual variation in flowering performance‐ 6) more plants flower and flowering plants produced more flowers in the two years following a warmer than average growing season.

The above factors are related to current site management and the implications are discussed. Suggestions are given for changes in management of the sites where this rare plant occurs.
Factors affecting habitat occupancy by wolves in northern Apennines (northern Italy): a model of habitat suitability
Authors: Massolo Alessandro , Meriggi Alberto
Published: July 2006

The expansion of the wolf population all over Europe has posed problems on wolf‐man coexistence in those areas where the wolf was not present for a long time. Breeding activities are now threatened by high predation on livestock. We investigated the relationship between wolf and its habitat, in order to evaluate wolf habitat suitability and to predict its presence. The study areas covered 3289 km2. A 23 km2 grid was used to identify 143 sample squares. For each sample square 58 habitat variables were measured from land‐use (1:25 000), and from topographical maps. Wolf presence (4 classes) was assessed by scat collection, direct observations, snow tracking, wolf‐howling, and predation records. Univariate and multivariate statistical analyses were carried out to investigate the influence of habitat features on wolf presence. The habitat suitability model was based on two different equations: a dichotomous logistic regression model, and a polytomous one. The first one discriminated between suitable and unsuitable habitats, and its predictions were confirmed in 93% of grouped cases; the second provided predicted values of wolf presence that were concordant with the observed response levels in 82.5% of contrasts. Both models underlined the importance of three factors in determining wolf habitat suitability: wild prey abundance, human presence and forest cover.
Experiments on adhesive dispersal by wood mouse: seed shadows and dispersal distances of 13 plant species from cultivated areas in southern Sweden
Authors: Kiviniemi Katariina , Telenius Anders
Published: July 2006

This study on epizoochory offers experimental data on retention times and potential dispersal distances of propagules of 13 plant species that commonly inhabit cultivated areas in the south of Sweden. Wood mouse Apodemus flavicollis was used as dispersal vector. Seven of the investigated species produce fruits that carry obvious hooks, barbs or bristles and for comparison the remaining six species, lacking such features, were also included. Excised fruits that initially carried appendages were used in a complementary comparison. Propagules were applied by hand to the back of the animals, which were which released in enclosures to move about freely. Observations were made continually until the seeds were dropped. The distance covered by the animals while moving was measured and the potential dispersal distances calculated. Small fruits were in general found to be more efficiently transported than large ones, but large propagules carrying appendages sometimes remained in place for considerable periods. The potential dispersal distances ranged up to nearly 30 m. The retention time was significantly enhanced by the presence of dispersal attributes. The behavioural pattern of the animals (grooming, movements) plays a significant part in the successful transportation of propagules. By comparing the result with similar experiments using fallow deer Dama dama and domestic cattle Bos taurus as dispersal vectors it can be stated that mice are surprisingly effective as seed dispersers. Large mammals disperse propagules on a larger scale (<1 km) compared with small mammals, that affect plant distribution more locally (<100 m). We consider adhesive dispersal a most significant component in plant metapopulation dynamics, considerably enhancing the probability of occasional propagules reaching suitable sites in a fragmented landscape.
Interspecific differences in intraspecific abundance‐range size relationships of British breeding birds
Authors: Gaston Kevin J. , Blackburn Tim M. , Gregory Richard D.
Published: July 2006

A general positive interspecific relationship between local abundance and geographic range size in animals has prompted speculation that a similar relationship might exist intraspecifically, such that a species is widespread at times when it is locally abundant, and more restricted in distribution when it is locally rare. Current evidence suggests that intraspecific relationships often are positive, but that there is considerable variation in the pattern exhibited by species. Here, we use data on British birds to test the hypotheses that species showing a high mean or wide spread of local densities or range sizes will be more likely to show strong intraspecific relationships between abundance and geographic range size. These data show only inconsistent support for an effect of the range of densities or of occupancies on intraspecific abundance‐range size relationships. However, the strength of an intraspecific relationship does seem to be related to the mean occupancy of species, and whether or not a species exhibits temporal trends in density, with the strongest relationships found in species with simultaneous trends in both density and occupancy. We suggest that these results are explained by time lags in the loss or gain of species at occupied sites in response to reductions or increases in density.
Structural heterogeneity and spatial autocorrelation in a natural mature Pinus sylvestris dominated forest
Authors: Kuuluvainen Timo , Järvinen Erkki , Hokkanen Timo J. , Rouvinen Seppo , Heikkinen Kari
Published: July 2006

The tree species composition, vertical stratification and patterns of spatial autocorrelation at the tree and quadrate (25 × 25 m) scales were studied in a natural mature PinuS sylvestris dominated forest in eastern Finland. For the analyses we mapped the locations and dimensions of trees taller than 10 m in a 9 ha (300 × 300 m) area, and within this area we mapped all trees taller than 0.3 m on a core plot of 4 ha (200 × 200 m). The overall tree size distribution was bimodal. the dominant layer and the understory forming the peak frequencies. Pinus sylvestris dominated the main canopy, together with scattered Betula pendula and Picea abies. Alnus incana, Populus tremula, Salix caprea, Sorbus aucuparia and Juniperus communis occurred only in the under‐ and middlestories. Autocorrelation analysis (semivarianee) of tree size variation revealed spatial patterns, which were strongly dependent on the size of trees included in the analysis. When all living trees, including the understory regeneration, were taken into account, the autocorrelation pattern ranged up to 35 m inter‐tree distances, reflecting the spatial scale of understory regeneration patches. Competitive interaction among middle‐ and upperstory trees (height>10 m) had contrasting effects on autocorrelation pattern depending on spatial scale. At the fine scale, dominant trees suppressed their smaller close neighbors (asymmetric competition), which was shown as increased tree size variation at small inter‐tree distances (<2 m). At slightly larger inter‐tree distances, specifically among large trees of similar size, competition was more symmetrical, which resulted in decreased tree size variation at these inter‐tree distances (3–4 m). This effect was seen most clearly in the dominant trees, there being a clear autocorrelation pattern in tree size up to inter‐tree distances of ∼4 m. At the quadrate scale (25 × 25 m) the analysis revealed high local variation in structural characteristics such as tree height diversity (THD), tree species diversity (H) and autocorrelation of tree height. The analysis suggests that naturally developed P. sylvestris forests exhibit complex small‐scale patterns of structural heterogeneity and spatial autocorrelation in tree size. These patterns may be important for stand‐scale habitat diversity and can have aggregated effects on ecosystem dynamics at larger spatial scales though their influence on the spread of disturbance and regeneration after disturbance.
Scale‐dependent spatial variance patterns and correlations of seabirds and prey in the southeastern Bering Sea as revealed by spectral analysis
Authors: Logerwell Elizabeth A. , Hewitt Roger P. , Demer David A.
Published: July 2006

Uni‐ and bivariate spectral analyses of the spatial distribution of thick‐billed murres Uria lomvia and acoustic estimates of prey biomass in the southeastern Bering Sea were used to examine the spatial variance patterns of a predator and its prey at multiple spatial scales. Power, phase and coherency spectra from individual transects, as well as those averaged over all transects, were examined. The average spectra, representing a temporal scale of months, showed that murres and prey had similar spatial variance patterns and were positively correlated over the range of spatial scales studied. The individual spectra, representing a temporal scale of hours, showed several patterns that were not evident in the average spectra. In particular, the transect‐level analyses showed that the correlation between murres and prey was poor at spatial scales where prey variance was relatively low. This result suggests a new hypothesis to explain poor small‐scale correlations between consumers and resources: resource distribution is relatively uniform at small scales resulting in only a slight increase in foraging return for consumers showing an aggregative response at these scales. The differences among spatial scales and between the average and individual spectra illustrate how ecological patterns can vary with temporal and spatial scale.
Distribution of birds in fragments of Mediterranean forests: the role of ecological densities
Authors: Tellería J. L. , Santos T.
Published: July 2006

This paper evaluates the role of ecological densities (densities in a given habitat) in predicting the ability of forest passerines to occupy fragments of eight oak Quercus spp. forest archipelagos of the Iberian Plateaux. Ecological density of individual species was the main predictor of their occurrence in fragments, whereas other biological traits (nesting site) and some potentially important landscape features (local cover of forests or distance to possible sources of individuals) were not correlated to fragment occupation. Feeding substrata of birds was also related to their comparative ability to occupy fragments since, after controlling for the effects of abundance and nesting site, foliage exploiters were more frequent in fragments. These results, that support the empirical usefulness of the random sampling hypothesis in predicting the ability of species to persist in fragments, may be affected by some particular features of the study area. Oak forests of the Iberian Peninsula have been heavily affected by human disturbance for a long time so that interior forest birds are now scarce or extinct and species adapted to shrubby forests form the bulk of these bird communities. It is possible that these species will not perceive differences in the habitat suitability of fragments, increasing the likelihood that stochastic sampling processes dictate their patch occupancy.
Body mass and winter mortality in red deer calves: disentangling sex and climate effects
Authors: Loison Anne , Langvatn Rolf , Solberg Erling Johan
Published: July 2006

Understanding population dynamics of large mammals requires studies of variation in the age and sex–specific demographic parameters over time and the factors causing this variation. Here, we have focused on the variation in body mass of 8‐10–month old red deer calves, in relation to climate and sex over a 20‐yr period (1977–1997). We investigated the relationship between body mass and over–winter mortality during 1985 and 1986 and thereby, the phenotypic selection on body mass. We found a high variability from year to year in calf body mass. Males were consistently heavier than females. No interaction between sex and year was detected. The body mass of individuals from the same cohort shot during the annual hunting season and snow depth in January each explained ca 20% of the variability in calf body mass. Body mass loss during winter did not differ between sexes, but increased with body mass and varied from year to year. The probability of surviving was strongly related to body mass in each sex. For a given body mass relative to the sex–specific mean, males had a lower probability of survival than females. Hence, males had to be 1 kg larger than their mean in order to achieve the same survival as average‐sized females. Our results suggested a directional phenotypic selection on body mass that led to an increasing body mass dimorphism in calves. The strength of this selection and the sex difference in the shape of the selection curve may depend, however, on the severity of winter and on sexual dimorphism in body mass at the beginning of winter.
Reproductive biology of the arctic collembolan Hypogastrura tullbergi
Authors: Birkemoe Tone , Leinaas Hans Petter
Published: July 2006

Terrestrial organisms of the Arctic are faced with strong climatic fluctuations. Predictable seasonality with cold/long winters and short/cool summers are combined with unpredictable between and within year variation. This indicates that various selection pressures act on the reproductive strategies of the populations. The arctic collembolanHypogastrura tullbergireproduces in a short period following snow melt. Hatching occurs in late summer, the animals grow to adult size within their second summer and reproduce for the first time in the beginning of their third summer. We performed several experiments to determine the reproductive investment and proximate mechanism that regulate timing and duration of reproduction. We found thatH. tullbergientered a reproductive diapause when reared at constant temperature, a diapause that was terminated by a cold exposure (winter). Surprisingly, cold exposure of small juveniles may also prevent development of a reproductive diapause in adults. Thus, the life‐cycle normally spanning 2 yr can potentially be reduced to one year if the overwintering juveniles reach maturity before the end of the reproductive period in the field. After termination of the diapause, the animals reproduced up to 3 times during a period of 6 weeks at 15°C. This reproductive period was considerably longer (measured in degree days) than the one observed in the field. Our results suggested that temperature quiescence, i.e. the inability to reproduce under a certain temperature threshold, may adjust the termination of the reproductive period with current temperature before a new diapause occurs in late summer. The cost of reproduction was low and suggests that it can be adaptive to spread reproduction over more than one year. The results are discussed in relation to the arctic climate and strategies favoured by unpredictable and predictable (seasonal) variations in the environment. The present study forms part of a larger investigation on population dynamics and life history strategies ofH. tullbergifrom the Arctic.
Bryophytes, lichens and phanerogams in an alvar grassland: relationships at different scales and contributions to plant community pattern
Authors: Zamfir Manuela , Dai Xiaobing , Maarel Eddy van der
Published: July 2006

The relationship between bryophytes and lichens versus phanerogams has been investigated in three stands of a limestone grassland community, along three transects of 500 10 X 10 cm plots. Ordination axes resulting from Detrended Correspondence Analysis for bryophytes and lichens versus phanerogams were correlated using Spearman rank correlation coefficient. The effect of grain (sample plot) size on relationships between species along the gradient and on the correlation between the layers formed by bryophytes and lichens (cryptogams) and phanerogams, and with environmental variables has been as well examined. Values for light, moisture, pH and nitrogen have been derived from the vegetation itself with the help of Ellenberg indicator values. The relative position of species in the ordination space is more or less the same until grain size 3 (10 x 40 cm) for cryptogams and phanerogams and until grain size 2 (10 × 20 cm) for all‐species together. Therefore, it is suggested that sample plot sizes of 10 × 10 cm to 10×20 cm are appropriate as units for field experiments testing interactions between cryptogams and phanerogams. The respective layers were weakly correlated and the correlation between them increased with increase in grain size. The correlation of DCA axis 1 from the ordination of cryptogams, phanerogams and all‐species with the environmental factors was weak and similar in order of magnitude. Only the environmental variables which were strongly correlated with the DCA axis 1 increased in correlation at larger grain sizes. The ordinations of cryptogams, phanerogams and all‐species were correlated along DCA axis 1 with pH in all investigated stands and at almost all grain sizes. Multi‐species patches have been detected by pattern analysis (PASFRAN) on DCA sample scores from ordinations of cryptogams, phanerogams and combined matrices. Multi‐species patterns with sizes between 20‐240 cm. composed by bryophytes and lichens and by phanerogams have been found. Complex patterns formed by cryptogams and phanerogams together, which are different in size than those in the separate layers, suggest that bryophytes + lichens and phanerogams may interact with each other.
Danish forest development during the last 3000 years reconstructed from regional pollen data
Authors: Bradshaw Richard , Holmqvist Björn H.
Published: July 2006

Most present Danish forest types are a direct result of recent silvicultural practice. We use fossil pollen data converted into estimates of tree abundance to map the development of forest types during the last 3000 radioearbon yr. The forest types were clusters in an artificial neural network based on all available European Holocene pollen data. Diverse deciduous forest types found 3000 yr ago were replaced by less diverse Fagus‐dominated types over a period of 2000 yr. The present day map contained many new combinations of tree species, dominated by Picea and Pinus. The association between the increase in non‐forest communities and establishment of Fagus suggests that anthropogenic activity has accelerated the loss of species‐rich deciduous forest with abundant .Alnus, Corylus, Quercus and Tilia. We conclude that the natural forest composition of Denmark would be deciduous forest today with a significant presence of Fugus sylvatica. Recent forest development has created a break in compositional continuity with the past that is unnatural and has posed problems for forest‐dependent biota.
Patterns of host use in solitary parasitoids (Hymenoptera, Ichneumonidae): field evidence from a homogeneous habitat
Authors: Teder Tiit , Tammaru Toomas , Pedmanson Rein
Published: July 2006

Teder, T., Tammaru, T. and Pedmanson, R. 1999. Patterns of host use in solitary parasitoids (Hymenoptera, Ichneumonidae): field evidence from a homogeneous habitat. ‐ Ecography 22: 79‐86.

We detected a significant inter‐ and intraspecific host preference on the level of individual host use in a system, in which three moth species (Lepidoptera: Noctuidae), feeding on a cattail Typha latifolia, are parasitized by three solitary parasitoid species (Hymenoptera: Ichneumonidae). The biology of the host species is similar but they exhibit remarkable inter‐ and intraspecific variance in body size. All the parasitoid species preferred the largest host species in this system whereas other host species were used only occasionally. We found that parasitoids which emerged from females of the preferred host species were larger than those which developed in males of the same species. Accordingly, two of the parasitoid species had a significant within‐host‐species preference: females of the largest moth species were used more often than males. No dependence of the preference pattern on host density was found. This pattern of host use is discussed in the light of the switching theory and the optimal host selection theory. Our results indicate that non‐random host use by parasitoids may have significant effects on host populations and communities, and forms a potential selective factor against large body size in herbivorous insects. Unlike the majority of ichneumonid wasps, these three parasitoid species have no remarkable female‐biased sexual size dimorphism, in accordance with the predictions of Charnov's sex allocation theory for this case, we did not observe any significant host quality dependent biases in sex allocation: there was no association between host sex and parasitoid sex, neither did parasitoid sex ratio differ between years with different host quality.
Effects of newly planted hedges on ground‐beetle diversity (Coleoptera, Carabidae) in an agricultural landscape
Authors: Fournier Elisabeth , Loreau Michel
Published: July 2006

The diversity of ground‐beetle communities (Coleoptera. Carabidae) was studied to assess the short‐term impact of new hedges planted in an intensive agro‐ecosystem. Hedges represent a new and undisturbed habitat for those polyphagous predators and may provide increased prey availability. Carabids were sampled with pitfall traps in a hedge and an adjacent cultivated field during the whole activity period of these insects to assess the effect of distance from the hedge on species diversity. Fenced pitfall traps were also used to estimate absolute population densities. Several diversity indices were calculated at various sampling levels (total area, distance treatment, trap). Kendall's coefficient of rank correlation between communities at adjacent distances showed that the greatest changes in species relative abundances occurred close to the hedge. Indices of species richness, dominance concentration, equitability and Fisher's a all indicated a significant decrease in species diversity with increasing distance from the hedge. These trends are explained by two complementary factors. First, the number of species decreased significantly with distance from the centre of the hedge. Second, the various species had different spatial patterns of total capture and absolute density. Four groups of species can thus be distinguished: species restricted to the hedge, species preferring the hedge, species preferring the crop, and species unaffected by the hedge. The respective roles of small‐scale abiotic changes in habitat structure and differences in prey availability are discussed.
On the relative importance of history and ecology in structuring communities of desert small animals
Authors: Kelt Douglas A.
Published: July 2006

Several recent studies have compared small mammal community structure across multiple deserts on different continents. These studies have tacitly assumed that variation in community structure was greater between continents than within, and so have not evaluated variation across desert regions within continents. I evaluated several metrics of community structure and a model of community assembly for four desert regions in North America ‐ the Great Basin, Mojave. Sonoran. and Chihuahuan Deserts in order to explicitly compare these metrics across these deserts. Additionally. I compared these results with similar analyses conducted on two desert regions in central Asia ‐ the Gobi Desert and the Turan Desert Region to evaluate the relative magnitude of intra‐ vs inter‐continental variation. Although the patterns observed are complex, they demonstrated marked heterogeneity in desert small mammal communities within North America. However, this heterogeneity is much less than that observed in inter‐continental comparisons, in which Asian and North American deserts differ markedly. These results agree with other recent studies providing limited or no support for the existence of substantial convergence in community characteristics or ecological function across geographically distant regions. Rather, the results support the hypothesis that the common evolutionary history of faunas in globally disjunct landmasses has had a stronger influence on the evolution of communities and faunas than do regional variations in climate, physiography, etc. Whereas a common ecological setting may have large impacts on some facets of organismal structure (e.g., bipedalism in desert small mammals), common evolutionary history appears to have a more profound influence on local dynamics.
Global distribution of free‐living microbial species
Authors: Finlay B. J. , Esteban G. F. , Olmo J. L. , Tyler P. A.
Published: July 2006

Species of large animals and plants have geographically restricted distributions, but it is unclear if this also applies to free‐living micro‐organisms. We have attempted to clarify this, by investigating the ciliated protozoa living in a habitat that is separated from northern Europe by geographical barriers and great distance ‐ the sediment of a Holocene volcanic crater‐lake with brackish water, in Australia. Of the 85 ciliate species recorded, none was ‘new’, and all (apart from one species previously described only from tropical Africa) are known from northern Europe. All species appear to have reached the crater by passive dispersal from other freshwater and marine environments. The significance of this finding lies in the fact that ciliates are among the largest and most fragile of microbes. If ciliate species have global distributions, it is likely that the same is true for the many smaller, more abundant and more easily dispersed microbial species, including bacteria. There is some support for this in the literature, and most species smaller than ca 1 mm may have global distributions. Biodiversity at the microbial level is fundamentally different from that of macroscopic animals and plants, and it may be difficult to make realistic extrapolations from the attributes of microbial communities, to biodiversity in general.
The role of local adaptation in the relationship between an endangered root hemiparasite Euphrasia rostkoviana, and its host, Agrostis capillaris
Authors: Lammi Antti , Siikamäki Pirkko , Salonen Veikko
Published: July 2006

We experimentally studied the role of local adaptation and the co‐evolutionary relationship between an annual, endangered root hemiparasiteEuphrasia rostkovianaand its main hostAgrostis capillaris.According to our hypothesis, the existence of local adaptation in hemiparasites should be observable in better hemiparasite performance when attached toA. capillarishosts originating FromEuphrasiapopulations. After one month of growth, the height and the number of leaves of hemiparasites were not affected by the origin of their hosts. The differences in growth were due to between population effects. The situation remained constant after three months. Hemiparasite biomass was not affected by the origin of the hosts. The percentage of hemiparasites surviving after one. two and three months was not affected by the origin of the hosts although there was a weak tendency towards better survival of hemiparasites with familiar hosts than with unfamiliar hosts. All variables used to measure hemiparasite performance during its complete life‐cycle gave only limited support for the local adaptation hypothesis. Nevertheless, the familiar hosts suffered less from parasitism as indicated by their higher biomass after the experiment. This suggests that there may be some interactions between hemiparasites and their hosts based on their spatial population structure and common history as competitors.
Small‐scale plant species richness in calcareous grasslands determined by the species pool, community age and shoot density
Authors: Pärtel Meelis , Zobel Martin
Published: July 2006

Variation in small‐scale plant species richness was examined between twenty discrete sites of calcareous alvar grasslands in the western Estonian coastal area. This community type is very species rich at the small‐scale. The pattern of diversity has often been explained by variation in ecological conditions which makes it possible to avoid competitive exclusion. Here we test an alternative species pool hypothesis. The species pool was defined as the set of species present in a community, but excluding all those species whose presence may be connected with exceptional environmental conditions for this community. Monte Carlo modelling was used to determine the strengths of the relationships between the non‐independent variables: richness vs species pool and average shoot density vs richness. Site age was characterized by its elevation above sea level, since there is a continuous land uplift in the study area. Species richness was positively correlated to the size of the species pool, community age and vegetation density. We conclude that historical processes on both the regional and local levels, which determine the arrival of any particular species to a target community, and not environmental heterogeneity, are responsible for the variations in species richness between communities of this type.
Spatial patterns of ground vegetation, soil microbial biomass and activity in a mixed spruce‐birch stand
Authors: Saetre Peter
Published: July 2006

Trees directly and indirectly influence the above‐ and below‐ground environment, and can be expected to modify the spatial patterns of organisms associated with the forest floor. This study aimed to examine the effects of a coniferous (Picea abies) and a broad‐leaved (Betula pubescens) tree species on the spatial pattern of ground vegetation and soil microbial properties in a mixed stand in central Sweden. I have characterised the species composition of ground vegetation, soil microbial biomass and activity, photosynthetic active radiation (PAR), soil water content and soil pH in the stand, and tested whether the spatial patterns of these variables were related to the positioning of trees. Geostatistics were used to describe the spatial variation in ground vegetation, soil mirobiological properties and the soil surface environment. PAR, soil water content and the cover of the moss Brachytecium reflexum and associated herb species decreased with the influence of spruce trees. Microbial biomass, measured as the amount of phospholipid fatty acids, decreased with spruce influence but increased with the influence of birch trees. Microbial respiration was not affected by spruce but increased with the influence of birch. Ground vegetation and microbial respiration, which were influenced by one tree species only, aggregate on a scale of 4‐5 m, corresponding fairly well with patches of a single tree species. Soil microbial biomass, which was affected by both tree species, aggregated on a scale of 7‐8 m. roughly corresponding to the distance between patches of spruce and birch trees respectively. I suggest that spruce trees influenced vegetation mainly through shading, and that a difference in the availability of organic matter under birch and spruce trees caused spatial variation in microbial biomass and activity. Thus, spatial patterns in ground vegetation and soil microbial properties may develop in a mixed forest of coniferous‐broad leaved trees, as a result of the difference in influence of tree species and nested variation associated with the arrangement of the trees.
Dispersal of Spanish juniper Juniperus thurifera by birds and mammals in a fragmented landscape
Authors: Santos Tomás , Tellería José L. , Virgós Emilio
Published: July 2006

Dispersal of Spanish juniper Juniperus thurifera was examined in a farming landscape of central Spain to study the effects of fragmentation on the dispersal effectiveness of the different dispersers. and the consequences for the plant. The study was conducted in two large forests (LF: 280 and 150 ha) representative of unfragmented conditions, and 18 small isolated fragments (0.1 ‐3 ha) which were classified in two groups: 1) F1, forest remnants with both high juniper cover and cone production (N = 5): and 2) F2, remnants in which fragmentation has caused a heavy reduction in junipers (N = 13). Cone production, disperser abundances and quantity of dispersal by birds (Turdus thrushes) and mammals (carnivores, rabbits and sheep) were estimated throughout two study years. Dispersal by thrushes was measured in three types of trees representing a decreasing attraction focus to birds: Spanish junipers with cones (SJI). Spanish junipers without cones (SJ2) and holm oaks (HO).

Cone production greatly decreased from LF to F1 and F2 in both study years, affecting F2 dramatically. Thrush abundances were similar in LF and F1, but thrushes lacked or were very scarce in F2, Carnivores showed an even distribution throughout the whole area, but herbivores were relatively scarce in F2 fragments, especially rabbits, which were lacking in the fragments under 0.6 ha. Patterns of seed deposition around trees showed decreasing dispersal activity of thrushes from SJ1 (83.1% of the examined trees had seed‐packets thrush pellets) to SJ2 (53.6%) and HO (23.6%.). Both distribution patterns and density of pellets were roughly similar in LF and F1. but pellets were only recorded in one (SJ1) out of 159 trees examined in F2. supporting thrushes behaved as specialist feeders and thus avoided the patches devoid of juniper cones. Average densities of pellets in LF reached 397.6 pellets ha‐1, surpassing at least 30 times the quantitative effectiveness (seed‐packets ha‐1) of mammal dispersers. Juniper seeds were present but very scarce in the mammal faeces collected in both fragments F1 and F2. Overall, the quantitative effectiveness of carnivores was nearly 4 times lower in the fragments than in LF, and that of herbivores 11 times lower. This result is consistent with the lower availability of juniper cones in the fragments and. together the distribution of mammal abundances, fits the prediction that mammals (except rabbits) moved among landscape patches according to the total availability of food supplies.

Overall, results showed that dispersal of Spanish juniper in fragments F2 is seriously impaired by the loss of their main dispersers (thrushes), and that recruitment became dependent upon mammal dispersers with a low quantitative effectiveness, namely carnivores and sheep.
Habitat fragmentation and large‐scale conservation: what do we know for sure?
Authors: Harrison Susan , Bruna Emilio
Published: July 2006

We review the ecological effects of habitat fragmentation, comparing the theoretical approaches that have been taken to understanding it with the existing evidence from empirical studies. Theory has emphasized the spatial aspects of fragmentation and the role of dispersal among patches, and has generated interesting predictions such as a nonlinear relationship between the amount of remaining habitat and the probability of species persistence. However, while the few available large‐scale empirical studies of fragmentation all tend to show that it has major effects, these documented effects tend to be relatively simple ones such as the degradation of habitat quality within fragments. There is good reason to be cautious of any claim that corridors or the spatial configuration of remaining habitat can compensate for the overall loss of habitat.

This is an invited Minireview on the occasion of the 50th anniversary of the Nordic Ecological Society Oikos.
Body size vs abundance among parasite species: positive relationships?
Authors: Poulin Robert
Published: July 2006

Across species, abundance usually correlates negatively with body size. This intuitive pattern may result from size‐dependent resource requirements in habitats where only finite amounts of resources are available. Among parasite species, it is possible that some resource limitations arc less severe than for free‐living animals although this may depend on the type of parasites. The interspecific relationship between body size and abundance (measured as prevalence and intensity of infection) among parasites was tested in two groups of parasites. Among helminth endoparasites of fish, parasite body size correlated positively with prevalence and negatively with intensity of infection. Among copepod ectoparasites of fish, body size correlated positively with both prevalence and intensity. These trends were observed after controlling for the confounding influences of phylogeny and sampling effort. These contrasting patterns may result from the more intense link between body size and intensity‐dependent regulation in endoparasites than in ectoparasites. The results of this comparative analysis suggest that parasite body size could be an important factor determining aspects of parasite abundance and distribution, including aggregation.
Modelling wildlife distributions: Logistic Multiple Regression vs Overlap Analysis
Authors: Brito C. , Crespo E. G. , Paulo O. S.
Published: July 2006

We compare the results, benefits and disadvantages of two techniques for modelling wildlife species distribution: Logistic Regression and Overlap Analysis. While Logistic Regression uses mathematic equations to correlate variables with presence/absence of the species. Overlap Analysis simply combine variables with the presence points, eliminating the non‐explanatory variables and recombining the others. Both techniques were performed in a Geographic Information System and we attempted to minimise the spatial autocorrelation of data. The species used was the Schreiber's green lizard Lacerta schreiberi and the study area was Portugal, using 10 X 10 km UTM squares. Both techniques identified the same group of variables as the most important for explaining the distribution of the species. Both techniques gave high average correct classification rates for the squares with presence of the species (79% for Logistic Regression and 92% for Overlap Analysis). Correct absence classification was higher with Logistic Regression (73%) than with Overlap Analysis (32%), Overlap Analysis tends to maximise the potential area of occurrence of the species, which induces a reduced correct classification of absences, since many absences will fall in the potential area. This is because a single presence in a given class of a variable makes all the area of that class to be considered as potential. The technique does not consider that the species may occasionally occupy an unfavourable region. Although, in Logistic Regression, modelling procedures are more complex and time‐consuming, the results are more statistically robust. Moreover. Logistic Regression has the capability of associating probability of occurrence to the potential area. Overlap Analysis is very simple in building procedures and swift in obtaining reliable potential areas. It is a valid technique especially in exploratory analysis of species distributions or in the initial stages of research when data may be scarce.
Can natural enemies enforce geographical range limits?
Authors: Hochberg Michael E. , Ives Anthony R.
Published: July 2006

We develop a simple mathematical model to investigate the question as to whether a specialised consumer can be responsible for creating a range limit in the population of its dynamic resource. The model is most attuned for parasitoid‐host relationships, but the central results should apply to a broad range of systems. Specifically, at the beginning of each simulation host and parasitoid populations are distributed at random along a string of patches. In each discrete generation and for each patch, host and parasitoid populations grow and interact, and then a constant fraction of those remaining disperses one or more patch distances in either direction according to a geometric distribution. We iterate the model 200 generations, and in any generation for any patch, either host and/or parasitoid can go locally extinct if its population falls below a threshold density. We find that a specialised parasitoid can enforce a limit, and it is even more likely to fragment its host population. The two most important conditions for parasitoid‐enforced range limits are: 1) the theoretical host equilibrium density in the presence of the parasitoid be very small at sites eliminated from the host's range, and 2) the parasitoid disperses at high rates. We close by discussing our findings for specialist and generalist natural enemies, and the relevance of our study to the wealth of investigations on the causes of geographical range limits.