Fractal dimension estimates of a fragmented landscape: sources of variability   总被引：9，自引：0，他引：9  

Alain Leduc  Yves T. Prairie  Yves Bergeron 《Landscape Ecology》1994,9(4):279-286

Although often seen as a scale-independent measure, we show that the fractal dimension of the forest cover of the Cazaville Region changes with spatial scale. Sources of variability in the estimation of fractal dimensions are multiple. First, the measured phenomenon does not always show the properties of a pure fractal for all scales, but rather exhibits local self-similarity within certain scale ranges. Moreover, some sampling components such as area of sampling unit, the use of a transect in the estimation of the variability of a plane, the location, and the orientation of a transect all affect, to different degrees, the estimation of the fractal dimension. This paper assesses the relative importance of these components in the estimation of the fractal dimension of the spatial distribution of woodlots in a fragmented landscape. Results show that different sources of variability should be considered when comparing fractal dimensions from different studies or regions.  相似文献   

Effect of the Pietrain breed used as terminal boar on Post-weaning Multisystemic Wasting Syndrome (PMWS) in the offspring in four PMWS-affected farms     

Nicolas Rose  Alain Abhervé-Guéguen  Gérald Le Diguerher  Eric Eveno  Jean-Pierre Jolly  Philippe Blanchard  Aurélie Oger  André Jestin  François Madec 《Livestock Production Science》2005,95(3):177-186

The aim of this study was to determine the potential risk factors for PMWS at the individual pig level and assess the effect of the Pietrain paternal genetic background of the animals in a cohort study. The survey was set up in four PMWS-affected farms with 2 repetitions (batches) per farm. A representative sample of 60 pigs per batch, stratified according to the paternal genetic background (Pietrain: yes vs. no), was randomly selected after farrowing. The representative cohort was divided into 8 batches and the pigs were individually monitored from birth to slaughter. Survival analysis was used to determine the factors related to the time to PMWS. The litter-cluster effect was taken into account using the marginal Cox model (robust estimation of the covariance matrix) and the gamma shared frailty model which were compared.No protective effect of the Pietrain breed on the time to PMWS and the proportion of affected pigs in the offspring was found in this study. Piglets showing low circovirus type 2 (PCV2) titres at 7 weeks-old with no subsequent seroconversion and piglets from PCV2 negative sows were most likely to be affected by PMWS (HR=7.0 and 2.8, respectively). Active infection of the pregnant dams with parvovirus was related to an increased risk of PMWS in the offspring (HR=2.3). Neck injuries due to poorly performed injections in the dams were associated with an increased risk of PMWS with the marginal model (HR=2.1). Oxytocin injection (dams) during farrowing was protective against PMWS in the offspring (HR=0.6).  相似文献   

Current therapies in exotic animal oncology.     

Jennifer E Graham  Michael S Kent  Alain Théon 《Veterinary Clinics of North America: Exotic Animal Practice》2004,7(3):757-81, vii

The majority of information on oncology therapies has been reported in humans, canine, and feline patients, and laboratory animals with experimentally induced tumors. A variety of treatments,including radiation therapy, chemotherapy, photodynamic therapy, and others have been used with exotic animals. There are many species of exotic pets, and anatomic differences, as well as husbandry and nutritional requirements, must be taken into account to provide optimal care. By providing a broad overview of therapies and considerations for treatment, this article is intended to provide the practitioner with an overview of approach and options when addressing oncology cases in exotic animals.  相似文献   

Comparative efficacy of three antiseptics as surgical skin preparations in dogs          下载免费PDF全文

Charles Boucher BVSc  MMedVet  Maryke M. Henton BVSc  MMedVet  Piet J. Becker BSc  MSc  PhD 《Veterinary surgery : VS》2018,47(6):792-801

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Effects of sporidesmin on cultured biliary tract cells from Romney lambs that differed in their sensitivity to sporidesmin     

GC Lindsay  CA Morris  M Boucher  K Capundan 《New Zealand veterinary journal》2018,66(6):325-331

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Difference in factors explaining growth rate variability in European eel subpopulations: the possible role of habitat carrying capacity          下载免费PDF全文

Clarisse Boulenger  Alain J. Crivelli  Fabien Charrier  Jean‐Marc Roussel  Eric Feunteun  Anthony Acou 《Ecology of Freshwater Fish》2016,25(2):281-294

As a key parameter in the management of fish populations, individual growth rate (GR) variations were examined in the European eel (Anguilla anguilla; > 150 mm) using extensive mark–recapture surveys in the lotic habitats of two small rivers of western France: the Frémur, supposed to be saturated, and at the same latitude, the Oir with densities fivefold lower than those of the Frémur. In both systems, generalised linear models were used to test whether spatiotemporal factors such as dominant habitat type or local density affect GR variability. In the presumed unsaturated system, the Oir, GR variability is mainly explained by a set of habitat suitability drivers (density, dominant habitat type). In the Frémur, GRs appear independent of differences in habitat density or productivity. Below saturation, an increase in density will decrease the GR through intraspecific competition. At saturation, intraspecific competition reaches such high levels that regardless of eel density and productivity, the resources available by individual are similar throughout the system. In these circumstances, the effect of density on growth was presumed undetectable. Despite these contrasted results, mean GRs observed in both catchments were closed (~20 mm·year^?1). This is an unexpected result as GR is expected to be higher in unsaturated systems. This similarity could be explained by the difference between the two systems in terms of: (i) sex ratio (the Frémur is dominated by male, whereas the female is dominant in the Oir), (ii) habitat type distribution or (iii) possible interspecific competition (important salmonid populations in the Oir).  相似文献   

Direct impacts of recent climate warming on insect populations     

Christelle ROBINET  Alain ROQUES 《Integrative zoology》2010,5(2):132-142

Effects of recent climate change have already been detected in many species, and, in particular, in insects. The present paper reviews the key impacts of global warming on insect development and dispersal. The effects of climate change appear to be much more complex than a simple linear response to an average increase in temperature. They can differ between seasons and bioclimatic regions. Earlier flight periods, enhanced winter survival and acceleration of development rates are the major insect responses. Differential response of insects and hosts to warming up might also lead to disruption of their phenological synchrony, but adaptive genetic processes are likely to quickly restore this synchrony. In a number of cases, warming results in removing or relocating the barriers that limit present species' ranges. It is also likely to facilitate the establishment and spread of invasive alien species. Finally, knowledge gaps are identified and future research interests are suggested.  相似文献   

Early harvest and ensilage of forage sorghum infected with ergot (Claviceps africana) reduces the risk of livestock poisoning     

BJ Blaney  MJ Ryley  BD Boucher 《Australian veterinary journal》2010,88(8):311-312

Sorghum ergot produces dihydroergosine (DHES) and related alkaloids, which cause hyperthermia in cattle. Proportions of infected panicles (grain heads), leaves and stems were determined in two forage sorghum crops extensively infected 2 to 4 weeks prior to sampling and the panicles were assayed for DHES. Composite samples from each crop, plus a third grain variety crop, were coarsely chopped and half of each sealed in plastic buckets for 6 weeks to simulate ensilation. The worst-infected panicles contained up to 55 mg DHES/kg, but dilution reduced average concentrations of DHES in crops to approximately 1 mg/kg, a relatively safe level for cattle. Ensilation significantly (P = 0.043) reduced mean DHES concentrations from 0.85 to 0.46 mg/kg.  相似文献   

Cell surfaces in plant micro-organism interactions. VIII. Increased proteinase inhibitor activity in melon plants in response to infection by Colletotrichum lagenarium or to treatment with an elicitor fraction from this fungus     

Dominique Roby  Alain Toppan  Marie-Thrse Esquerr-Tugay 《Physiological and Molecular Plant Pathology》1987,30(3)

Proteinase inhibitor activity had increased sharply in melon seedlings infected by Colletotrichum lagenarium 3 days after inoculation. The activity was associated with heat stable proteins and was effective against the protease produced by the fungus as well as against trypsin. Treatment of healthy melon leaves with an elicitor of ethylene isolated from the pathogen, resulted in a three-fold increase in proteinase inhibitor activity after 24 h. Ethylene production increased early in elicitor-treated leaves and may be involved in the elicitation of proteinase inhibitor activity. In the presence of aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, both elicitor-induced ethylene and, to a lesser extent, elicitor-induced proteinase inhibitor activity were inhibited. In contrast, 1-aminocyclopropane-1-carboxylic acid, the direct precursor of ethylene, triggers proteinase inhibitor activity. It is concluded that ethylene is involved in the elicitation of proteinase inhibitor activity, but its exact role remains to be defined.  相似文献   

Systematic status of Manaosia bracodemoca Woodland, 1935 and Paramonticellia itaipuensis Pavanelli et Rego, 1991 (Eucestoda: Proteocephalidea), parasites of Sorubim lima (Siluriformes: Pimelodidae) from South America     

de Chambrier A 《Folia parasitologica》2003,50(2):121-127

Type material of the proteocephalidean cestodes Manaosia bracodemoca Woodland, 1935 and Paramonticellia itaipuensis Pavanelli et Rego, 1991 (both monotypic genera) as well as recently collected material of the latter species are redescribed. A close similarity between both species was observed: the shape of scoleces is identical, both possess a globular scolex with hidden suckers, a well-developed circular, horseshoe-shaped musculature surrounding suckers; the measurements of both taxa are also similar (scolex, suckers, young proglottides). Both cestodes possess a medullary ovary crossing the dorsal muscle layer and ending in the dorsal cortex, the testes are in the dorsal cortex and the cortical vitellarium is laterally situated. Both species parasitize the same fish host. Therefore Paramonticellia is considered a junior synonym of Manaosia and Paramonticellia itaipuensis becomes a junior synonym of Manaosia bracodemoca. An emended diagnosis of Manaosia, which is a monotypic genus, is provided.  相似文献