bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of an ecotone to test the effects of soil and desert rodents on the distribution of Indian ricegrass
Authors: Breck Stewart W. , Jenkins Stephen H.
Published: July 2006

Effects of soil factors and seed‐dispersing heteromyid rodents on the distribution of Indian ricegrass Achnatherum hymenoides were studied at a sharp ecotone between a sandy area with abundant Indian ricegrass and a rocky area where Indian ricegrass was scarce Two hypotheses were tested 1) Soil factors limited the recruitment rate of Indian ricegrass in the rocky habitat, and 2) Heteromyid rodents limited the distribution of Indian ricegrass because they did not scatterhoard seeds in the rocky habitat Seed‐planting experiments and soil analyses showed that soil characteristics, especially texture and salinity, limited the distribution of Indian ricegrass, but also that microsites existed in the rocky habitat that were suitable for germination and growth of Indian ricegrass In particular, as many plants survived over their first winter in the rocky habitat as in the sandy habitat, although surviving plants were taller in the sandy habitat Analysis of the soil seed bank indicated that fewer seeds were dispersed to the rocky habitat than to the sandy habitat To determine whether scatterhoards were being made in the rocky habitat, seeds dyed with fluorescent powder were placed along the ecotone and the fates of these seeds were assessed Twice as many of these seeds were scatterhoarded in the sandy habitat as in the rocky habitat and seeds were cached further from the ecotone in the sandy habitat The results suggest that both soil characteristics and heteromyid rodents influence the distribution of Indian ricegrass in westem Nevada
Substrate use of three epiphytic bromeliads
Authors: Zotz Gerhard
Published: July 2006

In the moist tropical forest of Barro Colorado Island, Panama, the distribution of three epiphytic bromehads growing on the host tree species Annona glabra was studied with respect to size of the epiphyte, substrate height, diameter, branch inclination and position relative to the periphery of the crown There were significant interspecific differences for almost all environmental variables, but there were no size‐related changes in distribution patterns The results suggest that a safe germination site is also a potential growing site for mature plants, and that mortality does not correlate with any of the measured parameters
Effects of habitat fragmentation on foraging behaviour of tits and related species: does niche space vary in relation to size and degree of isolation of forest fragments?
Authors: Nour Nadia , Matthysen Erik , Dhondt André A.
Published: July 2006

We studied the winter foraging niches of tits and related species in deciduous forest fragments varying in size between 1 and 30 ha (plus one forest of 200 ha) in order to investigate the influence of forest fragmentation on foraging niches Very few correlations between niche structure (foraging niche, width and overlap) and forest size or isolation turned out to be significant This implies that either the species that disappear in small fragments are those that suffer most from competition (making the effect unmeasurable), or that competition is relatively unimportant for niche structure In any case we find no evidence that foraging niches are strongly affected by the changes (in habitat and/or community structure) associated with fragmentation
Nest predation in hole‐nesting birds in relation to habitat edge: an experiment
Authors: Pöysä Hannu , Milonoff Markku , Virtanen Juha
Published: July 2006

We experimentally tested the hypothesis that nest predation rate in hole‐nesting birds, especially the common goldeneye Bucephala clangula, was related to the edge between aquatic and terrestrial habitats We also studied whether nest predation rate was related to habitat patch (lake) size In three study areas nest‐boxes were erected in pairs one nest‐box was erected at the shoreline and the other one inside the forest at a varying distance (range from 14 to 140 m) from the shoreline One chicken egg was placed in each nest‐box (dummy nest) Overall predation rate on dummy nests varied from 34 6% to 52 6% depending on the study area The pine marten Martes manes was the primary nest predator m all study areas Daily predation rates did not differ between natural and dummy nests Predation rate on dummy nests was not related to the distance of the nest‐box from the shoreline in any study area Predation rate was not related to lake size in two study areas but in one area predation rate on dummy nests was lower around largest lakes However, the result may be accidental and not because of lake size per se because the proportion of forest was exceptionally low in that part of the study area
Predicting plant species distribution patterns using simple climatic parameters: a case study of Ecuadorian palms
Authors: Skov Flemming , Borchsenius Finn
Published: July 2006

A Geographic Information System (GIS) is used to model plant distributions The model IS based on annual mean temperature, humidity, and a georeferenced specimen data base and predicts potential and probable distribution for each taxa in the data base Potential distribution range is suitable area determined by climatic constraints Probable distribution range is here defined as the pan of the potential range where a taxon is most likely lo be found based on distance to existing collections Gridded estimates of climatic parameters were calculated based on a Digital Elevation Model and data from ca 100 weather stations The palm family in Ecuador was used to demonstrate the model Potential and probable distribution ranges were calculated for each of the 127 Ecuadorian palm species Maps of potential and probable species richness were calculated by overlaying and accumulating individual distribution maps Potential species richness was highest in the Amazon lowland where it reached 60 species and lowest in the higher parts of the Andes and drier parts of the coastal plain The probable species richness followed a similar pattern but was nowhere higher than 47 species The ratio between potential species richness and probable species richness was used to find areas that are insufficiently sampled
Spruce‐fir growth form changes in the forest‐tundra ecotone of Rocky Mountain National Park, Colorado, USA
Authors: Hessl Amy E. , Baker William L.
Published: July 2006

Tree regeneration has traditionally been used as a measure of the response of treeline to climate Changes in growth form of krummholz trees may also indicate whether treeline is responding to changes in climate The purpose of this study was to determine whether krummholz trees m the forest‐tundra ecotone of Rocky Mountain National Park, Colorado have experienced significant vertical stem growth, in the absence of mortality, and if this growth occurred in response to recent changes in climate We sampled and dated Engelmann spruce and subalpine fir krummholz leaders stratified by height class at three sampling locations to determine the dates leaders initiated growth above mean snow depth At one sampling location, 215 additional leaders were sampled to construct an age structure of leader release dates Dates of leader release taken from the age structure were compared with seasonal temperatures, seasonal precipitation, winter snow depths, and annual runoff using t‐tests Dates of leader release were also compared to proxy climate records for the southern Rocky Mountain region Based on historical photos as well as the data presented here, both spruce and fir krummholz trees experienced significant height growth as early as the 1850's and continued to grow vertically, at least through the 1970's This vertical stem growth occurred in the absence of significant mortality Running mean annual temperature and May snow depth are both positively associated with years of leader release, suggesting that a warmer, wetter climate, possibly following the end of the Little Ice Age ca 1850, may have induced these changes in the ecotone
Space use in the root vole: basic patterns and variability
Authors: Gliwicz Joanna
Published: July 2006

Home range characteristics and spatial organization of the root vole Microtus oeconomus were assessed by radio‐tracking The aim of this paper is to test the assumption that each microtine species employs a certain modal spatial system around which there is considerable flexibility In the studied population the basic modes of spatial organization were female territoriality and male use of overlapping home ranges Female territories were significantly smaller and less diversified in size than male ranges The size of male home ranges was positively correlated with body mass Each female territory was overlapped by several male ranges, larger male ranges usually overlapped more female territories The above spatial organization suggests that the prevailing mating system in the root vole is promiscuity, and larger males have an access to more receptive females than have small‐sized males

Departures from these basic modes were found among young mature females from summer cohort, forming clusters even at low density, and occasionally among females in locally crowded habitat patches, where they held overlapping home ranges A single male usually monopolized such a cluster, excluding other males from the area used by the females
Floristic changes related to grazing intensity in a Patagonian shrub steppe
Authors: Perelman Susana B. , León Rolando J. C. , Bussacca Juan P.
Published: July 2006

Sheep grazing in and and semiarid Patagonia have the natural vegetation as their exclusive source of food This paper studies the flonstic changes that occur as a response to grazing in the Stipa speciosa, Stipa humilis, Adesmta campestris, Berberis heterophylla, and Poa lanugmosa community in the SW of Chubut (Argentina) by companson of community characters between areas with different degrees of histoncal grazing Stands located on typical zonal soils with sandy cover were sampled, including pairs of stands from neighbouring fields with different grazing history and two areas where large herbivores had been excluded for 27 and 9 yr, respectively Species cover values were recorded m 37 samples of ca 500 m2 each A PCA species ordination with the aid of site biplot graphs and species cluster analysis allowed for the identification of five groups of species with differential response to grazing Relative cover of shrub species was positively correlated with grazing intensity, but total plant cover and flonstic nchness showed a less obvious decreasing tendency Diversity was not correlated with this gradient Some of the decreasing species belong to the group shared with the more mesic grassy steppe, and some of the increasing ones belong to the one shared with the more xenc low shrub steppe These results are in accordance with models which propose that continuous grazing promotes a xerophytization of and and semiarid plant communities
Distribution of birds in natural landscape mosaics of old‐growth forests in northern Sweden: relations to habitat area and landscape context
Authors: Edenius Lars , Sjöberg Kjell
Published: July 2006

We censused breeding birds for three years in natural landscape mosaics of virgin old‐growth spruce forest and mire in a large protected forest area in northern Sweden Twenty forest patches, ranging from 0 2 to 17 8 ha in size, were selected in two matrix types, dominated by forest and mire, respectively Patches were very similar with regards to habitat features There was a strong effect of patch area on species richness, but no effect of matrix type Standardization of species richness by rarefaction revealed that small patches (<5 ha) had fewer and large patches (>10 ha) more species than expected Overall distribution of species across patches showed a highly significant nested pattern, indicating that a few habitat generalists occupy all size classes, whereas more demanding species avoid small patches regardless of landscape composition Individual species tended to be distributed evenly across patch classes and no significant edge effect in terms of density of birds was found Our results have bearings on actions to preserve avian diversity in northern boreal forests small patches (<5 ha) provide habitat only for habitat generalists, and therefore larger (>10 ha) patches should be preserved
Feeding ecology of barnacle geese on their spring staging grounds in northern Iceland
Authors: Percival S. M. , Percival T.
Published: July 2006

The distribution and abundance of barnacle geese, Branta leucopsis. staging in northern Iceland was determined in May 1987 and 1994 A similar proportion of the total population (70%) was located in the two years The distribution differed between the two years, with a higher proportion of the geese found in more westerly sites in 1994 Over 80% of records of birds feeding were on improved agricultural pasture though this made up only 47% of the available feeding habitat Some geese fed on riverine and coastal grasslands but this was in a much smaller proportion than the availability of these habitats The number of geese using a site was positively correlated with the area of improved pasture Birds fed intensively through the day, suggesting that the area is important for the accumulation of nutrient stores No differences in habitat use or feeding behaviour were found between 1987 and 1994
The diversity of cloud forest birds on the eastern and western slopes of the Ecuadorian Andes: a latitudinal and comparative analysis with implications for conservation
Authors: Poulsen Bent Otto , Krabbe Niels
Published: July 2006

We studied the avifaunas of five cloud forest localities at 3000–3350 mas1 on the eastern slope of the Andes of Ecuador A method standardised for area, altitude and effort was the basis for obtaining data on species richness and abundances Richness and abundances (diversity) were unchanged along the limned latitudinal gradient (530 km) studied, whereas there was a considerable turnover in community structure between localities This result has important implications for ranking conservation priorities the total community richness and the dominance/evenness component of diversity does not provide a basis for making priorities along this limited latitudinal gradient Instead, species compositions and species referred to threatened categories (e g, endemics, restricted–range, IUCN threatened/near–threatened, CITES) will be the most meaningful data for making priorities for conservation We compared our results with similar results from the Andean western slope of Ecuador, obtained with the same method and standardised for time of the year The number of species was significantly higher on the eastern slope than on the western slope, a characteristic that can be explained from differences in extension of adjacent source areas and geohistory However, because the species compositions on the two slopes are rather different, it is not recommended to use the difference in richness to rank conservation priorities Abundances were quite similar on both sides of the Andes Contrary to the general belief, the montane avifaunas investigated have tropical and not temperate species richness which agrees with the tropical clutch sizes found among montane birds The avian richness found on the eastern slope of Ecuador near the Equator is definitely among the highest m the world for this altitude
Long‐term variation in, and effects of fertiliser addition on, flower, fruit and seed production in the tree Sorbus aucuparia (Rosaceae)
Authors: Sperens Ulf
Published: July 2006

In this paper, I present long‐term data on reproduction for the tree Sorbus aucuparia Variation in fruit‐set (6 yr) m 22 trees in one population is described and related to flower predation, climate and floral display size Fruit production is described for 7 yr m eight trees in each of four populations and related to climate An additional study, application of a mineral fertiliser, was conducted to test if nutrient availability affected flower, fruit and seed production

The descriptive study showed that mean fruit‐set differed significantly between individuals and years The ranges of yearly mean proportion of initiated fruit/flower, mature fruit/initiated fruit and mature fruit/flower were large (12‐41%, 2‐72% and 0 3‐23%, respectively) Predation of flowers was low, 1% on average (range 0 3‐2%) Between‐year variations in fruit‐set were positively correlated (though not significant) with precipitation during the phase of initiation and maturation of fruits, respectively

Fruit‐set was independent of floral display size when expressed as number of inflorescences per tree However, when floral display size was expressed as number of flowers per inflorescence, there was a tendency for large inflorescences to have a smaller proportion of initiated fruit/flower and mature fruit/flower than small inflorescences

The number of fruits produced by the four populations studied varied significantly among years, populations and individuals Individual fruit production varied considerably between the worst and the best fruiting year (range = 101‐103'x) Annual average fruit production m the populations was found to be in general positively correlated with precipitation the preceding year and negatively correlated with temperature, irradiance and fruit production the preceding year However, none of these correlations reached statistical significance

In the fertilisation experiment, experimental trees produced significantly more flowers, fruits and seeds per tree, compared with control trees This increase was due to an increased number of inflorescences per tree and number of flowers per inflorescence In none of the years, irrespective of flowering, did experimental trees produce proportionally more fruits (i e larger fruit‐flower ratio) and more seeds per fruit than control trees Furthermore, experimental and control trees showed similar inter‐annual variation m flower and fruit production
Mass balance and nitrogen accumulation in hummocks on a South Swedish bog during the late Holocene
Authors: Malmer Nils , Svensson Göran , Wallén Bo
Published: July 2006

Two peat cores from the Store Mosse mire in the central part of South Sweden have been analyzed for dry bulk density, carbon, and nitrogen They cover the development of the peat mound from the time of the conversion of the initial fen to an ombrotrophic bog at 5450 BP through three different bog stages, the Fuscum. the Rubellum‐Fuscum and the Magellanicum bog stages, each one characterized by a specific macrofossil assemblage

All N supplied to the bog surface is assumed to be contained in the organic matter At the beginning of the Magellanicum bog stage, 1000 BP, the nitrogen accumulation rate increased from an earlier value of ca 0.4 g m–2 yr–1 to 0.8 g m–2 yr–1 These accumulation rates for N have been used to establish time scales for the periods between the 14C‐datings

The estimated litter deposition rate in the hummocks is 120 g m–2 yr–1 in the two older bog stages and 270 g m–2 yr–1 in the Magellanicum bog stage The decay losses in the acrotelm increased, as a proportion of the addition, with time through each one of the bog stages The range of variation in the cores for the acrotelm decay losses was 25‐80%. and the annual input of organic matter to the catotelm, 30‐130 g m–2 These ranges are greater than those found among recent bog hummocks in NW Europe and North America The decay losses during 5000 yr in the catotelm may not have exceeded 20% of the original input The over‐all net rate of accumulation of C was highest, ca 40 g m–2 yr–1, at the beginning of the Fuscum bog stage

The changes in the macrofossil assemblages are all associated with rapid increases in the peat accumulation rate, but decreases in accumulation rate are not At the conversion from fen to bog the increased input of organic matter to the catotelm depended on expansion of Sphagnum fuscum which formed a decay resistant litter Later increases depended on rapid rises of the mean water table, resulting in shorter residence times and smaller decay losses from the acrotelm The periods of decreases in input of organic matter to the catotelm depended on longer residence times in the acrotelm when the water table fell relative to the bog surface However, comparisons with recent conditions suggest that the variation in mean water level relative to the surface may not have exceeded 10‐15 cm
Patterns of arthropod abundance and diversity in an Arabian desert
Authors: Tigar Barbara J. , Osborne Patrick E.
Published: July 2006

We captured desert arthropods from sand and gravel substrates at five coastal or inland locations m Abu Dhabi around the new moon once every 28 days for two years Three replicated lines of 20 unbaited pitfall traps were used from two hours before dusk until two hours after dawn We examined the data for spatial and temporal variation, especially in relation to climate Around 53 400 arthropods were caught, 97.3% being insects and the rest arachnids Ants were most common (75.4%), followed by the Thysanura (12%), Coleoptera (8.4%), Araneae (1.5%) and Scorpiones (1.1%) Catches differed significantly among sites, substrates and time of year In general, the number of arthropods caught matched the annual temperature cycle Peak catches also followed the annual rains Summer catches were higher at coastal than inland sites Fewer arthropods were caught at gravel sites than on sand, but the number of taxa did not differ consistently between substrates Community composition was generally less similar among sites than between substrates although this was not always the case Inland communities had fewer taxa and generally fewer individuals than those near the coast Isoptera, Tettigonndae and Carabidae occurred less frequently (if at all) inland We suggest that the higher humidity at sites near the coast allows more taxa to occur and to remain active during the extreme heat of summer Further into the Empty Quarter we would expect a decline in the number of taxa and in the total catch
Airborne dispersal of antarctic terrestrial algae and cyanobacteria
Authors: Marshall William A. , Chalmers Matthew O.
Published: July 2006

The dispersal of algae and cyanobacteria at three Antarctic fellfield sites was investigated using microscopic and culture analysis of samples from active and passive air samplers Intersite variation in the mean number of large algal propagules (>5 μm diameter) sampled was dependent on the niche space available for algal growth and the degree to which soil was exposed to desiccating influences, these factors could be related to the degree of maturity of the sue The numbers of large algal propagules were lowest at sites from which permanent snow cover had recently disappeared and highest at sites with developed soil circles but poorly developed moss and lichen flora Mature sites with diverse and developed moss and lichen flora produced intermediate numbers of algal propagules Propagules of multicellular algae, cyanobacteria and large‐celled unicellular algae were found in the air at the end of the growing season of the respective algal groups as the soil surface dried This was the case for Prasiola crispa, Pmnularia borealis, snow algae and filamentous chlorophytes and cyanobacteria Dispersal of unicellular chlorophytes was greatest during the summer period and at sites with developed secondary flora, but also occurred at other sites and in association with small thaw events during winter Cultures were obtained from samples collected whilst an air mass that had originated in South America, deposited material on Signy Island This suggests that algal propagules have the ability to survive long‐distance transport and potentially provide mocula for colonization of Antarctica as regional warming continues to expose fresh habitats
Insular patterns of calicioid lichens in a boreal old‐growth forest‐wetland mosaic
Authors: Kruys Nicholas , Jonsson Bengt Gunnar
Published: July 2006

Fragmentation of the forested landscape poses a threat to many aspects of biodiversity associated with old‐growth forests Studies of the effects of forest fragmentation are often complicated by the variation in composition and age of patches and the matrix This study used a system of isolated stands where patch age and composition were similar and the matrix variability negligible The patches were composed of old‐growth Picea abies stands of varying size and shape in a wetland matrix The study organisms were epiphytic crustose calicioid lichens (also known as Caliciales), many of which are very substrate‐specific and restricted to old‐growth stands The aim of the study was to measure the effect of patch size, patch isolation, habitat and substrate quality on the species riochness and composition of epiphytic calicioids Twenty‐four patches ranging from 0 4 to 15 9 ha in size were studied All species of calicioid lichens were registered in 0 1 ha plots in each patch Isolation was measured as the percentage of available habitat within 400 m of a patch Twenty‐two species were found with an average of 9 48 ± 0 26 (SE) species per patch and 292 ± 0 18 (SE) species per tree Species richness at patch level correlated with stand structure, primarily tree density, while number of species per tree (reflecting population size) was strongly correlated with island size and several stand variables There was no effect of isolation on species richness Species composition was influenced by both substrate variables and patch size The species composition on the islands showed a significant nestedness, i e species composition on species‐poor islands constituted a non‐random subset of the species composition on species‐rich islands

We propose that the explanation for the strong relationship between species richness at tree level and stand size is an edge effect which implies that unaffected interior areas only occur on large islands The different microclimate of the patch edge enables only the hardiest species to establish large populations there whilst shade and moisture demanding species are restricted to the interiors of larger islands
Carabid community succession during the forestry cycle in conifer plantations
Authors: Butterfield Jennifer
Published: July 2006

Pitfalls and soil heat extraction were used to sample Carabidae in recently felled (1 –4 yr from felling), young (5–22 yr after planting), and old plantations (42–63 yr after planting) of Picea sitchensis in northern England Pitfall catches were useful in recording swift‐running species, present at low densities, and a DCA ordination based on the pitfall catches indicated major distribution changes during the plantation cycle Soil extractions allowed estimation of minimum densities of the abundant species and indicated that both diversity and density were highest m young plantations and lowest in the old plantations The flightless Trechus obtusus (3 8 mm) was the most abundant species m the soil samples and its population density did not differ significantly between the three stages in the forestry cycle The winged, highly surface‐active species that were early colonisers of clear felled sites and formed a high proportion of the pitfall catch were present at low densities only The peak in carabid density and diversity coincided with the stage at which the ground flora was most diverse (in both species and structure) and the densities of other soil surface macro‐invertebrates were highest The high carabid density in the young plantations coincided with a the presence of a relatively high proportion of larger carabids (> 59 mm) and it is suggested that the increased carabid biomass m‐2could reflect increased prey availability The density of winged individuals was higher in the soil samples of carabids from the young plantations than from the clear felled areas and this is attributed to a build up over time of colonising species, adapted to exploiting the short‐lived open habitat stage Species that overwinter m the adult stage were more abundant in the young than in the old plantations and it is suggested that these species are favoured by the relatively high summer daytime temperatures of the open habitat The interpretation of the successional sequence in the Carabidae was enhanced by the use of heat extraction sampling in conjunction with pitfall catches
Ecophysiological adaptations of Asphodelus aestivus to Mediterranean climate periodicity: water relations and energetic status
Authors: Rhizopoulou S. , Pantis J. D. , Triantafylli E. , Vokou D.
Published: July 2006

During the course of a year, we studied the water and metabolic status of Asphodelus aestivus, a native geophyte of East Mediterranean, dominant in areas degraded by overgrazing and fire The species proved to be very efficient m storing water during the long summer drought At soil water content values around zero, in the upper part of the soil profile (10–20 cm in depth), the roots remained hydrated and turgid, their relative water content was > 60% and water potential > ‐ 1 6 MPa Accumulation of proline during winter in leaves (ca 5 mg g–1 dry weight) and tubers (though at significantly lower levels, ca 1.5 mg g–1) might be taken as evidence of a winter cold stress response Proline accumulation in tubers, under summer drought, was similar to that in winter Maximal values of caloric content were recorded in expanding leaves (ca 5600 cal g–1 dry weight) and minimal before leaf senescence In contrast, root caloric content remained fairly constant for most of the year (ca 4550 cal g–1 dry weight) in spite of drastic changes in the concentrations of soluble sugars, starch and lipids Long before senescence, photosynthetic products were translocated to the below ground system, where they were stored Drastic changes of the storage compounds were observed before emergence of the flowering stalk, far greater in magnitude than those before leaf emergence The below ground part of the species was found to be less susceptible to climatic stress and to constitute an energetically rather stable system The physiological processes of the species were well synchronised to the fluctuations of the Mediterranean climate
In vitro digestibility of seasonal forages used by wapiti and roe deer in northeastern China
Authors: Chen Huapeng , Ma Jianzhang , Sun Zhongwu , Li Feng , Wang Huai , Luo Liyang , Li Fei
Published: July 2006

Seasonal changes in in vitro dry matter digestibility (IVDMD) of five forage classes (browses, sedges, forbs. ferns and the bark of Ulmus spp.) used by wapiti and roe deer were determined in relation to chemical composition, using the two‐stage technique of in vitro trial with rumen inocula from one wapiti and one roe deer captured in winter. Wapiti and roe deer showed remarkable fluctuation in IVDMD among seasons and forage classes. IVDMD decreased from 43.8‐64.3% in spring to 29.4‐40.5% in winter for wapiti, and from 52.4‐77.4% in spring to 25.9‐36.5% in winter for roe deer. There was significant variation in IVDMD among species of browses for wapiti and roe deer. IVDMD ranged from 28.5% to 58.7% in twigs and from 39.8% to 58.2% in leaves for wapiti, and from 24.1% to 67.7% in twigs and from 40.0% to 71.7% in leaves for roe deer. Roe deer had higher IVDMD (40.0‐71.7%) in both leaves and twigs of browses than wapiti (35.9‐58.7%) during snow‐free seasons, but IVDMD of twigs was lower for roc deer (25.9‐36.5%) than wapiti (29.4‐38.4%) in winter. Significant multiple correlation was found between NDF and ADF, and IVDMD in sedges, forbs and ferns for both wapiti and roe deer, whereas only roe deer showed the significant multiple correlation for leaves of browses.
Regional distribution of Thymus serpyllum: management history and dispersal limitation
Authors: Eriksson ÄRsa
Published: July 2006

Local and regional distributions of Thymus serpyllum, in the southeastern part of Sweden, were examined by combining experimental studies of recruitment limitation and germination, and descriptive studies of distribution range in relation to habitat and management history. The spatial pattern at a regional scale in the county of Södermanland was examined in relation to semi‐natural pastures and graves from the Iron Age. The distribution of T. serpyllum was also examined in two parishes. Thymus serpyllum was exclusively found in managed, unfertilized areas, mainly semi‐natural pastures and to some extent in road verges, and almost always in dry parts. Populations of T. serpyllum were found in 32 of the 42 pastures that contained Iron Age graves, but only in 5 of 42 pastures without graves. The distribution of T. serpyllum was also more or less congruent with the distribution of Iron Age graves, in both parishes. The seed sowing experiment showed that the germination rate, winter survival and recruitment were significantly higher in disturbed (removal of ground cover) plots, for both dry and mesic vegetation. Since the establishment of T. serpyllum occurred both in dry and mesic parts of semi‐natural pastures, whereas T. serpyllum is confined to dry parts, the local limitation of distribution may be due to poor dispersal or due to effects acting on later life cycle stages. The results showed that the regional distribution of T. serpyllum is likely to be dispersal limited recruitment after seed sowing was equally good at sites with or without established populations. Seeds survived and germinated after heat treatment, with temperatures at 60°C. 80°C and 100°C, but germination rates were not higher than in the control. The results of this study indicate that the distribution of T. serpyllum is dependent on human activities, both for dispersal and for the maintenance of established populations. Long, continuous management by grazing is obviously important for the maintenance of these populations. The association with Iron Age graves may reflect either long continuity, or accidental or intentional dispersal by humans.
Horizontal distribution of pelagic zooplankton in relation to predation gradients
Authors: White Michael D.
Published: July 2006

An investigation was conducted examining the horizontal and vertical distribution of zooplankton in Lake Miramar, a southern California reservoir. Daphnia and Mesocyclops populations were most abundant offshore and in deeper water during the day but appeared to move toward shore and upward at night. The results of inshore zooplankton sampling provided no evidence chat the diel horizontal migration pattern was a result of sampler avoidance by zooplankton. Inshore‐offshore differences in Daphnia and Mesocyclops abundance and diel migrations were reduced during winter and early spring. Rotifer zooplankters exhibited less seasonal variation in their horizontal distributions than did the large crustacean zooplankters at all times of the year. It is hypothesized that the spatial distribution of zooplankton is related to predation gradients in Lake Miramar. The dominant planktivore in the reservoir, young‐of‐the‐year Micropterus salmoides. was abundant from late May through December and much less so from January to early May. They were largely restricted to the littoral zone and this produced horizontal gradients of planktivory which varied in strength seasonally and from day lo night. It appears that crustacean zooplankton in Lake Miramar avoid areas with abundant planktivores during the day but migrate into these areas at night when the intensity of planktivory is reduced. Rotifers exhibit less horizontal heterogeneity and no significant diel migrations, which is attributed to the reduced risk of predation that rotifers experience relative to crustacean zooplankters. A graphical model is proposed to integrate our understanding of diel vertical and horizontal migrations of zooplankton. In this model, gradients of predation are completely vertical in offshore areas and strongly horizontal in near shore areas. Gradients of food availability are roughly similar to those of predation intensity. Plankiers respond to these gradients by migrating in a path parallel to gradients of predation at dawn and parallel to gradients of food availability after dark.
The dynamics of abundance and incidence of annual plant species during colonization in a desert
Authors: Boeken Bertrand , Shachak Moshc
Published: July 2006

We studied colonization of annual plants in small‐scale disturbances and undisturbed soil for four years in the northern Negev desert. The experiment consisted of 24 patches of I m2: eight undisturbed patches, eight 30 cm deep pits and eight 20 cm high mounds. Disturbance removed the seed bank from the pits and mounds. Rainfall was average during 1992 and 1993 (163.5 and 157.0 mm), very low in 1994 (97.5 mm) and very high in 1995 (283.0 mm). For all ca 100 species in the assemblage, we measured abundance, as the average local density in patches occupied by the species, and incidence, the proportion of patches occupied. Abundance and incidence were positively correlated in the four years of the study (R2‐= 0.71, 0.56. 0. 56 and 0.64). The relationship became steeper during the course of colonization. A minority of species colonized all patches rapidly and increased exponentially in abundance. These high incidence and abundance species responded little or not at all to variations in rainfall. Most of the species experienced frequent local extinctions and colonizations in few patches. These low abundance and low to medium incidence species responded strongly to rainfall by fluctuations in abundance. Differences per species between abundance and/or incidence in pits, mounds and matrix were evident in many species along the entire relationship. These were mostly in favor of pits. We propose that the positions and trajectories of the individual species in the abundance‐incidence phase plane signify constraints on population growth along the abundance axis, and on colonization and population persistence along the incidence axis. Since species with lower incidence and abundance respond strongly to rainfall variation, we conclude that their local populations and spatial distribution are to a large extent site‐limited. High‐abundance and high‐incidence species have few or weak constraints and experience density‐independent population growth, which is only seed‐limited. The causes of site limitation and its effect on population growth and on eotonization and extinction processes differ for different species. In a number of species, abundance and incidence may be limited by dispersal, in conjunction with dispersal mode and patch‐specific seed capture. Based on our case study we suggest that the trajectories of the species in the abundance‐incidence phase plane are a useful tool for investigating assemblage dynamics.
An isozyme study of clone diversity and relative importance of sexual and vegetative recruitment in the grass Brachypodium pinnatum
Authors: Schläpfer Felix , Fischer Markus
Published: July 2006

We asked whether differences in abundance and seed prodtiction of Brachypodium pinnatum after 16 yr of four different experimental land use regimes were reflected in differences in vegetative dispersal distance, clone diversity, clone area, and the proportions of sexual and vegetative recruitment. Mean vegetative dispersal distance was 5.5 mm yr‘. Electrophoresis of 5 polymorphic isozyme loci of 20 tillers sampled at defined positions in each of twelve 1 × 6 m sampling areas (3 per treatment) revealed considerable clonal diversity. Per sampling area we found on average 9.98 enzyme phenotypes (clones), mean Simpson index was 0.825. and mean Shannon index 0.801. The mean ratio of sexual vs vegetative recruitment was about 1:32000. Despite this low ratio, clonal diversity within the population of” B. pinnatum was higher than reported for other clonal plant populations, possibly because of its high ramet densities. Moan clone area was 5.73 m2‐. i.e. mean clone radius was 1.35 m. None of the 10 pairwise correlations between abundance and seed production on the one hand, and number of clones per plot sample, plot Simpson index, plot Shannon index, ratio of vegetative vs sexual recruitment, and clone area on the other, was significant. Mean clone radius was 245 times larger than the mean distance of yearly vegetative dispersal which suggests old ages and low turnover rates of clones. The time scale of the inert response of clonal diversity of B. pinnatum to changes in land use appears to largely exceed the experimental period of 16 yr.
Biogeographical regions of the Iberian peninsula based on freshwater fish and amphibian distributions
Authors: Vargas J. Mario , Real Raimundo , Guerrero José C.
Published: July 2006

We classified the main Iberian river basins based on the presence and absence of freshwater fishes and amphibians. For both taxonomic groups we analysed three data sets; 1) endemic species only, to search for biotic boundaries related to historical events, 2) indigenous species, which include endemic ones, to search for biotic boundaries related to ecological factors, 3) indigenous and well‐established introduced species, to assess the influence of man in the current biogeographical patterns of fishes and amphibians. We used both phenetic and cladistic methods, followed by a consensus analysis to provide an overall biogeographical pattern. Based on all fish distributions, the Iberian Peninsula is divided into three biogeographical regions: Cantabrian, Atlantic and Mediterranean, No boundary existed between the Cantabrian and Atlantic regions when only indigenous fish species were considered. This suggests that this boundary has been induced by man, probably through the differential introduction of fish species into reservoirs at one or other side of the boundary. Run‐off and the size of the river basins are the environmental factors that distinguished the Atlantic and Mediterranean regions. However, regionalization based only on endemic freshwater fishes showed a latitudinal pattern that agrees with the paleogeographic events of the Upper Oligocene‐Lower Miocene period. By contrast, one northern and one southern region were distinguished based on all amphibian distributions and on indigenous amphibians only, which suggests that human activity has not significantly affected the overall biogeographical pattern of amphibians in the Iberian Peninsula. Interannual predictability of precipitation best accounts for this regionalization. Based on endemic amphibians, the Iberian Peninsula is divided into three regions that closely resemble the three separate land areas of the Upper Eocene‐Lower Oligocene period. The consensus between the biogeographical regions based on fishes and amphibians yields five pairs of basins. Geological origin of the basins seems to better explain the consensus between the biogeographical patterns of fishes and amphibians, whereas ecological factors probably contribute to the differences between them.
Forest fragmentation and colony performance of forest tent caterpillar
Authors: Rothman Lome D. , Roland Jens
Published: July 2006

We monitored survival and egg production in colonies of Malacosoma disstria in the understorey to examine relationships between colony performance and forest structure at several spatial scales. As forest cover increased, fewer moths survived. Increased mortality from a virus and a parasitoid assemblage were the main causes of this result. Forest cover measured at the smallest spatial scale (53 × 53 m) was the best predictor of colony performance. We attribute these effects of fragmentation to fine‐scale differences in microclimate betweeen edge and interior habitats (edge effects).
The effects of scale and sample size on the accuracy of spatial predictions of tiger beetle (Cicindelidae) species richness
Authors: Carroll Steven S. , Pearson David L.
Published: July 2006

We apply geostatistical modeling techniques to investigate spatial patterns of species richness. Unlike most other statistical modeling techniques that are valid only when observations are independent, geostatistical methods are designed for applications involving spatially dependent observations. When spatial dependencies, which are sometimes called autocorrelations, exist, geostatistical techniques can be applied to produce optimal predictions in areas (typically proximate to observed data) where no observed data exist. Using tiger beetle species (Cicindelidae) data collected in western North America, we investigate the characteristics of spatial relationships in species numbers data, First, we compare the accuracy of spatial predictions of species richness when data from grid squares of two different sizes (scales) are used to form the predictions. Next we examine how prediction accuracy varies as a function of areal extent of the region under investigation. Then we explore the relationship between the number of observations used to build spatial prediction models and prediction accuracy. Our results indicate that, within the taxon of tiger beetles and for the two scales we investigate, the accuracy of spatial predictions is unrelated to scale and that prediction accuracy is not obviously related lo the areal extent of the region under investigation. We also provide information about the relationship between sample size and prediction accuracy, and, finally, we show that prediction accuracy may be substantially diminished if spatial correlations in the data are ignored.
A re‐examination of geographical variation in Nepenthes food webs
Authors: Clarke Charles
Published: July 2006

The metazoan food webs ofNepenthespitcher plants exhibit marked geographical variation In previous studies this was attributed lo a number of biogeographical factors including island area. local arthropod biodiversity and degrees of spatial and temporal variation of the hostNepenthesspecies. Recent investigations showed that some assumptions made in compiling these webs are erroneous and that predation is more widespread in these communities than previously assumed. In this study the new data are used to revise several webs from the geographical studies for comparison with the original versions. Conneetance values and predator:prey ratios increased significantly after revision (though all other food web statistics did not), providing evidence for widespread predation. This is presumed to be a result of some metazoan species adopting variable feeding strategies, depending on which food sources are available in their piteher. Despite this, the geographical patterns are still evident alter revision of the webs. Whether or not these are actually due to geographical Victors is discussed, h is suggested that the structure ofNepentheswebs is influenced by tour major factors‐ “geographical, deterministic, stochastic and host pitcher (the latter was discounted in previous studies), but that the relative importance of each factor is highly variable and cannot be quantified at present.
Summer food composition and food niche overlap of the raccoon dog, red fox and badger in Finland
Authors: Kauhala Kaarina , Laukkanen Paula , von Rége Inez
Published: July 2006

Diets of raccoon dog, red fox and badger were studied in southern Finland from 1990 to 1996 by collecting faeces from dens and latrines during May‐July of each year. The frequency of occurrence and relative volume of each food item in the faeces were calculated. The raccoon dog was the most and the red fox the least omnivorous of these carnivores, according to the diversity index. Diet composition of all these species varied among areas, indicating that they are opportunistic feeders. Mammals and birds constituted the bulk of the fox diet, while invertebrates, frogs and plants were most frequently eaten by the badger. The frequency of earthworms in badger faeces varied between 16 and 77%, according to area. Voles and shrews were important to the raccoon dog, but it also frequently consumed other food items. The food niches of the badger and the raccoon dog overlapped more than that of the red fox and other species. The red fox was more carnivorous and fed on larger prey items than the others, but the food composition of the red fox in the present study reflects the prey carried to the den for the pups; thus, the diet of adult foxes may be more similar to that of the raccoon dog. In conclusion, these 3 carnivores share many resources, suggesting that competition may occur among them: however, their diets also differ to some extent, which helps them to avoid competition. Furthermore, the badger and the raccoon dog are dormant during winter, when food is scarcest, which may be the reason why all these species can coexist in rather unproductive boreal forests.