Pasture Populations Research Articles

Gene flow in Plantago I. Gene flow and neighbourhood size in P. lanceolata

The genetic population structure and gene flow in the obligatory outbreeding plant species Plantago lanceolata L. were determined in the Westduinen (Wd) pasture population in the South-West of the Netherlands. Three experiments were performed: the measurement of genetic structure using allozyme variation, pollen flow in a wind-tunnel and the distribution of an allozyme marker in a garden experiment. The position and allozyme genotype of 524 plants from eight subpopulations in the Westduinen population were determined. The population exhibited local differentiation: genotype frequencies within subpopulations were mostly in Hardy-Weinberg equilibrium, and gene frequencies varied significantly between subpopulations. The wind-tunnel experiments showed that wind speed, source height and capture height of pollen influenced the pollen-mediated gene flow and therefore neighbourhood sizes. In the garden experiment a clear picture of actual pollen flow could be shown. Estimates of neighbourhood and gene transport parameters from the data of the three experiments indicated restricted gene flow: neighbourhood size (Ne) was between 14 and 20 plants, mean gene transport per generation (M) between 0·2 and 1·4 metres. We argue that this combination of small effective number and low gene transport leads to the substructuring of the Westduinen population of P. lanceolata.

Population studies on Pennyroyal Mint (Mentha pulegium L.) II. Seed banks

SummaryAn investigation of seed banks found under populations of M. pulegium located within and outside pasture systems revealed that seed densities were sixteen times greater when this species occurred in pastures. The sizes of seed banks were not positively related to current seed production, but larger seed banks appeared to be associated with higher levels of soil disturbance arising from trampling by grazing stock. Densities of buried seed were very high under pasture populations (range 55 000–176 000 m−2), which illustrates the impracticality of attempts to eliminate M. pulegium from this type of community.

Seasonal changes in pasture populations of infective larvae of gastrointestinal nematodes of cattle in eastern Nigeria

The seasonal changes in the populations of trichostrongylid infective larvae (L3) on herbage and in soil samples collected from pastures grazed by beef cattle were studied at Nsukka, eastern Nigeria, from April 1980 to July 1981. Large numbers of L3 were recovered from all samples collected during the rainy season (April to October). The rainy season herbage infestation was characterised by three clearly defined peaks. The first, which followed an 'early rains' (April) rise, occurred in the second half of May while the larger second and third peaks occurred in late July and October respectively. It is suggested that each of these peaks represented a distinct wave of infestation by a separate generation consisting of the three trichostrongylids concerned, namely Cooperia, Haemonchus and Trichostrongylus species. Although there was a sharp fall in pasture infestation following the onset of the dry season, appreciable numbers of L3 were still present on herbage in early December. The implications of these findings have been discussed in relation to the choice of effective strategic anthelmintic programmes for the prophylaxis and control of bovine parasitic gastroenteritis in the Nsukka area.

Colour Pattern Polymorphism in the Grasshopper Phaulacridium Vittatum. I. Geographic Variation in Victoria and Evidence of Habitat Association.

The frequencies of the 3 colour pattern morphs (plain, striped and incomplete-striped) in samples of Phaulacridium vittatum (Sjost). from pasture sites in Victoria, Australia, did not conform to the pattern predicted by the latitudinal cline in morph frequencies previously described in south-eastern Australia. Data from 2 transects across pasture-forest boundaries revealed the existence of habitat associations, with forest habitats having a higher frequency of the plain morph. The proximity of some pasture populations to forests may explain some of the variation in morph frequencies observed among pasture sites. However, the frequency of the striped morph was relatively low in all the populations examined; this suggests that there are strong selective constraints on the frequency of striped individuals.

Grass grub (Costelytra zealandica) population collapse in the northern North Island

Abstract Annual surveys of grass grub populations in early autumn from 1979 to 1982 at Tihoi near Lake Taupo and at Waingaro in the western Waikato have revealed that populations in old pastures (at least 7 years old) increased to a peak by 1979 or 1980 and subsequently declined naturally to low levels. Populations in newly sown pastures increased to a peak in the second or third autumn after sowing and then declined. Application of lindane at Tihoi in 1979 reduced grass grub numbers by an average of 840/0 in the year after treatment, but 3 of the 5 treated populations have since increased to higher levels than the untreated. A life table study of the 1981-82 grass grub generation at Tihoi showed that variation in summer mortality was responsible for differences in population trend. Weather, pasture composition, gcazing management, depletion of the food supply, and predation did not appear to be major causes of summer mortality. This mortality was not significantly related to population density on a conti...

Energetics of earthworm populations in tropical pastures from India

This paper reports our results of studies connected with the energy flow in earthworm populations in an upland and a lowland pasture where grazing by large herbivores were not allowed. The net annual energy input was more than double in the lowand pasture. Flooding during the rainy season caused heavy mortality and migration of worms in lowland pasture. Higher energy consumption through respiration in the upland pasture was due to difference in environmental conditions. Lower amount of secondary production (P) and higher amount of energy utilized in respiration (R) cause an increased R:P ratio in upland pasture. Energy channelization in both the sites has been represented in box type energy flow models. Management of these pasture lands depends on the understanding of the dynamics of energy flow in these systems.

Insecticidal control of black beetle (Heteronychus arator) in pasture

Abstract The effectiveness of insecticides applied in early December to control black beetle larval populations in pasture was investigated on sand, loam, clay, and peat soils. Fensulfothion and isazophos, applied using a commercial granule spreader, gave, on average over all 10 sites larval reductions of 88% at 2 kg/ha, and 73% at i kg/ha rates. Liquid Isazophos applied by a ‘jet squirt’ techmque gave an average of 21% poorer control than broadcast granules. Diazinon granules gave poor control with average reductions of 41% at 2 kg/ha and 23% at 1 kg/ha rates. A wide range of soil moisture leve1s occurred over the 3-week post-application penod. Higher levels of control were achieved on moist organic peat soil (50% Mv) than on drier mineral sand and clay soils (15–37% Mv), with mtermediate control on podzolised loam soil (32% Mv). It was concluded that 1 kg/ha of fensulfothion or isazophos applied in November or early December when soil moisture levels are moderate will give control (e.g., 52–82% reductions) of black beetle larvae in pasture.

Combined Tolerance to Copper, Zinc and Lead by Populations of Agrostis Tenuis

The tolerance of populations of Agrostis tennis Sibth. growing in mining areas in Wales to the heavy metals Cu, Zn and Pb was investigated by exposing tillers to different concentrations of the metals in nutrient solutions. An index of tolerance (IT) was calculated by comparing root length with specimens grown in solutions without heavy metals. The data indicate a concomitant expression of tolerance towards the three metals. It was also shown that there is a close relationship between the IT values of the populations towards Cu, Zn and Pb, and the contents of the metals in the soils. A basic prerequisite for the development of tolerance towards toxic heavy metals is their presence in the soil, and the adaptation of the organism. Consequently, the expression of tolerance to one or more metals does not necessarily involve tolerance to other metals not present in the soil. The variability of the IT values within the populations is most probably explained by an intrinsic genetic heterogeneity in the populations, in contrast to populations growing in pastures, which demonstrate genetic homogeneity. Thus, it is evident that a static gene balance is maintained in pasture populations, whereas in mine populations the balance is dynamic.

Egg clumping, host plant selection and population regulation in Cactoblastis cactorum (Lepidoptera).

Since the successful control of prickly pear cactus by Cactoblastis cactorum in Australia, populations of plants and moths have persisted at low densities in open woodland sites. A contagious egg distribution causes overcrowding of larvae on some plants but insures low levels or no attack of other plants. This prevents extinction of plants and insects. Cactoblastis moths choose plants with characteristics which may increase the success of their larvae. Field observations and cage experiments indicate that large, green cactuses near previously attacked cactuses receive more eggs. Plants which are actively photosynthesizing are also more attractive as oviposition sites. These oviposition preferences contribute to the observed contagious egg distribution.While open woodland Opuntia and Cactoblastis populations fluctuate around an equilibrium, pasture populations may better be described by the "hide and seek" model, with the woodland populations serving as refuges. Average plant quality and variation in quality are suggested as important components in the dynamics of this system.

A methodological problem in genecology. Seeds versus clones as source material for uniform gardens

Plants derived from both achenes and rootstock cuttings (ramets) were used to examine genetically based differences between two populations of Rumex crispus L. from two contrasting habitats, i.e., flood plain and pasture. Offspring from both sources were grown under cultivation in a uniform garden. Fifty-eight characters were determined for each individual. Within the pasture population only, seedling offspring differed significantly from plants obtained from ramets. Characteristics of the two populations were compared using (i) seedling offspring and (ii) ramets. More significant differences were found in the former set of comparisons.In the harsh but predictable flood plain habitat, genetic heterogeneity within the population was less than that found among plants from the pasture. Reasons for this difference are discussed.

AN ASSOCIATION BETWEEN PASYALUM DILATATUM AND BLACK BEETLE IN PASTURE

Field monitoring of black beetle, Heteronychus arutor (F.), populations in Waikato pasture showed a strong association between black beetle numbers and the presence of Paspalum dilatatum Poir. Increasing paspalum gave higher adult numbers in spring resulting from increased overwintering survival, and in some seasons, reduced autumn dispersal. Numbers of larvae damaging pasture in February were directly related to adult numbers in September. Black beetle preferentially select paspalum plants in mixed pasture. This can place paspalum at a competitive disadvantage relative to other pasture species, but also permits the retention of higher adult black beetle numbers, even at low paspalum levels.

Arthropod Populations in Permanent Pastures Treated and Untreated With Mirex for Red Imported Fire Ant 1 Control 2

Experiments were conducted in 1972–73 to study interrelationships between red imported fire ants, Solenopsis invicta Buren, and associated arthropods in pastures. The fire ant populations were suppressed with one application of mixrex bait each year. Frequencies of 30 arthropod taxa caught in pitfall traps and 5 insect taxa in dung samples were determined in mirex treated and untreated pastures. The population of Vacusus vicinus (LaFerte) (Anthicidae), Lycosa riparia-helluo complex (Lycosidae) and pupae of hom flies, Haemotobia irritans (L.) (Diptera) were significantly higher ( P <0.05) and Aphodiinae (Scarabaeidae), S. invicta and Nylanderia spp. (Formicidae) were significantly lower ( P < 0.05) in treated compared to untreated pastrues in 1972. In 1973 significantly greater numbers of Trachelas deceptus (Banks) (Clubionidae), Carabidae, and H. irritans pupae were found in treated pastures. Significantly lower numbers of Schizoeoza avida (Walkenaer) (Lycosidae), Xyleborinus saxeseni (Ratzeburg) (Scolytidae), Staphylinidae, Aphodiinae, (Scarabaeidae), Gryllidae, S. invicta and Nylanderia spp. were detected in the treated pastures ( P <0.05). Examinations showed that S. invicta preyed upon immature forms of H. irritans in cattle dung pats. Where predation of immature horn flies was intense, associated rove beetles also were apparently preyed upon.

Dalapon resistance in Lolium perenne populations

AbstractThe resistance often early, ten medium late and ten late flowering ryegrass populations to two rates of dalapon (2.8 and 5.6 kg ha‐1 acid equivalent) was measured in a box experiment. There was no difference in the mean effect of dalapon on the maturity groups at the time of greatest yield reduction, but the recovery of the late flowering population was, on average, better than that of the medium late group. There was a range of reaction to herbicide within all three maturity groups and, in general, the high yielding populations without dalapon were the most resistant, but there were exceptions. Assessment at 2.8 kg ha‐1 acid equivalent gave a similar ranking order to that using twice the amount of dalapon. The results of the current box experiment with seedlings were consistent with those obtained in the field at another location (Faulkner, 1974) for the eleven cultivars common to both trials. The resistance of a permanent pasture population was much lower than that of some cuttivars.

THE LEGUME—A REAPPRAISAL OF ITS PLACE IN TODAY'S FARMING*

ABSTRACTThe last 10 years have seen a marked shift in Britain from the growing of legumes towards the use of fertilizer N. Many farmers are now reassessing the position Decause of increasing fertilizer prices and because of improvements in clovers and lucerne through plant breeding.On the intensive dairy farm legumes can play an important part in the conseravation block. The yield of lucerne without applied N is as high as from ryegrass with 250 units N/ac. Red clover is also useful over a wide range of soil types.On the less intensive farm, white clover should be contributing throughout the grazing area. there are many reasons for poor white clover populations in pastures; one of these is the fungus disease Sclerotinia trifoliorum, commonly known as clover rot. Varieties resistant to this disease are available in both red and white‐clover. Verticillium wilt in lucerne bas also been checked by the plant breeder.Improved legume varieties justify a completely new look at these crops and the possibilities for lucerne in this country appear to be particularly good.

Zonation and regulation of old pasture populations of Hieracium floribundum

Colonies of the perennial Hieracium floribundum Wimm. and Grab, had four zones, identified by the density of the rosettes. Belts of sod were analyzed to determine the characteristics of these zones in a pasture which had not been grazed for 5 years. The advancing outer zone consisted of widely spaced rosettes that were less than 2 years old. These rosettes had short rhizomes and large leaves, reproduced by stolons, and flowered abundantly, producing numerous heads per inflorescence. In the central zone, which had the highest density, the rosettes were more than 2 years old, had long rhizomes and small leaves, and did not flower. Seedling numbers were insignificant in all zones. In this species stolons are produced only on plants that have flowered. At high densities curtailment of population growth resulted from reduced flower production and the number of associated stolons initiated per flowering plant.

A comparison of ryegrass populations from intensively managed permanent pastures and leys

SummaryRyegrass populations collected from intensively used swards, both leys and permanent pastures, were compared under spaced plant and sward conditions.On average, the bred ryegrasses were higher yielding, more resistant to crown rust, and more persistent under intensive conditions than the permanent pasture populations, but there was no significant difference in cold-resistance between these two groups.The potential yield of dry matter of the best of the permanent pasture populations was similar to that of the highest-yielding leys. Several of even the most intensively used pastures were, however, dominated by ryegrass that was not nearly as high yielding as the best of the bred varieties. In addition to differences in yield of dry matter, there was a wide range in persistency, resistance to low temperature and crown rust (Puccinia coronata), as well as in mean date and variance of inflorescence emergence and in yield of digestible organic matter in dry matter (DOMD). Thus, no one type of ryegrass could be associated with permanent pastures, even when the sample was restricted to a narrow range of managements associated with intensive use.Some of the highest-yielding swards were based on complex mixtures of ryegrass cultivars; this might give rise to difficulty in relating management to stage of maturity and in predicting the composition of the sward established.A comparison of survivor material derived from S·23 leys revealed no difference in yield of dry matter or DOMD under sward conditions. Other data, however, showed that the populations differed in yield as spaced plants, rust resistance, cold-hardiness, persistency and date and variance of inflorescence emergence.There was no indication of ryegrass yield decreasing with the age of the ley from which the plants were derived.

HEAVY METAL TOLERANCE IN POPULATIONS OF AGROSTIS TENUIS SIBTH. AND OTHER GRASSES

SummaryPopulations of Agrostis tenuis can be found growing on a variety of different mine workings in conditions of metal contamination toxic to most higher plants. Samples of such populations together with samples of populations taken from ordinary pastures were tested for tolerance to high concentrations of copper, nickel, lead and zinc by measuring the effect of these metals on the rooting of tillers. The soils in which the populations were originally growing were analysed for each of the four metals and the tolerances of the populations have been related to the levels of the metals in the soils.In general, the mine populations show remarkable tolerance to the particular metals present in high quantities in the soils of their original habitats: the pasture populations do not show this tolerance. The tolerance is specific, for, except in the case of zinc and nickel, tolerance to one metal is not accompanied by tolerance to any other. There must, therefore, be three specific tolerances in the one species. Individual tolerances can however occur together and this can be related to the occurrence of the two metals together in toxic quantities in the soil.The tolerances must be genetically controlled but the physiological mechanism involved is not clear. A number of other species were also shown to have populations tolerant to high levels of zinc.

Chemical Control of Slugs in Orchard Grass-Ladino White Clover Pastures in the Pacific Northwest 1

Experiments were conducted in Western Washington on the control of slugs affecting orchard grass-ladino white clover pastures. Slug populations for the most part consisted of Deroceras agreste (Linnaeus) and Arion ater (Linnaeus) although several other species were found. The best method of determining slug populations in pastures involved the use of boxes. It was found that slugs would seek shelter under upturned boxes during the day if the boxes were made light-proof. It was demonstrated that slugs could destroy ladino white clover in a single growing season. Slug populations varied greatly within a season. The slug Population was greatly increase at the surface by over head irrigation. When colloidal suspensions of metaldehyde were pumped into the irrigation system at this time, seasonal control of slugs was obtained.

Biology of the Oligochaete Eisenia rosea (Savigny) in an Upland Forest Soil of Southern Michigan

For over 50 years, the contribution of Charles Darwin (1881) relating to the natural history of earthworms remained a foundation and point of departure for studies on field populations of earthworms. With the introduction of more modern methods of habitat analysis, particularly physico-chemical factors, and the development of statistical tools for population studies, there has been a renewal of investigative effort on the biology of the Oligochaeta. Despite the amount of information recently accumulated, however, the role of earthworms in forest soils is poorly understood. In part, this may be attributed to the fact that a large proportion of the research has been related to agricultural problems and to oligochaete populations in pasture and crop soils. Such investigations, their objectives, methods, and results, are often of limited applicability to forest conditions. Moreover, the complexity of forest soils and the difficulty of simulating field conditions in laboratory cultures impose restrictions on experimentation and

The ecology of immature phases of trichostrongyle nematodes

Observations on the larvae of sheep trichostrongyles on hill pastures showed:1. A reduction in larval populations occurred when the ‘moving-flock’ type management was used. The large proportion of eggs passed in faeces is deposited on a part of the pasture where little or no grazing occurs.2. Local concentrations of larvae occurred on the grazed portions of a pasture when grazing was uneven. Thus, the apparent low rate of stocking on hill pastures does not give a true picture of the potential dangers of parasitic disease. Estimates of pasture contamination by Taylor's method of sampling were deceptively low.3. The number of larvae on grass blades was lowest when the grass was wet with dew. Sampling of pastures between 12 noon and 5 p.m g.m.t. gave maximal and most constant estimates.4. There was an increase in the number of larvae on a pasture during the warmer months of the year. While low temperatures prevent or delay hatching, the increase in population was not entirely due to the increased rate of development when temperature was high. The increase in numbers was partly due to an increase in the number of adult worms in the sheep hosts.5. Removal of sheep for 3 weeks reduced the number of larvae on a pasture. This reduction was not apparent, however, until after the first 12 days. After 3 weeks the pasture population was reduced by 55 %, while after 4 weeks (i.e. 7 days after the return of the sheep) the reduction was 90%. Two weeks later there was a small increase in the larval population, but this was again reduced with the onset of colder conditions.