Landscape,fire and habitat: which features of recently burned heathland influence site occupancy of an early successional specialist?

Context

Multiple ecological drivers generate spatial patterns in species’ distributions. Changes to natural disturbance regimes can place early successional habitat specialists at an increased risk of extinction by altering landscape patterns of habitat suitability.

Objectives

We developed a series of hypotheses to evaluate the effects of landscape structure, fire history, and site-level habitat quality on site occupancy by an early successional specialist, the eastern chestnut mouse (Pseudomys gracilicaudatus).

Methods

We obtained eight years of monitoring data from 26 sites in recently burned heathland in southeast Australia. We used generalised linear models to determine which explanatory variables were related to occupancy. We also explored predictability in patterns of small mammal species co-occurrence.

Results

Landscape structure (patch area, landscape heterogeneity) was strongly related to site occupancy. Site occupancy was associated with dead shrubs in the understory and rock cover on ground layer, but was not directly influenced by recent or historical fire. Contrary to contemporary ecological theory, we found no predictable species associations in our early successional community.

Conclusions

We recommend surveys take account of landscape configuration and proximity to suitable habitat for optimal results. Fire regimes expected to promote eastern chestnut mouse population growth should encourage the retention of critical habitat features rather than be based on temporal rates of successional stages. For management to adequately account for post-disturbance patterns in early successional communities, a species-by-species, multi-scaled approach to research is necessary.

     

Radical Lateral Body-Wall Resection for Fibrosarcoma With Reconstruction Using Polypropylene Mesh and a Caudal Superficial Epigastric Axial Pattern Flap: A Prospective Clinical Study of the Technique and Results in 6 Cats

OBJECTIVE: To describe and evaluate a technique for radical resection of the lateral body wall for treatment of fibrosarcoma with reconstruction using polypropylene mesh and a caudal superficial epigastric axial pattern flap in cats. STUDY DESIGN: Prospective, clinical study. ANIMALS OR SAMPLE POPULATION: Six client-owned cats with fibrosarcoma. METHODS: Six cats with histologically confirmed fibrosarcoma of the lateral body wall were staged using radiography and/or computer tomography scanning. Preoperative radiotherapy was used in 3 cats. All cats had the lateral abdominal wall resected and reconstructed with polypropylene mesh. A caudal superficial epigastric flap was mobilized and rotated to close the skin deficit. The animals were evaluated after surgery for wound complications, tumor recurrence, and metastasis. Outcome was assessed by patient examination and client consultation. RESULTS: Minor dehiscence of the skin flaps occurred in 2 cats, and 1 other cat was successfully resuscitated from respiratory and cardiac arrest after surgery. All tissue specimens were tumor-free at the surgical margins. Follow-up times ranged from 12 to 21 months, with a mean time of 17.2 months. None of the cats had evidence of local tumor recurrence or metastasis; outcome was judged good to excellent in all cats. CONCLUSIONS AND CLINICAL RELEVANCE: Radical lateral body-wall resection and reconstruction is an effective technique for achieving local tumor control with acceptable patient morbidity. Further studies are needed to assess whether the technique will result in improved tumor-free intervals and survival times.     

Die Entwicklung des Dottersackes beim Wiederkäuer (Schaf und Rind)

Yolk sac development was investigated in 69 ovine and 10 bovine embryos from the blastocyst stage to the 7th week of gestation. Light and electron microscopical findings are reported. The yolk sac in sheep and cattle is composed of an enlarged sac-like portion lying below the embryo and two ends which follow the elongated course of the trophoblast. In sheep, an open connection exists between the intestines and the yolk sac up to a crown-rump length (CRL) of 9 mm. It is closed by 12 mm CRL. The wall of the yolk sac is especially well vascularized in the enlarged, sac-like portion. Primary erythropoiesis occurs within the blood capillaries. In the blastocyst, the yolk sac entoderm is made up of elongated, flat cells. It becomes cuboidal in the 3 mm embryo (ovine) and later columnar. The up to 20 microns tall cells stain darkly and contain numerous light-colored vesicles. At 4.5 mm CRL light cells appear between the dark ones. Both cells are rich in rough endoplasmic reticulum (rER). The increased staining of the darker cells is due to an osmophilic cytoplasm and numerous, often parallel lamella of rER. The rER of the light cells is enlarged to irregularly-shaped cisternae, which nearly fill the entire cytoplasm and give them a rounded appearance. The dark cells contain polygonal nuclei, whereas those in the light cells are round with one or two nucleoli. The oval mitochondria have only a few peripheral cristae. Golgi fields are not very common. Cells of the entoderm are connected to one another over zonulae occludentes. They possess microvilli on the luminal surface and are supported by a basement membrane. From 5 mm CRL onwards (ovine), the yolk sac entoderm folds itself between the capillaries, thereby becoming stratified. The intercellular space between the cells expands as projections between neighboring cells interlock. Canaliculi arise between adjacent epithelia. The wall of the yolk sac thickens as a result of this infolding and the densely packed capillaries. Infoldings are especially predominant in the sac-like portion of the yolk sac, and only suggested in the ends. Involution of the yolk sac begins in the peripheral end segments and proceeds centripetally. Numerous glycogen particles appear in the yolk sac entoderm cells of the ovine fetus at a CRL of 36 mm, and by a CRL of 42 mm, the sac-like portion has also begun to show signs of degeneration. Mesenchyme is very sparse within the wall of the yolk sac throughout the entire period of development.(ABSTRACT TRUNCATED AT 400 WORDS)     

Red Oak Borer, Enaphalodes rufulus (Coleoptera: Cerambycidae), in the Ozark Mountains of Arkansas, U.S.A.: An Unexpected and Remarkable Forest Disturbance

A complex interaction of multiple factors has resulted in an oak decline event in oak-hickory forests of the Ozark Mountains of Arkansas and Missouri, U.S.A. The most striking feature of this situation is an unprecedented population explosion of red oak borer, a species of cerambycid beetle, Enaphalodes rufulus (Haldeman), which appears to be causing extensive mortality to mature red oaks (Quercus, subgenus Erythrobalanus). The insect is a native species, historically a minor pest of oaks, found throughout the eastern United States. Beetles normally reproduce in living oaks, as larvae initially feed in phloem tissue and subsequently bore into xylem where pupation occurs. The life cycle is two years in length and synchronous adult emergence occurs in odd-numbered years. Data from previous research indicate average attack densities of less than four per tree with a high of 71 on a single tree. Historical emergence densities are similarly low and the highest reported was 15 adults from one tree. Our research is concerned with understanding factors contributing to this outbreak; developing sampling methods for red oak borer; assessing oak mortality; and evaluating site and stand conditions associated with the current outbreak. Results of our initial sampling reveal dramatically higher average attack densities of 244 per m2 and emergence densities of 18 per m2 of bark surface area. We confirm a three-week period of adult emergence and activity during mid-June to early July. We also report on possible management responses by federal and state agencies to this remarkable epidemic and oak mortality crisis.     

Fate of the benzoylphenyl urea CGA-184699 in the cat flea Ctenocephalides felis

HPLC was used to determine levels of the benzoylphenyl urea, CGA-184699, in cat blood, flea faeces and eggs. Rate constants were determined for the decline of CGA-184699 concentration in flea faeces of fleas that fed on both high (696 ng ml^?1) and low (305 ng ml^?1) host blood concentrations. There were strong correlations between the concentration of the drug in the host's blood and in flea eggs, between egg concentration and egg hatch and between the concentration of CGA-184699 in faeces and mortality to larvae feeding upon faeces.     

Switchgrass Compositional Variations Arising from Spatial Distribution and Legume Intercropping

Due to genetic diversity within and among switchgrass (Panicum virgatum), there may be genotype x environment and management-induced differences among secondary cell walls. Consequently, two separate experiments were conducted to determine feedstock variance using near-infrared spectrometry (NIRS). One experiment tested legume-intercrops [red clover (RC; Trifolium pratense), crimson clover (CC; Trifolium incarnatum), hairy vetch (HV; Vicia villosa), and partridge pea (PP; Chamaechrista fasciculata)], nitrogen (N) fertilization (0, 67, and 135 kg-N ha^?1), and location impacts on characteristics. The second one determined on-farm bale variance within and across locations. Clustering NIRS data indicated that chemical signatures differed among locations and N-levels, but less so among intercrops. Results suggest that homogeneity may vary within a region responsible for supplying biomass to a biorefinery. Thus, conversion efficiencies and enzymatic requirements for ethanol production may be affected. Consequently, legumes may displace inorganic-N with minimal compositional changes, whereas location and N-level influence feedstock quality and recalcitrance level to a greater extent.     

Genetics of Heliothis and Helicoverpa resistance to chemical insecticides and to Bacillus thuringiensis

Genetic linkage maps of Heliothis virescens and Helicoverpa armigera are being used to identify and characterize resistance-conferring genes. The insensitive acetylcholinesterase conferring resistance to organophosphorus insecticides and the insensitive sodium channel conferring resistance to pyrethroids have both been mapped in H. virescens. The linkage mapping approach permits a genetic dissection of resistance, even when the mode of action and lethal target are not precisely known, such as for the insecticidal toxins from the bacterium Bacillus thuringiensis (Bt). We have identified and mapped a major Bt-resistance locus in a strain of H. virescens exhibiting up to 10000-fold resistance to Cry1Ac toxin and are currently developing a linkage map for H. armigera with a set of ‘anchor’ loci to facilitate comparison with H. virescens. Both species are currently experiencing their first significant selective pressure in the field by transgenic cotton expressing Cry1Ac, and timely identification of resistance mechanisms and their underlying genetic basis will be essential in successfully managing the Bt resistance that will eventually appear. ©1997 SCI     

The effects of dietary n-3 vs. n-6 fatty acids on ex-vivo LTB4 generation by canine neutrophils

Dietary n-3 polyunsaturated fatty acids are widely used for amelioration of inflammatory skin disease in dogs. In this study, a diet containing two different sources of n-3 polyunsaturated fatty acid–triglyceride (from menhaden oil) and concentrated ethyl esters–was fed to one group of six purpose-bred dogs, while an isocaloric isonitrogenous diet with corn oil (n-6 polyunsaturated fatty acids) was fed to another group of eight purpose-bred dogs for six weeks. Peripheral blood neutrophils, isolated at week–1 (baseline), week 2 and week 6, were stimulated with calcium ionophore A23187 and the amount of leukotriene B₄ produced was determined via reversed-phase high performance liquid chromatography. Analysis of variance of log-transformed data revealed a significant effect for diet ( P  = 0.005) at six weeks, with dogs fed the high n-3 polyunsaturated fatty acid diet having significantly less mean ex vivo neutrophil leukotriene B₄ production than dogs fed the high n-6 polyunsaturated fatty acid diet. Further studies on the clinical usefulness of n-3 polyunsaturated fatty acid ethyl esters are warranted.