Low Population Levels Research Articles

Seasonal Foods of Blacktail Jackrabbits and Nuttall Cottontails in Southeastern Idaho

The diets of blacktail jackrabbits (Lepus californicus) and nuttall cottontails (Sylvilagus nuttalli) were estimated by examination of fecal pellet botanical composition. The deficiencies of fecal analysis are noted, but dietary trends and relative importance of forage plants are accurate. Cluster analysis combined leporid pellets into 2 distinct groups based on botanical composition, representing feeding during spring-summer and fall-winter periods. Seven variables (plant species) accounted for significant differences (P<O.05) within and among the leporids studied in seasonal food selection. Generally, grasses and forbs were most abundant in blacktail jackrabbit and nuttall cottontail pellets during the spring-summer period, whereas shrubs were most abundant during the fall-winter period. Diet similarity was greatest between blacktail jackrabbits and nuttall cottontails during the same season. Diversity of forage consumed was greatest for both leporids during spring-summer periods. Habitat segregation minimizes competition for forage between the leporids studied. Livestock grazing appears to limit leporid population density rather than alter leporid food habits. During the period of research, authors were graduate research assistant and professor, respectively, Department of Range Science, Colorado State University, Fort Collins 80523. MacCracken's present address is P.O. Box 3145, Palmer, AK 99645. The authors thank O.D. Markham, W.J. Arthur, D.K. Halford, M.K. Johnson, G.C. Lucich, R.L. Potter, E.R. Johnson, and D. Simonson for their participation in this study. M.E. Voorhees did the microhistological work. This project was supported in part through grant DE-A507-761D-1526, MOD 006 from the U.S. Department of Energy, Idaho National Engineering Laboratory Ecology Program to Colorado State University. Manuscript received September 28, 1982. Leporids play a major role in the ecology of the Great Basin area of the western USA. They compete with livestock and other wildlife for forage, cause extensive crop damage, and are a major food source for coyotes (Clark 1972, MacCracken and Hansen 1982a) and other predators which in turn kill livestock and game animals. Leporids are primarily herbivorous, but have been reported to consume carrion (Hansen and Flinders 1969, DeCalesta 1971). When jackrabbits (Lepus spp.) become overly abundant, about every 10 years, their impact on the ecosystem is tremendous. In January 1982 such a situation existed, and it was estimated that local people killed about 64,000 jackrabbits during 6 different roundups at Mud Lake, Ida., bordering our study area. Information on food selection by jackrabbits during low and high population levels helps to determine if such controversial management procedures are justified. The foods of most species of leporids have been documented in the literature (Hansen and Flinders 1969, DeCalesta 1971). Feeding by blacktail jackrabbits (Lepus californicus) may have been the most thoroughly examined (Uresk 1978, Westoby 1980). Even though studies dealing with leporid food habits have been published, few have investigated seasonal food selection by sympatric leporids. The purpose of this paper is to present the results of a study which examined seasonal food habits of sympatric blacktail jackrabbits, and nuttall cottontail (Sylvilagus nuttalli) in southeastern Idaho when the jackrabbit population was at low levels. 256 JOURNAL OF RANGE MANAGEMENT 37(3), May 1984 This content downloaded from 40.77.167.54 on Wed, 06 Jul 2016 04:25:14 UTC All use subject to http://about.jstor.org/terms

Epidemiology of Cereal Aphids on Winter Wheat in Norfolk, 1978-1981

(1) The cereal aphid outbreaks of 1979 (Metopolophium dirhodum) and 1980 (Sitobion avenae) and their lower population levels in 1981, in Norfolk, are described. (2) The high incidence of cereal aphid outbreaks in Norfolk are probably due to a combination of factors, including: the high hectarage devoted to cereals; the low numbers of aphid-specific and polyphagous predators present early in the season; and the dry conditions during the immigration period. (3) It is suggested that monitoring for M. dirhodum could be carried out on roses in the spring, while a forecasting scheme for S. avenae can only be developed when a greater understanding of its life cycle is obtained.

Consequences of a lower level population on the modeling of a homogeneously broadened injection laser

An exact, analytic solution has been found for the coupled, nonlinear differential equations which describe the amplification of mode intensities for propagation through a homogeneously broadened amplifier with negligible population in the lower level. It is shown in this letter that the predictions of an analytic laser model based on the solutions to these equations can be scaled in a straight forward and easy manner to include the effects of a constant, lower level population.

Leaf consumption by insects in three Eucalyptus forest types in Southeastern Australia and their role in short-term nutrient cycling.

Leaf consumption by insects in three Eucalyptus forest types (E. delegatensis, E. dives and E. pauciflora) in the Brindabella mountains, A.C.T., was studied over a two year period. Foliage consumption was calculated using two methods: (1) sampling of foliage repeatedly through the season and measurement of leaf area loss due to insects and (2) calculation of the mass of leaves consumed, based on frass-fall measurements. Intensive sampling of tree canopies for defoliating insects was also carried out in all three forest types. Defoliation, as estimated by measurement of leaf area loss, did not exceed 10% in any of the forest types except on current year's foliage for two months of one year in the E. dives and E. pauciflora stands. Insect consumption of foliage in all three forest types, as calculated from frass-fall measurements, varied from 2-3% of annual leaf production. The nitrogen, phosphorus, and potassium passing through insect bodies and frass was less than 4% of the total amount falling in other litter. The small amount of leaf consumption occurring in these stands and the small amount of associated nutrient transfer indicate that insect defoliators at low population levels do not affect forest productivity or have significant effects on short term nutrient cycling.

Destructive insects of wild plants in the Egyptian Western Desert

Destructive insects of wild plants in two different habitats in the Egyptian Western Desert are discussed. It is concluded that: (a) flowers and fruits are the most liable parts for insect infestation; (b) harvesting ants constitute a destructive agent in the desert ecosystem; (c) some of the common pests play a beneficial role in plant reproduction under desert conditions; (d) some of the potential entomophagous agents which have disappeared or maintain low population levels are associated with insect pests and (e) some plants form unknown factors which disturb the life cycles of insects that feed on them.

Fire history and grassland vegetation change: three pollen diagrams from southern British Columbia

Recent vegetation change in the grasslands of southern British Columbia is examined using pollen analysis, and the results are compared with documentary records. The increasing dominance of the grasslands after 1890 by Artemisia tridentata and other woody shrubs has often been attributed to overgrazing by domestic livestock, but pollen data indicate that shrub populations were substantial in presettlement times, and that the recent "invasion" represents a recovery from anomalously low population levels during the middle 19th century. These low Artemisia populations were probably due to a high frequency of fire in the early settlement period, and the subsequent recovery is probably related to fire suppression. Fire appears to have been an important element in the ecology of these grasslands over a long period, and it may have a place in modern management schemes.

Changes in Danish farmland habitats and their populations of breeding birds

Habitat changes and the breeding bird populations were studied at Kraghede, N Jutland the years 1970–1980. Generally, agricultural practice was intensified leading to an increase in the area used permanently for growing barley, and the abandonment of grasslands and meadows. Animal husbandry decreased, until it was restricted to a small number of farms.These habitat changes were the largest ones to occur in the Danish landscape for some 150–200 yr and had a significant influence on the breeding birds. Species confined to the meadows, such as the lapwing Vanellus vanellus, meadow pipit Anthus pratensis and others, decreased by 50–80% or even more. Species associated with the grassland when feeding, like the swallow Hirundo rustica, starling Sturnns vulgaris and magpie Pica pica, all had lower population levels at the end of the 1970's compared to those at the beginning of the decade.

Age at Menarche and Fertility in Haiti

This article presents findings from surveys conducted in Haiti as part of the Haiti Fertility Survey in 1977 that provide retrospective data on the age at menarche of women between the ages of 15 and 49 years. It considers the demographic and nutritional situation in Haiti the cultural meaning of menarche and the sources of data. After reviewing findings from other contemporary and historical populations it discusses the implications of the data with respect to Haitian fertility patterns. The tables provide data on the following: age at menarche for women of rural Haiti and Port au Prince; age at menarche by current age; average age at menarche for selected populations; age specific fertility and total fertility rates for rural Haiti selected African countries and the Dominican Republic; and proportions of women never in union from rural Haiti and Port au Prince. The data in the tables indicate the relationship between age at menarche and fertility in contemporary Haiti. The comparatively low fertility levels of the Haitian population the very low level of adolescent fertility and the high ages at menarche and low nutritional status appear to support the view that late age at menarche plays a role in reducing fertility. While the Haitian fertility levels are far below the biological maximum the high proportions of Haitian women entering unions at relatively late age seems a more important factor in depressing fertility levels than late menarcheal age. Further research should deal with socioeconoimc factors that influence age at menarche in Haiti.

Laser-excitation technique for the measurement of absolute transition probabilities of weak atomic lines

A new technique is presented for the measurement of transition probabilities for weak allowed, intersystem, and forbidden lines. The method exploits the fact that oscillator strength is proportional to the number of stimulated absorptions and emissions produced by a narrow-band laser pulse of known energy which is in resonance with an atomic transition. The method is tested for a particular transition of Mg I with a known oscillator strength value and of appropriate magnitude. The number densities are measured using a Mach-Zehnder interferometer and the hook method for the lower level population and by measuring an absorption-equivalent width for the other. The apparatus consisted of a high-power tunable laser and a magnesium oven to produce excited Mg vapor, and a laser-plasma background continuum. The results are in good agreement with theoretical and other experimental data.

Temporal Occurrence, Sampling, and Within-Field Distribution of Aphids on Broccoli in Coastal California1

Aphid occurrence, population dynamics, and sampling procedures were studied in three consecutive broccoli plantings in southern California. Myzus persicae (Sulzer) was dominant during the fall and spring, and Brevicoryne brassicae (L) was prevalent in winter. B. brassicae was the primary aphid contaminant of broccoli heads in all crops. Hyadaphis erysimi (Kaltenbach) and Macrosiphum euphorbiae (Thomas) occurred at low population levels and were of minor importance. Aphid distribution was aggregated when densities were low [log (x + 1) <1.0 per plant] but became random as populations increased. Sampling procedures based on 10-plant samples were useful in estimating aphid population when densities exceeded a log (x + 1) value of 0.65 per plant. Aphid parasitization did not exceed 6% of available hosts in any planting and was not a major mortality factor.

Suppression of crossover signals by modulated lower level population

Using an additional saturating beam, taken from a second laser at fixed frequency, a modification of saturation spectroscopy allows to eliminate or strongly suppress crossover signals. The technique has been applied to the sodium D 1 line.

Spider Mite Interactions with Photosynthesis, Transpiration and Productivity of Strawberry 2

Studie were conducted in 1978 and 1979 to evaluate the effects of varying twospotted spider mite populations on photosynthesis, transpiration, and productivy of strawberry plants under field conditions. Both photosynthesis and transpiration were significantly reduced by high levels of spider mite populations. Early season infestations caused reductions in physiological parameters at much lower population levels than was necessary to cause similar injury later in the season. Reduced physiological activity of mite-stressed plants persisted until plant recovery was observed following a rapid decline in spider mite populations. The number of fruit produced was significantly increased from plants experiencing low level stress from mite populations. After the initial increase, the number of fruit from infested plants decreased significanyly and the difference was greatest from plants that experienced early season stress. Fruit size was reduced significantly for all mite-stressed plants.

Density Dependence as Related to Life History Strategy

Both theory and empirical information support the conclusion that most density—dependent change occurs at high population levels (close to the carrying capacity) for species with life history strategies typical of large mammals. The reverse is true for species with life history strategies typical of insects and some fishes. Theoretical considerations that give rise to these conclusions involve natural selection and trophic dynamics. There is a large body of literature that contains descriptions of density dependence as based on empirical observations. These data, and the models used to represent them, indicate that species with high reproductive rates, short life—spans and populations held below the limits of environmental resources exhibit most density—dependent change at low population levels. Similar data for species with low reproductive rates, long life—spans and populations that are more limited by resources (large mammals in particular) indicate that most density—dependent changes in vital rates occur at levels of the population quite close to the carrying capacity.

Biological Control of Comstock Mealybug12

The successful importation, mass release and establishment of exotic natural enemies on the Comstock mealybug, Pseudococcus comstocki (Kuwana), in the residential area of Porterville, CA, within the San Joaquin Valley have resulted in the biological control of this mealybug. Other infested areas in the Valley receiving parasite introductions followed the same pattern. The natural enemy complex consists of 3 imported parasites, Pseudaphycus malinus Gahan, Allotropa burrelli Muesebeck, A. convexifrons Muesebeck, and Zarhopalus corvinus (Girault), an indigenous parasite of P. maritimus (Ehrhorn), plus native predators, mainly Leucopis ocellaris Malloch and Chrysopa spp. A. convexifrons, the last to be established, is now the dominant parasite. The population density of P. comstocki was reduced by a maximum of 68% in East Porterville from 1972 through 1976, 71% in Central Porterville, and 73% in West Porterville from 1974 through 1976 as a result of the newly established natural enemy complex. The regulation of the mealybug by its natural enemy complex at these lower population levels was below economic importance in residential areas which contributed to the termination of the California Department of Food and Agriculture’s eradication program.

Allowing for risks in setting catch limits based on MSY

A number of fisheries, particularly those managed by international regulatory agencies, are managed on a total allowable catch or quota system, with the aim of taking the maximum sustainable yield (MSY) from the fishery. Such a procedure can involve considerable risk, particularly in the presence of environmental fluctuations. In this paper, an approximate stochastic model of an MSY quota managed fishery is analysed, and the distribution of first passage times through a defined low population level is obtained. This allows partial quantification of the risks associated with misestimation of the true MSY. A minimum expected risk estimator of the MSY is derived, and the implications for management of fisheries on an MSY basis are discussed. Numerical examples illustrating the application of the results obtained to the management of whale stocks are given.

Parasites of Lepidopterous Larvae in Insect Resistant and Susceptible Soybeans in South Carolina

Thirty-three species of parasites were reared from four species of lepidopterous larvae. Larvae collected from insect resistant and susceptible soybeans showed no differences in insect parasitism. Hosts and parasitism levels for 1976 and 1977 respectively were: green cloverworm, Plathypena scabra (F.), 11.2 and 8.5%; corn earworm, Heliothis zea (Boddie), 1.2 and 5.7%; soybean looper, Pseudoplusia includens Walker, 9.7 and 16.0%; and velvetbean caterpillar, Anticarsia gemmatalis Hubner, 0.4 and 1.9%. The most prevalent parasite reared from P. scabra , H. zea and P. includens was Apanteles marginiventris (Cresson). P. includens was a new host record for A. marginiventris . Meteorus autographae (Vier.) was the most prevalent parasite of A. gemmatalis . P. scabra was the only host exhibiting lower population levels in the insect resistant ED73-37l than in the susceptible soybean variety ‘Bragg’.

Sorghum Webworm Control, 1980

Abstract Three tests evaluated various materials in suppressing sorghum webworm populations on grain sorghum heads. All tests were planted with Funk’s G522DR on July 2 by minimal tillage methods following wheat. Plots were 6.1 m x 3 rows and were separated by 1 untreated row or 1 m alley. Treatments were replicated 4 times in a randomized complete block design. Applications were made with compressed-air sprayers calibrated to deliver 50 gal per acre at 30 psi. Spray was directed to opposite sides of heads to insure thorough coverage. One application on Sept 18 was used in Test 1. Low pest population levels did not merit a second application. Two applications were made on Oct 3 and 8 in Tests 2 and 3. Larval populations were estimated on each sampling date by shag-bagging 10 randomly-selected heads from each plot.

Enumeration and Confirmation of Bacillus cereus in Foods: Collaborative Study

A collaborative study was conducted in 15 laboratories to evaluate 2 different techniques for enumerating Bacillus cereus in foods. A direct plating technique using mannitol-egg yolk-poly-myxin agar and a most probable number (MPN) technique using trypticase-soy-polymyxin broth were compared for the enumeration of high and low populations of B. cereus in mashed potatoes. The collaborative results showed that the overall mean recovery obtained with the low population level was essentially the same by both techniques. However, the overall mean recovery was significantly higher by the direct plating technique at the high population level. A statistical evaluation of the data also showed that the direct plating technique had better repeatability and reproducibility than did the MPN technique at both the high and low population levels. These results suggest that the MPN technique is suitable for examining foods containing low populations of B. cereus, but that the direct plating technique is preferable for foods that contain a high population of this organism. The confirmatory technique used in the proposed method is reliable for presumptive identification of isolates as B. cereus. The method has been adopted as official first action.

The population ecology of Onchidoris bilamellata (L.) (Gastropoda: Nudibranchia)

Onchidoris bilamellata (L.) appears to be largely intertidal in distribution although it does not extend as high up the shore as Balanus balanoides (L.), the major prey organism. Local distribution of the nudibranch is largely determined by desiccation and is, therefore, an expression of the coincidence of certain prerequisite physical (shade and dampness) and biological (presence of Balanus) factors. Mortality has been shown to be density-dependent, resulting in breeding populations of similar size and structure from year to year, in spite of widely differing levels of annual recruitment. Although as yet not proved, it seems probable that most mortality, in lower level populations, will be due to predation and intraspecific competition, with physical control being of secondary importance. Intraspecific competition for food does, however, exert a considerable constraint on the growth rates of these local populations. The highest growth rates in the field, equating those observed in the laboratory, are found at higher levels where there are abundant barnacles. In view of the increased rigour of these latter habitats physical factors are the major cause of mortality, particularly at the juvenile stage during the summer months, with the result that only few individuals survive to reproduce the following winter. Intraspecific competition for food is also reflected in reproductive output, which increases allometrically with body size. Observations that the planktotrophic veliger larva will only metamorphose in the presence of live barnacles, and that recruitment is only detectable in June (after B. balanoides has settled) suggests that successful establishment of the benthic phase of the life cycle depends upon the coincidence of pediveligers competent to settle, and the presence of young barnacle spat. No evidence for an intermediate diet can be found, and it is probably the extent to which the larval settlement of both predator and prey coincide which is the major factor determining the absolute level of recruitment of Onchidoris bilamellata for any one year. In consequence, wide fluctuations in recruitment over the three generations studied were both anticipated and observed. Post-spawning mortality is generally complete by April, although a few individuals may survive into June, at which time recruitment of the succeeding generation begins. With peak spawning in mid-January, the bulk of the larvae will hatch around late February spending some 2 1 2 –3 months feeding and growing in the plankton before settling amongst the barnacles. Pediveligers settling too early will be subjected to starvation through an absence of barnacle spat, while those settling too late will be liable to food shortage due to juvenile barnacles having outgrown the prey size-range of the post-metamorph nudi-branchs. It is of particular interest that some rapidly-growing individuals in certain habitats undergo precocious maturation with spawning and death in August. In view of the necessary gearing of the predator and prey life-cycles it is unlikely that there will be recruitment from such spawnings, unless juvenile Balanus crenatus Brug., or other species with more extended reproductive periods, are exploited. No evidence could be found to suggest that any nudibranchs survived for more than the normal 9–10 months.

Effects in s.e. Queensland during 1967–72 of insects introduced to controlLantana camara

Seasonal fluctuations in populations of the introduced speciesTeleonemia scrupulosaStal and damage by this insect to common taxa ofLantana camara, were observed at several field sites and experimental plots. At 2 plots effects ofT. scrupulosa populations on untreated plants were compared with plants protected by application of insecticides. On untreated plants damage varied seasonally and between taxa ofL. camara. In general attack byT. scrupulosa reduced fruiting and caused severe short term foliage damage. Combined with severe stress from some other cause heavy attack may result in long term damage or death to plants. However Common PinkL. camara was more resistant to damage than were the other taxa studied. At the time of these experiments other insect species were at very low population levels and did not have observable effects onL. camara.