Showing papers in "Journal of Applied Ecology in 1981"
641 citations
635 citations
286 citations
TL;DR: The re-analysis of survival data for wild populations of eleven tropical species of mosquitoes revealed that in most of these populations the adult female mortality rates were not independent of age, as had commonly been supposed, but increased with age.
Abstract: SUMMARY (1) Methods are described for the analysis of survival data. (2) The re-analysis of survival data for wild populations of eleven tropical species of mosquitoes revealed that in most of these populations the adult female mortality rates were not independent of age, as had commonly been supposed, but increased with age. (3) The patterns of mortality of most of the populations were well described by the Gompertz function, according to which the rate of mortality increases with age in such a manner that its logarithm is directly proportional to age. (4) The epidemiological implications of these findings were examined by calculating the 'longevity factor', which is a component of vectorial capacity, for seven of these populations. Considerable differences were obtained in estimates of the longevity factor when the Gompertz model of mortality was substituted, in appropriate cases, for the widely used exponential model.
207 citations
TL;DR: It is argued from this result that the genetic structure of the target species has important implications with respect to the selection of species to be controlled using biological agents.
Abstract: (1) The genetic structure of agricultural plant populations has long been recognized as an important factor in their vulnerability or resistance to disease and pest attack. However, in the biological control of weedy plants, the potential significance of the population genetic structure of the target species appears to have been severely underestimated. (2) An examination of the degree of control achieved in eighty-one different control attempts demonstrated a significant correlation between the degree of control achieved and the predominant mode of reproduction of the target plant; asexually reproducing species were effectively controlled significantly more often than sexually reproducing ones. (3) It is argued from this result that the genetic structure of the target species has important implications with respect to the selection of species to be controlled using biological agents.
205 citations
TL;DR: In this paper, the authors measured the rate of increase in the CO2 concentration within a chamber placed on the soil surface, with an opening to the soil, to an accuracy of 2% and with a precision of 10%.
Abstract: SUMMARY (1) Soil respiration is commonly determined by measuring the rate of increase in the CO2 concentration within a chamber placed on the soil surface, with an opening to the soil. (2) In the present method the errors associated with the technique have been minimized by careful design of the chamber and the sampling system, and by the use of a sensitive infra-red gas analyser for the analysis of the CO2 concentration. (3) Small (5 cm3) samples of the chamber air are taken at I min intervals over a 4 min period. From the measured CO2 concentrations, the respiration rate is determined, using a graphical technique, to an accuracy of 2% and with a precision of 10%.
202 citations
191 citations
TL;DR: It is likely that anatomical-physiological adaptations, including a relatively large rumeno-reticulum allow domestic sheep to utilize more forage plant species and inhabit a wider variety of niches and ecosystems than most ungulates.
Abstract: (1) Using the results of diet selection studies and two wild and two domestic species, we compare some aspects of ecology in relation to body size, the recent evolutionary history of the species and current forage conditions. (2) Food niche breadth and inter-species diet overlap seemed dependent upon recent evolutionary history as well as upon body size, but values were strongly influenced by forage quantity and quality. (3) Dietary selectivity appears especially sensitive to seasonal changes in forage quality, e.g. large as well as small animals pursued relatively selective strategies when forage conditions permitted, but body size and related nutritional-energetic demands appeared to set the limits where switches from selective to non-selective tactics took place. (4) Sensitivity to diet composition and quality increased with decreasing size except in the domestic sheep. It is likely that anatomical-physiological adaptations, including a relatively large rumeno-reticulum allow domestic sheep to utilize more forage plant species and inhabit a wider variety of niches and ecosystems than most ungulates. Human selection has made the sheep food and habitat generalists despite their relatively small size.
178 citations
TL;DR: In this article, the foraging activities of a large flock of barnacle geese (Branta leucopsis Bechstein) wintering on the West Frisian island of Schiermonnikoog were monitored during the spring of 1978.
Abstract: (1) The foraging activities of a large flock of barnacle geese (Branta leucopsis Bechstein) wintering on the West Frisian island of Schiermonnikoog were monitored during the spring of 1978. On fourteen sites distributed over the grazing area we measured grazing intensity, plant species presence and abundance, standing cropherbage accumulation, and crude protein content of Festuca rubra L., the primary food plant of barnacle geese. Two of the sites had nitrogen fertilizer applied to them. (2) Almost all the sites were grazed repeatedly, but barnacle geese utilized different areas with different mtensities. In spite of this, the standing crops did not differ between sites, and the standing crop on all the sites remained relatively constant throughout the spring, including the sites that received a nitrogen fertilizer. (3) Areas with the highest rates of herbage accumulation were grazed most intensely. Barnacle geese displayed no consistent preference for other site characteristics. (4) High levels of protein in Festuca rubra were a direct result of repeated grazing of sites by barnacle geese, and the consequent sustained regeneration of young, protein-rich plant tissues.
168 citations
TL;DR: Changes in the distribution, frequency and abundance of three forms of Chondrilla juncea occurring in south-eastern Australia are documented for the period 1968-1980, with the abundance of the most widespread form declining as a result of the impact of a number of host-specific natural enemies deliberately introduced as biological agents.
Abstract: SUMMARY (1) Changes in the distribution, frequency and abundance of three forms of Chondrilla juncea occurring in south-eastern Australia are documented for the period 1968-1980. (2) The abundance of the most widespread form has declined as a result of the impact of a number of host-specific natural enemies deliberately introduced as biological agents. The distribution of the other two forms has extended. (3) The effect of the most aggressive of these agents, Puccinia chondrillina, on the competitive interaction between the two morphologically most dissimilar forms of C. juncea is demonstrated in a replacement series experiment. When grown in the absence of P. chondrillina both forms competed equally; when form A plants were regularly infected with P. chondrillina, dry weight of the non-susceptible form C was increased by at least 10%, whilst that of form A declined substantially.
161 citations
TL;DR: In this article, the authors measured the fast chlorophyll a fluorescence transient and its parameters and showed that PS II construction became more sensitive to heat stress when ambient temperature was higher than 40 degrees C.
Abstract: With lower-and higher heat-resistant varieties of eggplant (Solanum melongena L.) Heibei I and Heibei II as test materials, and by using Plant Efficiency Analyzer (PEA) from Hansatech, this paper measured the fast chlorophyll a fluorescence transient and its parameters. The results showed that PS II construction became more sensitive to heat stress when ambient temperature was higher than 40 degrees C. The F0 went up slowly, and Fv/Fm and deltaF/Fm' came down dramatically. Heibei II had a longer semi-attenuation temperature of Fv/Fm (T50) and deltaF/Fm' (t50) than Heibei I. Under strong heat stress (5 min at 48 degrees C or 20-30 min at 44 degrees C), the K-step in relation to the inactivation of oxygen-evolving complex appeared in fluorescence rise at about 700 micros, and the regular O-J-I-P transient was transformed to O-K-J-I-P one. The K-phase of Heibei I and Heibei II appeared when the treatment time was up to 20 and 30 minutes at 44 degrees C, respectively. In comparing with 35 degrees C heat treatment, the DI0/RC in the parameters of Strasser's specific energy fluxes model was increased by a great extent under 48 degrees C or more heat stress, reflecting a strong safeguard of energy dissipation to PS II. When the temperature of heat stress increased from 35 degrees C to 52 degrees C, the Fvi/Fv of PS II silent reaction centers of Heibei I and Heibei II increased remarkably.
TL;DR: Fox distribution in the city was uneven, and fox density was not found to correlate with household density, housing type, age of housing stock, or any other obvious habitat feature, and there was a negative correlation between the distribution of stray dogs and urban foxes.
Abstract: (1) In two areas of Bristol, one 5.5 km2, the other 3.2 kM2, fox litter counts in two consecutive years were used to estimate the number of fox family groups. There were 3.64 family groups/km2 in the larger area, 3.13/km2 in the smaller. In parts of the larger area densities of 4-5 family groups/km2 were recorded. (2) To obtain data on the distribution and relative densities of foxes throughout Bristol, nearly 88 000 school children were asked to record fox sightings for a period of one month. Since the absolute fox densities were known for two areas, the distribution of recorded sightings could then be used to estimate fox densities throughout the city. By this means it was calculated that there were 211 fox family groups in an area of 116 sq km, a mean density of 1.82 fox family groups/km2. (3) Fox distribution in the city was uneven, and fox density was not found to correlate with household density, housing type, age of housing stock, or any other obvious habitat feature. There was a negative correlation (P < 0.001) between the distribution of stray dogs and urban foxes. This was attributed to disturbance of the fox population by stray dogs. It is suggested that disturbance may be particularly important in the breeding season; dogs were the second major cause of mortality in young fox cubs. (4) Based on post-mortem material, it was calculated that the ratio of breeding to non-breeding vixens was 1:0.35, and so the adult fox population consisted of 211 males, 211 breeding females and 74 barren females. Assuming that all fox family groups breed each year, with a mean birth litter size of 4.80 (calculated from placental scars), the annual cub production would be 1013.
TL;DR: It is concluded that other factors, perhaps related to soil water and nutrient movement, are in large part responsible for the increased nutrient status and production of vehicle tracks and exert an important control over growth in undisturbed tundra.
Abstract: (1) Soil characteristics and vegetation were studied in vehicle tracks and adjacent undisturbed tundra along local moisture gradients at four tundra sites in northern Alaska. Vehicle tracks generally had 2 OC higher soil temperatures, deeper thaw, and higher concentrations of available soil phosphate than adjacent undisturbed tundra, but did not differ consistently from controls in soil bulk density, volumetric moisture content, pH, or soil organic content. (2) Vegetation in vehicle tracks had fewer species than controls, reflecting decreased abundance of shrubs, particularly evergreens, and increased dominance by a few species of graminoids. (3) Wet and mesic tracks exhibited a 2to 15-fold increase in above-ground standing crop of nitrogen and phosphorus as a result of increased leaf nutrient concentrations and increased leaf biomass of graminoids, a consequence of increases in both shoot density and shoot weight. (4) We reject our original hypothesis that the known temperature effects upon root growth, nutrient absorption, and organic matter mineralization account for the increased standing crop of biomass and nutrients in vehicle trails. We conclude that other factors, perhaps related to soil water and nutrient movement, are in large part responsible for the increased nutrient status and production of vehicle tracks and exert an important control over growth in undisturbed tundra.
TL;DR: In this paper, a null-balance diffusion porometer was used to measure stomatal conductance in both Gmelina and teak on 6 days during the dry season in Nigeria and the use of these measurements in predicting transpiration rates by the species from weather station data is discussed.
Abstract: SUMMARY (1) Measurements of stomatal conductance using a null-balance diffusion porometer were made on Gmelina and teak on 6 days during the dry season in Nigeria. Stomatal conductance increased rapidly in the early morning and decreased after midday in both species but values in Gmelina were less than those in teak. Leaf water potential, measured with a pressure chamber, was usually lower in Gmelina than in teak. (2) Stomatal conductance in both species was dominantly controlled by irradiance and air saturation deficit and a model, relating stomatal conductance to these two variables accounted for more than 80% of the variation in the measurements. (3) The Penman-Monteith equation was used to calculate transpiration rates from measured stomatal conductances and environmental variables. Transpiration rates using conductances predicted from the model agreed closely with the calculated ones. (4) Hydraulic resistances were similar for both species. (5) The use of these measurements in predicting transpiration rates by the species from weather station data is discussed.
TL;DR: A discrete (difference) population dynamics model is used to show that pure populations of Agrostemma can exhibit damped oscillations towards equilibrium whilst populations grown with wheat show monotonic damping.
Abstract: (1) The responses to density of the annual Agrostemma githago were investigated over a wide range of densities in pure populations and also in the presence of a constant density of wheat. In monoculture a 2500-fold variation in the input of seeds gave only a 1.6-fold range of seed output, whilst in the presence of wheat, yield varied to a much greater extent. (2) Considerable self-thinning occurred in both sets of populations at high densities. Agrostemma responded to increasing density not only through an increase in mortality but also through a plastic reduction in the shoot dry weight of survivors, the number of capsules per plant, the number of seeds per capsule and mean seed weight. (3) There was a clear negatively density-dependent relationship between fecundity and density in both pure and mixed populations of Agrostemma. Simple mathematical models based on a reciprocal equation provided a very good fit to these data. (4) It is suggested that the models provide the basis for an analysis of additive interference experiments in which both density and frequency are varied. (5) The biological interpretation of the model parameters is discussed in relation to the seed production of isolated plants, ecological neighbourhood areas, the efficiency of resource utilization and equivalence between species. (6) A discrete (difference) population dynamics model is used to show that pure populations of Agrostemma can exhibit damped oscillations towards equilibrium whilst populations grown with wheat show monotonic damping.
TL;DR: Elephants appear to have been responsible for the decreases in biomass but fire has also contributed to the decreases.
Abstract: (1) Changes in biomass and annual production measured over the period 1972 to 1976 in four woodlands, the miombo, the Sengwa/Lutope riverine, the Manyoni riverine and the mopane woodland, are described. (2) The greatest changes in biomass were recorded in the miombo woodland where it is estimated that the biomass decreased by 45%. The biomass of the Sengwa/Lutope riverine, a woodland with three strata, increased by 14%, whilst that of the Manyoni riverine changed little. The biomass of the mopane woodland decreased by over 6%. (3) The annual production of the miombo, the Manyoni riverine and the mopane woodlands decreased between 1972 and 1976, whereas that of the Sengwa/Lutope riverine woodland increased. (4) The change in the biomass of the miombo woodland was primarily a result of the removal by elephant of large trees which were not replaced due to the effects of elephant and fire. (5) The increase in biomass of the Sengwa/Lutope riverine woodland was a result of recruitment to both the tree and shrub layers. The tree biomass increased by 394%, and the shrub biomass by 207% but the biomass of the upper canopy trees decreased by 10%. (6) The decrease in biomass of the mopane woodland which is seldom affected by fierce fires, was almost certainly due to the effects of elephant. (7) Due to the opening up of the canopy and the coppicing of damaged trees, more browse is now in reach of the smaller browsing animals in all woodlands except the Manyoni riverine. (8) Elephant appear to have been responsible for the decreases in biomass but fire has also contributed.
TL;DR: The influence of trampling was studied on the outer dune heath of Skallingen, southwest Jutland and it was emphasized that all the consequences of a management operation need to be considered before it is carried out.
Abstract: (1) The influence of trampling was studied on the outer dune heath of Skallingen, southwest Jutland. The total number of passages and the period of time over which trampling occurred were varied independently, on areas that had either received fertilizer applications or were unfertilized. The depth and width of paths were measured and the relative cover of the vegetation and species frequency determined. (2) There was a linear relationship between the depth of the paths and the number of passages. 2560 passes lowered the soil surface by 28 mm. The width of paths increased with increasing numbers of passages. The paths were slightly deeper when trampled on a single day as opposed to the effect of trampling over a period of 4 months. (3) Relative cover was reduced with increasing numbers of passages; after 200 passages cover was only 50%. This low carrying capacity is suggested to be the consequence of reduced vigour of the dominant species Empetrum nigrum, although it is not reflected in frequency measurements of this species. The frequency of four species E. nigrum, Festuca rubra, Ammophila arenaria and Veronica officinalis was largely unaffected by 150 passages but only two species, Empetrum nigrum and Hypnum cupressiforme survived 2560 passages. (4) Addition of fertilizer only slightly increased plant cover on the paths but tended to produce a vegetation dominated by grasses. (5) It is emphasized that all the consequences of a management operation need to be considered before it is carried out.
TL;DR: It is concluded that grazing by coypus could be primarily responsible for the major part of the reed decline, particularly from 1950 to 1963, and could explain the present limitation of reedswamp in Bure and Ant Broads.
Abstract: (1) A study was made of changes in the distribution and area of reedswamp in eighteen Broads by the use of aerial photographs, which covered the period 1945 to 1978. Additional information was obtained from the c. 1880, 1905 and 1926 Ordnance Survey maps. (2) Between 1880 and 1905 the colonization, by reedswamp, of open water exceeded losses, by succession, to fen. After 1905 the area of reedswamp decreased mainly by rapid succession to fen, and a slower rate of colonization. (3) From 1946 onwards there was a dramatic loss of reedswamp. The area decreased from 121.5 ha in 1946 to 49-2 in 1977. These losses were almost entirely through reversion of reedswamp to open water. (4) It is concluded that grazing by coypus could be primarily responsible for the major part of the reed decline, particularly from 1950 to 1963. Evidence is presented showing that if reedswamp, a food source preferred by coypus, formed not more than 66% of the coypu-diet this could account for all the changes observed. Further, if the coypus selected only buds and young shoots this figure might be as low as 6-6%. (5) Grazing by wildfowl, especially feral geese, could explain the present limitation of reedswamp in Bure and Ant Broads. (6) Experiments designed to test for direct effects of eutrophication on reedswamp were inconclusive. The growth of Phragmites australis was not inhibited by an atmosphere of nitrogen surrounding roots and stem bases, nor when potted in mud from sites where regression had occurred. (7) Eutrophication, however, could have had an indirect effect on reedswamp. It raised the rate of sedimentation, and so could have increased the susceptibility of reeds to grazing, because the buds are more accessible in soft mud and because, under anaerobic conditions, the plants might be more susceptible to damage when shoot grazing cuts off the oxygen supply to the roots.
TL;DR: It is indicated that long-term starvation had a greater effect on the glucose concentration in haemolymph than in groups C and S1 and S2, but was markedly less in group S3 than in group C.
Abstract: This paper studied the variations of glucose concentration in haemolymph and glycogen concentration in hepatopancreas and muscle of Marsupenaeus japonicus under starvation and re-feeding. Groups C, S1, S2 and S3 were deprived of food for 0, 10, 15 and 25 days, respectively, and then re-fed for 10 days. Under starvation, the glucose concentration in haemolymph and glycogen concentration in hepatopancreas decreased rapidly at the beginning, and the glycogen concentration in muscle was the lowest after 10-day fasting. In the following 5 days, the glucose concentration in haemolymph and glycogen concentration in hepatopancreas and muscle recovered to their initial levels due to gluconeogenesis, but the glycogen concentration kept declining with fasting. After refeeding, the glycogen concentration in hepatopancreas and muscle recovered well, and the glucose concentration in haemolymph had a sharper increase in groups S1 and S2 than in group C, but was markedly less in group S3 than in group C. These results indicated that long-term starvation had a greater effect on the glucose concentration in haemolymph.
TL;DR: The aim of the IBP is to provide a meta-model for the simulation of intensively managed grazing systems and to demonstrate the role of simulation in the development of knowledge of ecosystem function.
Abstract: List of contributors Foreword J. B. Cragg Contents of IBP 18 Introduction A. I. Breymeyer Part I. Processes and Productivity: 1. Abiotic subsystem W. T. Hinds and G. M. van Dyne 2. Autotrophic subsystem J. S. Singh, M. J. Trlica, P. G. Risser, R. E. Redmann and J. K. Marshall 3. Small herbivore subsystem L. Andrzejewska and G. Gyllenberg 4. Large herbivore subsystem G. M. van Dyne, N. R. Brockington, Z. Szocs, J. Duek and C. A. Ribic 5. Invertebrate predator subsystem A. Kajak 6. Vertebrate predator subsystem L. D. Harris and G. B. Bowman 7. Decomposer subsystem D. C. Coleman, A. Sasson, A. I. Breymeyer, M. C. Dash, Y. Dommergues, H. W. Hunt, E. A. Paul, R. Schaefer, B. Ulehlova and R. I. Zlotin Part II. Systems Synthesis: 8. Nutrient cycling F. E. Clark, C. V. Cole and R. A. Bowman 9. Comparative studies of ecosystem function N. I. Bazilevich and A. A. Titlyanova 10. Total-system simulation models G. S. Innis, I. Noy-Meir, M. Godron and G. M. van Dyne 11. Trophic structure and relationships A. I. Breymeyer Part III. System Utilization: 12. Management impacts on structure and function of sown grasslands K. J. Hutchinson and K. L. King 13. Simulation of intensively managed grazing systems N. G. Seligman and G. W. Arnold 14. Reflections and projections G. M. van Dyne Index.
TL;DR: Pot experiment showed that the plant height, stem diameter, and dry mass of corn seedling were significantly higher in PSB treatments than in CK, and applying PSB agent with manure as a carrier could significantly increase the seedling's dry mass, in comparing with applyingPSB agent alone.
Abstract: By using modified PVK plate method, 44 strains of phosphate-solubilizing bacteria (PSB) were isolated from the root surface of wild plants growing well in calcareous soil. After 7-day incubation in a liquid medium NBRIP, the total P in the cultures of strains K3 and K9 reached 643.2 microg x ml(-1) and 608.5 microg x ml(-1), and soluble P was 584.8 microg x ml(-1) and 606.4 microg x ml(-1), respectively. About 12.9% of tricalcium phosphate was dissolved, being 9.5 times higher than CK. Pot experiment showed that the plant height, stem diameter, and dry mass of corn seedling were significantly higher in PSB treatments than in CK. Applying PSB agent with manure as a carrier could significantly increase the seedling's dry mass, in comparing with applying PSB agent alone. The strains K3 and K9 were identified as Pseudomonas.
TL;DR: In 1911 and 1925 reindeer were introduced to the subantarctic island of South Georgia, where there is a species-poor vascular flora and no interspecific competition, and tussock grassland was affected only at high population densities.
Abstract: SUMMARY (1) In 1911 and 1925 reindeer, Rangifer tarandus L., were introduced to the subantarctic island of South Georgia, where there is a species-poor vascular flora and no interspecific competition. (2) Snow cover limits the choice of forage almost exclusively to coastal tussock grass, Poa flabellata, for up to 3 months, and certain forage species remain unavailable for up to 6 months. (3) During summer reindeer select forage species high in N and P, notably Deschampsia antarctica, Acaena magellanica and the alien Poa annua. (4) Native species (lichens and A. magellanica) responded quickly and unfavourably to grazing, but tussock grassland was affected only at high population densities. (5) This contrasts with the sequence of overgrazing by introduced herbivores on other subantarctic islands, where tussock grassland has been the most susceptible vegetation type. (6) This dependence on tussock grass, rather than lichens, for winter forage is a major reason for the absence of a population crash.
TL;DR: In this paper, the precision of estimates of soil bulk density from organic matter content, expressed as % loss onignition of dry weight, was examined for eight groups of data collected from surface and sub-surface soils on various sites by different workers.
Abstract: (1) The precision of estimates of soil bulk density from organic matter content, expressed as % loss-on-ignition of dry weight, was examined for eight groups of data collected from surface and sub-surface soils on various sites by different workers. (2) The regression derived by pooling all data for surface soils differed significantly in elevation from its counterpart for sub-surface soils. (3) Regressions for individual groups of data for both surface and sub-surface soils, differed in slope and elevation from their respective overall equations and from each other. (4) For greatest precision in estimating soil bulk-densities, the authors recommend research workers to derive equations for their own research sites rather than to rely on general equations.
TL;DR: In this article, Grazing preferences of Shorthorn cattle for seven major and four minor range communities were determined from 108 aerial surveys over 41 years during climatic conditions ranging from drought to the wettest on record.
Abstract: SUMMARY (1) Grazing preferences of Shorthorn cattle for seven major and four minor range communities were determined from 108 aerial surveys over 41 years during climatic conditions ranging from drought to the wettest on record. Principal Component Analysis was used to summarize the variation in patterns of choice between communities. Variation in use was related to changes in quality and quantity of forage. Sporadic environmental disturbances such as excessive rains, drying out of watering points or cold winds disrupted the pattern of grazing determined by forage conditions. (2) Woodland and Flood plain were the most preferred communities, particularly during good forage conditions, while Hills and Mulga-perennial grass communities were refuge areas during drought periods. Gilgaied plains and Foothill fans were moderately used mainly during good to moderate forage conditions. This preferential use of different communities under different forage conditions showed the benefit of a complex of communities in a grazing system in allowing cattle to seek the best forage to maintain body condition. In such a complex, grazing distribution could be used as an indication of condition of the forage. Use of less preferred communities, which would allow regeneration of heavily used communities, could be achieved by manipulating availability of water sites and choice of grazing areas.