Demographic analysis of trade-offs with deliberate fragmentation of streams: Control of invasive species versus protection of native species

Tools restricting the movements of invasive species (e.g. barriers) and reducing habitat fragmentation for native species (e.g. corridors, fishways) provide examples where actions taken to address one environmental concern can hinder efforts to address another environmental concern. We used perturbation analysis of stage-structured projection matrices to evaluate the efficacy of seasonally operated barriers and fishways for controlling non-native sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes while minimizing effects on non-target fishes. For non-jumping fishes migrating in spring, seasonally operated barriers without a fishway will not balance the management objectives satisfactorily. Migration phenologies of the seven common non-target fishes considered in our analyses overlapped considerably with the migration phenology of sea lamprey, with peaks in migration typically being 7–43 days (median 12) from the peak in the sea lamprey migration. Consequently, across species, years, and tributaries, 44–100% of the migratory runs of non-target fishes would be blocked under the 75-day operation period required to block 99% of the sea lamprey spawning run, on average. Reductions in the production of non-target fishes due to blocking were also projected to be similar in magnitude to reductions projected in the production of sea lamprey, unless density-dependent compensation was strong or overlap in migration phenologies between a non-target species and sea lamprey was low. Even under density-dependent compensation, providing a fishway is advisable and passage of non-target fishes may have to be highly effective to avoid population declines in non-jumping species that migrate between a Great Lake and its tributaries.     

Effects of tillage and traffic on crop production in dryland farming systems: II. Long-term simulation of crop production using the PERFECT model

Soil water conservation is critical to long-term crop production in dryland cropping areas in Northeast Australia. Many field studies have shown the benefits of controlled traffic and zero tillage in terms of runoff and soil erosion reduction, soil moisture retention and crop yield improvement. However, there is lack of understanding of the long-term effect of the combination of controlled traffic and zero tillage practices, as compared with other tillage and traffic management practices.In this study, a modeling approach was used to estimate the long-term effect of tillage, traffic, crop rotation and type, and soil management practices in a heavy clay soil. The PERFECT soil–crop simulation model was calibrated with data from a 5-year field experiment in Northeast Australia in terms of runoff, available soil water and crop yield; the procedure and outcomes of this calibration were given in a previous contribution. Three cropping systems with different tillage and traffic treatments were simulated with the model over a 44-year-period using archived weather data.Results showed higher runoff, and lower soil moisture and crop production with conventional tillage and accompanying field traffic than with controlled traffic and zero tillage. The effect of traffic is greater than the effect of tillage over the long-term. The best traffic, tillage and crop management system was controlled traffic zero tillage in a high crop intensity rotation, and the worst was conventional traffic and stubble mulch with continuous wheat. Increased water infiltration and reduced runoff under controlled traffic resulted in more available soil water and higher crop yield under opportunity cropping systems.     

Evaluation of compression generated by self compressing Orthofix bone pins and lag screws in simulated lateral humeral condylar fractures.

A simulated lateral humeral condylar fracture was created in each of the 52 humeri collected from 26 dogs. One humerus from each pair was stabilized with a 2.0 mm cortical bone screw which was inserted in lag fashion. The other humerus from each pair was stabilized with a 2.2 mm threaded diameter Orthofix pin inserted across the condyle. Prior to each repair, an antirotational K-wire was placed and then the Pressurex Sensitive film was inserted in the osteotomy site in order to determine the compressive pressure (MPa), compressive force (KN), and area of compression (cm(2)) achieved during fixation. The maximum insertional torque achieved before stripping was measured for each implant. The mean compression generated by insertion of a 2.0 mm lag screw was 20.36 +/- 1.51 MPa compared to 18.88 +/- 1.76 MPa generated by a 2.2 mm Orthofix pin (p < 0.003). The mean area of compression generated by insertion of a 2.0 mm lag screw was 2.39 +/- 1.29 cm(2), compared to 1.16 +/- 0.84 cm(2) generated by insertion of a 2.2 mm Orthofix pin (p < 0.0001). The mean compressive force (compression x area compressed) generated by insertion of a 2.0 mm lag screw was 4.96 +/- 2.90 Kn, compared to 2.20 +/- 1.65 Kn generated by insertion of a 2.2 mm Orthofix pin (p < 0.0001). The mean insertion torque to failure for the lag screws was 0.49 +/- 0.07 NM, compared to 0.91 NM +/- 0.18 NM generated by the Orthofix pins (P < 0.0001). Both repair methods are likely to be acceptable for the repair of similar fractures in small breed dogs.     

Kinetic and kinematic gait analysis in dogs.

Kinetic and kinematic gait analysis provides objective, quantifiable, and repeatable information on normal and abnormal gait in dogs. Data collection requires specialized equipment, and techniques must be carefully controlled to ensure that accurate measurements are obtained. Force-plate and kinematic analysis is currently used primarily as a research tool to study various gait abnormalities and objectively assess treatment efficacy. As future research identifies characteristic changes associated with specific types of lameness, the use of gait analysis to evaluate individual clinical patients with lameness should become more valuable. Specialized gait analysis techniques may eventually enable veterinarians to accurately diagnose subtle lameness, better evaluate dogs with resolving lameness, and accurately select the appropriate time to return an athletic dog to exercise after recovery from an injury.     

Association of a Pasteurella haemolytica-like organism with enteritis in swine.

A Pasteurella haemolytica-like organism was isolated from the intestines of 28 swine with clinical, gross, or microscopic evidence of enteritis. In 15 cases, other known enteric pathogens were also demonstrated, and in 13 cases, no other pathogens were detected. The mean age of affected animals was 44 days. Most of the animals had clinical evidence of diarrhea. Gross enteric lesions were present in 17 of 21 cases. Microscopic lesions were present in 24 of 26 cases. A diffuse or segmental moderate to severe necrotizing enteritis was the most common lesion in cases in which only the Pasteurella haemolytica-like organism was isolated. Biochemical tests gave results consistent with Pasteurella haemolytica, and 5 of 15 isolates met criteria for biotype A. Negative results were found with an indirect haemagglutination procedure for P. haemolytica.     

Intestinal strangulation caused by intra-abdominal lipomas in a dog.

Pedunculated, intra-abdominal lipomas caused intestinal strangulation in a Doberman Pinscher. The dog was treated surgically to remove the lipomas and the devitalized intestine but died soon after surgery. Histologic evaluation confirmed the diagnosis of lipoma.     

Trifluoromethylketones as possible transition state analog inhibitors of juvenile hormone esterase

A series of compounds containing the trifluoromethylketone group have been synthesized utilizing either a modified Grignard procedure or by reacting selected aliphatic bromides or tosylates with the Collman reagent [Na₂Fe(CO)₄]. When tested in vitro as inhibitors of crude juvenile hormone esterase from the hemolymph of the cabbage looper, Trichoplusia ni (Noctuidae), the most active compounds were trifluoromethylketones possessing either a juvenoid-like structure or a straight aliphatic chain. The logarithm of the inhibitory potency of the aliphatic compounds was proportional to their chain length, up to 1,1,1-trifluorotetradecan-2-one (I₅₀ = 1 × 10^?7M). This powerful inhibition was found to be highly selective for JHE, reversible, competitive by Lineweaver-Burk analysis, and was characterized by high affinity of the inhibitor for the esterase (K_i = 3.2 × 10^?9M, K_m JH III = 2 × 10^?7M). Other trifluoromethylketones were shown to be inhibitors of T. ni α-naphthylacetate esterase and bovine trypsin. By analogy with the mechanism of trypsin action, trifluoromethylketones are probably potent inhibitors due to their resemblance to a tetrahedral transition state on the reaction coordinate to the acylated enzyme.