Modelling the impacts of agriculture in mixed-use landscapes: a review and case study involving two species of dabbling ducks

Context

This study synthesizes evidence from three separate surveys of American Black Duck and Mallard breeding habitat usage to quantify the effects of agriculture at the landscape scale.

Objectives

To assess duck breeding activity in agricultural landscapes within the Canadian maritimes in order to measure the overall impact of agricultural land use, the response to particular agricultural activities, and the influence of landscape configuration.

Methods

Models, constructed using a long-term census (SURVEY1), were used to predict habitat selection for two other independent surveys (SURVEY2, SURVEY3). Predictions incorporated information about wetland area and diversity, as well as anthropogenic factors, allowing subsequent analyses to focus on the remaining residual error attributable to agricultural effects.

Results

SURVEY2 results demonstrated that the proportion of active agriculture is an important indicator of the severity of human disturbance, yielding threshold estimates of 39% for Mallards and 60% for Black Ducks, with an overall average of 50%. Agricultural conversion beyond these thresholds deterred breeding ducks independently of other factors. SURVEY3 land cover information demonstrated that the presence of cropland intensified this deterrence effect, even at levels as low as 10%. Woodland cover (in excess of 30%) was important for both species, but its configuration was not.

Conclusions

In addition to quantifying threshold effects, this study reaffirms that woodland is an important part of the maritime landscape matrix, and contributes positively to habitat diversity in mixed use, moderate intensity agricultural regions. Wetland restoration in agricultural landscapes should monitor and promote less crop-intensive, mixed-use practices.

     

Veterinary ocular microbiome: Lessons learned beyond the culture

Ocular pathogens cause many painful and vision‐threatening diseases such as infectious keratitis, uveitis, and endophthalmitis. While virulent pathogens and pathobionts play important roles in disease pathogenesis, the scientific community has long assumed disruption of the ocular surface occurs prior to microbial colonization and subsequent infection. While nonpathogenic bacteria are often detected in corneal and conjunctival cultures from healthy eyes, cultures also frequently fail to yield growth of common ocular pathogens or nonpathogenic bacteria. This prompts the following question: Is the ocular surface populated by a stable microbial population that cannot be detected using standard culture techniques? The study of the microbiome has recently become a widespread focus in physician and veterinary medicine. Research suggests a pivotal symbiotic relationship with these microbes to maintain healthy host tissues, and when altered is associated with various disease states (“dysbiosis”). The microbiota that lives within and on mammalian bodies have long been known to influence health and susceptibility to infection. However, limitations of traditional culture methods have resulted in an incomplete understanding of what many now call the “forgotten organ,” that is, the microbiome. With the introduction of high‐throughput sequencing, physician ophthalmology has recognized an ocular surface with much more diverse microbial communities than suspected based on traditional culture. This article reviews the salient features of the ocular surface microbiome and highlights important future applications following the advent of molecular techniques for microbial identification, including characterizing ocular surface microbiomes in our veterinary species and their potential role in management of infectious and inflammatory ocular diseases.     

The use of traits to interpret responses to large scale - edge effects: a study of epigaeic beetle assemblages across a <Emphasis Type="Italic">Eucalyptus</Emphasis> forest and pine plantation edge

Context

Edge effects due to habitat loss and fragmentation have pervasive impacts on many natural ecosystems worldwide.

Objective

We aimed to explore whether, in tandem with the resource-based model of edge effects, species feeding-guild and flight-capacity can help explain species responses to an edge.

Methods

We used a two-sided edge gradient that extended from 1000 m into native Eucalyptus forest to 316 m into an exotic pine plantation. We used generalised additive models to examine the continuous responses of beetle species, feeding-guild species richness and flight-capable group species richness to the edge gradient and environmental covariates.

Results

Phytophagous species richness was directly related to variation in vegetation along the edge gradient. There were more flight-capable species in Eucalyptus forest and more flightless species in exotic pine plantation. Many individual species exhibited multiple-peaked edge-profiles.

Conclusions

The resource based model for edge effects can be used in tandem with traits such as feeding-guild and flight-capacity to understand drivers of large scale edge responses. Some trait-groups can show generalisable responses that can be linked with drivers such as vegetation richness and habitat structure. Many trait-group responses, however, are less generalisable and not explained by easily measured habitat variables. Difficulties in linking traits with resources along the edge could be due to unmeasured variation and indirect effects. Some species’ responses reached the limits of the edge gradient demonstrating the need to examine edge effects at large scales, such as kilometres.

     

Growth and water relations of seedlings of two subspecies of Eucalyptus globulus

Seedlings of Eucalyptus globulus Labill subsp. globulus grown in soil in pots in the greenhouse grew faster than seedlings of E. globulus subsp. bicostata, and responded better to added nutrients and water. However, water stress caused a greater reduction in the growth of shoots and roots, and in the root/shoot ratios of fertilized seedlings of subsp. globulus than in those of bicostata. More leaf surface wax was produced by seedlings grown in the presence of fertilizer and an adequate supply of water than by seedlings subjected to nutrient or water stress. Despite larger amounts of leaf surface wax, seedlings of subsp. bicostata had higher epidermal conductances than seedlings of subspecies globulus. However, epidermal conductances were reduced more by water stress and by fertilization in seedlings of subsp. bicostata than in subsp. globulus. Tissue osmotic potentials at full and zero turgor were reduced by water stress only in seedlings of subsp. bicostata and were increased by fertilizer only in seedlings of subsp. globulus. The results indicate that although seedlings of subsp. globulus have inherently higher growth rates, seedlings of subsp. bicostata are better adapted to drought.     

An evaluation of methods for characterising and monitoring gum arabic of commerce and related Acacia gums

Summary Three methods that have been suggested as inexpensive for characterisation of gum arabic were evaluated in characterising and monitoring gum arabic of commerce. The methods were; physico-chemical and carbohydrate analysis (analytical), determination of molecular mass by gel permeation chromatography (gpc) and an Enzyme Linked Immunosorbent Assay (ELISA). The results revealed that gpc provides quick and consistent information on gum arabic of commerce from Acacia senegal. It was able to detect the three chemical species; Arabinogalactan protein complex (AGP), Arabinogalactan (AG) and Glycoprotein (GP) fractions that are typical of A. senegal and could differentiate gum from the two varieties of A. senegal, i.e., var. senegal and var. kerensis on the basis of the enhanced UV peaks in the later. It was able to distinguish gums from different Acacia species as well as suspected contaminants. The analytical method could differentiate between the two varieties of A. senegal on the basis of optical rotation, protein content and viscosity which were noted as basic parameters for comparison. However, where the proposed FAO (1990) specifiction was applied in its present form, it failed to adequately characterise gum from var. kerensis as gum arabic. Secondly, natural product variability i.e., the observed between sample variation made the method to have limited application in adequately characterising gum arabic from even a single source. The method was able to distinguish gums from the other Acacia species purely on the basis of optical rotation though information on nitrogen and sugar composition was also invaluable. Generating data on the composition of sugars requires time that militates against the method as a slow process. Because of the overlap in the analytical parameters for some samples, it could be adequately characterise two of the samples that were presented as suspected contaminants. Nonetheless, by combining information of gpc and analytical data, a better evaluation of the gums was achieved. The method of Elisa has a future scope but will require refining it by utilising monoclonal antibodies to be developed for it to be more specifc in characterising gum arabic from A. senegal. The authors wish to thank Dr. P. A. Williams of the North East Wales Institute, Deeside, Clwyd, UK for the use of the gpc and Elisa facilities. B.N.C. is grateful to the Kenyan and British governments for financial support.     

Reactions between Cr(VI) and wood and its model compounds

Hexavalent chromium solutions at two pH levels (about 1.3 and 7.8) were reacted with wood, gum ghatti, lignin, cellulose and simple model compounds representing wood chemical structures (guaiacol, vanillin, vanillyl alcohol, homovanillyl alcohol, methyl-(β-D-glucoside, and methyl-β-cellobioside). Reaction products were isolated and characterised by elemental analysis, magnetic susceptibility, and Fourier-transform infrared spectroscopy (FTIR). Data suggest that all the chromium present in the reaction products is in its trivalent oxidation state. After reduction reactions, wood and macromolecular substances generally fixed a relatively low level of chromium, which contrasts with the high level in the products isolated from the reaction with the model compounds. It appears that the reaction of the simple model compounds with Cr(VI) did not produce complex adducts of Cr(III) but inorganic substances, of the hydrated chromium oxide type. Therefore, under the experimental conditions applied, simple model compounds do not seem to behave chemically as wood or as the macromolecular substances investigated. Hence, their significance as model compounds must be object of further assessment. An exception is the product from the reaction of vanillyl alcohol and K₂CrO₄ aq. This contains a relatively small amount of chromium and its FTIR spectrum presents rather well defined bands indicating reaction of the phenolic hydroxyl and secondary alcohol groups. This system must be worthy of further investigation as a model for lignin.