Densities Of Individual Species Research Articles

Intersexual Variation in Densities of Plant Bugs (Hemiptera: Miridae) on Juniperus scopulorum

Demographic and phytochemical investigations involving a group of specialized phytophagous plant bugs ( Dichrooscytus spp.) on dioecious Rocky Mountain juniper, Juniperus scopulorum Sargent, reveal patterns of individual host plant use correlated to tree sex and phytochemistry. Male trees support higher diversities of mirid species and higher peak densities of individual species; the latter are correlated with the levels of certain sesquiterpenoids and phenyl propanoids in the trees' volatile oils. Compounds correlated with variations in bug density occur in higher levels in female trees, and transferred insects have lower rates of survival to sexual maturity on female trees. The sex of the host thus appears to represent a potentially important factor that influences the choice of host for plant bugs feeding on dioecious species.

Concept of planktonic species diversity in small water bodies – a case study of lake Rangasagar (Udaipur: Rajasthan)

AbstractThe quantitative and qualitative relationships within phyto‐ and zooplanktonic communities were examined for a period of one year in a small eutrophic lake in Udaipur, through the application of diversity indices. The results revealed that a higher plankton diversity needs not necessarily lead to a greater community diversity or evenness of species diversity. The phytoplankton species diversity was related to nutrients and ambient environmental factors. Within zooplankton groups, the diversity index was found influenced by the evenness and richness of the species. On the other hand, the strong correlation between individual species density and community diversity in the cladocera was influenced by food availability. The total zooplankton diversity was also strongly correlated (P < 0.01) with the number of species and equality. There was no spatial variation in species composition because of smaller spread of the water body. It is felt that the diversity indices could get influenced by the dominance or scarcity of one or more species or communities giving a deceptive picture of planktonic panorama.

Variation in herbivore density among host plants and its consequences for community structure : Field studies on willow sawflies.

The densities of four species of gall-forming sawflies were found to vary significantly among willow host plant clones. Two of the speices varied among host plants at four sites in each of three years. The other two species varied in density among host plants at most of the sites in two of the three years. Total sawfly density also varied significantly among clones. Individual species densities on willow clones were significantly positively correlated between years when all sites were combined and frequently when sites were considered separately. Most pairwise species combinations were independent in density between years, but some negative correlations existed between the stem galler and the leaf galler. Gall-former densities also were largely independent among clones within years with all sites combined and with sites considered separately. The significant correlations were nearly all positive. At all four sites the combination of significant variation in sawfly densities among willow clones in the field and independence of species densities among clones resulted in significantly different communities (relative abundance of species) among willow clones in three years. Although sawfly abundances differed substantially among the four sites, this remained true. It is argued that the pattern of community structure among clones is the result of variation in host plant quality of clones. We propose an hypothesis to account for patterns of herbivore species associations based on intrapopulation host plant variation.

Potato Insect Control, 1985

Abstract Potatoes were planted on 9 May in So. Deerfield, MA. Fertilizer (700 lb. 10N:10P2O3:10K2O/acre) was broadcast and incorporated prior to planting. An additional 700 lb/acre was side dressed on 26 Jun. Soil type was a fine sandy loam with a pH of ca. 5.3. The land was rotated from corn and no other potato crops were planted within 0.5 miles. Hence, Colorado potato beetle (CPB) pressure was moderate. Treatment blocks were replicated 4 times in a randomized complete block design. Each plot consisted of two 30-ft rows with a 3-ft fallow area between each plot. Treatments were applied with C02 pressurized sprayers at 40 psi with a delivery rate of ca. 65 gal/acre. Applications were made on 3, 11 and 17 Jul. In one treatment, Alsystin 4F at 0.5 lb (AI)/acre was applied on 3 and 11 Jul, and on 17 Jul, Alsystin 4F at 0.25 lb (AI)/acre plus Monitor 4 at 0.5 lb (AI)/acre was applied. CPB densities were assessed on 3 Jul and 4-5 days after treatment by counting adults and larvae on 10 primary stalks in each plot. Green peach aphids (GPA) were sampled on 29 Jul by counting those found on 10 terminal leaflets from lower leaves. Predators were assessed on 29 Jul by counting individual larvae, pupae and adults per 10 stalks. Coleomegilla maculata was the dominant predator species. Because densities of individual species were not high, predator numbers were pooled. Each plot was rated for defoliation on a scale from 1 (0-20%) to 5 (80-100%). Potato leafhopper (PLH) damage was assessed by ranking damage from 1 (no damage) to 3 (severe). Due to their clumped distribution, CPB and GPA counts were transformed by log(x = 1); means reported here are back transformed. No effects from blocking were observed for CPB.

Potato Insect Control, 1985

Abstract Potatoes were planted on 9 May in So. Deerfield, MA. Fertilizer (700 lb 10N:10P2O5:10K2O/acre) was broadcast and incorporated prior to planting. An additional 700 lb/acre was sidedressed on 26 Jun. Soil type was a fine sandy loam with a pH of ca 5.3. The land was rotated from corn, and no other potato crops were planted within 0.5 miles; therefore, Colorado potato beetle (CPB) pressure was moderate. Treatment blocks were replicated 4 times in a randomized complete block design. Each plot consisted of 2 30-ft rows with a 3 ft fallow area separating each plot. Insecticides were applied with C02 pressurized sprayers at 40 psi, with a delivery rate of ca. 65 gal/acre. Applications were made on 3, 11, and 17 Jul. Temik 15G (3.0 lb (AI)/acre) was applied at planting, and Temik 15G (2.0 lb (AI)/acre) at plant emergence. For this reason, the pre-counts (3 Jul) for these two treatments were significantly lower than all the other treatments. Because Kryocide 8F was not available for the first generation applications, a separate trial, adjacent to the trial area at a location where first generation CPB larval counts were still high, was carried out on 18 Jul (Kryocide 8F and control). The mean number of larvae per ten stalks before treatment was 83.4 for the control and 88.8 for the Kryocide 8F plots. After treatment (22 Jul), the control had 94.5 larvae/10 stalks; the Kryocide treatment had 14.3 larvae/10 stalks. CPB densities were determined on 3 Jul (before treatment) and 4-5 days after treatment by counting adults and larvae on 10 primary stalks in each plot. Green peach aphids (GPA) were sampled on 29 Jul by counting those found on 10 terminal leaflets from lower leaves. Predators were assessed on 29 Jul by counting individual larvae, pupae and adults per 10 stalks. Coleomegilla maculata was the dominant predator species. Because densities of individual species were not high, predator numbers were pooled. Each plot was rated for defoliation on a scale from 1 (0-20%) to 5 (80-100%). Potato leafhopper (PLH) damage was assessed by ranking damage from 1 (no damage) to 3 (severe).

Experimental Study of Avian Predation on Coexisting Grasshopper Populations (Orthoptera: Acrididae) in a Sandhills Grassland

An experiment was performed to examine the impact of avian predation on populations and assemblages of insect herbivores in a grassland system. Here, I examine the effect of avian predators on grasshopper populations in regard to overall density, densities of individual species, species diversity, and overall taxonomic composition. Predation pressure was examined by comparing each of these attributes of grasshopper populations in 10 m x 10 m exclosures where birds were excluded with equally sized plots where birds were allowed to forage normally. In general, avian predation significantly affected grasshopper populations in a sandhills grassland. Overall densities were reduced 27.4% in the predation treatment, most species occurred in lower numbers (though some exceptions were observed), and fewer species coexisted. Specific differences in overall taxonomic composition between the treatments were not detected using MANOVA. The relevance of these results to understanding community organization of herbivorous insects is discussed; the compensatory mortality hypothesis is not supported although other plausible hypotheses cannot be further evaluated with the present data.

Bird community ecology on power-line corridors in East Tennessee

Breeding bird density and vegetation structure were determined during three breeding seasons in 14 plots on power-line corridors through forests in East Tennessee. The purpose was to describe the corridor bird community and to relate bird density and diversity to a number of environmental variables. The relative abundance of forbs, blackberry Rubus ssp., saplings, and areas of planted grasses varied significantly among plots. Thirteen bird species appeared to be attracted to the corridors. Seven of these species were classified as brush species, three as edge species, and three as generalist species, depending on their relative abundance in corridor, edge, and forest, respectively. Control of bird community density on the corridors was complex because individual species densities correlated significantly with several different variables. These variables were Rubus density and patchiness, sapling density and patchiness, corridor width, length of coniferous or deciduous forest edge, coverage of planted grasses, and number of years following vegetation maintenance by cutting. Bird community density varied among plots from 210 to 750 pairs km −2, and increased asymptotically with Rubus density. Rubus density explained most of the variation and Rubus patchiness explained a significant additional portion. Species number varied little. Within plots, birds were registered significantly less often in grass-dominated areas than in forb- Rubus-dominated areas.

The E and F region ionospheric response to solar flares: 1. Effects of approximations of solar flare EUV fluxes

SOLRAD and many other satellite systems have provided a large data base showing the time‐dependent behavior of broadband solar fluxes in the X ray and EUV spectral regions. These bands are broad in the sense that one band may contain many ionospherically important spectral lines. We present results of tests performed to determine how this information can best be used to predict the effects of a solar flare on the ionosphere. Our approach has been to first adopt a model of the spectral line and continuum enhancements based on a synthesis of many types of flare observations. This detailed spectral model is used in a time‐dependent ionosphere model to calculate the response of the electron and ion density profiles. Then the spectral model is mathematically filtered to show how it would appear to the SOLRAD EUV detectors, and this degraded information is used in the ionosphere model. Comparison of the two ionosphere calculations shows that the two spectra produce changes in the total electron content in the ionosphere that differ by only a few percent. Thus, given the present uncertainty in our knowledge of solar flare EUV spectra, SOLRAD broadband EUV solar flux measurements can be used to calculate the ionospheric effects of EUV flare enhancements. Significant changes due to the flare which occur in the individual species densities are described.

Production of Larval Tanypodinae (Insecta: Chironomidae) in the Mud at Loch Leven, Kinross

Life histories and production of the five common species of Tanypodinae (Pentaneura monilis, Procladius simplicistilus, P. crassinervis, P. choreus and Psilotanypus rufovittatus) in the mud at Loch Leven were measured from March 1971 to March 1972. The methods used to identify each species of larva are described. All were univoltine except Pentaneura monilis which had two generations per year, but the seasonal patterns of the life cycles were different. The average density of third and fourth instar Tanypodinae was 3100/m2 and densities of individual species exceeded 2500/m2 for short periods in Procladius crassinervis and P. choreus. Net annual dry weight production by this subfamily was 2-6 g/m2 (57 KJ/m2), with individual species ranging from 1-1 g/m2 (P. crassinervis) to 0-16 g/m2 (Pentaneura monilis). These results are discussed briefly and compared with production estimates for other zoobenthos.

Use of Lasers for Local Measurement of Velocity Components, Species Densities, and Temperatures

Laser sources provide intense, monochromatic, and coherent radiation. The use of one or more of these properties allows diagnostic measurements that either were infeasible with conventional light sources or else could be performed only with great difficulty before the development of lasers. The laser-Doppler velocimeter allows measurement of local velocity compo­ nents through determination of frequency shifts between incident and scattered radiation. Velocity measurements have been performed in laminar pipe flows, in rotating flows, in exhaust-jet flows, and in turbulent flows. Laser-Raman scattering permits measurement of local species densities and temperatures in gas mixtures. The scattered radiation is shifted by different char­ acteristic frequencies (Le., the Raman shifts) for different chemical species. The intensities at these shifted frequencies are direct measures of individual species densities. The intensity distributions of Raman-scattered frequencies for a given species permit, for example, local measurements of rotational or vibrational tem­ peratures. Lasers that are tunable over narrow frequency ranges may be usable for remote probing of nonisothermal and nonisobaric gas regions through observation of frequency-depend ent absorption intensities. By use of appropriate inversion pro­

Sampling Predator Populations on Apple Trees in Nova Scotia

AbstractProblems associated with quantitative estimations of mixed populations of several species of predators on apple trees are discussed. The problems arise largely because of the inherently high variability in such populations and because of the mechanical difficulties of counting predators on some basic unit of tree. In this investigation two devices used in sampling are described and their efficiency rated. One, a vacuum sampler, that removed predators from samples of leaf clusters on the tree failed to meet the standards set. The other, called the shaker sampler, tumbled clusters about in a revolving wire screen cage to dislodge predators for counting. The amount of processing with this device to remove practically all predacious specimens was calibrated. When the shaker-sampler technique was applied to studies in two orchards it proved to be practical for quantitative estimation of predator populations per large limb. The error associated with estimations of the density of individual species was usually very high so that pooling of the results for several or all species was required to reduce the variance to an acceptable level.

Effects of chronic gamma irradiation on the development of old field plant communities

First- and second-year old field plant communities were allowed to develop in sections of the Gamma Radiation Field at Brookhaven National Laboratory. The communities developing under irradiation differed in general from non-irradiated communities in lower diversity of species, in lower total plant cover, and in the densities of individual species. Changes in species composition of the communities along the radiation gradient were proportional to the daily radiation exposure, a 50 per cent reduction in the coefficient of community corresponding to an approximately 3-fold change in radiation exposure rate. While there was an overall decline in total density along the gradient of increasing radiation, densities of individual species varied greatly without simple relationship to radiation exposure. Individual plants in the irradiated communities differed in form and in reproductive potential from those in non-irradiated communities. At exposures in excess of 320 r/day growth of most species was inhibited and anomalies in form were common. The reproductive potential of Erigeron canadensis, one of the relatively resistant species of the second year communities, was zero at exposures of 320 r/day and above, although individual plants survived 640 r/day. This work shows: (1) that any threshold for effects of radiation on species composition of old field communities lies at less than 50 r/day; (2) changes in species composition are approximately linearly related to the logarithm of daily radiation exposure; (3) the principle of species individuality appears to apply to communities exposed to ionizing radiation as it does to communities along other environmental gradients ; (4) the individuality of species' responses to radiation results in a different community at each radiation exposure; (5) all the higher plants of the old field communities in this study are relatively radioresistant; (6) resistance is correlated in these field studies with low average interphase chromosome volumes and with relatively high degrees of polyploidy; (7) using the effects of irradiation on the reproductive capacity of Erigeron as an example, sexual reproduction remains substantially intact at exposures as high as 1/6–1/3 those required to exclude the species from the community: reduced quantities of viable seeds are produced at exposures about 1/2 those which excluded the species; (8) there is at present no clear relationship between the LD 50's of laboratory studies and criteria useful in appraising effects on communities.