Investigating the effects of predator removal and habitat management on nest success and breeding population size of a farmland passerine: a case study

Passerines are especially vulnerable to predation at the pre-independence stage. Although the role of nest success in British farmland passerine declines is contentious, improvement in nest success through sympathetic management could play a role in their reversal. Because habitat is known to interact with predation, management options for mitigation will need to consider effects of nest predation. We present results from an observational study of a population of Common Blackbird Turdus merula on a farm which has experienced a range of agri-environment and game-management options, including a period with nest predator control, as a case study to address some of these issues. We used an information theoretic model comparison procedure to look for evidence of interactions between habitat and nest predation, and then asked whether habitat management and nest predator abundances could explain population trends at the site through their effects on nest success. Interactions were detected between measures of predator abundance and habitat variables, and these varied with nest stage – habitat within the vicinity of the nest appeared to be important at the egg stage, and nest-placement characteristics were important at the nestling stage. Although predator control appeared to have a positive influence on Blackbird breeding population size, the non-experimental set-up meant we could not eliminate other potential explanations. Variation in breeding population size did not appear to be influenced by variation in nest success alone. Our study demonstrates that observational data can only go so far in detection of such effects, and we discuss how it might be taken further. Agri-environment and game-management techniques are likely to influence nest predation pressure on farmland passerines, but the patterns, mechanisms and importance to population processes remain not wholly understood.     

Invasion status of Florida bass Micropterus floridanus (Lesueur, 1822) in South Africa

Largemouth bass Micropterus salmoides are a popular North American angling species that was introduced into South Africa in 1928. To enhance the largemouth bass fisheries, Florida bass Micropterus floridanus were introduced into KwaZulu Natal, South Africa, in 1980. Knowledge on the status of M. floridanus in South Africa is required, because it lives longer and reaches larger sizes than M. salmoides, which may result in heightened impacts on native biota. Because M. floridanus are morphologically similar, but genetically distinct from M. salmoides, the distribution of this species was assessed by genetically screening 185 Micropterus sp. individuals sampled from 20 localities across South Africa using the mitochondrial ND2 gene. Individuals with mitochondrial DNA matching M. salmoides were recovered from 16 localities, whereas M. floridanus mitochondrial DNA was recovered from 13 localities. At nine localities (45%), the mitochondrial DNA of both species was detected. These results demonstrate M. floridanus dispersal to multiple sites across South Africa.     

Magnetic Resonance of Isotope Hybrid Flavoprotein <Superscript>2</Superscript>H-Flavoprotein (<Superscript>1</Superscript>-Flavin Mononucleotide)

FLAVOPROTEINS lend themselves particularly well to study by the combined techniques of magnetic resonance and isotope substitution^1–3. Recent electron spin resonance (ESR) and electron-nuclear double resonance (ENDOR) investigations have already indicated the utility of this approach to the study of the structure and function of flavin and flavoproteins^4–8. We have now prepared an unusual isotope hybrid flavoprotein that gives promise of great value for magnetic resonance studies. This substance is obtained by the introduction (by exchange) of an ¹H-flavin mononucleotide (¹H-FMN) prosthetic group into (fully deuterated) ²H-flavoprotein that can be isolated from the blue-green thermophilic alga Synechococcus lividus. This isotope hybrid protein makes it possible to apply in a unique way proton magnetic resonance (PMR) and ESR to the chemistry of protein-bound FMN.     

The effects of gibberellin A3 on white clover during floral development

Hokkanen & Pimentel (1984) proposed a novel approach for the selection of biocontrol agents. They advocated the selection of agents from a relative of the weed plant rather than from the target weed species itself. The new relationship that such agents would have with the weed would be characterised by a relative lack of homeostasis compared with the old herbivore-plant associations traditionally used in weed biocontrol, and would consequently be more effective. There are few examples to support these contentions because of the traditional use of old herbivore-plant associations in weed biocontrol. In the present study, herbivore-plant associations in agricultural situations, which are analogous to agent-weed associations, are examined to assess the potential of new associations for weed biocontrol. The herbivores on 14 introduced crop plants which have salient similarities to the major weeds in the south-western Cape were surveyed: (a) 68% of the 188 insect and mite herbivores are indigenous species in new associations with these host plants, and (b) of the five most damaging pests on each of 13 of the crop plants, 53% are in new associations with the plants. Of the 40 most important agricultural pests in South Africa, 58% are in new associations, confirming these results. About 50% of the insect and mite herbivores in new associations with their host plants are oligophagous, indicating that new associations are not necessarily characterised by polyphagy and hence unsafe for use in weed biocontrol. We conclude that new associations between herbivore species and host plants have strong potential in weed biocontrol because (a) their frequency in agriculture indicates that they can easily be established in weed biocontrol situations, (b) they are as damaging as old associations and (c) they are not necessarily unsafe as regards host specificity. We therefore advocate the use of both the classical approach and that of Hokkanen & Pimentel (1984). Our support for Hokkanen & Pimentel (1984) is, however, based on evidence and rationale clearly different to theirs, and we provide novel guidelines, which can be routinely and practically applied in the selection of agents for weed biocontrol.     

A Survey of the Rates and Products of Short-term Photosynthesis in Plants of Nine Phyla

1. Short-term photosynthetic experiments using C¹⁴O₂ and paperchromatography were performed with 27 different plants representingnine phyla: Schizophyta (Schizophyceae), Euglenophyta, Chlorophyta,Charophyta, Chrysophyta, Rhodophyta, Bryophyta, Pteridophyta,and Spermatophyts.
2. There is a remarkable uniformity in thetypes of ethanol-solublecompounds which became radioactivein the entire group of plantsused. The amounts of the differentcompounds varied considerablypercentagewise among the variousplants as would be expectedbecause of their inherent metabolicdifferences and the variationsin their physiological statesinduced by experimental conditions.
3. Sucrose became radioactivein very different amounts in twomajor groupings of plants:(a) those containing only photosynthetictissue, and (b) thosecontaining non-photosynthetic tissue aswell. The amount ofradioactive sucrose in the former groupwas much lower thanthat in the latter.
4. An unidentified compound became radioactivein appreciable amountsin two of the blue-green algae, but wasradioactive in verysmall amounts or not visible at all on thechromatograms ofall other plants.

     

A Pyrolysis Gas-liquid Chromatography Study of Clostridium botulinum and Related Organisms

Low resolution pyrolysis gas-liquid chromatography could differentiate the following groups of Clostridium botulinum and related organisms: (1) Cl. botulinum type A. proteolytic types B and F and Cl. sporogenes ; (2) Cl. botulinum types C and D. and (3) Cl. botulinum type E and non-proteolytic types B and F. Toxin types A and B could be distinguished from type E and from type F.     

Enhanced Susceptibility of Melanocytes to Different Immunologic Effector Mechanisms In Vitro: Potential Mechanisms for Postinflammatory Hypopigmentation and Vitiligo

In postinflammatory hypopigmentation and in vitiligo, one observes histologic evidence of melanocyte damage, disappearance of melanocytes, and clinical loss of pigmentation. In the case of vitiligo, this loss of pigment is complete. There is considerable evidence that melanocytes are highly susceptible to autocytotoxic damage and perhaps to specific immunologic damage. We directly compared the susceptibility of cultures of melanocytes (M), keratinocytes (K), endothelial cells (EC), and fibroblasts (F) to hydrogen peroxide damage across a Wide range of concentrations (10^-7-10^-2 M) and analyzed the differences by computerized Probit analysis. Cytotoxicity was measured by three dye techniques: acridine orange/ethidium bromide (AO/EB), fluorescein diacetate (FD), and nigrosin (N). All three assays produced similar results. The order of susceptibility to H₂0₂ was M < EC < K < F. The LD₅₀ of melanocyte targets was two orders of magnitude lower than that of fibroblasts. The AO/EB assay was used to study immunologic cytotoxicity of melanocytes in the presence of sera from vitiligo patients plus either complement or cellular effectors of antibody-dependent cellular cytotoxicity (ADCC). Eleven vitiligo sera and 11 control sera were contrasted in 4- and 16-hr cytotoxicity assays. Vitiligo patients' sera containing antimelanocyte antibodies induced both complement lysis and ADCC of melanocytes. Thus the melanocyte is highly susceptible to peroxide-induced damage, complement lysis, and ADCC. In addition, antibodies in vitiligo sera appear to be an important trigger of melanocyte damage by complement and ADCC effectors and are likely to be involved in the melanocyte damage observed in vitiligo.     

Floral Initiation of White Clover (Trifolium repens L.) in Response to Daylength and Temperature

The response to different combinations of daylength (14, 15and 16 h) and day/night temperature (20/10°C, 30/15°C)of four white clover (Trifolium repens) varieties in terms offloral initiation and development was studied. More plants flowered under long days (16 h) at 30°C thanin any other combination. Varietal differences in response todaylength were large but temperature was the factor controllinginitiation. Daylength was more important in regulating peduncle length,floret and ovule numbers than was temperature. The amount ofnectar produced was lowest at the higher temperature althoughnectar concentration was unaffected by temperature. Nectar concentrationwas lowest in the shortest daylength (14 h). White clover, floral initiation, temperature, daylength