Graph theory as an invasive species management tool: case study in the Sonoran Desert

Context

Biodiversity in arid regions is usually concentrated around limited water resources, so natural resource managers have constructed artificial water catchments in many areas to supplement natural waters. Because invasive species may also use these waters, dispersing into previously inaccessible areas, the costs and benefits of artificial waters must be gauged and potential invasion- and climate change-management strategies assayed.

Objectives

We present a network analysis framework to identify waters that likely contribute to the spread of invasive species.

Methods

Using the Sonoran Desert waters network and the American bullfrog (Lithobates catesbeianus)—a known predator, competitor, and carrier of pathogens deadly to other amphibians—as an example, we quantified the structural connectivity of the network to predict regional invasion potential under current and two future scenarios (climate change and management reduction) to identify waters to manage and monitor for invasive species.

Results

We identified important and vulnerable waters based on connectivity metrics under scenarios representing current conditions, projected climate-limited conditions, and conditions based on removal of artificial waters. We identified 122,607 km² of land that could be used as a buffer against invasion and 67,745 km² of land that could be augmented by artificial water placement without facilitating invasive species spread.

Conclusions

Structural connectivity metrics can be used to evaluate alternative management strategies for invasive species and climate mitigation.

     

Fungi and the Decrease of Cereal Cyst-nematode Populations in Cereal Monoculture1

Populations of the cereal cyst-nematode decrease when cereals are grown frequently or continuously because the females that develop on the roots between May and July fail to produce eggs, or produce a smaller number than expected. Consequently, cysts in the soil after harvest are fewer and contain fewer eggs. The role of fungal parasites and competitors in limiting populations of cyst-nematodes is reviewed. Parasites of eggs and females of Heterodera avenae Woll. were widespread in British cereal fields, an Entomophthora-like fungus and Verticillium chlamydosporium Barron & Onions being the most common species found. Although fungal parasites may be the cause of the failure of the nematode to increase, it has not yet been established unequivocally.     

Emergence of four weed species in response to rainfall and temperature

The key to achieving effective weed control is to target them when they are young. Understanding their temperature and moisture requirements for emergence will help growers to develop timely control strategies. This study examined the emergence requirements of four key species: Conyza bonariensis, Sonchus oleraceus, Echinochloa colona and Chloris virgata. Two experiments were conducted in a growth room with temperatures of 25/15 and 30/20°C day/night with a photoperiod of 12 h. The first experiment examined emergence under single rainfall events of 0, 2, 5, 10, 20, 30 and 50 mm. The second experiment examined emergence under accumulated rainfall events of 0 mm, 5 mm × 2 (consecutive) days, 5 mm × 4 days, 5 mm × 6 days, 10 mm × 1 day, 10 mm × 2 days and 10 mm × 3 days. The temperature was not significant on emergence in both experiments. In the first experiment, at least 10 mm of rainfall was required for the emergence of all the species, with significantly higher germination rates at rainfall amounts of >20 mm. In the second experiment, the species had higher emergence rates with accumulated rainfall over consecutive days, rather than single rainfall events of the same amount. The length of time that the soil surface remained above the permanent wilting point, allowing the imbibition of water, was also an important factor. This study has provided information on the drivers for emergence of these species and will assist growers in determining what rainfall events are likely to trigger emergence in the field and make timely weed management decisions.     

The utility of ketoprofen for alleviating pain following dehorning in young dairy calves

To determine if ketoprofen, in addition to local anaesthesia, reduces pain following dehorning, we experimentally dehorned dairy calves, less than 2 weeks of age, with (20 calves) or without (20 calves) intramuscular injections of ketoprofen. All calves received a local anesthetic (lidocaine) prior to dehorning and were dehorned with heat cauterization. Cortisol concentration was measured via jugular blood samples taken immediately before dehorning and at 3 and 6 hours following dehorning. Calf behavior was recorded between 0 and 2, 3 and 5, and 6 and 8 hours following dehorning. There was no significant (P > 0.10) effect on creep feed consumption, cortisol concentration, or any of the behavioral measures during the time periods studied. However, the difference in cortisol concentrations from the time of dehorning until 3 hours later was significantly lower (P < 0.05) in the ketoprofen-treated group. These results suggest that ketoprofen, in addition to local anesthesia, may alleviate short-term pain following dehorning with a butane dehorning device in dairy calves less than 2 weeks of age.     

Prevalence of and risk factors for paratuberculosis in purebred beef cattle

OBJECTIVE: To estimate the prevalence of paratuberculosis in purebred beef cattle in Texas and identify risk factors for seropositivity. DESIGN: Epidemiologic survey. ANIMALS: 4,579 purebred cattle from 115 beef ranches in Texas. PROCEDURE: Blood was collected, and serum was analyzed for antibodies with a commercial ELISA. Fecal samples were collected and frozen at -80 degrees C until results of the ELISA were obtained, and feces from seropositive cattle were submitted for mycobacterial culture. Herd owners completed a survey form on management factors. RESULTS: Results of the ELISA were positive for 137 of the 4,579 (3.0%) cattle, and 50 of the 115 (43.8%) herds had at least 1 seropositive animal. Results of mycobacterial culture were positive for 10 of the 137 (7.3%) seropositive cattle, and 9 of the 50 (18%) seropositive herds had at least 1 animal for which results of mycobacterial culture were positive. Risk factors for seropositivity included water source, use of dairy-type nurse cows, previous clinical signs of paratuberculosis, species of cattle (Bos taurus vs Bos indicus), and location. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that seroprevalence of paratuberculosis among purebred beef cattle in Texas may be greater than seroprevalence among beef cattle in the United States as a whole; however, this difference could be attributable to breed or regional differences in infection rates or interference by cross-reacting organisms. Veterinarians should be aware of risk factors for paratuberculosis as well as the possibility that unexpected serologic results may be found in some herds.     

When the species is also a habitat: Comparing the predictively modelled distributions of Lophelia pertusa and the reef habitat it forms

Internationally there is political momentum to establish networks of marine protected areas for the conservation of threatened species and habitats. Practical implementation of such networks requires an understanding of the distribution of these species and habitats. Predictive modelling provides a method by which continuous distribution maps can be produced from limited sample data. This method is particularly useful in the deep sea where a number of biological communities have been identified as vulnerable ‘habitats’, including Lophelia pertusa reefs. Recent modelling efforts have focused on predicting the distribution of this species. However the species is widely distributed where as reef habitat is not. This study uses Maxent predictive modelling to investigate whether the distribution of the species acts as a suitable proxy for the reef habitat. Models of both species and habitat distribution across Hatton Bank and George Bligh Bank are constructed using multibeam bathymetry, interpreted substrate and geomorphology layers, and derived layers of bathymetric position index (BPI), rugosity, slope and aspect. Species and reef presence records were obtained from video observations. For both models performance is fair to excellent assessed using AUC and additional threshold dependant metrics. 7.17% of the study area is predicted as highly suitable for the species presence while only 0.56% is suitable for reef presence, using the sensitivity–specificity sum maximisation approach to determine the appropriate threshold. Substrate is the most important variable in the both models followed by geomorphology in the RD model and fine scale BPI in the SD model. The difference in the distributions of reef and species suggest that mapping efforts should focus on the habitat rather than the species at fine (100 m) scales.     

Variograms of Ancillary Data to Aid Sampling for Soil Surveys

To provide reliable estimates for mapping soil properties for precision agriculture requires intensive sampling and costly laboratory analyses. If the spatial structure of ancillary data, such as yield, digital information from aerial photographs, and soil electrical conductivity (EC) measurements, relates to that of soil properties they could be used to guide the sampling intensity for soil surveys. Variograms of permanent soil properties at two study sites on different parent materials were compared with each other and with those for ancillary data. The ranges of spatial dependence identified by the variograms of both sets of properties are of similar orders of magnitude for each study site. Maps of the ancillary data appear to show similar patterns of variation and these seem to relate to those of the permanent properties of the soil. Correlation analysis has confirmed these relations. Maps of kriged estimates from sub-sampled data and the original variograms showed that the main patterns of variation were preserved when a sampling interval of less than half the average variogram range of ancillary data was used. Digital data from aerial photographs for different years and EC appear to show a more consistent relation with the soil properties than does yield. Aerial photographs, in particular those of bare soil, seem to be the most useful ancillary data and they are often cheaper to obtain than yield and EC data.     

Visualization of Channels and Cavities of Corn and Sorghum Starch Granules

Evidence is presented that corn (maize) and sorghum starch granules have channels that connect a central cavity to the external environment. A mutant sorghum starch with numerous, large surface pores was treated with a methanolic solution of merbromin and sectioned. Light, fluorescence, and compositional backscattering electron microscopy revealed channels connecting an internal cavity to the external surface in most granules. Cavities and channels could also be seen in whole corn and sorghum starch granules treated with merbromin in methanol and viewed by fluorescence microscopy. Treatment of sorghum starch granules with an aqueous solution of merbromin revealed that the molecule penetrated the granule matrix under even slightly swelling conditions. Light microscopy showed cavities in unstained, whole, dry corn and sorghum starch granules mounted in immersion oil.