Showing papers in "Ecography in 1984"
TL;DR: The data from the present and from other studies suggest that the foraging efficiency of wild reindeer, expressed as their daily food intake follows a Holling type II functional response as food availability changes, is suggested.
Abstract: Part 1: Diet selection was studied on free-ranging reindeer fitted with an esophageal fistula (EF) and by analysis of rumen samples from reindeer shot in the field. Plant density was assessed from quadrats on field plots. Three measures of palatability were used, the nitrogen, fiber, and total non structural carbohydrate (TNC) contents of samples from clipped vegetation. As lichen density decreased the EK reindeer included progressively more vascular litter and pieces of winter dormant species in their diet. Diets with highest TNC and N/F and the lowest fiber, providing the most readily digestible diets, were selected. The combined density-quality criterion gave the best prediction of their diets. In summer, forbs, and to some extent grasses and dwarf shrubs, were selected. Plants of highest density and in an early growth phase gave the best prediction of summer diets.
In winter the variety of vascular plants utilized increased with increasing herd size and decreasing density of lichens in the vegetation. The width of diets was a function of diversity of available plants. It is suggested that dietary selection by reindeer has been a three stage process: evolution of a gastro-intestinal system capable of digesting lichens containing secondary compounds, behavioural tracking of the plant production pulse, and diet width scaling according to density-quality of all potential foods.
Part 2: Wild reindeer closely followed the wave of vascular plant production in spring and summer with a significant correlation being found between the daily foraging time per habitat type and the highest concentration of green phytomass. Snow-bed meadows were the most consistently selected vegetation type by the four herds studied, viz. Hardangervidda, Snohetta, Prudhoe Bay, and Svalbard, during the summer. Habitat niche-breadths were narrow during the winter, largely due to the limitation of access to the food supply by the snow-cover, broadened as the landscape became clear of snow, narrowed again with the initiation of plant growth and broadened once more as the wave of plant production reached all habitat types.
At high levels of food resources the alpine herd (Hardangervidda) narrowed the feeding niche breadth (or adopted a selective feeding strategy) as the habitat niche breadth increased. The high arctic herd (Svalbard) living in the least productive environment, at the same time of year adopted a generalist feeding strategy as their habitat niche breadth expanded.
Part 3: In this part the temporal organization of a low-alpine herd of reindeer (Hardangervidda) is described, and subsequently compared with those of two arctic herds. Their foraging efficiencies under different degrees of food availability were analysed, in order to test the hypothesis that food intake changes in response to the prevailing state of the food resources.
The number of daily feeding bouts increased from 2 to 6 as the diet changed from the winter to the summer pasturage. Strong winds in winter and insect harassment in summer severely depressed the daily time spent foraging. When these environmental factors were accounted for no significant inter-seasonal differences in daily foraging time of the low alpine herd were found; on average 50% of each day was spent grazing, of which 78% of the time was spent on actual ingestion (feeding rate). The feeding rate within the active periods varied with the snow-depth, due to the need to dig a food crater in the snow and due to the particular selective feeding strategy adopted. The data from the present and from other studies suggest that the foraging efficiency of wild reindeer, expressed as their daily food intake follows a Holling type II functional response as food availability changes.
Part 4: Sheep is the only sympatric ruminant which grazes with the reindeer on alpine pastures in Norway. The inter-specific niche relationships ot the wild reindeer and the domestic sheep in summer were studied on part of the western Hardangervidda. to test the hypothesis of inter-specific competition. Three niche dimensions were meas-ured, diel, habitat utilization, and spatial distribution. The estimates of the degree of overlap obtained suggest that this is relatively high for diet and habitat utilization but low for spatial distribution, which leads to a low degree of foraging interference. Since the intensity of both interspeeific and intra-specific competition depends on the ratio of the herbivore densities to the food resource density, the degree ol overlap in utilization by the two species tell us nothing about the degree of competition. Present numbers of both species on Hardangervidda have a beneficial influence on the vegetation, by opening-up the shrub-layer canopy and thus facilitating the main-tenance of grasses and forbs in the field layer, which has a higher carrying capacity for ruminants. The balance between the beneficial effects and inter-generic competition (if any) deriving from the present-day stocking rales is so tar unknown. Only long-term monitoring of the performance of both populations will shed light on this competitive aspect.
175 citations
TL;DR: In this article, an analysis of a recent N. sertifer outbreak in southern Sweden was made during on-going attack, comprising a regional and local mapping of defoliation severity, as well as a study of intensity of larval consumption, abundance of cocoons and parasitation of larvae in relation to fertilizer application.
Abstract: Analyses of a recent N. sertifer outbreak in southern Sweden were made during on-going attack, comprising a regional and local mapping of defoliation severity, as well as a study of intensity of larval consumption, abundance of cocoons and parasitation of larvae in relation to fertilizer application. It was found that (1) the outbreak was preceded by summer and autumn droughts, (2) it was limited to infertile soils, (3) pine stands aged 20–40 yr suffered most, (4) it was less severe in trees benefiting from a reduced inter-tree competition, as measured from tree-ring growth, and (5) less severe in a fertilized stand. The findings support the hypothesis on a fundamental effect of stand nutritive state on changes in number of the sawfly.
107 citations
TL;DR: Although compensatory growth in weight appears to occur, between-year differences in newborn lengths persist to weaning, various reproductive strategies of female harp seals faced with reduced energy stores are discussed.
Abstract: Lactating female harp seals, most with their pups, were collected on the “whelping” ice in the Gulf of St. Lawrence in 1976 and from 1978 to 1980. During lactation females lost weight at an average rate of 3.17±0.52 (SEb) kg d−1, for a total energy loss of approximately 250000 kcal. Pups grew at a mean rate of 2.78±0.19 kg d−1 for a gain in production energy of about 194000 kcal. Compared to 1976, adult females sampled in 1978 to 1980 had lower energy reserves at the onset of lactation. Coincidentally there has been a decrease in newborn lengths and girths. Although compensatory growth in weight appears to occur, between-year differences in newborn lengths persist to weaning. Various reproductive strategies of female harp seals faced with reduced energy stores are discussed.
93 citations
TL;DR: Treefall gaps sampled for size, age, and woody vegetation in 1977 were resampled in 1981 and most species showed little change in their relative importance values in gaps of different sizes or ages, but the four main canopy species differed in their responses.
Abstract: Treefall gaps sampled for size, age, and woody vegetation in 1977 were resampled in 1981. Large gaps had more and larger stems than did small gaps; however, basal area and number of stems per unit area remained fairly constant over the range of gap sizes encountered. Overall, most species showed little change in their relative importance values in gaps of different sizes or ages. However, the four main canopy species differed in their responses. Acer saccharum Marsh, reached maximum importance in small gaps, Liriodendron tulipifera L. and Fraxinus americana L. in large ones. As gaps aged, Fraxinus decreased in importance while Fagus grandifolia Ehrh. gained in importance for all gap sizes. For about half the gaps studied, some new adjacent disturbance had occurred between 1977 and 1981.
90 citations
TL;DR: In this paper, two possible anti-predator strategies of prey were suggested by the distribution of moose at Isle Royale, a 544 km2 island with numerous offshore islets.
Abstract: Two possible anti-predator strategies of prey were suggested by the distribution of moose at Isle Royale, a 544 km2 island with numerous offshore islets. Aerial surveys in winter indicated that moose density on small islets (<1.5 km2) averaged 415% greater than on the main island, with about 11% of the calf population existing on the small islets which comprise less than 2% of the total land area. On small islets and shorelines, protection from wolves (in the form of escape terrain) is provided by nearby water in summer and coniferous cover in winter. Calves on islands appear to have a higher survival rate. In summer, cow moose with calves were seen more commonly in camps with human activity (and no wolves) than away from camps, suggesting that people provided a refuge from wolf predation for this unhunted moose population. These subtle patterns of habitat selection by moose are attributed to the intensive natural selection pressure of wolf predation.
76 citations
TL;DR: The ability of mosses to hold moisture and the presence of limited bluegreen algae that fix nitrogen appear essential to the maintenance of greater species richness, plant cover and plant production compared with the barren polar deserts that are often nearby.
Abstract: A study of soils, plant communities, and net annual plant production was conducted with 41 stands at 3 sites on 3 arctic islands. Twelve additional sites were studied in less detail on Ellef Ringnes, King Christian and Melville islands and on four other islands. Through polar ordination five groupings were recognized. Alopecurus and Puccinellia barrens on sand to silty soils and on silty soils, high in sodium salts respectively. Species richness averaged 2.6 ± 2.0 and total plant cover 6.8 ± 2.7%. The Phippsia barrens occur on sheet eroded surfaces and in gulleys with deep winter snow. Species richness was 9.8 ± 5.0 and total plant cover 14.8 ± 9.6%. The graminoid steppes on sandy soils averaged 7.6 ± 2.4 species and total plant cover 40.0 ± 2.8%. Eight stands were dominated by moss-graminoids, mostly on loam soils. Species richness was 24.9 ± 3.4 and total plant cover 77.7 ± 16.1%. Plant producion was 8.0 g m−2 in a Puccinellia barren and 9.4 g m−2 in a Luzula confusa graminoid steppe. Net annual production ranged from 18.8 to 58.7 in 6 other stands. The 13 stands within the cryptogam-herb community complex occur on sandy loam to clay-loam soils. Species richness averaged 26.3 ± 6.2 and total plant cover 61.2 ± 24.7%.
Mosses and lichens play a significant role in the establishment and maintenance of communities with a greater species richness and plant production of vascular plant species. The ability of mosses to hold moisture and the presence of limited bluegreen algae that fix nitrogen appear essential to the maintenance of greater species richness, plant cover and plant production compared with the barren polar deserts that are often nearby.
73 citations
TL;DR: It is concluded that the area effect is here a good predictor of species richness only within ponds of a similar successional stage.
Abstract: Ten closely-located kettle-hole ponds in northern Sweden were ordered along a vegetational, successional gradient from the present-day representation of the six vegetational units distinguished. Different rates of vegetational development caused by differences in depths of basins have made possible the long-term existence of early successional stages. A fact that has offered the possibility of studying most of the vegetational succession of these habitats.
The number of water beetle species inhabiting each pond were correlated to successional stage and area of pond. Mean species numbers decreased from 34 to 14 per pond with increasing maturity of the vegetational succession. This decrease in species richness of water beetles is caused by a decrease in number of habitats or vegetational units present. The increased floral conformity is mainly due to a more stable water-level caused by lower rates of bottom seepage from the accumulation of organic deposits. Besides the extended zonation of littoral vegetation, a high water-amplitude is also connected with recurrent nutrient pulses caused by the faster detritus composition during drought periods. Thus the changing water-levels contribute to a high water beetle diversity through the maintenance of both a high habitat complexity and a high production.
A positive correlation between pond size and number of water beetle species were only found if the fen ponds were excluded. From this it is concluded that the area effect is here a good predictor of species richness only within ponds of a similar successional stage.
44 citations
TL;DR: The biomass and respiration of the annelids and arthropods at Andersby were lower than in some other oak forests in northwestern Europe, probably because of lower soil temperature, lower litter supply and because some lumbricid and diplopod species were at their northern border of distribution.
Abstract: Soil/litter inhabiting annelids and arthropods were studied for one year in a mesic deciduous woodland, Andersby angsbackar, one of the most northerly areas in Sweden to possess unbroken oak/hazel vegetation. Lumbricidae, Enchytraeidae, Collembola, Acari, Coleoptera, Diptera and Araneae were important faunal groups with regard to abundance, biomass and respiratory metabolism. Annual mean biomass (8 g dw m−2) and respiration (450 kJ m −2 yr−1) of the joint annelid and arthropod community were dominated by lumbricids (76 and 50%, respectively). The biomass and respiration of the annelids and arthropods at Andersby were lower than in some other oak forests in northwestern Europe, probably because of lower soil temperature, lower litter supply and because some lumbricid and diplopod species were at their northern border of distribution.
Of the annual respiration, saprovores, fungivores, carnivores and root-feeders contributed 65, 19, 14 and 1.5%, respectively. The saprovore percentage was lower at Andersby than at other mull sites compared, probably as an effect of the northern climate, which might favour microbial saprovory. The fungivore and carnivore percentages were higher, which might be due to the presence of a litter layer throughout the year.
40 citations
TL;DR: Because fecal detritus is abundant throughout the year, and is treated by many species as a source of food, it could be a major mechanism by which seasonal fluctuation in availability of allochthonous litter input is minimized and homeostasis of structure and function maintained.
Abstract: The feces of stream insects may be a major component of fine particulate organic matter (FPOM) available to collector organisms. In Mink Creek, Idaho, winter defecation rates for 9 species ranged from 86 mg dry feces (g dry body wt)−1 d−1(Ephemerella spinifera) to 154 mg g−1 d−1(Paraleptophlebia heteronea). Detailed studies of 3 species in summer revealed that rates were much greater than in winter and exhibited high between-individual variation (e.g., 695 ± 184.8 mg (g body wt)−1 d−1 for Baetis tricaudatus). By combining measured and literature values, it is estimated that the benthic insect community egests approximately 3.4 kg feces m−2 yr−1. This value lies within the range of FPOM estimated to be derived from degradation of leaf litter input (0.7–9.9 kg m−2 yr−1, depending upon assimilation efficiency of the organisms).
Short-term winter growth experiments showed that, with two exceptions, collectors fed on fecal detritus will grow as well as on other food resources; relative growth rates depend upon the species. Because fecal detritus is abundant throughout the year, and is treated by many species as a source of food, it could be a major mechanism by which seasonal fluctuation in availability of allochthonous litter input is minimized and homeostasis of structure and function maintained.
29 citations
TL;DR: The main conclusions are that after the first seedling stage the mountain birch survives broad climatic variation, however, normal completion of the life-cycle is only possible within more narrow limits.
Abstract: Saplings of mountain birch Betula pubescens Ehrh ssp tortuosa (Ledeb) Nyman, three years old, were transplanted into three contrasting habitats, viz moderate and extreme snow-bed and windswept crest The experimental sites were situated just below the present local tree-limit of birch During 1978–1983 mortality and height increment were monitored High initial mortality was succeeded by lower mortality at all three sites The height increment was significantly higher in moderate snow-bed compared with the two extreme habitats (winswept crest and extreme snow-bed) The main conclusions are that after the first seedling stage the mountain birch survives broad climatic variation However, normal completion of the life-cycle is only possible within more narrow limits A minimum amount of the snow-free preriod is needed, eg to satisfy the requirements of nitrogen nutrition The results Stress the opportunistic nature of the mountain birch which gives it a selective advantage in the extremely unpredictable climate in mountainous areas in Scandinavia The reproductive strategy of mountain birch apparently includes having a bank of persistent saplings
27 citations
TL;DR: In this paper, the authors investigate the processing of Salix drummondiana Barratt leaves in two second order Alberta Rocky Mountain Creeks, Twin Creek, and Cabin Creek and find that micro-organism processing and macroinvertebrate shredding of the leaves were significantly greater in Twin Creek where it was estimated that macroinverse shredding was responsible for 45% of the weight loss.
Abstract: Nylon bags of 3.5 mm and 0.25 mm mesh were used lo investigate the processing of Salix drummondiana Barratt leaves in two second order Alberta Rocky Mountain Creeks, Twin Creek and Cabin Creek. Micro-organism processing and macroinvertebrate shredding of the leaves were significantly greater in Twin Creek where it was estimated that macroinvertebrate shredding was responsible for 45% of the weight loss. The decay coefficient (k = 0.0209) for the leaves in Twin Creek, the more typical Rocky Mountain stream, was similar to that reported for the fastest decaying leaves in warmer streams. The predominant shredder among the leaves in the mesh bags, Zapada columbiana (Classen) (Plecoptera, Nemouridae) was also the most abundant macroinvertebrate in the benthos of Twin Creek. In Cabin Creek the predominant organism in the benthos, Oreogeton sp. was poorly represented in the leaves. Low orthophosphate concentration of the water and precipitation of calcium carbonate onto the leaves may have inhibited the biotic processing of leaves in Cabin Creek.
TL;DR: In an open field area in southern Sweden, biomass and numbers of hares and pheasants eaten by the predators were calculated from data on food habits, food requirements, andNumbers of the mammalian prey were calculated.
Abstract: in an open field area in southern Sweden. Biomass and numbers of hares and pheasants eaten by the predators were calculated from data on food habits, food requirements, and numbers of the mammalian ...
TL;DR: Fish production was estimated at three sites on the Jarama River, a small, typical upland river in Central Spain, by the successive removal method of electrofishing, and mortality curves were 7.5% lower than those based on estimated from the number of eggs laid.
Abstract: Fish production was estimated at three sites on the Jarama River, a small, typical upland river in Central Spain. Population estimates were made by the successive removal method of electrofishing. The same six species were recorded at each of the sites: Chondrostoma polylepis, Barbus barbus bocagei, Leuciscus cephalus pyraenaicus, Salmo trutta m. fario, Gobio gobio and Cobitis paludicola, with the first three species always dominant. Density, biomass, production (assuming that No is the total number of eggs spawned), and available production were, respectively: 13502-85776 ind. ha−1, 178.6–221.3 kg ha−1, 221.7–583.6 kg ha−1 yr−1, 118.1–271.9 kg ha−1 yr−1. Production estimates based on mortality curves were 7.9–19.5% (mean: 13.7) lower than those based on estimated from the number of eggs laid. Production per unit of area was highest at the widest and deepest site. Brown trout production contributed only 2–4% of the total production for all sites.
TL;DR: In the Oslofjord the amphipods Gammarus oceanicus Segerstrale, 1947 and G. salinus Spooner, 1947 were estimated to live for a maximum of 15 months and the sex ratio was mostly female dominated, a shift to male dominance was noted in one population and was related to possible infections.
Abstract: In the Oslofjord the amphipods Gammarus oceanicus Segerstrale, 1947 and G. salinus Spooner, 1947 were estimated to live for a maximum of 15 months. All specimens which survived during winter died in spring, mainly in May. A G. oceanicus population living on a freshwater influenced shore contained smaller specimens, had a lower proportion of the female population in breeding condition and probably produced fewer broods than a population living on a fully marine shore. The differences are discussed in relation to environmental factors and the distribution of G. salinus. Gammarus oceanicus possibly was breeding from December to May, some females even in June, resulting in an estimated maximum of three broods from December to May. Gammarus salinus showed two breeding periods, the first from December to May, a few of these females even bred in June, while new females bred from June to October, giving estimated maxima of respectively three (December to May) and five broods. Gammarus salinus females entered a reproductive resting stage in September-October. The sex ratio was mostly female dominated. A shift to male dominance was noted in one population and was related to possible infections. Information from the literature on longevity and breeding periods was compiled and compared to the Oslofjord data.
TL;DR: Fungal biomass and growth and microbial respiration were studied for two field seasons in a second-order subarctic stream where water temperature is 0°C for approximately 6 months and calculated leaf weight loss was small in all leaf species, compared with total weight loss over 98 d.
Abstract: Fungal biomass and growth and microbial respiration were studied for two field seasons in a second-order subarctic stream where water temperature is 0°C for approximately 6 months. Leaf packs (5-g) of alder Alnus tenuifolia, birch Betula papyrifera and willows Salix alaxensis and Salix arbusculoides immersed in autumn of 1979 and 1980 were sampled until June 1980 and January 1981, respectively. Fungal growth and microbial respiration occurred in submerged detritus at 0°C. Total and FDA-active hyphal lengths were measured, the active proportion averaging 25% of the total (all leaf species, both years). Generally, microbial respiration peaked in all leaf species after two weeks in the stream. As water approached 0°C, respiration declined by 20–50% depending on leaf species, but often increased later in decomposition (at 0°C). Seasonal trends in microbial respiration and FDA-active hyphal lengths were not similar although maximal respiration usually occurred as FDA-active hyphae were growing most rapidly. The calculated leaf weight loss due to microbial respiration was small (7–10%) in all leaf species, compared with total weight loss over 98 d. Scanning electron microscopy provided a visual record of leaf surface microorganisms and apparent leaf cuticle dissolution by fungi and bacteria.
TL;DR: Estimates of silk production indicate that the net cost is minimized by spinning a very fine silken strand and by adding silk over a period of time, which is offset by a large capture rate of prey.
Abstract: Larvae of Neureclipsis bimaculata (Trichoptera: Polycentropodidae) construct elaborate catchnets in lotic habitats to trap small drifting invertebrate prey. Three populations located at two oligotrophic and one eutrophic site were studied in southern Sweden. Measurements were made of larval weight, net size, seston quality and quantity, and stream velocity.
Neureclipsis larvae alter their net dimensions in response to both velocity and seston concentration. This was determined by comparing net structure and seston at the three locations. Larvae from the eutrophic, high quality seston site attain a significantly (P < 0.001) heavier instar V dry weight, spin a smaller catchnet, filter a volume of water dependent on body size, and slightly alter their catchnet dimensions with velocity. Larvae from the two oligothrophic sites are significantly smaller than those from the eutrophic site, spin a larger net at comparable velocities, filter a larger volume of water at comparable weights, and alter net dimensions with velocity.
Estimates of silk production indicate that the net cost is minimized by spinning a very fine silken strand and by adding silk over a period of time. The cost while large is offset by a large capture rate of prey.
The structure of Neureclipsis nets appears to be the result of a trade-off between maximizing food capture and minimizing hydraulic stress on the net.
TL;DR: A population dynamics analysis for planktonic diatoms is presented that allows estimates of the net rate of increase (k), the death rate (δ), the sedimentation rate and, in absence of grazing, the growth rate (μ).
Abstract: A population dynamics analysis for planktonic diatoms is presented that allows estimates of the net rate of increase (k), the death rate (δ), the sedimentation rate (σ) and, in absence of grazing, the growth rate (μ). It requires counts of live and dead cells suspended in the euphotic part of the water column and accumulated in sedimentation traps. The application of the model is demonstrated for the three dominant summe diatom species in Lake Constance. Asterionella formosa Hass, Fragilaria crotonensis Kitton and Stephanodiscus binderanus Krieger. Only during the first two weeks of the summer bloom of diatoms the loss rates were unimportant in comparison to the growth rates. Thereafter diatom population dynamics was strongly influenced by sedimentation and mortality, which sometimes led to a decrease in population density even when cell division continued at high rates. There were two periods of extraordinarily high death rates, which were associated in the case of A. formosa with silicon depletion and in the case of F crotensis with fungal parasitism.
TL;DR: Seedlings of the annual, Salicornia europaea (sensu stricto), germinated in the outer marsh sand flats at Skallingen in early May, and the relative growth rates of root and shoot were high during the establishment phase, which reflected differences in plant architecture.
Abstract: Seedlings of the annual, Salicornia europaea (sensu stricto), germinated in the outer marsh sand flats at Skallingen in early May, and the relative growth rates of root and shoot were high during the establishment phase. Mortality of plants, which was not density-dependent, was greater than 70% in most plots from early May to early October, as a result of wave action, desiccation and the presence of algal mats.
Salicornia ramosissima was present in the outer and inner marshes mixed with Puccinellia maritima. Seedling densities of this annual were high, and in early May growth rates were lower than those for Salicornia europaea. Overall mortality of plants from early May to early October was density-independent. Mortality of S. ramosissima in the inner marsh was only 50% from May to October, whereas the mortality of S. ramosissima in the outer marsh was 95% in the same period.
Different levels of seed production per plant, which reflected differences in plant architecture, were evident between the two micro-species.
Reciprocal transplants from the inner marsh failed to survive on the outer marsh sand-flat. Mean seed production per plant in plants transplanted from the outer marsh sand-flat to the inner marsh was only 10% of the value of the control populations. The distances of seed dispersal were different in the outer and inner marsh. Low recruitment occurred in areas cleared of Salicornia plants in the inner marsh, unlike the situation in the outer marsh sand-flat where tides dispersed seed.
TL;DR: Estimates of decay rate and turnover times for beech and oak branches and twigs decomposing on the forest floor and these were critically evaluated fell within the range found in the few other comparable studies.
Abstract: The rate of litter decomposition is often expressed as a constant decay rate (k; g g-1 yr-1) or as the time required for a certain percentage (often 95% and estimated as 3/k) of it to decompose (termed turnover time) Estimates of k may be obtained by determining the weight loss of litter in the field and also by assuming a steady state and obtaining the ratio of litter input: standing crop Both methods were used to estimate decay rate and turnover times for beech and oak branches and twigs decomposing on the forest floor and these were critically evaluated Considerable variation, ranging between 18-1445 yr, was found between the 95% turnover time estimates of various size components of the two species, obtained from woodfall and standing crop data Likewise variation in decay rate of 2-25 cm diameter beech branches, estimated from field experiments, was large both between and within groups of branches categorised according to initial state of decay and presence or absence of bark The mean annual decay rate for the various categories ranged between k = 0165-0452 g g -1yr' Branches without bark generally decomposed more slowly than those with bark Beech twig (<05 cm diameter) decomposition rates, from field experiments, ranged between k = 0149-0220 g g -lyr-1 and variation was relatively low compared with that of branches No significant differences (P<005)were detected between twig decomposition rates obtained from experiments initiated at different seasons although there was a slight decline in decay rate in winter months Twig and branch decomposition rates fell within the range found in the few other comparable studies
TL;DR: The species composition, biomass, and chlorophyll concentration of epipelic algae was studied before (1977) and during (1978-1979) fertilization with phosphorus and nitrogen of Lake Gunillajaure, a small subarctic lake in northern Sweden as mentioned in this paper.
Abstract: The species composition, biomass (measured as algal volumes) and chlorophyll concentration of epipelic algae was studies before (1977) and during (1978–1979) fertilization with phosphorus and nitrogen of Lake Gunillajaure, a small subarctic lake in northern Sweden.
The epipelic biomass, dominated by Cyanophyceae and Bacillariophyceae, was high (5.6–20.1 cm3 m−2) at all depths in the lake with the highest values in the hypolimnion (8–13.7 m). Calculated over mean depth it was 20 times higher than that of the phytoplankton. There was no significant increase in biomass during fertilization and neither did the species composition change. The chlorophyll concentration on the other hand were significantly higher in late 1978 and in 1979 which was probably an effect of the declining light climate caused by a large phytoplankton development in the lake. Constant seasonal biomass and species composition indicate a perennial epipelic community in this lake.
TL;DR: The seasonal on-and offshore migrations of the epibenthic community on a marine shallow soft bottom in Gullmar Fjord (Sweden) was recorded for a period of three years as discussed by the authors.
Abstract: The seasonal on- and offshore migrations of the epibenthic community on a marine shallow soft bottom in Gullmar Fjord (Sweden) was recorded for a period of three years. Quantitative sampling was carried out in shallow water (≤ 1 m depth) using drop-nets. A new sampling device was also introduced which allowed quantitative sampling in deeper water. The brown shrimp Crangon crangon L., juvenile plaice Pleuronectes platessa L. and the gobiid fish species Pomatoschistus minutus (Pallas) and P. microps (Kroyer) constituted the dominant inhabitants of shallow water, contributing >90% of the total number. The annual production was 2.2–2.9 g m−2 yr−1 dry wt with the brown shrimp as the dominant contributor. The abundance in shallow water fluctuated strongly between the seasons, while a relatively small seasonal variation was recorded in deeper water (2.5–10 m depth). The shallow/deep water abundance ratio for the epibenthic community heavily increased during the summer months, for the brown shrimp the ratio exceeded 200 in July. However, the heavy concentration in shallow water did not correspond to the reduced density of animals in deeper water. The boardering deeper water seemed to serve only as a transition area for animals arriving from or migrating to still deeper areas. Heavy mortality in the shallow nursery due to predation by the small epibenthic carnivores may also explain the low abundance in deeper areas during the autumn migration.
TL;DR: Nitrogen fixation activity was determined for Lotus tenuis, Medicago lupulina and Trifolium pratense and the three species grew in clones in grassland in an area reclaimed from brackish water in the 1940s.
Abstract: Nitrogen fixation activity was determined for Lotus tenuis. Medicago lupulina and Trifolium pratense. The three species grew in clones in grassland in an area reclaimed from brackish water in the 1940s. The N2[C2H2]-fixation was measured in soil cores throughout 1974 and 1975. From cores taken in dense and uniform stands of the species, the yearly N2[C2H2]-fixation at maximum cover was estimated. L. tenuis fixed about 4 g N m−2 yr−1 (area with max. cover 130%), i.e. 30–56% of its requirement. Both M. lupulina and T. pratense fixed about 7 g N m−2 yr−1 (maximum cover 37% and 80%) i.e. 67% of their N-requirement. Average N2[C2H2]-fixation for the whole area was 0.4 g N m−2 yr−1, considerably less than the N-addition through rainfall.
TL;DR: The dynamics of a Plantago maritima population was studied along a distributional gradient on a sea shore meadow during four years and the density peak was found at the intersect of these two variables.
Abstract: The dynamics of a Plantago maritima population was studied along a distributional gradient on a sea shore meadow during four years. The dynamics of the population varied along the gradient. In the lower parts there was a high flux with high mortality due to flooding but also a higher reproductive effort and good establishment. In the upper parts the flux was slower with lower reproductive effort and lower seedling success but instead longer lifespans. Population growth in these upper areas was primarily restricted by competition for light which prevented flowering and lowered the seedling success. Both cover values and the number of species decreased seawards and consequently the strength of competition. Simultaneously the risk of flooding increased. Thus the density peak was found at the intersect of these two variables. The plants showed differences in behaviour along the gradient in reproductive effort, growth rate, phenology etc. Whether this variation was phenotypical or genotypical is not known.
TL;DR: Radiotelemetry was used to study the movements of female meadow voles Microtus pennsylvanicus Ord through the reproductive cycle and revealed a significant positive association of females with non-crownvetch plants during the first six days of lactation but no association withNon-c Crownvetch was found before parturition.
Abstract: Radiotelemetry was used to study the movements of female meadow voles Microtus pennsylvanicus Ord through the reproductive cycle. The study was conducted on a commercial field of crownvetch Coronilla varia L., a plant which provides excellent cover but contains a toxin making it unsuitable as forage. In this habitat, food is limited to small patches of grass and other non-crownvetch species dispersed throughout the fields. Four measures of movement (activity radius, distance moved per hour, nest radius, and area covered) showed significant reductions at parturition. Females maintained low levels of movement throughout the first week of nursing as they concentrated activity around the brood nest. After seven days of lactation, they began to spend less time at the nest. A slight increase in median activity radius occurred through the last six days of gestation.
Brood nests were constructed in a portion of the home range that contained a relatively high concentration of food. Chi-square tests revealed a significant positive association of females with non-crownvetch plants during the first six days of lactation but no association with non-crownvetch was found before parturition. Females chose nest locations in which, prior to parturition, they had spent little or no time presumably because nutritious plants were less grazed there.
TL;DR: Winter breeding, as judged from heavy reproductive organs in both males and females, was observed in bank voles, yellow-necked mice and wood mice in south Sweden during the winter of 1976–1977.
Abstract: Winter breeding, as judged from heavy reproductive organs in both males and females, was observed in bank voles, yellow-necked mice and wood mice in south Sweden during the winter of 1976–1977. The breeding was probably a result of unusually favourable feeding conditions created by an extremely rich beech mast crop.
TL;DR: Bryophyte species distributions were analyzed with respect to microtopography at an alpine tundra site in central Alaska which is dominated by tussocks of Eriophorum vaginatum as mentioned in this paper.
Abstract: Bryophyte species distributions were analyzed with respect to microtopography at an alpine tundra site in central Alaska which is dominated by tussocks of Eriophorum vaginatum. Bryophyte distributions were found to be significantly correlated with slope but not with azimuth. Different types of tussocks and hollows and mats between tussocks also supported different bryophyte floras. Water loss resistances of three species of moss did not account for differences in their distributions.
TL;DR: The establishment and survival of seedlings cannot fully explain the distribution of adults, and self thinning occurred most likely as a result of competition for light.
Abstract: The establishment of Plantago maritima seedlings and juveniles along a distributional gradient was investigated with pantograph technique. Mortality was closely dependent on vegetational characters such as cover, height of vegetation and amount of litter. Superimposed on these factors was mortality due to flooding. The density dependent mortality of seedlings was also investigated. The number of surrounding seedlings seemed to be of vital importance for survival, i.e. self thinning occurred most likely as a result of competition for light. The establishment and survival of seedlings cannot fully explain the distribution of adults.
TL;DR: The spatial distribution of bird species was studied by grid mapping in 273 (250 × 250 m) squares in an open rural area in Denmark in summer and in winter, where species frequency probably reflects relative abundance as the two variables were highly positively correlated.
Abstract: The spatial distribution of bird species was studied by grid mapping in 273 (250 × 250 m) squares in an open rural area in Denmark in summer and in winter. Species frequencies (fraction of squares with species present) followed a logarithmic linear distribution when arranged by their rank. Species frequency probably reflects relative abundance as the two variables were highly positively correlated. The number of species increased with the number of vegetation layers, ground water level, and habitat diversity. The distributional segregation of species was similar in summer and in winter, even though the winter assemblage only comprised 62% of the species present in summer. The number of species per square in winter was positively correlated with the number of species in summer; the fraction of species wintering in various habitats increased with the number of vegetation layers and the presence of human habitation. Species that flocked had a low similarity between their summer and winter distributions. Among pairs of potential competitors the smaller species either changed distribution locally or emigrated from the area in winter. The number of habitat types was reduced from 5 in summer to 4 in winter, and the number of species assemblages decreased from 5 in summer to 3 in winter. Birds were absent from 52% of the squares in winter.
TL;DR: The species composition, species richness, and the general characteristics of the Corsican bird fauna are compared to those of similar French mainland areas and indicate that species impoverishment is not evenly distributed among different species groups.
Abstract: The species composition, species richness, and the general characteristics of the Corsican bird fauna are compared to those of similar French mainland areas. Species richness on Corsica is approximately 30% lower than on similar-sized reference areas on the mainland. A comparative study of the species composition Indicates that species impoverishment is not evenly distributed among different species groups. These groups were defined on three levels: taxonomical, biogeographical, and ecological. The sea bird fauna appears not to be impoverished. Freshwater and anthropophileous bird species groups show only little impoverishment, which is to be related to their good dispersal ability as a consequence of the discontinuous distribution of their habitats even on the mainland. The mainland forest species group is one of the most impoverished, but mainland forest species having colonised Corsica show important habitat expansion and increased densities on the island. The sedentarity of these species and particular features of the Corsican environment are proposed as explanations.